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Method of adhering mineral deposit in wood fragment surfaces |
| RE32329 |
Method of adhering mineral deposit in wood fragment surfaces
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| Patent Drawings: | |
| Inventor: |
Paszner |
| Date Issued: |
January 13, 1987 |
| Application: |
06/630,388 |
| Filed: |
July 13, 1984 |
| Inventors: |
Paszner; Laszlo (Vancouver, British Columbia, CA)
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| Assignee: |
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| Primary Examiner: |
Czaja; Donald |
| Assistant Examiner: |
Fer tig; Mary L. |
| Attorney Or Agent: |
Hughes & Cassidy |
| U.S. Class: |
106/683; 106/689; 106/691; 264/108; 264/113; 264/115; 264/122; 264/135; 264/309; 427/4; 501/111 |
| Field Of Search: |
264/108; 264/113; 264/114; 264/115; 264/122; 264/135; 264/136; 264/309; 106/18.16; 106/18.31; 106/105; 106/121; 427/4; 427/205; 427/333&; 501/111 |
| International Class: |
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| U.S Patent Documents: |
1568507; 2175568; 2456138; 2837435; 3271492; 3278320; 3285758; 3285759; 3413385; 3475188; 3525632; 3821006; 3879209; 3950472; 3972972; 4008342; 4102691; 4115431; 4228202; 4339405 |
| Foreign Patent Documents: |
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| Other References: |
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| Abstract: |
The disclosed process for making cast vegetable/mineral structural products having flame retardant properties utilize a major volume portion of ligneus plant fragments such as soft and hardwoods, sugarcane, cereal and fiber plant stalks, and a minor volume proportion of a mineral binder deposit comprised of magnesium or calcium oxyphosphates and inert filler particles. Fragments having thickness ranging from 0.3 mm to 8 mm including chips, shavings, strips, strands, fibre bundles, slivers, fibres and peeled and sawn veneer sheets, have applied to their surfaces an aqueous solution of ammonium polyphosphate or soluble acid phosphate salt supplying from 0.15 to 0.40 parts of P.sub.2 O.sub.5 as phosphate ion per part of fragments by weight, and particulate cement solids comprised of MgO or CaO or Mg(OH).sub.2 or Ca(OH).sub.2 or MgCO.sub.3 or CaCO.sub.3 ranging from 0.25 to 1.0 part per part of fragment, and from 0.01 to 0.80 parts of inert filler particles and the mixture is molded and held under predetermined compaction pressure until the product has rigidified, in about 10 minutes' times. .Iadd.The molded mass is held under compaction with unit pressures in the range from about 0.3 to about 14 kg/cm.sup.2.Iaddend.. The process is practically immune to cement poisoning sugars and polyphenolics which were found to be detrimental to other cement mixes. |
| Claim: |
The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:
1. .[.The.]. .Iadd.A .Iaddend.method of making a .[.molded.]. composite product.[.including.]. .Iadd.by joining a plurality of individual members, each of which is made of .Iaddend.a .[.ligneus.]. .Iadd.ligneous .Iaddend.plant material with surfaces having internal pore spaces.Iadd., .Iaddend..[.which is bonded with a mineralbinder which comprises.]. .Iadd.the method comprising the steps of.Iaddend.:
(a) .[.providing.]. .Iadd.applying .Iaddend.an aqueous solution of an ammonium phosphate or ammonium polyphosphate on the plant material .[.so as.]. .Iadd.of the individual members in a manner to allow the aqueous solution .Iaddend.to beabsorbed within the pore spaces and to wet the surfaces.Iadd., .Iaddend..[.along with.]. .Iadd.and .Iaddend.a particulate alkaline earth metal oxide, hydroxide.Iadd., .Iaddend.or carbonate on the wetted surfaces which reacts with the ammonium phosphateor ammonium polyphosphate .Iadd.in the pore spaces and on the wetted surfaces .Iaddend.to form an alkaline earth metal oxyphosphate .Iadd.wet paste .Iaddend.as .[.the.]. .Iadd.a .Iaddend.binder within the pores and as a .[.wet paste.]. coating on the.[.surfaces.]. .Iadd.surface.Iaddend.; and
(b) .[.molding.]. .Iadd.curing .Iaddend.the wet paste .[.coated material.]. until the oxyphosphate is solidified within the pores and on the surfaces .Iadd.to bond with the ligneous plant material and to join the individual members .Iaddend.toform the composite product.
2. The method of claim 1 wherein the .[.plant material is.]. .Iadd.individual members are .Iaddend.in the form of multiple wood sheets bonded together by the mineral binder at a pressure during .[.molding of 2.]. .Iadd.curing of up .Iaddend.to14 kg/cm.sup.2.
3. The method of making a .[.molded.]. composite article comprised of a mass of .[.ligneus.]. .Iadd.ligneous .Iaddend.plant fragments with surfaces having internal pore spaces and a mineral binder bonding the fragments together at the surfacesand in the pores, which comprises:
(a) applying to the surfaces and pore spaces of a mass of .[.ligneus.]. .Iadd.ligneous .Iaddend.fragments an aqueous solution of ammonium phosphate or polyphosphate .Iadd.in a manner to allow the aqueous solution to be absorbed within the porespaces and to wet the surfaces, and .Iaddend.in an amount of from about 0.85 to about 1.8 parts by weight per part of said fragments calculated on their dried weight as a .[.setting.].wetting film supplying from about 0.22 to about 0.70 parts of P.sub.2O.sub.5, and a loading of particulate mineral solids in .Iadd.an .Iaddend.amount of from about .[.0.65 to 1.50.]. .Iadd.0.93 to 4.0 .Iaddend.parts comprised of dead-burned magnesium oxide admixed with finely particulate mineral filler, said filler beingpresent in an amount between a trace and three times the weight of the magnesium oxide, said mineral solids comprising grains of size ranging from 149 micron to 53 micron, so that the ammonium polyphosphate and magnesium oxide reacts .Iadd.within thepore spaces and on the wetted surfaces .Iaddend.to form the mineral binder within the pore spaces and on the surfaces of the fragments; .Iadd.and .Iaddend.
(b) .[.molding.]. .Iadd.curing .Iaddend.the mass of fragments and the particulate mineral solids .[.with compaction.]. to form said composite article while said binder is at a temperature so as to be substantially as a wet paste
.[.(c) holding the molded mass until the binder has solidified to form the composite article..]. .Iadd., the oxyphosphate material solidifying within the pores and on the surfaces to bond with the ligneous plant fragments to form the compositearticle. .Iaddend.
4. The method of claim 3 wherein the composite article is .[.released from holding within.]. .Iadd.cured for about .Iaddend.20 to 30 minutes and subjected to drying at a temperature between about 10.degree. C. and 50.degree. C.
5. The method of claim 3.Iadd., 4 or 46 .Iaddend.wherein said fragments have a moisture content between about 0.5% and 100% by weight prior to application of said mineral binder.
6. The method of claim 3.Iadd., 4 or 46 .Iaddend.wherein the fragments have .[.means.]. .Iadd.mean .Iaddend.thickness dimensions of from about 0.3 mm to about 8 mm and have combined length and breadth dimensions in the range from about 7combined millimeters to about 4,000 combined millimeters.
7. The method of claim 3, 4 or .[.5.]. .Iadd.46 .Iaddend.wherein the .[.molded.]. .Iadd.cured .Iaddend.mass is held under compaction produced only by gravity-induced pressures of the fragments, solution and solids against each other.
8. The method of claim 3, 4 or .[.5.]. .Iadd.46 .Iaddend.wherein the .[.molded.]. .Iadd.cured .Iaddend.mass is held under compaction with unit pressures in the range from about 0.3 to 14 kg/cm.sup.2.
9. The method of claim 3, 4 or .[.5.]. .Iadd.46 .Iaddend.wherein the aqueous solution and mineral solids are applied by simultaneous spraying and dusting operations while the mass of fragments is undergoing mixing, and is mixed further for from4 seconds to about 4 minutes before .[.molding..]. .Iadd.curing..Iaddend.
10. The method of claim 3, 4 or .[.5.]. .Iadd.46 .Iaddend.wherein the aqueous solution and mineral solids are applied separately and either component is applied first.
11. The method of claim 3, 4 or .[.5.]. .Iadd.46 .Iaddend.wherein the aqueous solution is applied first to the fragments and the wetted mass of fragments is held for a time sufficient to allow said solution to become almost wholly absorbed intothe pores spaces in the fragment surfaces while retaining a wetting film on the surfaces and the said mineral solids are applied as a coating on said wetting film and fragments.
12. The method of claim 3, 4 or .[.5.]. .Iadd.46 .Iaddend.wherein said aqueous solution is applied as an initial application of a fractional portion less than one-half of said amount of solution to said fragments and the fragments are storedunder non-drying conditions, and the remainder of said amount of solution is applied to the fragments subsequently and the mass held for a time sufficient to allow the added solution to become substantially absorbed into fragment surfaces while retaininga surface wetting film, and the said mineral solids are thereafter applied as a coating on said wetting film and fragments.
13. The method of claim 3, 4 or .[.5.]. .Iadd.46 .Iaddend.wherein the aqueous solution and mineral solids are applied to the fragments without significant mechanical mixing other than the mixing effected by .[.molding.]. and compacting said.Iadd.curing .Iaddend.mass.
14. The method of claim 3, 4 or .[.5.]. .Iadd.46 .Iaddend.wherein said fragments are adhered to at least one sheet of wood having opposed surfaces of substantial lateral extent, and said aqueous solution and said solids are distributed bymechanical spreading action over at least one surface of each sheet, and said sheet and fragments are assembled in superimposed contacting relation under a pressure of 2 to 14 kg/cm.sup.2 with solution and solids to form a laminated board product.
15. The method of claim 3, 4 or .[.5.]. .Iadd.46 .Iaddend.wherein the ammonium polyphosphate solution comprises mixed ammonium phosphates including about 35% to 40% of ammonium orthophosphate, about 45% to 50% of ammonium pyrophosphate, about9% to 11% of ammonium tripolyphosphate, and about 2% to 5% higher ammonium polyphosphates, the solution having an ammonium content equivalent to a nitrogen analysis of 10% to 11% and having a phosphate ion content equivalent to a P.sub.2 O.sub.5 analysisof about 34% to 37% by weight.
16. The method of claim 3, 4 or .[.5.]. .Iadd.46 .Iaddend.wherein the particulate mineral filler is selected from the group consisting of silica, alumina, zirconia, magnesium silicate, magnesium phosphate, aluminum phosphate, calcium silicate,calcium phosphate, pulverised firebrick, burnt shale, dolomite and limestone.
17. The method of claim 3, 4 or .[.5.]. .Iadd.46 .Iaddend.wherein the aqueous solution is applied first for a time sufficient to allow said solution to become almost wholly absorbed into fragment surfaces while retaining a surface wetting film,and particulate solids comprising dead-burned magnesium oxide and ground dolomite are loaded on said film as an adherent coating, the dolomite comprising 2 to 3 parts by weight per part of magnesium oxide.
18. The method of claim 3, 4 or .[.5.]. .Iadd.46 .Iaddend.wherein said ligneus plant fragments are shaped from the woody parts of softwood trees, hardwood trees, cereal plant stalks, bamboo, sugar cane and fiber plant stalks.
19. The process of forming a structural product comprised of a mass of ligneus plant fragments having surfaces with internal pore spaces bonded together by a mineral binder comprising the metal oxyphosphate reaction product of a base metalcompound selected from the class consisting of magnesium and calcium oxides, hydroxides and carbonates with an aqueous solution of an ammonium polyphosphate or ammonium phosphate compound, the fragments having thickness dimensions between surfaces ofbetween about 0.3 mm and 8 mm, comprising the steps:
(a) applying to the surfaces and pore spaces of a mass of ligneus plant fragments an aqueous solution of the ammonium polyphosphate compound to form a wetting coating providing from about 12 to about 20 mg of P.sub.2 O.sub.5 per square centimeterof fragment surface per millimeter of half-thickness;
(b) holding said wetted, coated mass for a time sufficient to allow said solution to become absorbed almost wholly into the internal pore spaces in the fragments while retaining a moistened surface;
(c) depositing finely particulate powder comprised of said base metal compound and a particulate solid mineral filler as a coating on said moistened surfaces in an amount from about 20 to about 90 milligrams per square centimeter of fragmentsurface per millimeter of half-thickness, said base metal compound comprising about 20 to about 50 milligrams of said amount and said filler being in the range from a trace to about three times the weight of the base metal compound to form the metaloxyphosphate as a wet paste within the pore spaces and on the fragments;
(d) molding the coated fragments into a structural shape while the metal oxyphosphate is a wet paste until the mineral binder has solidified;
(e) and drying the product at a temperature between 10.degree. C. and 50.degree. C.
20. The process according to claim 19 wherein said solution comprises mixed ammonium phosphates produced by reacting concentrated ammonium hydroxide solution with polyphosphoric acid having a P.sub.2 O.sub.5 content of about 83 to produce anaqueous solution providing about 28% to 37% of P.sub.2 O.sub.5 by weight.
21. The process according to claim 19 or 20 wherein said mineral filler is inert with respect to said solution.
22. The process according to claim 20 wherein said mineral solid filler is a magnesium-containing compound which is weakly reactive with said solution and is selected from the group consisting of dolomites and raw magnesium carbonate and thebase metal compound is dead-burned magnesia, said filler and said magnesia being of grain sizes ranging from about 50 microns to about 250 microns.
23. The process according to claim 20 wherein said mineral solid filler is selected from the group consisting of dolomite, dolomitic limestone and limestone, and the base metal compound is oxide of calcium, said filler and base metal compoundbeing of grain sizes ranging from about 50 microns to about 250 microns.
24. The process according to claim 22 or 23 wherein said powder is applied first as finely divided particles of magnesium hydroxide as the base metal compound in amount of from about 1.5 to about 3.5 milligrams per square centimeter of fragmentsurface, followed by additional base metal compound mixed with said filler.
25. The process according to claim 19 wherein said ligneus plant fragments have a length dimension generally aligned with a fiber length direction within the fragments and a thickness dimension in the range from about 300 microns to about 8,000microns and are selected from the group of fragment forms including shavings, flakes, veneers, chips and strands.
26. The process according to claim 25 wherein said ligneus fragments are formed from the woody parts of softwood trees, hardwood trees, cereal plant stalks, bamboo, sugar cane and fiber plant stalks.
27. The process according to claim 26 wherein said fragments are formed by slicing wood billets to form sheets and then slicing the sheets to form strands of wood having a width between about 1.5 millimeters and about 5 millimeters.
28. The process according to claim 26 wherein said fragments comprise sugar cane having the pith removed and the rind cut into inter-node lengths, the lengths divided into segments, and the segments flattened to form loosely-connected strands ofwidth from about 3 millimeters to about 10 millimeters.
29. The process according to claim 28 wherein said cane lengths are further prepared by scraping to remove waxy and siliceous outer layers.
30. The process according to claim 25 wherein the fragments comprise straw of cereal grain plants, and the straw has been roller-flattened to crush nodes and to fissure the straw.
31. The process according to claim 25 wherein the fragments comprise bagasse.
32. The process according to claim 27, 28 or 30 wherein the fragments are assembled as a board product having the fragments predominantly oriented with their thickness dimension parallel to the thickness dimension of the board.
33. The process according to claim 27, 28 or 30 wherein the fragments are assembled by tumble-mixing of the wetted clad mass of fragments and the mix is transferred while the binder remains as a wet paste into a mold as one or more layers toform a board product.
34. The process according to claim 27, 28 or 30 wherein the powder is applied by sifting through a screen to coat the fragments while the wetted mass is undergoing tumble-mixing and the mixing is continued for a period of about 4 seconds toabout 4 minutes, and then the coated fragments are molded into the structural shape.
35. The process according to claim 27, 28 or 30 wherein said deposit of particulate powder is applied as a first deposit of magnesium hydroxide as the base metal compound of particle size ranging from sub-micronic to a few microns in an amountof from 1.5 to about 3.5 milligrams per square centimeter of fragment surface area, and then additional base metal compound and filler is thereafter applied.
36. The process according to claim 28 or 29 wherein the strands are assembled in layers with strand lengths parallel in any layer and angularly related to strand lengths of an adjacent layer to form a board product and said product is held undera compaction pressure such that said board when dried has a specific gravity from about 0.38 to about 0.9.
37. The process according to claim 28 or 29 wherein the strands are assembled in parallel relation to form a board product, and said product is held under a compaction pressure such that said board when dried has a specific gravity from about0.38 to about 0.9.
38. The process according to claim 27, 28 or 30 wherein said fragments with the solution, base metal compound and filler are tumble-mixed for a period of from about 4 seconds to 2 minutes and the mixture is spread in a mold to orient thefragments as one or more layers to form a board product, and are held under a compaction pressure such that said board when dried has a specific gravity from about 0.38 to about 0.95.
39. The process according to claim 25 wherein the aqueous solution and said powder are continuously deposited on the fragments which are continuously assembled into the structural product.
40. The process according to claim 20 wherein said curing step is carried out with circulation of air of low relative humidity about the product surfaces to entrain liberated ammonia gas as a by-product from the metal oxyphosphate reaction andsaid ammonia is recovered from exhaust air to provide a portion of the ammonium hydroxide reacted with polyphosphoric acid to form the ammonia polyphosphate.
41. The process of claim 3 or claim 19 wherein said solution of ammonium phosphate or ammonium polyphosphate is selected from the group consisting of monoammonium orthophosphate and ammonium polyphosphate in amount to supply said amount ofP.sub.2 O.sub.5 and the mixture is wetted by applying water in amount about equal to the weight of the salt.
42. The process of claim 25 wherein said ligneus fragments may include bark portions of tree plants from which said fragments are removed.
43. .[.The.]. .Iadd.A .Iaddend.method of making a cast composite structural product comprised of .[.ligneus.]. .Iadd.ligneous .Iaddend.plant fragments bonded together by an adhered mineral binder, comprising:
(a) applying to the .[.ligneus.]. .Iadd.ligneous .Iaddend.fragments having mean thickness dimensions between surfaces ranging from about one mm to about 8 mm as binder-forming components finely-particulate dead-burned magnesia and an aqueoussolution of ammonium polyphosphate providing phosphate ions equivalent to about 32% to about 37% of solution weight as P.sub.2 O.sub.5, said components being in the weight proportion of one part magnesia to .Badd..[.0.9.]..Baddend. .Iadd.0.5 .Iaddend.to1.2 parts of solution, and mineral solid particulate filler in the proportion of a trace to about 3 parts per weight of magnesia, .Iadd.in a manner to allow the aqueous solution to be absorbed within pore spaces and to wet surfaces of the ligneousfragments .Iaddend.so that said solution coats and wets the magnesia, filler and fragments to initiate chemical reaction producing a wet paste of a magnesium oxyphosphate binder settable as a solid adherent binder anchored in the .Iadd.pores and on thesurfaces of the .Iaddend.fragments and ammonia gas, said binder forming a layer of mean weight ranging from about 15 milligrams to about 120 milligrams per square centimeter of fragment surface area;
(b) molding the coated fragments while the binder remains as the wet paste to form a shaped product;
(c) holding the molded fragments until the binder has solidified from the wet paste; and
(d) drying the product.
44. The method of making a cast composite structural product as set forth in claim 43 wherein said drying step is carried out by circulating air at low relative humidity about the product at a temperature between about 20.degree. C. and about50.degree. C., and recovering the ammonia gas which is released as a by-product of the reaction of the ammonium phosphate and magnesia from the air. .Iadd.45. The method of claim 1 wherein said step of curing said material includes the step of moldingsaid wet paste coated material until said oxyphosphate is solidified. .Iaddend. .Iadd.46. The method of claim 3 wherein said curing step includes the step of molding said mass of fragments with compaction; said method further comprising the step ofholding the molded mass until said
binder has solidified to form said composite article. .Iaddend. .Iadd.47. The method as set forth in claim 1 wherein the individual members are in the form of fragmented pieces. .Iaddend. .Iadd.48. The method as set forth in claim 1wherein the wet paste is characterized by the absence of added water. .Iaddend. .Iadd.49. A method of making a composite product by joining a plurality of individual members, each of which is made of a ligneous plant material with surfaces havinginternal pore spaces, the method comprising the steps of:
a. applying an aqueous solution consisting essentially of an ammonium phosphate or ammonium polyphosphate on the plant material of the individual members in a manner to allow the aqueous solution to be absorbed within the pore spaces and to wetthe surfaces of the ligneous plant material, along with a particulate alkaline earth metal oxide, hydroxide, or carbonate on the wetted surfaces which reacts with the ammonium phosphate or ammonium polyphosphate in the pore spaces and on the wettedsurfaces to form an alkaline earth metal oxyphosphate wet paste as a binder within the pores and as a coating on the surfaces; and
b. curing the wet paste until the oxyphosphate is solidified within the pores and on the surfaces to form a bond with the ligneous plant material and to join the individual members to form the composite product. .Iaddend. .Iadd.50. The methodas set forth in claim 1 additionally comprising the step of air drying the individual members prior to step a to reduce an amount of moisture present in said ligneous plant material. .Iaddend. .Iadd.51. The method of claim 1 wherein the aqueoussolution comprises:
a. from 0.15 to 0.40 parts by weight of P.sub.2 O.sub.5 as phosphate ion per part by weight of ligneous plant material; and
b. from 0.93 to 4.0 parts by weight of alkaline earth metal oxide, hydroxide, or carbonate per part by weight of ligneous plant material. .Iaddend. .Iadd.52. The method of claim 3 wherein:
a. the aqueous solution of ammonium phosphate or polyphosphate is applied in an amount from about 0.85 to about 1.8 parts by weight per part ligneous fragments; and
b. the loading of particulate mineral solids is in an amount from about 0.93 to 1.50 parts comprised of dead-burned magnesium oxide admixed with finely particulate mineral filler. .Iaddend. .Iadd.53. The method of claim 43 wherein the weightproportion of magnesia to solution is one part magnesia to 0.9 to 1.2 parts of solution. .Iaddend. .Iadd.54. The method of making a composite article comprised of a mass of ligneous plant fragments with surfaces having internal pore spaces and amineral binder bonding the fragments together at the surfaces and in the pores, which comprises:
a. applying to the surfaces and pore spaces of a mass of ligneous fragments an aqueous solution of ammonium phosphate or polyphosphate in amount of from about 0.85 to about 1.8 parts by weight per part of said fragments calculated on their driedweight as a wetting film supplying from about 0.22 to about 0.70 parts of P.sub.2 O.sub.5, and a loading of particulate mineral solids in amount of from about 0.65 to 1.50 parts comprised of dead-burned magnesium oxide admixed with finely particulatemineral filler, said filler being present in amounts between a trace and three times the weight of the magnesium oxide, said mineral solids comprising grains of size ranging from 149 micron to 53 micron, so that the ammonium polyphosphate and magnesiumoxide reacts to form the mineral binder within the pore spaces and on the surfaces of the fragments, wherein the aqueous solution is applied first to the fragments and the wetted mass of fragments is held for a time sufficient to allow said solution tobecome almost wholly absorbed into the pore spaces in the fragment surfaces while retaining a wetting film on the surfaces and the said mineral solids are applied as a coating on said wetting film and fragments; and
b. curing the mass of fragments and the particulate mineral solids to form said composite article while said binder is at a temperature so as to be substantially as a wet paste. .Iadd.55. The method of making a composite article comprised of amass of ligneous plant fragments with surfaces having internal pore spaces and a mineral binder bonding the fragments together at the surfaces and in the pores, which comprises:
a. applying to the surfaces and pore spaces of a mass of ligneous fragments an aqueous solution of ammonium phosphate or polyphosphate in amount of from about 0.85 to about 1.8 parts by weight per part of said fragments calculated on their driedweight as a wetting film supplying from about 0.22 to about 0.70 parts of P.sub.2 O.sub.5, and a loading of particulate mineral solids in amount of from about 0.65 to 1.50 parts comprised of dead-burned magnesium oxide admixed with finely particulatemineral filler, said filler being present in amount between a trace and three times the weight of the magnesium oxide, said mineral solids comprising grains of size ranging from 149 micron to 53 micron, so that the ammonium phosphate and magnesium oxidereacts to form the mineral binder within the pore spaces and on the surfaces of the fragments, wherein the aqueous solution is applied first to the fragments and the wetted mass of fragments is held for a time sufficient to allow said solution to becomealmost wholly absorbed into the pore spaces in the fragment surfaces while retaining a wetting film on the surfaces and the said mineral solids are applied as a coating on said wetting film and fragments; and
b. curing the mass of fragments and the particulate mineral solids to form said composite article while said binder is at a temperature so as to be substantially as a wet paste, wherein the composite article is cured for about twenty to thirtyminutes and is subjected to drying at a temperature between about 10.degree. C. and 50.degree. C. .Iaddend. .Iadd.56. The method of making a composite article comprised of a mass of ligneous plant fragments with surfaces having internal pore spacesand a mineral binder bonding the fragments together at the surfaces and in the pores, which comprises:
a. applying to the surfaces and pore spaces of a mass of ligneous fragments an aqueous solution of ammonium phosphate or polyphosphate in amount of from about 0.85 to about 1.8 parts by weight per part of said fragments calculated on their driedweight as a wetting film supplying from about 0.22 to about 0.70 parts of P.sub.2 O.sub.5, and a loading of particulate mineral solids in amount of from about 0.65 to 1.50 parts comprised of dead-burned magnesium oxide admixed with finely particulatemineral filler, said filler being present in amount between a trace and three times the weight of the magnesium oxide, said mineral solids comprising grains of size ranging from 149 micron to 53 micron, so that the ammonium polyphosphate and magnesiumoxide reacts to form the mineral binder within the pore spaces and on the surfaces of the fragments, wherein the aqueous solution is applied first to the fragments and the wetted mass of fragments is held for a time sufficient to allow said solution tobecome almost wholly absorbed into the pore spaces in the fragment surfaces while retaining a wetting film on the surfaces and the said mineral solids are applied as a coating on said wetting film and fragments, wherein the fragments have a moisturecontent between about 0.5% and 100% by weight prior to application of said mineral binder; and
b. curing the mass of fragments and the particulate mineral solids to form said composite article while said binder is at a temperature so as to be substantially as a wet paste, wherein the composite article is cured for about twenty to thirtyminutes and is subjected to drying at a temperature between about 10.degree. C. and 50.degree. C. .Iaddend. .Iadd.57. The method of making a composite article comprised of a mass of ligneous plant fragments with surfaces having internal pore spacesand a mineral binder bonding the fragments together at the surfaces and in the pores, which comprises:
a. applying to the surfaces and pore spaces of a mass of ligneous fragments an aqueous solution of ammonium phosphate or polyphosphate in an amount of from about 0.85 to about 1.8 parts by weight per part of said fragments calculated on theirdried weight as a wetting film supplying from about 0.22 to about 0.70 parts of P.sub.2 O.sub.5, and a loading of particulate mineral solids in amount of from about 0.65 to 1.50 parts comprised of dead-burned magnesium oxide admixed with finelyparticulate mineral filler, said filler being present in an amount between a trace and three times the weight of the magnesium oxide, said mineral solids comprising grains of size ranging from 149 micron to 53 micron, so that the ammonium polyphosphateand magnesium oxide reacts to form the mineral binder within the pore spaces and on the surfaces of the fragments, and wherein the aqueous solution is applied first for a time sufficient to allow said solution to become almost wholly absorbed intofragment surfaces while retaining a surface wetting film, and particulate solids comprising dead-burned magnesium oxide and ground dolomite are loaded on said film as an adherent coating, the dolomite comprising two to three parts by weight per part ofmagnesium oxide; and
b. curing the mass of fragment and the particulate mineral solids to form said composite article while said binder is at a temperature so as to be substantially as a wet paste. .Iaddend. .Iadd.58. The method of making a composite articlecomprised of a mass of ligneous plant fragments with surfaces having internal pore spaces and a mineral binder bonding the fragments together at the surfaces and in the pores, which comprises:
a. applying to the surfaces and pore spaces of a mass of ligneous fragments an aqueous solution of ammonium phosphate or polyphosphate in amount of from about 0.85 to about 1.8 parts by weight per part of said fragments calculated on their driedweight as a wetting film supplying from about 0.22 to about 0.70 parts of P.sub.2 O.sub.5, and a loading of particulate mineral solids in amount of from about 0.65 to 1.50 parts comprised of dead-burned magnesium oxide admixed with finely particulatemineral filler, said filler being present in amount between a trace and three times the weight of the magnesium oxide, said mineral solids comprising grains of size ranging from 149 micron to 53 micron, so that the ammonium polyphosphate and magnesiumoxide reacts to form the mineral binder within the pore spaces and on the surfaces of the fragments, wherein the aqueous solution is applied first for a time sufficient to allow said solution to become almost wholly absorbed into fragment surfaces whileretaining a surface wetting film, and particulate solids comprising dead-burned magnesium oxide and ground dolomite are loaded on said film as an adherent coating, the dolomite comprising two to three parts by weight per part of magnesium oxide;
b. curing the mass of fragments and the particulate mineral solids to form said composite article while said binder is at a temperature so as to be substantially as a wet paste, wherein the composite article is cured for about twenty to thirtyminutes and is subjected to drying at a temperature between about 10.degree. C. and 50.degree. C., and wherein the aqueous solution is applied first for a time sufficient to allow said solution to become almost wholly absorbed into fragment surfaceswhile retaining a surface wetting film, and particulate solids comprising dead-burned magnesium oxide and ground dolomite are loaded on said film as an adherent coating, the dolomite comprising two to three parts by weight per part of magnesium oxide andwherein said fragments have a moisture content between about 0.5% and 100% by weight prior to application of said mineral binder. .Iaddend. .Iadd.59. The method of making a composite article comprised of a mass of ligneous plant fragments withsurfaces having internal pore spaces and a mineral binder bonding the fragments together at the surfaces and in the pores, which comprises:
a. applying to the surfaces and pore spaces of a mass of ligneous fragments an aqueous solution of ammonium phosphate or polyphosphate in an amount of from about 0.85 to about 1.8 parts by weight per part of said fragments calculated on theirdried weight as a wetting film supplying from about 0.22 to about 0.70 parts of P.sub.2 O.sub.5, and a loading of particulate mineral solids in an amount of from about 0.65 to 1.50 parts comprised of dead-burned magnesium oxide admixed with finelyparticulate mineral filler, said filler being present in an amount between a trace and three times the weight of the magnesium oxide, said mineral solids comprising grains of size ranging from 149 micron to 53 micron, so that the ammonium polyphosphateand magnesium oxide reacts to form the mineral binder within the pore spaces and on the surfaces of the fragments, and wherein the aqueous solution is applied first for a time sufficient to allow said solution to become almost wholly absorbed intofragment surfaces while retaining a surface wetting film, and particulate solids comprising dead-burned magnesium oxide and ground dolomite are loaded on said film as an adherent coating, the dolomite comprising two to three parts by weight per part ofmagnesium oxide and wherein said fragments have a moisture content between about 0.5% and 100% by weight prior to application of said mineral binder; and
b. curing the mass of fragments and the particulate mineral solids to form said composite article while said binder is at a temperature so as to be substantially as a wet paste, wherein the composite article is cured for about twenty to thirtyminutes and is subjected to drying at a temperature between about 10.degree. C. and 50.degree. C. .Iadd.60. The method of making a cast composite structural product comprised of ligneous plant fragments bonded together by adhered mineral binder,comprising:
a. applying to the ligneous fragments having mean thickness dimensions between surfaces ranging from about one mm to about eight mm as binder-forming components finely-particulate dead-burned magnesia and an aqueous solution of ammoniumpolyphosphate providing phosphate ions equivalent to about 32% to about 37% of solution weight as P.sub.2 O.sub.5, said components being in the weight proportion of one part magnesia to 0.9 to 1.2 parts of solution, and mineral solid particulate fillerin the proportion of a trace to about 3 parts per part of magnesia, so that said solution coats and wets the magnesia, filler and fragments to initiate chemical reaction producing a paste of a magnesium oxyphosphate binder setable as a solid adherentbinder anchored in the fragments and ammonia gas, said binder forming a layer of mean weight ranging from about 15 milligrams to about 120 milligrams per square centimeter of fragment surface area;
b. molding the coated fragments while the binder remains as the wet paste to form a shaped product;
c. holding the molded fragments until the binder has solidified from the wet paste; and
d. drying the product by circulating air at low relative humidity about the product at a temperature between about 10.degree. C. and about 50.degree. C., and recovering the ammonia gas which is released as a by-product of the reaction of theammonium phosphate and magnesia from the air.
.Iaddend. .Iadd.61. The method of claim 1 wherein the particulate alkaline earth metal oxide, hydroxide or carbonate is applied to the plant material separately from the application of the aqueous solution of ammonium phosphate or ammoniumpolyphosphate. .Iaddend. |
| Description: |
This invention concerns an improved process for bonding or combining lignocellulosic fragments with mineral inorganic binder materials and forming the admixture into astructural product.
The invention particularly relates to such processes wherein the binder materials comprise selected alkaline earth metal compounds and solutions of salts of phosphoric acid reactive therewith capable of developing a bond mass which is distributedinitially on fragment surfaces as a gel coating that sets rapidly to a rigid stone-like solid strongly bonding the fragments to each other.
.Iadd.Fragments having thicknesses ranging from 0.3 mm to 8 mm including chips, shavings, strips, strands, fibre bundles, slivers, fibers and peeled and sawn veneer sheets, have applied to their surfaces an aqueous solution of ammoniumpolyphosphate or soluble acid phosphate salt supplying from 0.15 to 0.40 parts of P.sub.2 O.sub.5 as phosphate ion per part of fragments by weight, and particulate cement solids comprised of MgO or CaO or Mg(OH).sub.2 or Ca(OH).sub.2 or MgCO.sub.3 orCaCO.sub.3 ranging from 0.25 to 1.0 part per part of fragment, and from 0.01 to 0.80 parts of inert filler particles and the mixture is molded and held under predetermined compaction pressure until the product has rigidified, in about ten minutes time. The molded mass is held under compaction with unit pressures in the range from about 0.3 to about 14 kg/cm.sup.2. .Iaddend.
The present invention is based on the discovery that when a major volume proportion of lignocellulosic fragments are admixed with aqueous solutions of phosphoric acids or solutions of nearly neutral phosphate salts, particularly aqueous solutionsof ammonium salts of polyphosphoric acid in amount to partially impregnate the fragments, and the admixture is then dusted with a minor volume proportion of magnesium or calcium oxides, hydroxides, or carbonates, a bond mass is developed at the fragmentsurfaces which sets rapidly from a gel phase to a strongly adhered rigid concrete integral with the fragments regardless of the presence of sugars, phenolics water or extractables in the fragments.
Products molded by the processes according to the invention may comprise any of the common structural shapes such as boards, panels, slabs, beams and blocks, and may comprise frames, trusses, poles, tubes, and virtually any castableconfigurations. Such products may be made economically with little or even no mixing in a wide range of product bulk densities according to the degree of compaction maintained during setting, and require very short molding and curing times. Suchproducts after curing are flame resistant, rot resistant, weather resistant, and are not attacked by termites.
BACKGROUND OF THE INVENTION
Heretofore much effort has been made to realize lightweight and low-cost concreted products utilizing as filler material lignocellulosic fragments, and employing as bonding agent some form of mineral cement, to produce building materials. Typical cements have comprised Portland and other hydraulic cements and pozzolans, and magnesia cements such as Sorel cement. The problems of forming products of adequate strength and with densities less than unity arise because of inferior junctionbond strength, that is, the adherence of the mineral mass to the woody filler. An understanding of the composition of wood fragments, and the chemistry of the reactants producing the mineral bond mass, may be gained by considering the followingdiscussion.
Woody plant structures comprise arrays of hollow cells (tracheids) having fiber constituents comprised as cellulose which is present as high-polymer strong micro-fibril wall structure surrounded by non-fiber carbohydrate, constituents whichencompass the lignins, sugars, starches, extractives, proteins polyphenolics, resins, waxes, fatty substances, and gums. Various sequestered minerals may also be occluded, chiefly silica. When woody plant materials are comminuted to product fragmentsby mechanical processes a wide range of fragment shapes, .[.porosites.]. .Iadd.porosities, .Iaddend.pore opening area, sizes and ratios of surface area to volume can be produced; for example, the fragments may be crumb-like saw-generated particles anddusts; rough lumps, slivers and dusts made by hammer milling or hogging; pulp fibers made by wet grinding; and shavings, veneers, strands, wood-wools and excelsiors made by slicing with knife-edge tools.
The prior art has shown amply that although fragments of a range of sizes may be admixed with a minor volume proportion of cementitious binder material such as a hydraulic cement or magnesium oxychloride cement, the cast product may be uselessdue to poor bonding between the gelling bond mass and the fragment surfaces, or due to poor setting or even total absence of setting of the .[.bonder remants.]. .Iadd.binder reactants.Iaddend.. For example, any attempt to make a lightweight concretedproduct using Western Red Cedar (Thuja Plicata) fragments made from bark-free boles, combined with Portland cement, results in a non-setting mixture which never hardens or forms a bond. The failure to achieve set has been ascribed to the detrimentaleffects on the cement hydration process of certain extractives, chiefly wood sugars and polyphenolics. Poor sets with hydraulic cements also result from combinations of many other wood species, notably most tropical woods, and at the present timecement-bonded compositions are restricted to a few species such as the spruces (Picea Stitchensis), true firs (Abies Sp.), aspens (Populus Sp.) and some pines (Pinus palustris, Pinus Lambertiana). However, even preferred species which have lesseramounts of adversely-reacting extractables require precleaning and migration-blocking treatments to either remove inhibiting substances, or to seal fragment surfaces, or to convert near-surface contaminants to innocuous residues. The contaminatingsubstances present in untreated fragments become partly dissolved as water from the cement slurry migrates through the fragment openings, and the extracted material has ample time to become distributed in the slurry to impede or prevent gelling; it mayalso be conjectured that the fragment surfaces become coated with extracted material, impairing the adherence of the bond mass.
Typical treatments hitherto resorted to comprise: (a) impregnating fragment surfaces with soluble metal salts such as chlorides of calcium or magnesium, which hasten the set of hydraulic cement slurry adjacent the fragment; (b) digestingextractables at and near fragment surfaces by treatment with baths of lime or caustic soda, with or without further stabilizing by a pozzolan or a polyvalent metal salt; and (c) loading surfaces of fragments with a mineral gel, e.g. sodium silicate. Despite such costly pre-treatment procedures, which necessitate at least an additional drying step, the adhesion of the mineral bond mass is relatively poor, as compared for example with that of thermosetting resinous adhesives currently employed forbonding wood fragments as boards. The inferior adhesion of such prior junction bond masses to wood fragments is thought to arise from the failure to develop a gel phase of reacting binder materials extending within pores and lumen openings presented atfragment surfaces, with consequent non-integral deposit of mineral bond mass following hardening. Such bonding as is observed is speculated to be mainly the result of embedment of fragment portions by a partial matrix of the bond mass. Examples ofprior art lignocellulose/mineral composite products are described in United Kingdom specification No. 1,089,777 of Nov. 8, 1967, and in U.S. Pat. Nos. 2,175,568 of Oct. 10, 1939 to Haustein, 2,837,435 of June 3, 1958 to Miller et al, and 1,568,507of Jan. 5, 1926 to Jaeger. Nailing concretes are described in United States Department of the Interior, Bureau of Reclamation text "Concrete Manual", Sept. 1949, pp. 351-352.
The prior art has proposed dry cement compositions comprising phosphorous containing compounds including phosphoric acid, and basic metal oxides such as aluminum and magnesium oxides and their oxyphosphate compounds, settable on mixing with waterto form a concrete binder, as dislosed in U.S. Pat. No. 3,525,632 dated Aug. 25, 1970 issued to Enoch, C. R. Such cements are intended to be used with mineral aggregates.
A number of prior workers have combined water-soluble or dissolved acid phosphates with magnesia in rapid-setting compositions incorporating refractory fillers. In U.S. Pat. No. 2,456,138 issued to Wainer, dated Apr. 5, 1949, a mold of thistype uses ammonium di-acid phosphate and dead-burned magnesia as cementing constituents which set rapidly to a refractory solid. Gunning mixes for repairs to linings of metal-melting furnaces have proposed alkaline polyphosphates, iron oxide, withmagnesia or chromite non-acid constituents, in U.S. Pat. No. 3,278,320 dated Oct. 11, 1966, issued to Neely et al. Suggested polyphosphates named include sodium and ammonium polyphosphates.
Another wet-chemistry composition intended for a casting or pressing mix in repairing furnace linings has been proposed by Limes et al in U.S. Pat. No. 3,285,758 issued Nov. 15, 1966 using ammonium polyphosphates in water solutions of analysis10% ammoniacal nitrogen and 34% P.sub.2 O.sub.5, further diluted and mixed with a minor weight proportion of magnesia or calcined magnesite and a major proportion of refractory aggregates.
A similar composition intended for very rapid chemical reaction and gunning application to hot oven walls, disclosed in U.S. Pat. No. 3,413,385 issued Nov. 26, 1968 to Komac et al, utilizes mixed ammonium phosphates combined in the gun with aminor weight proportion of magnesia dispersed in a dry aggregate.
It has been proposed in U.S. Pat. No. 3,821,006 issued June 28, 1974 to Schwartz to make a castable concrete by admixing water to dry constituents comprising dead-burned magnesia, an acid phosphate salt such as ammonium orthophosphate, and afinely-divided inert aggregate, utilizing heat of the exothermic reaction yielding magnesium phosphate binder to set the concrete within minutes and develop a cure within a day.
A fast-setting concrete of low porosity disclosed in U.S. Pat. No. 3,879,209 issued Apr. 22, 1975 to Limes et al, is made with 15 parts by weight of 34 percent P.sub.2 O.sub.5 ammonium polyphosphate solution and an equal weight of -150 meshmagnesia, admixed with 70 parts limestone, dolomite, sand, or gravel, 3 parts salt, and 15 parts water; such concrete develops an early set and high compressive strength in a few hours.
The formulation of a substantially dry mix wherein one constituent is an acid that is normally liquid such as hydrochloric or phosphoric, or ammonium polyphosphate solution, and another constituent is alumina, dead-burned magnesia or chromite, isproposed in U.S. Pat. No. 3,475,188 dated Oct. 28, 1969 issued to Woodhouse et al, wherein the liquid chemical is adsorbed in a chemically inert pulverulent mineral solid such as bentonite or kieselguhr. Upon adding water to the dry mix thebond-forming liquid is flushed from the absorbent mineral to react with the base constituents to form a refractory solid.
While the formulations hitherto proposed are efficaceous in binding granular mineral aggregates such as refractories to form high-density products, the substitution of wood fragments in the mixes has failed to produce high-strength, low densitystructural products. Only when a major volume proportion of mineral cementing materials is present, yielding product densities well above 1.5 characterized by nearly complete occlusion of any fragment in a mineral matrix, can products of significantcompressive strength be realised. However, the composite product proves weak in shear and tension, due to inferior bond adhesion.
The binding together of mineral solids by a cementing agent essentially requires that such agent be a viscous liquid, paste, or slurry, capable of wetting all surfaces of the mineral solids while plastic, and capable of gelation and developmentof interlocked crystal groups adhered to at least some portions of the aggregate materials. Cast bodies have high compressive strengths due to the effective support column created by the cement matrix surrounding the aggregate grains, but low tensilestrength due to relatively low shear strengths of the bonds.
The problem of producing a truly strong lignocellulose/mineral composite product has not heretofore been met. As an objective, the production of low weight structural products with bulk density under 0.8, and preferably under 0.65, with Modulusof Rupture in static bending above 10 kg/cm.sup.2 and preferably above 100 kg/cm.sup.2, is highly desirable in order to provide cheap building materials utilizing forest and crop residues. Generally, the proportional limit of fiber stress for averagewoods in tension is above 350 kg/cm.sup.2 in air-dry condition; the weakest strength is in shear parallel to the grain, usually above 35 kg/cm.sup.2. It can therefore readily be appreciated that provided a sufficiently strong junction bond can bedeveloped between assembled wood fragments, structural products potentially having excellent Modulus of Rupture strength properties would be feasible. The following discussion elucidates the problem of achieving such structures.
DISCUSSION OF STRESSES IN MOLDED COMPOSITE MINERAL-BONDED LIGNOCELLULOSIC FRAGMENT ASSEMBLIES
When wood fragments in a range of sizes are packed together with a binder material in such volume proportions that the binder volume is a fraction of the actual wood volume, and the binder coats the fragment surfaces to form linking and bridgingdomains between adjacent fragments pressed together under molding pressure, the product inherently includes voids. If very great compaction pressures are applied, the void volume may be less than 10%; however when assemblies having densities of 0.5 to0.9 are desired the ratio of internal spaces to total molded volume may range from 30 to 75% or more. It will be evident that the stress-resisting structure is weakened by the presence of such voids as compared to a specimen of whole, clear wood.
The ability of the composite molded assembly to resist an applied load, as in pure tension, or as a column in compression, or a torque, or as a beam supported at its ends subjected to a load intermediate the ends, will depend on the ability ofthe fragments as laid up and on the junction bond cross-section and strength to withstand the localized stresses. The directions of principal tensile and compressive stresses do not follow smooth curves, as in an ideal homogeneous beam, because of thepresence of voids. Consequently, in light-weight molded structural products the bond adhesion to fragment surfaces, and the actual strength of the binder itself, are the critical parameters which determine the capacity of the molded product to resistloads.
In panels, sheet, post, beam and slab product forms which the invention primarily is intended to make, an analysis of the stress-resisting structure undergoing lateral bending as a beam will show the magnitude of principal tensile stress to bemaximum at mid-span and parallel with the span length, the magnitude decreasing and the direction of stress sloping increasingly upward until it reaches about 45.degree. at the supports. Because the span length is a large multiple of the beam depth inpanels and boards, and since the constituent fragments will usually have thickness dimensions a small fraction of the beam depth, a large number of linked fragments are involved in a three-dimensional chain or lattice resisting the tensile stress, thefragments and their associated bond bridges located along the lower mid-span surface carrying the largest bond loads. A similar chain or lattice adjacent the upper beam surface at mid-span opposes the largest compressive stresses. When a facing sheetof veneer or paper is adhered such member obviously shields the outer chains from part of the stress.
In any randomly compacted group of fragments which are coated with a volume of binder less than the amount that would fill all inter-fragment spaces, the actual cross-sectional area of the junctions which are included in any stress-resistingchain will be less than the fragment cross-sectional areas. It will also be obvious that the bond bridges will have different directions, i.e. the fragment contact planes will usually not be parallel with the direction of the principal tensile stress,hence the bridges will be subjected to varying proportions of shearing and tensile stresses. Because a chain is no stronger than its weakest link it may be seen that those bond bridges subjected solely or mainly to tension represent concentrated stressregions limiting the flexural strength of the product.
For the majority of fragments derived from stalks, stems, boles and branches of woody plants and trees by breaking or cutting operations, the exterior surface of each fragment will be irregular and will comprise partly crushed, deformed, andfissured fiber groups, presenting a relatively large area of openings extending into the woody fragment as compared to the minimum enclosing surface for the fragment volume. Such individual fragments therefore represent lignocellulosic fiber structurewhich is significantly less strong than the volumes of wood in the plant or tree before the fragment was removed. It becomes highly desirable, therefore, that the setting of the binder mass around and upon the fragment should enhance the flexural andcompressive strengths as well as the flexural and compressive moduli of elasticity.
More specifically, the nature of the desired junction bond should be such as to lock the domain of binder between and surrounding fragments integrally to the greatest possible surface area of the fragments; this implies a substantial penetrationby binder material into all fissures, apertures and pores opening to fragment surfaces, and no degradation of the strength of binder material by extractables present in the plant materials.
STATEMENT OF THE INVENTION
The present invention contemplates a process for making an adhered mineral cladding layer on a surface area of a ligneus body by applying to the surface an amount of ammonium polyphosphate aqueous solution sufficient to initially wet the surfaceand a deposit of particulate mineral solids such as magnesium or calcium oxide, or magnesium or calcium hydroxide or magnesium or calcium carbonate in an amount to form a clinging layer adhered to the wet surface, and drying the body. .Iadd.The dryingstep is carried out by circulating air at low relative humidity about the product at a temperature of between about 10.degree. C. and about 50.degree. C., and recovering the ammonia gas which is released as a by-product of the reaction of the ammoniumphosphate and magnesia from the air. .Iaddend.
The invention in a principal aspect envisages the use of ligneus material which has a moisture content in the range between essentially dehydrated state and about 100% by weight of water, and also envisages use of particulate mineral solids in anamount of between about 15 mg and 200 mg of MgO per cm.sup.2 of the ligneus surface of grain sizes ranging between 149 microns and about 15 microns, with an amount of solution supplying from 12 to 20 mg of P.sub.2 O.sub.5 per cm.sup.2 of surface. .Iadd.The fragments have a moisture content between about 0.5% and 100% by weight prior to the application of the mineral binder. The ammonium polyphosphate solution comprises mixed ammonium phosphates including about 35% up to 40% of ammoniumorthophosphate, about 45% to 50% of ammonium pyrophosphate, about 9% to 11% of ammonium tripolyphosphate, and about 2% to 5% higher ammonium polyphosphates, a solution having an ammonium content equivalent to a nitrogen analysis of 10% to 11% and havinga phosphate iron content equivalent to a P.sub.2 O.sub.5 analysis of about 34% to 37% by weight. The solution comprises mixed ammonium phosphates produced by reacting concentrated ammonium hydroxiode solution with polyphosphoric acid having a P.sub.2O.sub.5 content of about 83 to produce an aqueous solution providing about 28% to 37% of P.sub.2 O.sub.5 by weight. .Iaddend.
In yet another aspect the invention may be understood to provide a ligneus body having in its pore spaces a deposit of ammonium phosphate salt and having a surface volume of metal oxyphosphate compounds of a metal which may be magnesium orcalcium crystallised in micro-cavities and recesses in the surface volume, the body having an adhered mineral deposit of particulate solids bonded together and to the body by said compounds. .Iadd.There is applied to the surfaces and pour spaces of amass of ligneous fragments, an aqueous solution of ammonium phosphate or polyphosphate in an amount of from about 0.85 to about 1.8 parts by weight per part of the fragments calculated on their dried weight as a wetting film supplying from about 0.22 toabout 0.70 parts of P.sub.2 O.sub.5..Iaddend.
A still further aspect of the invention shows that the invention as recited may provide the body with a salt deposit of 40 mg to 70 mg per cubic centimeter of wood volume and an adhered mineral deposit ranging from about 65 to 400 mg per squarecentimeter of body surface area.
It will also be obvious that when the fragments are parallel-sided strips such as veneers, shavings, and oriented slivers, laid up as stacks with the longest fragment dimension parallel with the span length, the role of the binder is mainly toresist shearing stresses, which increase generally toward the span ends. As in conventional multi-ply board products assembled from veneer sheets, the adhesion of the binder should be such that a significant shear failure of wood should result when theproduct is tested to rupture rather than shear failure of the bond.
The present invention is directed to improved bond formation between a wide range of lignocellulosic materials available in nature and mineral binder masses cementing fragments of such materials together as porous compositions.
The invention is directed especially to providing concreted lignocellulose fragment assemblies which have exceptionally high strength properties, as represented by the Modulus of Rupture in bending, while at the same time having light weight andlow cost.
The invention is also directed to novel methods of admixing a basic metal compound such as magnesium or calcium oxides, hydroxides and carbonates with a phosphate compound so as to anchor a metal oxyphosphate-cemented bond mass intimately tolignocellulose fragment surfaces, resulting in high bond shear strength.
It is also a purpose of the invention to provide an economical method of mixing and casting a composition having a major volume proportion of lignocellulose fragments and a minor volume proportion of a magnesium .[.of.]. .Iadd.or.Iaddend.calcium oxyphosphate binder mass cementing the fragments together, the composition having a high degree of flame retardation.
Other purposes and advantages of the invention will be made apparent and the practice thereof exposed in and by the following description of its preferred embodiments.
From another aspect the invention is to be understood as providing for the application of the mineral solids as an initial layer of magnesium or calcium oxide, hydroxide or carbonate followed by a second deposit of larger grain sizes and weightper unit area, the initial solids being of particle sizes ranging from sub-micronic to a few microns and in amount of from about 1.5 mg to about 3.5 mg per cm.sup.2 of body surface.
The invention can be further comprehended as providing a process for attaching a metal oxyphosphate mineral binder mass as an integral cladding on the surfaces of ligneus fragments bonding to the fragment surfaces a mineral solids layer, and forimparting strength enhancement, fire-retardancy and decay-resistant properties to the fragments by an impregnation treatment of constituent surfaces with an aqueous solution of ammonium polyphosphate and a deposition of the mineral solids layer comprisedof a magnesium or calcium compound reactive with the solution to form metal oxyphosphate binder compounds, the solids being of grain sizes in a range from sub-micronic to about 250 microns.
The invention also contemplates processes for attainment of low density structural composites of board form having a core portion of wood fragments incorporating surface impregnating amounts of an electrolyte supplying phosphate ions and carryingan adherent binder mass formed by the reaction of calcium or magnesium oxide, hydroxide or carbonate grains applied as a surface deposit with the electrolyte, the binder mass bridging fragment portions as junction bonding masses, the core portion beingbonded to veneer sheets of wood by the binder mass.
It is yet another provision of the invention as recited that sheet-like lignocellulose fragments are utilised having contacting surfaces impregnated with an adhered integral mineral binder mass comprised of the reaction products with ammoniumpolyphosphate solution and calcium or magnesium oxides, hydroxides or carbonates.
The manner in which the invention may be put into effect, and a description of its preferred embodiments as directed to the production of a wide range of molded composite products such as slabs, panels, boards, beams, columns, posts .[.ahd.]. .Iadd.and .Iaddend.hollow tubes, may be more particularly understood from the description and examples which follow, to be read in conjunction with the several figures of the drawing accompanying, in which:
FIG. 1 is a greatly enlarged sectionalview on a .[.tengential.]. .Iadd.tangential .Iaddend.splicing plane of fragmental portion of a softwood (Pinus-Strobus L.) showing tracheids and cell structure;
FIG. 2 is a greatly enlarged sectional view on a tangential slicing plane of a fragmental portion of a hardwood (Populus tremuloides) also showing wood cell and vessel structure;
FIG. 3 is a graph diagram relating attained temperature with time following combination of magnesium oxide with ammonium polyphosphate;
FIG. 5 is a graph diagram relating the proportion of active MgO grains of specific grain size groups and the weight of binder compounds produced by reaction of the active portion with ammonium polyphosphate; and
FIG. 4 is a greatly-enlarged perspective view of a surface portion of a softwood constituent carrying an adhered deposit of mineral solids bonded to the wood and to grains of MgO reacted to form the binding compounds and phosphate deposit.
In the description which follows the examples given are intended to instruct and guide in the application of the invention to certain practical embodiments, which are illustrative and in no way to be construed as limiting of the scope and utilityof the invention.
PENETRATION OF LIGNOCELLULOSIC PLANT STRUCTURE BY FLUIDS
Micro-structures of ligneus fragments cut from softwood and hardwood species are shown in sectional views, FIG. 1 and FIG. 2, taken on tangential-axial slicing planes. As illustrative of the softwoods such as spruce, pine, fir, hemlock andlarch, FIG. 1 diagrams a section in greatly enlarged scale of a fragment of eastern pine (Pinus strobus L.) 10 having one sheared surface 11 lying in a diametral cutting plane, and, as viewed in section in radial projection, exposing arrays of conicalcells 12 arranged as sectors of growth rings. Other cell arrays may be understood to lie at radially varying distances of the tree bole.
The longitudinal tracheids 12 have lengths up to about 3 mm and are of hollow tubular form, the lumens 13 which are revealed by the cutting and sectioning ranging from about 5 microns to 10 microns in transverse dimension according to the seasonwhen they were generated. The tracheid outer transverse dimensions are about 25 to 30 microns. A plurality of very much smaller lateral openings 14, called `pits`, appear in the side walls of the cells. Summer cells have relatively larger lumens andradially thinner walls, whereas fall cells have lumens which are nearly closed by cell wall thickening.
The rupture strength of the cellular arrays in tension is greatest along the columnar direction, with a lesser strength in the radial direction, and least strength along the tangential direction. The relative dimensions of radially-extendingwood ray cells 15 and of tracheids 12 may be estimated by reference to a surface deposit of mineral grains 16 of grain sizes up to 100 microns maximum.
In FIG. 2 a similarly-cut fragment 20 of poplar wood (Populus tremuloides) representative of the class of hardwoods such as birch, maple, basswood, blue gum, elm, or ash, has opening to its upper surface 21 not only the reduced dimension lumens13, but also spaced tubular vessels 22 formed by coalescing of a group of adjacent cells. The vessels may measure up to 50 microns across, and are interrupted along their lengths at intervals by plate members 23 formed with small apertures 24, whichallow fluids transported along the vessels to move through the discs.
In both types of wood, numbers of very small pits 14 open through the side walls of the cells, measuring about 2 to 5 microns, and comprising only a very small part of the total wall area of any cell. The pits communicate between the lumens ofadjacent cells, affording means for lateral migration of gases or fluids in radial and tangential directions of the wood.
The relative dimensions of hardwood cellular and vessel structures may be understood by comparing the sizes of grains forming a surface mineral deposit of which the largest grains are of 100 micron size.
Referring to FIGS. 1 and 2 the nature of the wood surfaces which are exposed to applied liquid and solid binder-forming materials may be understood, and migration and penetration by liquids into or out of the wood, as well as transport of colloidproducts into wood spaces will be made apparent.
Considering the areas viewed in each fragment, which represent a wood surface as may be formed by tangentially slicing a growth ring, a fluid such as water or an electrolyte solution or a colloidal suspension may readily gain entry in axial,radial or tangential directions of the wood into the sliced or shattered surface cells. These materials may move beyond the surface layer, through interconnected cells, passing through the pits and discs to penetrate into adjacent cells. While thetotal cross-sectional area provided by the pit openings and disc apertures is small, the extent of radial migration may be considerable for gases and liquids of low viscosity. Colloid particles can pass through the pits and apertures provided that theviscosity of the suspension and the sizes of agglomerations of particles do not exceed about 2 microns. Solutions of salts, including ammonium polyphosphates, can readily penetrate the fragments from any surface for distances measured in millimeters oreven centimeters in a few minutes' time, the movement being more rapid when assisted by a pressure gradient.
Those tracheid walls which have been ruptured present surface recesses of dimensions 5 microns or larger in width and up to 3 mm in height into which both viscous colloids and very small grains of solids may enter. Some hardwood vessels arelarge enough to engulf solid grains smaller than about 40 microns.
The detailed microstructure of cells may be understood by reference to any text on wood technology detailing the organization of the layers of materials forming the cell walls, namely lignins, hemicelluloses and microfibrils of crystalline andparacrystalline cellulose, all of which have thickness dimensions which are small fractions of one micron. Even when tracheid walls have not been punctured or sheared, water and electrolytes may in time penetrate cell walls after gaining entry to thelumens and eventually occupy the minute spaces between microfibrils. This will be apparent on considering that lignocellulose planks of 5 cm thickness may be impregnated by surface application of ammonium polyphosphate aqueous solution through capillarymigration, the wood absorbing 70 milligrams of the dry salt per cubic centimeter of wood which enters as 140 milligrams of a solution of 50% solids by weight, of specific gravity 1.4.
Examinations of micro-sections of dried wood fragments which had been impregnated by ammonium polyphosphate solution of viscosity ranging from about 30 to 90 centipoise at room temperature, revealed a microcrystalline salt deposit extending intowood spaces to a depth of from a few hundred microns to several millimeters as partial or total filling of pits, discs, and lumens, and formed coatings on vessel walls. Such deposit contributes not only significant increases in compressive and bendingstrengths of the woody material, as will be discussed in detail at a later point, but confers fire-retarding properties to the wood.
Even greater absorption by wood of a surface application of a moderately viscous solution is observed when fragment surfaces are .[.fissued.]. .Iadd.fissured .Iaddend.due to the forces exerted by a forming tool causing partial fiber separationin portions of the wood. Plant fragments such as stalks, canes, straws and stems may be crushed, split or bent, present additional surface area penetrable by liquids and fine solids, and the rate of entry into the fragment is higher as liquid whichforms a capillary filling in fissures wets a total surface greater than the enveloping surface of the fragment.
CHEMICAL AND PHYSICAL ASPECTS OF OXYPHOSPHATES
Electric furnace reduction of apatite produces superphosphoric acid characterized in that two or more atoms of phosphorous are present in chain configuration, whereas wet process production of phosphoric acid leads to a single atom of phosphorousin the acid .[.radicle.]. .Iadd.radical.Iaddend., characterizing orthophosphoric acid. Acid preheat is required when producing polyphosphates, the extent of which depends on the conversion level desired and acid purity of at least 60% of P.sub.2O.sub.5.
Ammonium polyphosphate is made by reacting concentrated phosphoric acid and ammonia under controlled conditions. The salts of the respective acids differ in chemical activity and in their degree of polymerization. The polyphosphates arecharacterized by the repeating orthophosphate group diagrammed below wherein n must be 2 or a higher integer. When n=1 the group represents orthophosphoric acid: ##STR1##
Upon conversion of superphosphoric acid by any reaction producing a salt solution, a degree of depolymerization of the acid occurs, as when electric furnace acid is combined with 37% ammonium hydroxide solution in water to make ammoniumpolyphosphate of analysis 10-34-0.
The ammonium polyphosphate derived may consist of 65% to 85% of P.sub.2 O.sub.5 combined as polyphosphates, and 25% to 30% as orthophosphates, or by a different ammoniation a salt product having a P.sub.2 O.sub.5 content about equally dividedbetween ortho- and polyphosphate salts may be made. These products are highly reactive with the basic alkaline earth metal oxides, hydroxides and carbonates, especially those of magnesium and calcium, and the reaction products formed are classifiable asmetal oxyphosphates.
Structural diagrams illustrative of the formation of oxyphosphate reaction products of aqueous solutions of ammonium orthophosphate and ammonium pyrophosphate, respectively, with magnesium oxide, are diagrammed below: ##STR2##
The corresponding reaction between a calcium or magnesium hydroxide leads to the formation of the same amounts of ammonia with additional molecules of water.
The reaction of magnesium carbonate leads to the formation of ammonium carbonate dissolved in the aqueous medium, as may be understood from the equation for the reaction between ammonium pyrophosphate and magnesium carbonate:
Higher ammonium polyphosphates (e.g. tri-, tetra-, etc.) yield corresponding higher magnesium oxyphosphate compounds as may be understood from the examples of combining proportions of MgO and P.sub.2 O.sub.5 listed hereinbelow:
______________________________________ magnesium orthophosphate 1 MgO to 0.333 P.sub.2 O.sub.5 magnesium pyrophosphate 1 MgO to 0.500 P.sub.2 O.sub.5 magnesium tripolyphosphate 1 MgO to 0.600 P.sub.2 O.sub.5 magnesium tetrapolyphosphate 1MgO to 0.666 P.sub.2 O.sub.5 magnesium pentapolyphosphate 1 MgO to 0.7142 P.sub.2 O.sub.5 magnesium hexapolyphosphate 1 MgO to 0.750 P.sub.2 O.sub.5 ______________________________________
The relative weight proportions of the P.sub.2 O.sub.5 contents of the orthophosphate and polyphosphate compounds typical of commercial ammonium polyphosphate solution of analysis 10% nitrogen as ammonia and 34% P.sub.2 O.sub.5 phosphate ion,having a specific gravity of 1.4 and a solids content of 50% by weight, are indicated by the following listing, based on 100 gm of solution:
______________________________________ orthophosphate 6.3 to 7.2 parts pyrophosphate 9.2 to 10.1 parts tripolyphosphate 0.55 to 0.61 parts tetra and higher polyphosphates about 0.2 parts ______________________________________
The pyrophosphates of magnesium and calcium are especially water resistant and strong and are deemed slightly superior to orthophosphate compounds of these metals.
In the highly exothermic reaction of ammonium polyphosphates with the basic oxides and hydroxides water is produced in mol-formol amount and ammonia is liberated in 2:1 mol ratio with respect to the basic metal compounds MgO, CaO, Mg(OH).sub.2and Ca(OH).sub.2. The relatively large volume of ammonia gas, although highly soluble initially in the aqueous reacting medium, is eventually expelled as the temperature rises. A peak temperature of from 50.degree. C. to 65.degree. C. is attainedwhen even small amounts of magnesium oxide, for example, are reacted with an excess of ammonium polyphosphate solution within 10 to 20 minutes of mixing. A typical plot of attained temperature with time for a plug measuring 2.7 cm diameter by 4.0 cmlength is shown in FIG. 3.
That portion of curve 30 in FIG. 3 designated (A), indicating a fast initial rise in temperature, coincides with observed colloid dispersion of magnesium oxyphosphate compounds as colloidal masses ranging from a few hundred Angstrom units toabout 0.5 micron. The activation energy required to initiate the reaction of ammonium polyphosphate with MgO at the grain surfaces is supplied by hydration resulting from the wetting of grain surfaces by the liquid medium contiguous to the solidparticles. The colloid masses manifest a mobility which is of great importance in the present invention. Colloid migration has been observed through distances of several hundred microns while the reaction is proceeding. The migration appears to beeffected both by capillary transport of the suspending liquid or by mechanically-induced pressure gradients therein, and by electrostatic forces within the electrolyte solutions, i.e. by Brownian movement.
Substantial transport of colloid matter is effected by liquid issuing from a porous reservoir such as ligneus matter contiguous to MgO grains, and by re-absorption of liquid into the wood. This mechanism enables the distribution of reactionproducts and loading of pore spaces of a woody substrate thereby, in a manner quite dissimilar to the formation of a binding mass around refractory aggregate particles from a surrounding solution of ammonium polyphosphate. When the solution is carriedas a partial filling of hollow tracheid spaces in wood and the surface of the wood carries grains of MgO and mineral extender grains, an outward migration of liquid occurs which causes lively local motion of wetting films which move about grain surfacesand carry suspended colloid masses. A significantly large transport of such masses deposits them at some distance from the grains within the wood pores. The formation of crystallised oxyphosphate compounds loading a wood surface may be seen from FIG.4, which shows that mineral material 31 has been deposited within lumens of tracheids of a softwood by entry of colloid masses through bordered pits 32 accessible to fluid migrating from the vicinity of grains 33 of an adhered mineral deposit 34. Deposited Phosphate salt is 35.
No ammonia is liberated as gas during the initial warming represented by curve portion (A) (FIG. 3). As the reactants warm a decreasing capacity of the liquid to retain ammonia leads to evolution of gas.
A critical temperature must be reached before gelation takes place. The slightly endothermic process of breaking of the phosphate-NH.sub.3 bonds is evident from the temperature plateau at curve portion (B). The time interval between the wetpaste stage and its actual solidification may vary considerably, as the transition appears to depend on factors such as the composition of the grain mixture, the ratios and amounts of grain sizes, the concentration of dissolved ammonia, and thetemperature. For example, a high ratio of inert solid filler grains with respect to active MgO grains lengthens the interval, as does retention of dissolved ammonia, e.g. where the reaction proceeds at an elevated pressure.
With slowly-reacting grain mixtures, as where the inert grain mass is in high proportion, the initial temperature rise depicted by curve portions (A) to (B) may not exceed 30.degree. C. to 35.degree. C., and gelation may be delayed to 30minutes or longer following initiation of the reaction. In extreme cases gelation may take several hours. With small high-purity grain sizes, e.g. in the 5 micron to 20 micron range, and with a higher proportion of MgO to inert filler grains, theinitial exothermic reaction may raise the temperature of the reactants to 55.degree. C. to 60.degree. C., and the gelation may set in almost instantaneously or within 3 to 5 minutes. It will be evident that a setting behaviour can be selected tocorrelate with the particular process for which the invention is used.
The practical significance of the gel point in processes for bonding porous solids such as ligneus fragments is that colloid mass mobility at this state is greatly restricted by reduction of water volume and solution availability as immobilematerial encloses the surfaces of MgO grains. Virtual stoppage of the combination of phosphate ions with the grains may occur when only a 2 micron to 5 micron surface layer has been reacted. An increased evolution of ammonia gas also occurs at thisstage and continues as the compounds formed further harden. The surface appearance of the reacting grains dulls where earlier it had been wet and shiny. The reaction becomes irreversible once the stage represented by curve portion C has been reached,and cannot be stopped even if the reactants are exposed to a large excess of water, which may be sea water.
An important factor in reducing the amount of water present is the linking of molecules of water of crystallization to the oxyphosphate molecules, as may be seen from the equations previously mentioned. The reaction of magnesite which yields nofree water particularly reduces available fluid. The crystal forms of the orthophosphate and pyrophosphate, which are respectively in the monoclinic and tabular monoclinic systems, are established at growth sites and the compounds co-crystallise andinterlock to form relatively larger volumes of binder in relation to the volume reduction of MgO grains.
Hardening of the gelling compounds is correlateable with the final temperature rise indicated by transition from curve portion (C) to plateau (D) when the hardened reaction products attain 50% to 75% of their ultimate strength. The release ofammonia gas may continue slowly for some hours or even days, depending on the curing temperature. Maximum compound strength is reached at a moisture content of 8% to about 10%, and ammonia has largely escaped.
Continuous casting processes for which shorter reaction times for the basic metal compound with ammonium polyphosphates would be practicable may use a grain mixture (hereinafter to be referred to as "cement solids") with a high proportion of MgOof high density relative to the inert or weakly inert grain portion. The MgO preferably would be of highly reactive state, as represented by USP grade material or dead-burned dense grain rather than merely calcined magnesite. As inert orweakly-reactive filler solids there may be used magnesite of raw form, or a dolomite, or other inert solids of suitable particle sizes such as silica, zirconia, alumina, and alkaline earth metal phosphates and silicates, in the ratio of a fraction of theamount of MgO up to 100 times the weight of MgO.
When the surface of wood of high moisture content receives ammonium polyphosphate solution followed by deposition of powdered cement solids, a higher fluidity of the liquid/solid mixture prior to gelation tends to make .[.unneven.]. .Iadd.uneven.Iaddend.the cladding thickness by dripping and flowing. The early liberation of water produced in the reaction tends to prolong retention of ammonia and postpones gelation. In addition the reverse osmotic gradient present when air-dry wood ispre-impregnated and then coated by cement solids, which gradient draws water into the stored solution and transports colloidal oxyphosphates, is either absent or weak when the wood has a high moisture content, or when a mixture of cement solids andaqueous solution is applied to surfaces of wood devoid of solution.
It is generally desirable for optimum cladding layer formation and compound adhesion strength to wood of any plant species to pre-absorb the solution and then apply powdered cement solids, although satisfactory products can be realised whenair-dry ligneous fragments receive the liquid/solid mixture simultaneously; inferior products result from such application to green or wet fragments.
GRAIN SIZE AND GRADING
The selection of the maximum grain size of MgO and the weight ratios of a range of decreasing sizes of the grains to be used as the reactive portion of the cement solids, and the total bulk and weight of cement solids to be adhered on each squarecentimeter of fragments surfaces, requires taking into consideration such factors as the reactivity of the grain surfaces, the grain form, the ratio of true solid volume to deposit volume, the degree of penetration by colloidal reaction products intocontiguous wood zones, and the volume of gases entrained in the formed binder. A further, important concern is the speed of setting of the binder mass and the minimal application time needed to bring the grains into contact with the fragments andsolution and the minimal assembly and forming time for casting the composite into a mold under the desired compaction pressure.
The optimum binder deposit whether formed on an isolated wood surface area or as a junction binder mass between closely-spaced surfaces of fragments theoretically would comprise an almost wholly-absorbed crystalline mixture of magnesiumoxyphosphate compounds within pores and openings throughout a near-surface zone extending in depth up to 100 microns or more, and a minimal cladding layer of void-free mineral solids bonded together by the compounds and bonded to the wood surfaces. Forlowest binder cost such intervening layer of solids should be as thin as possible. If very small grains are used, having specific surface above about 1500 cm.sup.2 per gram, the amount of oxyphosphate compounds developed would suffice to supply a volumeof colloids capable of entering into the wood openings and of binding a very thin solids layer to the surface, but such material sets so rapidly that an assembly of fragments cannot be done quickly enough to ensure a strong bond. Nevertheless, a minoramount of magnesium oxide may usefully be applied as grains smaller than about 15 microns to develop a portion of the oxyphosphate compounds prior to application of the major deposit forming the actual binder mass.
If granular magnesia of high density and uniform particle size larger than about 0.3 mm is applied in an amount of 20 to 60 milligrams or more per square centimeter of fragment surface and exposed to contact with aqueous polyphosphate solution,the formed mineral deposit sets slowly and is weakly bonded, particularly at the lower applied weights, and little bond rooting is developed. A single layer of such grains, if of spherical form and closely packed, occupies only about 60% of a volumeequal to the plan area of the layer multiplied by the diameter of each grain. Such deposit cannot generate sufficient binding compounds to occupy the 40% void volume between the grains, and can supply only negligible colloidal material for entry intowood openings.
This may be appreciated by considering that if the surface reactivity of a grain of 0.3 mm transverse dimension of high quality dead-burned dense magnesia permits only an outer surface zone of thickness 3 or 4 microns to become converted to theorthophosphate and the pyrophosphate of magnesium regardless of the presence of an excess of aqueous ammonium polyphosphate solution, the core portion amounts to more than 96% of the original grain weight. By comparison, a smaller grain, of say 50micron transverse dimension, having a surface layer also of 3 to 4 microns reacted, will have an unreacted core portion which is 78% of the original weight. Even when a range of grain sizes having specific surface values from about 60 cm.sup.2 per gramto about 600 cm.sup.2 per gram forms the powdered cement solids applied to a wetted wood surface, a major weight portion remains unreacted and the deposit when cured has a thickness not less than the thickness of the initial deposit.
Efficient use of MgO as a surface deposit of given weight per square centimeter of wood surface necessitates packing the deposit with the least void space between grains, hence a range of grain sizes should be chosen which will minimize theinter-grain space which must be filled by oxyphosphate colloidal matter and therefore provide ample colloidal matter for entry into wood spaces. As known in the prior art of making concretes with graded sands, a packing ratio of at least 80% andpreferably above 90% favors the formation of a well-bonded mineral mass by a small volume proportion of setting compounds. One grading of granular dead-burned magnesium oxide which has provided a relatively high bulk density of applied cement solidspowder of approximately 150 micron depth, having suitable specific surface value and reactive weight percentage, is tabulated below:
TABLE I ______________________________________ GRAIN SIZES FOR 100-GRAM SAMPLE OF DEAD-BURNED MgO Screen opening, mm percentage retained on screen ______________________________________ 0.149 nil 0.105 22 0.074 26 0.052 28 0.044 18 pan6 ______________________________________
The screen sizes are based on square openings.
With reference to FIG. 5, the diagram represents the weight percentages of granular MgO of suitable gradings with different maximum grain sizes, and shows the weight percentages of MgO which remain unreacted, and of developed oxyphosphatecompounds resulting from the reaction with an excess of available ammonium polyphosphate solution of specific gravity 1.4. The diagram shows that a greatly increased weight proportion of oxyphosphate compounds is provided as the maximum grain size ofgraded MgO powder decreases from about 0.25 mm. If the actual volumes of unreacted MgO and of formed oxyphosphate compounds are plotted, the volume proportions are even more striking because of the lower density of the mixed oxyphosphates (about 2.65)in relation to the density of the MgO (about 3.36).
For a range of grain sizes as shown in the Table, the volume ratio of oxyphosphate compounds to grain core volumes was observed to be about 3.5 and the total binder deposit adhered on free wood surfaces was about 165 microns with evidence ofpenetration of crystalline binder material into wood openings to a depth at least 60 microns, and a junction bond mass of thickness at least 325 microns was formed between contiguous fragment surfaces held compacted during the setting of the binder.
It may also be seen from the diagram, FIG. 5 that when the packing ratio of the applied MgO grain layer of sizes below about 0.25 mm is 0.85 or higher, the volume of oxyphosphate compounds produced is more than sufficient to occupy all voidspaces in the layer and to provide compounds for filling accessible wood spaces adjacent to the layer. With certain lower-density magnesia grains of high specific surface value the chemical combination with the phosphate solution is likely to causerapid early set of the compounds, making difficult or impractical the assembly of fragments such as strip or straw elements requiring careful positioning in successive layers. It is however practicable to dilute the MgO layer by admixture with eitherpartly or wholly inert granular solids as earlier discussed, without impairing the strength of the binder mass or its adhesion to wood surfaces, provided that the volume of binding compounds generated is sufficient to wholly occlude both the grain coresand the filler grains. The range of sizes of the added solid grains should generally conform with the size range of MgO grains of the mixture.
The total surface area of cement solids containing inert or nearly-inert particles admixed with MgO grains is correspondingly increased, allowing aqueous solution to move by capillary action and colloidal products to disperse at least as freelyas when solely MgO grains constitute the layer.
When it is desired to substitute particulate solids for a portion of the MgO grains, the additive comprising a material of density lower than that of the MgO, the volume of such additive must be correlated with the available reduced quantity ofbinding compounds corresponding to the reduced amount of MgO remaining, in order that the increased bulk of solids may be adequately bound and the deposit anchored in the wood surfaces adjoining.
For example where silica grains of the same range of grain sizes and relative amounts, having a density of 2.63 are to be used to replace part of a 100-gram quantity of MgO grains of density 3.36, and where from inspection of volume yield ofoxyphosphate compounds indicated in FIG. 5 it is evident that only 60 grams of the MgO would bind the equivalent solids volume of 100 grams and also fill spaces of adjacent wood to a desired depth such as 60 microns, the amount of filler should notexceed the weight indicated from the following calculation: ##EQU1## which in the present case would be calculated as: ##EQU2## Accordingly the cement solids mix would include 60 grams MgO and 31.3 grams of silica grains.
When it is desired to design a mixture of cement solids to form a given thickness of mineral deposit anchored in the wood surface of a given species, assuming the penetration into wood spaces is to be 60 microns depth, the volume of bindercompound to fill accessible wood spaces in this zone may be assessed for a wood of density 0.41 by finding the void ratio from the relation: ##EQU3## where the assumed species wood solids density is taken as 1.4.
The estimated anchoring deposit of about 9 milligrams per cm.sup.2 of wood surface may be used as the basis for determining the ratio of MgO grains to total cement solids for a junction mass of thickness 250 microns bridging between extended flatsurfaces of wood by the following procedure.
The average mineral solids deposit on each wood surface will be half of the junction bond mass thickness, i.e. 125 microns.
The amount of oxyphosphate binder for binding a packing of mineral solids of a selected grain size range as in Table I may be reduced for a packing ratio of 86% as:
where the average density of the binder compounds is 2.2.
The supply of 31.14 mg of MgO grains per cm.sup.2 of surface area provides the combined binding and wood-filling requirements which are:
as may be verified by reference to FIG. 5 showing that 100 grams total MgO furnishes 131.31 grams of the binding compounds.
The weight of silica which may be used to make up the deposit thickness if found from the calculation:
Accordingly the cement solids comprise a total weight of 39.64 milligrams per cm.sup.2 of wood surface area, as a mixture of 78.55% by weight MgO and 21.45% silica.
When the sole reactive grain material in a cement solids mixture is magnesia, ammonia gas formed according to the chemical equation previously mentioned is expelled from the binder mass partly into wood spaces and into void spaces betweenfragments as the mineral deposit is heated by formation of oxyphosphate compounds. The greater part of the ammonia gas which is evolved in early stages, i.e. within a few minutes from the bringing together of the components, escapes while the colloidmaterials are plastic, and a minor portion remains trapped as the compounds gel, thereby imparting a vesicular character to the deposit. The bubble volume actually locked in the binder mass is not greater than from about 20 to 35% of its volume.
It has been found that raw dolomite, consisting chiefly of magnesium carbonate with impurities such as silica and calcium carbonate, when ground in its raw state and dried but not calcined and screened to a suitable range of particle sizes, is soweakly reactive with ammonium polyphosphate solution of 10-34-00 analysis that at room temperature there is negligible reactivity, unless external heat is applied to the reactants. The reactive portion of dolomite grains in the sizes and weightproportions of TABLE I has been found to be considerably less than for high-density MgO. One dolomite which was tested extensively, of density 2.62, exhibited between about 5% and 14% of the effectiveness in production of oxyphosphates as the sameweight of MgO of density 3.36. Nevertheless the addition of ground raw dolomite to MgO grains confers the advantage that the speed of setting of the mixture is moderated when up to three parts by weight of dolomite grains are admixed per part of MgO. The ratio of vesicle volume to total binder mass is reduced.
Ammonium carbonate which has been shown to be formed by combination of magnesium carbonate with ammonium phosphates is a weak electrolyte which migrates freely in liquid occupying wood spaces, eventually lodging as a crystalline deposit of thesalt within tracheids and wood pores, which deposit augments the ammonium phosphate compounds remaining in the wood after curing, if an excess of solution has been supplied. It is believed that the presence of ammonium carbonate enhances thefire-retarding action of the ammonium phosphate deposit.
The proportioning of a cement solids mixture including ground raw dolomite is far less critical than with wholly inert solids such as silica, alumina, zirconia, magnesium and calcium silicates, and magnesium and calcium phosphates. This will beevident if the effect of a given volume of dolomite on the supply and distribution of oxyphosphate compounds is considered. From FIG. 5 the yield of such compounds from the given volume calculated for the reactivity rates observed after adjustment forthe difference in density of dolomite as compared with that of magnesia, would range from about 0.19 to about 0.38 volumes per volume of nonreacting dolomite grain portions. At the packing factor of 0.86 for grain grading according to TABLE I, it can beseen that sufficient binding compound volume would be produced to bond completely relatively large volume ratios of dolomite to MgO. However as a practical limitation a ratio of 4 parts of dolomite by weight to one part of MgO tends to make for delayedsetting and insufficient bonding due to an insufficiently high temperature during the first five or ten minutes to accelerate the dolomite-phosphate reaction. A satisfactory ratio has been found to be from 2 to 1 to 3 to 1 by weight, and equal parts byweight perform well but are slightly less economical.
Other solid additives which may be very slightly reactive and which provide strong binder masses are the calcium and magnesium silicates and phosphates. These solids appear to form, when present in finely-divided state, sites for crystalattachment of the binding compounds undergoing gelling. Their use should be on the same basis as silica grains.
For a more complete illustration and understanding of the process details for making mineral clad and bonded ligneus bodies with ammonium polyphosphates and earth metal oxides, hydroxides and carbonates descriptions of practical procedures,arrangements and products are offered as outlined in the following examples.
EXAMPLE I
The fact that ligneus fragments of all species reported in following examples may be successfully bonded by the oxyphosphate mineral binder of this invention strongly suggests that the reaction between ammonium polyphosphate and .[.magnesianof.]. .Iadd.magnesium or .Iaddend.calcium cement solids is substantially unaffected by exudates such as sugars and polyphenolics. Heretofore it was known that many woody plants carry within their lignocellulosic structure quantities of organicsubstances which, on addition of water and prior art cementing mineral compounds, are leached from the woody material and affect adversely the setting reaction of the cement.
To determine the tolerance of magnesium oxyphosphate reaction compounds discussed in the present specification to soluble sugars, as represented by dextrose, a series of mineral plugs were cast from mixes consisting solely of dextrose sugar,ammonium polyphosphate aqueous solution, and cement solids, using constant proportions of cement (75% by weight) to solution (25%) and varying the weight percent of the sugar from zero to 5%, expressed as percentage of the combined weights of solutionand cement solids. The cement solids were of grain size passing 100 mesh and retained on 200 mesh screen, 70% passing 150 mesh. The cement comprised 25% by weight of dead-burned magnesia of density 3.26 and 75% of ground raw dolomite of density 2.62analysing 45.1% MgCO.sub.3, the balance being chiefly silica CaCO.sub.3.
All plugs were cast without compaction and were released from the plug mold after 15 minutes in hardened condition and allowed to dry for 7 days. The strengths observed show no significant impairment of compressive strength, but a consistentdecrease of MOE with increasing sugar content, which is inferred to result from the crystal volume of sugar distributed in the mineral concrete structure.
TABLE II ______________________________________ COMPRESSION STRENGTH MEASURED Modulus of DEXTROSE *Crushing strength Elasticity TEST No. % Kg/cm.sup.2 Kg/cm.sup.2 ______________________________________ 1 nil 255 283,300 2 1 241 231,100 3 2 284 217,400 4 3 202 205,100 5 5 241 160,500 ______________________________________ *Plugs diameter 3.0 cm, height & cm.
From the previously-observed satisfactory setting of the binder when the ligneus fragments comprised green Western Red cedar (Thuja plicata) including bark and heart-wood, the cementing action appears not to be affected by contaminants in thefragments which would impair or prevent setting of prior cementing compounds.
It has also been noted that the mineral binder mass hardens equally well when in direct contact with a pitch pocket in Sitka spruce (Picea sitchensis), with an adhesion strength such that on breaking the binder away, pitch remained adhered to themineral.
EXAMPLE II
The partial impregnation of wood by ammonium polyphosphate solution and subsequent drying to retain a crystalline residual salt deposit within lumens and pores greatly enhances the strength properties, the improvements increasing generally withloading up to the physical limit. It has also been observed that when an adhered mineral deposit of metal oxyphosphate is attached to the wood surfaces as a continuous anchored layer, the impairment of strength resulting from fissuring and crackingproduced by cutting and crushing processes of forming the fragments is not only offset, but the fragment gains in intrinsic bending and compressive strengths and in the modulus of elasticity of the wood, exceeding by a large percentage the air-dry valuesfor clear whole-wood specimens. The improvement is inferred to result from the presence of a shell of mineral-vegetable material at the fragment surfaces, in which the in-situ generated oxyphosphate compounds have migrated for distances up to 30 to 150microns .[.on.]. .Iadd.or .Iaddend.more prior to the setting of the compound. When both a crystalline salt deposit is retained within the fragment upon drying of absorbed ammonium phosphate solution, and an in-surface mineral layer is anchored bycrystallization of colloidal metal oxyphosphates which have migrated into minute surface openings, the total strength enhancement is outstanding. For example, the increase of compression strength parallel to the grain in Aspen, or Red Alder, rangesupwards of 100%, accompanied by large increases of modulus of rupture (MOR), modulus of elasticity (MOE) and tensile strength to a lesser degree.
To illustrate the beneficiation of wood fragment strength properties by impregnating into the wood sufficient amounts of ammonium phosphate salt to impart fire retardant properties, and by adhering a mineral deposit of oxyphosphate compounds inwhich filler solid grains are embedded, eight sets of specimens of Aspen wood of density 0.38 in air-dry state were prepared from clear billets as beams of section 9 mm by 9 mm, and lengths 11.0 cm.
Two specimens were used in each of four tests (A) to (D) to measure static bending strength as a beam and compression strength parallel to the grain as a short column held at its ends. Three specimens were prepared for each of the tests (E) to(F) to measure the MOR and MOE values, the compressive strength, and the tensile strength alone without bending at rupture.
Test (A) obtained reference strength values for whole wood as MOR, MOE and compression strength. The static bending test was carried out with the specimen resting at its ends on supports spaced by span distance L with a load applied at themid-span position increasing gradually, e.g. by advancing a load .[.heat.]. .Iadd.head .Iaddend.at the rate of 0.05 cm per minute with continuous indication of applied magnitude. The following formulae were used for calculation: ##EQU4## The beam depthand width respectively (d and b) are 0.9 cm. P' is the load to proportional limit at which time the deflection y in cm is read. P is the load read at rupture.
Compression parallel to the grain was determined by supporting a second specimen as a column with its ends held in close-fitting seats, applying a steadily-increasing load, and observing the magnitude at failure.
Tests (B) were carried out similarly, with oven-dried wood, showing expected strength increases as has long been understood.
Tests (C) involved wet wood, having absorbed therein an amount of solution 0.47 grams per gram of wood, corresponding to a salt loading of 178 milligrams per cubic centimeter, which is an amount nearly three times the amount regarded as impartingacceptable fire retardant properties. As expected, the MOR and compressive strength of the wet wood were lowered, but the MOE exceeded that of air-dry wood.
Tests (D) were carried out on sticks which had been tempered to air dry moisture content after absorption of solution to retain a lesser amount of salt deposit of 140 milligrams per cc and re-drying. All strength properties were exceptionallyimproved.
Tests (E) used air-dry sticks which had received an impregnation load of 65 milligrams of ammonium phosphate per cc whereas tests (F) were carried out on sticks which contained little salt residue but also were coated by a formed mineral depositon the wood surfaces weighing about 36.5 milligrams per cm.sup.2 which had been formed by in-situ reaction between a wetting film of aqueous ammonium phosphate solution and a powder coating of dead-burned magnesium oxide grains of density 3.36 in a rangeof particle sizes below 100 mesh down to +250 mesh, in amount 30 milligrams per cm.sup.2. The amount of the wetting film was about 15 milligrams per cm.sup.2 of stick surface. The cured deposit had a mean thickness estimated at 140 microns and bridgedthe residual magnesium oxide grains. The cementing material included about 10.5 milligrams of magnesium oxyphosphate compounds occluding about 26.5 milligrams of unreacted magnesium oxide grains. From microscopic examination the mineral deposit wasinferred to have extended into pores and tracheid openings and to have formed crystalline masses extending at least one cell depth from the wood surface, and to occupy at least portions of the microspaces within an outer 50-micron-deep wood zoneextending inwardly of the stick surface
From tests (D) it will be apparent that ligneus materials are strengthened and stiffened to a marked degree by an impregnating salt deposit. The combined effects of both internal salt deposition and surface cladding by intimately adhered mineralbinder is a still further strength gain. Tests (E) show the strength enhancement contributed by a minor volume of adhered surface mineral deposit. The absorption of ammonium polyphosphate in any practical amount leads to a surprising and unexpectedimprovement in bending and compression strengths. The test data reports strength values in cast structural products far exceeding those known from any prior art vegetable/mineral composites.
The modest or even negative tensile strength differences noted for tests (E) or (D) and (F) can be attributed to the fact that mineral binders are weak in tension. Claddings of 70 microns to 200 microns thickness cannot be expected to contributeusefully to the tensile strength of a vegetable substrate, especially in view of the large difference of the respective elastic moduli. The cement coating initially takes up most of the tension and shear stresses created by the differential elongationsof the substrate and coating, failing long before maximum tensile stress can be developed in the substrate. The initially-higher strength of cement-coated composites undergoing loading is evidenced in the stress/strain curve only up to 20% or 30% of thebreaking load, the more curved portion pertaining obviously only to elongation of the wood.
The most important benefit .[.comferred.]. .Iadd.conferred .Iaddend.by the combination of an internal impregnation load of salt and an adhered surface cladding of mineral deposit is obviously realised when the composite is subjected tocompressive stress parallel to the loaded surfaces, as may be seen from tests (E) showing a strength improvement of 175%.
TABLE II __________________________________________________________________________ EFFECTS OF LOADINGS OF AMMONIUM POLYPHOSPHATE AS IMPREGNATING SALT DEPOSIT IN ASPEN (Populus Tremuloides) CLEAR COLUMNS AND BEAMS, AND OF SURFACE DEPOSIT OFMAGNESIUM OXYPHOSPHATES OCCLUDING MAGNESIA GRAINS WOOD TREATMENTS Max. Moisture Surface grams Modulus of Modulus of Crush Tensile Modulus of TEST Content, Deposit Salt Rupture, incr Elasticity Incr. Strength Incr. Strength Elasticity No. Weight % mg/cm.sup.2 per cc kg/cm.sup.2 % kg/cm.sup.2 % kg/cm.sup.2 % Kg/cm.sup.2 kg/cm.sup.2 __________________________________________________________________________ A 8.72 -- -- 720 -- 73,000 -- 408 -- 1050 69,500 B 1 -- -- 820 +1498,000 +34 527 +29 -- -- C 56 -- 0.718 610 -- 92,300 -- 287 -- -- -- D 7.9 -- 0.140 1290 +79 125,000 +71 952 +133 670 72,000 E 8.72 36.5* 0.140 1740 +142 142,000 +95 1120 +175 1010 97,700 F 8.72 36.5* 0.005 950 +32 99,500 +36 -- --668 77,000 __________________________________________________________________________ *26.5 mg MgO, 10 mg magnesium oxyphosphates, 160 to 200 macron layer
MINERAL-LIGNEUS COMPOSITE STRUCTURAL PRODUCTS
EXAMPLE III
Screened spruce fragments passing 10 mesh and retained on 20 mesh screens, having 8.3% moisture content in air-dry condition were divided into nine samples and treated with varying amounts of ammonium polyphosphate solution of specific gravity of1.4 of analysis 10-34-0. Each sample was coated with a constant weight of cement solids passing 100 mesh screen consisting of 75% ground dolomite and 25% dead burned MgO in quantity equalling 2.5 times that of wood (weight). The weight of the solutionwas varied in three steps. No compaction pressure was applied to the mixture during casting into plugs of length and diameter respectively of 7.7 cm and 3.03 cm. Compression testing to failure was carried out on a universal testing machine just 30 minafter casting the plugs. The data shows highest early strength for samples 2, 3 and 6. The results are given in Table III
TABLE III ______________________________________ Com- pressive Wood Cement solids Solution Product Strength, Test Weight Dolomite MgO weight Density kg/cm.sup.2 ______________________________________ 1 1 2.25 0.75 1.50 0.82 17.9 2 12.25 0.75 2.10 0.86 26.4 3 1 2.25 0.75 2.70 0.93 26.7 4 1 -- 3.00 1.50 0.82 12.7 5 1 -- 3.00 2.10 0.86 20.0 6 1 -- 3.00 2.70 0.93 26.8 7 1 2.95 0.05 1.50 0.82 15.1 8 1 2.95 0.05 2.10 0.86 17.9 9 1 2.95 0.05 2.70 0.93 18.8 ______________________________________
EXAMPLE IV
In Table IV compressive strength for composite ligneous fragment castings of numerous species indicative of the wide range of applicability of this bonding technnology is given where the screening fragments of passing 5 mesh and retained on 20mesh were treated to remove the green moisture to 8% residual moisture content followed by application of weighed portions of ammonium polyphosphate solution of 10:34:0 analysis and uniform cement weights consisting of 75% dolomite and 25% MgO (deadburned). The wood:cement ratio was 1 part wood to 3 parts of cement solids and the wood to ammonium polyphosphate ratio was 1 part of wood to 2.10 parts of solution. The compaction pressure was 1.0 kg/cm.sup.2 and compression tests followed 30 min,after 15 min heating at 105.degree. C. and 7 days at .[.20 C.]. .Iadd.20.degree. C.Iaddend.. Variations noted in the early strength (30 min) samples are due to the intrinsic particle strength rather the interferance of some wood constituents with thebonding process as noted from the prior art dealing with wood products bonded with Portland cement and other magnesite cements.
TABLE IV ______________________________________ Compressive strength, kg/cm.sup.2 Curing Mode Lignocellulosic Den- 30 15 min Test Species sity minutes @ 105.degree. 7 days ______________________________________ 1 Spruce 0.87 23.2 26.457.3 2 Spruce 1.07 23.5 35.0 94.1 3 Spruce 1.30 28.6 46.6 114.7 4 Spruce Excelsion 0.45 -- -- 15.1 5 W. Red Cedar 0.50 11.8 16.8 20.1 6 W. Red cedar 0.77 16.9 23.2 44.9 7 W. Red Cedar 0.96 25.5 33.2 48.8 8 W. Larch 0.89 22.7 -- 59.1 9 BlackLocust 1.09 25.7 43.9 93.2 10 Keruing 1.23 33.0 48.8 92.4 11 Beech 1.03 20.6 44.9 64.7 12 Hemlock Driftwood 0.86 21.2 -- -- 13 HembalFir Chips (Wet) 0.86 14.7 -- 36.6 14 Bark Douglas-Fir 0.75 17.1 -- 23.6 15 Cottonwood 0.58 18.0 19.2 28.5 16Rice Husks 0.97 -- 19.2 -- 17 Bagasse 0.89 17.2 -- 25.3 ______________________________________
Where the sample is shown with different cast density, compaction pressures were 1, 2 and 10 kg/cm.sup.2. The tests show that room temperature curing was superior to that of oven curing and that at higher compaction pressures the attainedstrength was highest with such cure (7 days at 20.degree. C.)
EXAMPLE V
A series of samples using air dried spruce fragments passing 5 mesh but retained on 20 mesh screen, in the form of slivers of a range of lengths approximately 0.5 cm to 3 cm, was mixed with ammonium polyphosphate solution and cement solids of thesame composition used in the previous example, by keeping the proportion of solution to cement solids constant as follows:
TABLE V ______________________________________ Compression Strength, kg/cm.sup.2 Cement Curing mode Wood Solids Solution 15 min 7 days Test Weight Weight Weight Density @ 105.degree. @ 20.degree. ______________________________________1 1 2.0 1.4 0.65 8.2 29.2 2 1 3.0 2.10 0.87 25.5 57.3 3 1 4.0 2.80 1.02 29.0 51.9 4 1 5.0 3.50 1.20 43.9 122.5 ______________________________________
The samples were formed with a low compaction pressure of about 0.5 kg/cm.sup.2 and the density variation being primarily due to the variation of cement solids used. Tests No. 1 and 2 show that high quality low density products are realisablewith relatively low reactant costs.
EXAMPLE VI
Board products of various fragment types, ligneous species and technical description were prepared in molds as described in TABLE VI. The weighed fragment masses were treated first with predetermined amounts of ammonium polyphosphate of 10:34:00NPK analysis and allowed to soak until all of the solution was absorbed in the fragments. The wet fragments were then dusted with the weighed amount of cement dust of predetermined composition and the mass poured into a mold having polished stainlesssteel surfaces. The molds were placed into a cold press and the mass compressed to a predetermined nominal thickness and held under pressure for 5 minutes. The hardened boards were removed from the molds and air dried in a forced air cabinet at roomtemperature for 7 days. The bending specimens measured 6.5 cm by 25 cm supported on a 15 cm span.
The cement filler was -100 mesh raw dolomite and the ammonium polyphosphate was either wet process green or black acid. The MgO was either dead burned or USP heavy powder of 3.54 specific gravity as noted in the TABLE.
TABLE VI __________________________________________________________________________ Compo- sition: kg Wood Cement Nominal Modulus Modulus solids Thick- of of Fragment Poly- ness Den- Rupture Elasticity Type phos | | | |
