NO151122B - PROCEDURE FOR THE PREPARATION OF A CASTED STRUCTURAL BODY WITH HIGH STRENGTH AND GOOD FLAMMABLE PROPERTIES - Google Patents

Description

The present invention relates to a method for producing a molded structural body with high strength and flame retardant properties and comprising a mineral mass which is integrally attached to particles of a lignocellulosic material embedded therein, as well as the structural body obtained by this method.

US patents 2,175,568 and 2,837,435 and British patent 1,089,777 describe methods for the production of lightweight concrete products containing as filler particles of lignocellulosic material. They use different cement compositions and all three patents point out that objects made by cementing lignocellulosic particles have poor strength properties due to the presence in the lignocellulosic material of certain substances, such as resins, gums, waxes, fats and wood sugars, which migrate from the particles into the cement and has a detrimental effect on its setting and hardening properties. As a method to overcome this problem, these patents describe a pre-treatment of lignocellulosic material with an aqueous solution of alkali metal hydroxide, and washing and drying of the treated material.

It is also well known to use ammonium, alkali metal, aluminum and chromium orthophosphates, pyrophosphates or polyphosphates together with magnesium oxide and non-reactive or only slightly reactive thickeners or fillers in mineral cement compositions. Thus describes US-

patent 3,525-632 a fast-setting mineral cement containing phosphoric acids and phosphates, as well as magnesium oxide and thickening agents. Somewhat similar compositions and their use for repairing furnace walls and furnace linings are described in US Patents 3,278,320; 3,285,758; 3,413,385 and 3,475,188;

and US Patents 3,821,006 and 3,879,209 describe such compositions and their use for the repair of deteriorated mortar, concrete, wood material, ceramics, plaster and the like, e.g. cracks in road bodies or a section of a concrete road.

The problem to be solved by the present invention is to provide a flame-resistant, molded structural body with high strength containing lignocellulosic fragments as filler material, and a method for producing such a shaped structural body which can be easily varied so that the densities of the bodies obtained and their porosities vary within a wide area.

A flame-resistant, molded, high-strength structural body according to the present invention comprises a mineral mass integrally attached to particles of a lignocellulosic material embedded therein, and is derived from a mixture of particulate lignocellulosic material, an aqueous ammonium polyphosphate solution, and dead burnt magnesium oxide, and calcium oxide and/or carbonate and/or magnesium carbonate and mineral softening agent particles.

The method according to the invention for producing a cast structural body with high strength and good flame retardant properties and comprising a mineral mass integrally attached to particles of a lignocellulosic material embedded therein comprises

a) mixing the lignocellulose particles with an aqueous ammonium polyphosphate solution or with powdered

ammonium polyphosphate salt and water in an amount from 0.26

to 1.33 parts by weight P2°5 Part by weight of the lignocellulose particles, and with mineral cement solids comprising a mixture of dead burnt magnesium oxide, as well as calcium oxide and/or carbonate and/or magnesium carbonate and mineral softening agent particles, the mineral cement solid being present in an amount from 0.93 to 5 times the weight of the lignocellulosic material and containing between 0.05 and 3.0 parts by weight of dead burnt magnesium oxide per weight fraction of the lignocellulosic particles,

b) molding the mixture into a shaped body, and

c) curing the shaped body between 10 and 50°C.

According to a preferred embodiment of the invention, mineral cement solids are used which are a mixture of dead burnt magnesite and ground dolomite in a weight ratio of from 1:3 to 1:59.

The casting can be carried out at atmospheric pressure or with a compression pressure, e.g. up to 12.0 kg/cm 2. Closed surfaces, tiles, pipes and the like can be produced by spin-moulding. Lightweight structural bodies with densities as low as 340 kg/cm can be achieved.

By mixing the lignocellulosic particles with the ammonium polyphosphate solution or ammonium polyphosphate and water, as well as softening agent particles, the dead burnt magnesium oxide reacts with the ammonium polyphosphate to form a gel that enters the pores and cracks of the lignocellulose particles, and this gel quickly solidifies into a stiff stone-forming solid that adheres adheres strongly to the lignocellulose fragments and binds them to each other. The binding strength is not weakened by any substances that migrate from the lignocellulosic particles into the mineral binding mass.

A wide range of lignocellulosic materials can be used in the present method, such as fibres, stems, trunks and branches of woody plants and forests and crop residues, obtained by breaking or cutting; and a variety of different structural bodies, such as panels, slabs, beams, columns, planks, tiles and tubes, can be produced by the method.

The reaction of the burnt magnesium oxide with the ammonium polyphosphate solution is strongly exothermic and releases water and ammonia. A peak temperature of 50-65°C is achieved even if small amounts of dead burnt MgO are reacted with an excess of ammonium polyphosphate solution during 10-20 minutes of mixing. At higher temperatures, magnesium and calcium carbons present in the mineral binder material also react with the ammonium phosphate solution so that carbon dioxide is released. Thereby, the product achieves a porous structure if it is allowed to solidify undisturbed. The reaction becomes irreversible once the gel point is

passed and cannot be stopped even if the reactants are exposed to large amounts of water, which may be seawater. Upon hardening of the gel, the reaction products achieve 50-75% of their final strength. Maximum compressive strength is reached at a moisture content of 8-10% and after most of the ammonia has disappeared.

in

In the present method, a liquid ammonium polyphosphate consisting of 65-85% ?2°2 combined as polyphosphates, and 25-30% as orthophosphates can be used, or by different ammonia treatment of a salt product with a P2^5~ content equally divided between ortho - and polyphosphate salts.

The magnesium oxide is dead-burnt, dense, granular magnesite or dead-burnt magnesium oxide rather than just calcined magnesite. In addition to the highly reactive, dead-burnt magnesium oxide, the mineral cement solids used contain less reactive components, such as calcium oxide and/or magnesium carbonate and/or calcium carbonate and inert softening agent components, such as silicon dioxide, zirconium oxide, aluminum oxide, alkaline earth metal phosphates and silicates and mixtures thereof.

The amount of ?2C>5 indicated in the following examples is provided and stated for a better understanding, from the amounts of ammonium polyphosphate solution or solid ammonium polyphosphate salt, respectively, as follows: 1 part by weight commercial ammonium polyphosphate solution of fertilizer quality and with a specific weight of 1 ,4 and an NPK analysis of 10:34:00, contains 0.5 parts by weight of salts of which 0,49 parts comprise ammonium polyphosphates with an average analysis NH4:P205:K corresponding to 10:34:00. This means that 1 part by weight of the solution contains Similarly, 1 part by weight of commercial ammonium polyphosphate salt with NPK analysis corresponding to 11:55:00, contains approx. 0.98 parts by weight ammonium polyphosphates with average analysis NH4:P205:K equal to 11:55:00 or

The amounts of ?2^5 °PPn=ls thus by multiplying the used amounts of solution (examples 2-7) and salt (example 8) by 0.38 and 0.82, respectively.

The quantity ratio stated above from 0.26 to 1.33 parts by weight of P2°5 per part by weight of lignocellulosic particles is based on the following: In example 8, 69 g of commercial ammonium polyphosphate salt is used with NPK analysis corresponding to 11:55:00 containing 0.82 parts by weight P2O5 Pr- part by weight salt and 215 g lignocellulosic particles Thus the ratio P^O,.:

In sample 4 in example 4, ammonium polyphosphate solution is used with NPK analysis corresponding to 10:34:00 and containing 0.38 parts by weight P2O5 Pr-part by weight solution and lignocellulose particles in a weight ratio of 3.5:1. Thus the ratio P„0C:lignocellulose = 0.38 x 3.5 : 1 = 1.33.

The following examples illustrate the invention.

Example 1

In order to determine the tolerance of the mineral binder used according to the invention to water-soluble plant constituents such as sugars, polyphenolic compounds and gums, a series of plugs with a diameter of 3 cm and a height of 8 cm were cast using constant proportions of solid cement substances NPK 10- 34-00 (25% by weight) and polyphosphate solution (75%) and a varying weight proportion of sugar of 0-5% expressed as a percentage of the total weight of solution and cement solids. The cement solids had a grain size that exceeded 100 mesh and was retained on the 200 mesh sieve; 70% passed 150 mesh. The cement consisted of 25% by weight dead burnt magnesium oxide with a density of 3.26

and 75% ground untreated dolomite with a density of 2.62 which assayed 45.1 MgCO^, the remainder being mainly silica and CaCO^. All plugs were cast without pressure and removed from the cylindrical molds within 15 minutes of curing and allowed to dry for 7 days before pressure testing. The mineral binder proved to cure just as well when in contact with a pocket of sieved spruce veneer in other samples, with a bond strength such that when the binder was broken away, there was still some attached to the mineral.

The consistent reduction in modulus of elasticity with increasing sugar content is assumed to be a result of the crystal volume of sugar distributed in the mineral binder.

Example 2

Sifted spruce fragments passing 10 mesh and retained on a 20 mesh sieve, with a moisture content of 8.3% in the air-dried state, were treated with varying amounts of ammonium polyphosphate with a specific gravity of 1.4 and with analysis NPK 10- 34-00. Each sample was coated with a constant weight of cement solids passing 100 mesh and consisting of 75% ground dolomite and 25% dead-burnt magnesite in an amount equal to 2.5 times the weight of the wood fragments. No compaction pressure was applied when making plugs 7.7 cm in length with a diameter of 3.03 cm. Pressure tests to failure were performed 30 minutes after casting the plugs. The results are given in Table II.

Example 3

The compressive strength in Table III for plugs cast as described in the preceding example is repeated for a large number of wood fragments to indicate the wide range of application of this bonding technology. The wood fragments passed 10 mesh but were retained on a 20 mesh sieve and were dried to a moisture content of 8.3% and treated with weighed portions of ammonium polyphosphate solution of 10:34:00 analysis and equal weights of cement consisting of 75% dolomite and

25% MgO (dead burnt). The ratio of wood to cement was 1:3 and the ratio of wood to P^jO,- was 1:2.1 of solution. The compression pressure in the mold was 1 kg/cm 2 and the pressure tests followed 30 minutes after 15 minutes of heating to 105°C and 7 days at 20°C after the original mixture. Variations in the early strength reflect the internal particle size rather than the influence of any wood constituents on the bonding process as noted in previous methods using Portland cement and other magnesite cements. Samples of the same wood species with different product densities were produced with 1, 2 and 10 kg/cm 2 compression pressure at the time of casting.

Example 4

A series of samples using air-dried spruce fragments that passed 5 mesh but were retained on a 20 mesh sieve, in the form of strips ranging in length from approx. 0.5-3 cm, was mixed with ammonium polyphosphate solution and cement in the same proportions as used in the previous example, keeping the ratio between solution and cement solids constant as follows:

The samples were produced with a low compression pressure of approx. 0.5 kg/cm 2 and the density variations are mainly due to variations in the solid cement substances that were used.

Samples no. 1 and 2 show that low-density products of high quality can be produced with relatively low reactant costs.

Example 5

Board products with different fragment types, wood species and technical descriptions were produced in forms as described in table V. The weighed fragment masses were first treated with specific amounts of ammonium polyphosphate with 10:34:00-NPK analysis and allowed to remain in the liquid until the entire solution was absorbed in the fragments. The moist fragments were then coated with the weighed amounts of cement dust of predetermined composition and the mass was poured into a mold with polished stainless steel surfaces. The molds were placed in a cold press and the mass compressed to a predetermined nominal thickness and held under pressure for 5 minutes. The cured sheets were removed from the molds and air dried with forced air circulation in a room at room temperature for 7 days. The specimens for bending measured 6.5 cm and were 25 cm long and were laid with a span of 15 cm.

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 burnt or USP heavy powder with a specific gravity of 3.54 as indicated in the table.

The weight ratio of wood:cement:P2°5 was 1:2.5:0.57 in tests 1-5 and 7-10; 1:2.9:0.68 in trial 6; and 1:3:0.34 in trial 11.

Example 6

A series of boards was produced using oriented wood fragments from sugar cane husks which are the outer,

the fibrous stem part which lies radially inwards from a hard, 5 waxy and silicon-containing skin layer, with a thickness of from 1.3-2.8 mm. The pith on the inside and the wax coating on the outside were removed by mechanical action and fibers with a cross section of 1.5-5 mm and a thickness and length of 1.0-2.0 mm were cut

up to lengths of 15-20 cm mechanically.

10

Known proportions by weight of the fibers were treated with different compositions of ammonium polyphosphate (the black acid type) and solid cement substances which consisted of approx. 0.75 parts MgO with hay

density and activity and 2.25 parts ground dolomite with an analysis of 4 5.1% MgCO^ where the rest is mainly silicon oxides and CaCO^. All cement solids passed a 20 mesh sieve. Compression pressure during casting was 0.5, 0.7 and 7.6 kg/cm 2 and nominal plate thickness was set to

2.12 and 1.19 cm respectively. The corresponding breaking strength and modulus of elasticity are given in Table VI. The plates were stored for 7 days before plating. The bending tests had a size that is described in the previous example.

Example 7

Structural board products with low density and which are fire-retardant were produced from sugar cane residues, i.e. bagasse which is the result of the mechanical expulsion of the cane juices by passing the pipes where the leaves have been removed, through crushing rollers followed by water rinsing. The compressed tubes were then crushed into particles consisting of the fibrous structure, pith and all other components of the plant, i.e. wax and siliceous coating usually found on the outside.

The crushed fragments had particles from 8 cm in length with

in

a thickness of between 1 and 4 mm. Dust and fine fragments smaller than 20 mesh in size were removed by sieving.

The specific gravity of the bagasse was estimated at 0.21, and the surface was determined to be 19,000 cm per square meter. 100 g of air-dry fragments.

A sample amount of 200 g of air-dried fragments was treated with 360 g of commercial ammonium polyphosphate fertilizer solution with a specific gravity of 1.4 and an analysis of 10:34 NPK, corresponding to wood: Po0c = 1:0.68.

A cementitious solids mixture of 150 g dead burnt magnesium oxide and 450 g powdered dolomite passing 100 mesh was screened onto the polyphosphate moistened fragments and mixed for 22 seconds. The amount of MgO grains judged from the measured density of 3.36 was assumed to provide 11.5% or 17.3 g of reactive MgO as oxyphosphate, therefore 132.7 g will only serve as a dense, inert filler. Similarly, it was assumed that the dolomite would give 10.5 g of MgO to the reaction, and the rest inert filler (428 g).

The mixture of bagasse and cement was immediately transferred

in a plate mold measuring 15 x 30 cm, leveled and pressed under a pressure plate with a pressure of 7.35 kg/cm 2. The thickness was kept at 2.53 cm. The pressure was removed after 12 minutes,

and the plate was air-dried for five days before testing. The temperature in the plate when it was removed from the mold was 54°C.

The resulting plate product had a hardened volume on it

1017 cm and weighed 998 g, giving a mass density of 0.98. The breaking strength and modulus of elasticity in static bending were 79.4 and 17,900 kg/cm 2 respectively.

A calculation of the residual amount of ammonium polyphosphate (when

disregarding ammonium carbonate formed from dolomite) solution that only remained as dried salt crystallized in the pores of the bagasse indicates an amount in excess of what is needed to meet the fire requirements in class A for lignocellulosic substances. Accordingly, the product was tested for flammability by exposing it to a direct flame of 800°C over an area of 4.5 cm x 4.5 cm for 15 minutes. At the end of this period, only minor surface burning could be seen without flames having arisen. You could see a smaller gas outflow and evaporation from the beginning when the side facing the flame became red-hot, while the opposite side was only warmer than 40°C.

In another test, the flame temperature was increased to 1200-1400°C where the surface exposed to the flame became glowing hot at approx. 30 seconds, and the mass of material was gradually removed by forming a crater. After 3.5 minutes the opposite surface began to glow, and by 5 minutes the 2.25 cm plate had burned through to the other side.

Example 8

Ammonium polyphosphate in solid form such as TVA's NPK 11:55:00 or 12:54:00 is also useful as an impregnating salt in a one-step mixture of calcium and magnesium compounds with fragments, salt and water to achieve bonding.

In a first test, 69 g of 11:55:00 salt was added to 215 g of air-dried oar flakes with a thickness of 1.3 mm and with

a width and length of 2 and 6 cm respectively. A further 250 cement solids were added to the mixture, which consisted of 25 parts dead-burnt magnesite and 75 parts ground dolomite massing 100 mesh. After complete mixing of the dry solids, 100 g of water was sprayed over

the mixture with continuous stirring, and 30 seconds later the mass was poured into a mold, leveled and compressed under a pressure of 3 kg/cm 2 for 10 minutes, after which the pressure was released, and the plate was air-dried for 7 days before testing . The plate thickness was 1.9 cm, which gave a density of 0.54 g/cm 3. The breaking strength and modulus of elasticity were 18.6 and 10,200 kg/cm 2 respectively.

In another attempt to use solid ammonium polyphosphate

the salts were first dissolved in water, after which the solution was added to the flakes. The electrolyte-moistened flakes were applied with the same quantity of solid cement substances as in the previous example, and cast into a plate with the same dimensions. After curing for 7 days, the sample had a density of 0.54 g/cm 2 , a breaking strength of 20.0 and a modulus of elasticity of 12,100 kg/cm 2 . A sample prepared with liquid 10:34:00 ammonium polyphosphate of the same thickness had a density of 0.87, a tensile strength of 36.9 kg/cm 2 and a modulus of elasticity of 17,500 kg/cm 2 , suggesting that solid ammonium polyphosphate may be a suitable substitute for liquid salt.

Example 9

To test the durability of the composite material using wood fragments coated with magnesium oxyphosphate where powdered silica sand was used as an inert filler, two samples were prepared with an average thickness of 2.12 cm and a density of 0.55.

One set was tested in an air-dried state after 7 days of curing at room temperature. The breaking strength of the samples was 25.7 kg/cm 2, and the corresponding modulus of elasticity was determined to be 12,340 kg/cm 2.

The other test set was alternately immersed in tap water

and seawater with air drying between immersions.

A total of 7 such cycles were carried out, and the resulting samples were finally tested by bending in an air-dried state. The reduction in breaking strength was 7%, and the weight loss was 3% for the treated samples.

The relatively high degrees of bonding that are possible with the present invention make it possible to continuously cast wood products with a mineral binder of high strength and light weight that have hollow, circular or rectangular shapes such as are used in drainage pipes, culverts and longitudinal pipe sections. The usefulness of the invention for such applications becomes particularly obvious when porosity and permeability to liquids is made technically possible by choosing manufacturing conditions under which lightweight pipes can be produced. On the other hand, by choosing the conditions under which migration of colloidal substances to the product surfaces is promoted, as in rotational molding processes, drain pipes and pipes with closed surfaces can be produced. In a similar way, it will be possible to produce rods where high bending strength and light weight are important in continuous casting processes where a slow rotation of the mold is used during and after casting so that the wood and cement mixture is simultaneously densified and gets a colloidal migration to the surface due to the centrifugal force.

By varying this technology, a large amount of molded products can be produced.

Claims (2)

1. Process for producing a molded structural body with high strength and good flame retardant properties and comprising a mineral mass which is integrally attached to particles of a lignocellulosic material embedded therein, characterized in that (a) the lignocellulose particles are mixed with an aqueous ammonium polyphosphate solution or with powdered ammonium polyphosphate and water in an amount from 0.26 to 1.33 parts by weight ^ 2^ 5 ^ r' weight (3el) of the lignocellulose particles, and with mineral cement solids comprising a mixture of dead burnt magnesium oxide, as well as calcium oxide and/or carbonate and/or magnesium carbonate and mineral drier particles, the mineral cement solids being present in an amount from 0.93 to 5 times the weight of lignocellulosic material and containing between 0.05-3 .0 parts by weight of dead burnt magnesium oxide per part by weight of the lignocellulosic particles, (b) the mixture is molded into a shaped body, and (c) the shaped body is hardened between 10 and 50°C. 2. Method according to claim 1, characterized in that mineral-cement solids are used which are a mixture of dead-burnt magnesite and ground dolomite in a weight ratio from 1:3 to 1:59.