CA1241900A - Composite material based on particles of a plant origin and the method of manufacturing thereof - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE:

The present invention pertains to a composite material from parts of a plant origin, for example, from wooden elements, veneers, chips, sawdust, bark, corn cobs, stalks and straw, containing lignocellulose materials with the content of polysaccharides, lignin, tannins, essential oils, which parts are bound together in the said composite material. The invention consists in application of an activation agent, for example, sulfuric acid, on the parts of starting material, which causes transformation of the polymeric compound of parts to an active monomer. An ex-cess of activation agent is neutralized, if it is desired, by addition of a neutralization agent, for example, powder-ed urea. The activated parts are then put together and compressed under heating, to cause crosslinking of the activated monomer to a polymeric compound of similar char-acter as is the original polymeric compound and thus bind the parts together. The activation effect can be increased by addition of a catalyst, for example, potassium permanga-nate. The binding effect of the binder generated from the lignocellulose material may be increased by addition of furylalcohol, furylaldehyde, furylacetone, phenols, or their precondensates or thermoplastics.

Description

12,~9~0 The invention relates to a composite material from parts of a plant origin based on lignocellulose material, which are bound together with a polymeric com-pound derived from an original polymer of starting material 'by transformation of the original polymer through actiVatiQn to active compounds able to react and by crosslinking. The invention also pertains to a method o manufacturing the said composite material.
Composite materials based on plant raw materials, in particular on wooden elements, fibers, chips,~shavings, ' sawdust, and the like, are manufactured at the present by mixing dry and hydrophobizea particles with various binders, mainly with thermosetting binders, e.g., with an urea-formaldehyde resin, and subsequent pressure moulding at I 15 temperature above 130C to the required form of a construc-tion element, prevailingly;to boards. These materials are produced in many varieties, which difer from one another by the type of starting raw material, the type o-f binder, molding pressure, and temperature. Thelr main common ~20 disadvantage is a long-lasting escape of cleavage products' o the resinous binder, namely ormaldehyde, oligomers o urea with formaldehyde, or phenol, which have cancerogenic or other undesirable~metabolic efects on human organism.
' Because these materials, in particular chip boards, became recently a still more important construction components of living houses, the above said disadvantage of the known ; prior art composite materials from plant parts or particles ' became very serious. penetration of these products into the interior space of buildings should be preven-ted'by various measures, which increase the building cost.
Bonding of wooden elements is carried out so far by means of adhesives of various kinds, which are applied Jon contact surfaces of the bound elements. In addition to the necessary application o an adhesive layer on the sur-' .

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face of formed joint, which is performed either in a coldstate or under heating, depending on the type of adhesive used, the joint should be allowed to rest for a relatively long time to secure evaporation of water from aqueous adhesives, or evaporation of solvents from solvent adhesives to polymerize, in some cases at elevated temperature and pressure. Some adhesives are harmful to health during their preparation or also during usage of the adhesivebound parts.
This refers in particular to adhesives containing formaldehyde, which has cancerogenic or other undesirable metabolic effects to human. Therefore, the adhesive bonding of wood and lignocellulose materials is still rather time consuming and, in many cases, it has also high demands to energy consumption, in particular in the manufacturing of composite elements with large interfaces, namely ply-wood and veneering of wooden bases or bases from lignocellulose materials.
Another disadvantage of such prior art composite materials is the complexity of the manufacturing process, including the preparation of a p.econdensate and a strict observation of technological process, which is necessary to attain the required quality of products. Consequently, the materials do not allow to increase the productivity by reduction of the production cycle. During the production process, namely during pressure moulding, harmful reaction products with a high content of formaldehyde are liberated in a high concentration from the moulded material. Another shortcoming is also a high price of articles made from the said prior art materials, which is caused by relatively large amounts of the dosed binder, which is present in the articles in amount of from 10 to 30 weight percent as a rule.
The invention proposes a new method of manufacturing a composite material from particles of a ,, , I, polymeric lignocellulose material, which method overcomes -the above mentioned shortcomings.
According to the new method, the individual particles are bound together with a polymeric compound derived from the original polymer of the starting lignocellulose material, by transformation of this original polymer through activation, to active compounds able to react, which compounds are -then transferred into a final polymeric material by crosslinking.
More particularly, the method according to the invention comprises the steps of:

- contacting surface portions of at least one part of the lignocellulose matexial particles with an activation agent selected from the group consisting of concentrated H2S04, concentrated H3P04, HN03, urea sulfate, NH4HS04, concen-trated P205 and mixtures thereof, to depolymerize only said surface portions of said at least one part of the lignocellulose material and form a monomeric or oligomeric binding agent therefrom; and - heating and compressing said lignocellulose material particles and said monomeric binding agent for a time and under a temperature and a pressure sufficient to cause the said surface portions of said at least one part of the lignocellulose material particles to incorporate the said A monomeric or oligomeric binding agent therein and repolymerize to form a hardened mass with cohesion bonds among particles.
The main advantage of the composite material obtained by the method according to the invention is that the binder necessary for bonding of individual adjoining parts is formed directly from the material of these particles by means of an activation agent, for example, sulfuric acid, applied on the surface of the said particles.
Articles made from the composite material according to the invention contain exclusively the starting material and a small amount of deactivated 12419(~0 harmless to health, and, in addition to this, the cost for preparation of relatively expensive binders is avoided.
Preparation of the material before pressure moulding proceeds in one step and consists in application of the S activation agent of the surface of particles of a plant origin.
Another advantage of the method according to the invention is the possible utilization of a virtually waste material, e.g. of bark. At the same time, the content of water in particles need not to be diminished, in contradistinction to the known prior art methods, so that the energy necessary for drying of the starting material is saved.
Manufacturing of the composite material according to the invention is achieved by the action of an activation agent upon a part of the starting material of a plant origin, to degradate the original high-molecular-weight polymeric binder of the starting material to a monomer, followed by neutralization of the excess of activation agent, if this is desired, and by the action of pressure and heat on the parts, which are at least in part coated on the surface with a layer of monomer, to cause polymerization of the monomer to a polymer derivative, which binds individual parts of the ma.erial together.
The activation agent is added only to a portion of parts of the starting material of a plant origin, which portion is then mixed with the remaining portion of parts.
Then, an article is shaped from this mixture into a cohesive form.
The starting material used, in this manufacturing method are parts of a plant origin, which contain lignocellulose material comprising polysaccharides, lignin, tannins, essential oils and the like, for example, wooden elements, chips, flan chaff, sawdust, shavings, corn cobs, chopped straw and dry stalks in a crushed form, and various fibers. The resulting material is cohesive and is pressure moulded in particular into the shape of boards, blocks, which strength, other mechanical properties, and other parameters considerably depend on the starting material and the manufacturing procedure. The resulting material aan be used in the form of boards, blocks and other pressed mouldings for construction parts of buildings or furniture or insulation purposes.
The hydrolytic effect of acids is used in the method according to the invention to liberate furylaldehyde and its derivatives and thus activate the lignocellulose materials. Monomeric reactive compounds, which are liberated in this way, are transferred in the reverse way, in n acid medium and by means of elevated temperature and pressure, to a crosslinked polymeric material of structure similar to the original phytomass. The amount of liberated monomer is controlled by the degree of activation and determines, together with the moulding pressure, properties of the product. However, this fact does not exclude the possible modifications of product properties by addition of suitable additives, including binders of the furan type.
Another possible procedure consists in adding a strong mineral acid or a compound liberating such acid, Lewis acid, or their mixtures to at least one portion of particles of the starting material. Concentrated sulfuric acid, gaseous hydrogen chloride, zinc chloride, ammonium bisulphate, amine sulfates, or mixtures of these compounds can be added as an activation agent to the said parts.
Lewis acid has to be understood as a compound able to accept an electron pair. The excess of activation agent in admixture with the particles, is neutralized, before pressure moulding, by adding basic agents, in particular with urea, urea with ammonium sulphate alkaline soaps, Lewis bases, or with mixtures thereof. Lewis base should be understood here as a compound able to render an electron pair.
The activation agent is applied on particles in the form of gas, aerosol, or solution, which may be diluted with inert solvents. The particles of starting material are left with the same humidity content as they had before pro-/

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l,i cessing or, if it is desired, they can be provided on the surface with a hydrophobic coating.
Prior to pressure mouldingj heat is supplied to the particles in the amount sufficient to increase their temperature to 80 - 200C, whereas the particles, contain-ing the activated monomer at least on a part of their surface, are then compressed in a mould developing a clos-ing pressure of 0.2 to 10 MPa. Properties of the resulting material depend on the moulding pressure and also on the amount and kind of the activation agent.
Further possible procedure consists in the deposition of particles, having at least a part of the surface activated, into layers, whereas at least two layers contain deposited particles mixed with different amounts or kinds of the activation agent or the neutralization agent.
The method according to the invention permits to form an adhesive bonding of wooden or ligno-cellulose elements without using a special adhesive, because the necessary bonding structure is created directly on aontact surfaces or the joined elements from the material of these elements. Wooden and lignocellulose materials contain polysaccharides, lignin, tannins, essen-tial oils, and the like. By initiating a superficial hydro-lysis with acid agents or enzymatically on the surface of wood or similar materials, there are generated adhesive compounds present in the wood, which enable to form an integral joint because they create, after application of pressure, passing-through molecules of a new-formed polymer, which are partly in the joint and partly anchored in the original parts in a structural network of both joined elements.
Expensive or harmful adhesives are not needed for the formation of an adhesive bond, which then contains exclusively compounds of virtually the same composition as ~L2419~1~

had the original material. The main advantage is a great facilitation, lower cost, and acceleration of the produc-tion process.
The method according to the invention can serve for manufacturing of plywood, sticking of veneers on various lignocellulose bases, and formation of various articles from laminated wood. Such performance of a laminated article is especially advantageous, where a central core is formed from pressure moulded particles of wood bound together with a regenerated polymeric material and where the central core is jacketed from both sides with a wooden veneer or plywood stuck also with the regenerated active material.
Pressure moulding of the particles with binding compounds, based on a furan binder and on activated binding compounds of phytomass, proceeds at the particle tempera-ture of 12CC to 200C in the mould, which closing pressure is 1 to 10 MPa. Properties-of final products depend on the moulding pressure and on the amount of binder on the con-tact surfaces of moulded particles and may be the same inthe whole thickness of product or may change in various layers of the product. The resulting products from the compos-te material acquire mainly the shape of boards, blocks, and other moulded articles and may be used as

2~ various construction, insulation, or other-purpose partsO
The method according to the invention permits produce useful products also from materials which are virtually wastes from the production of furylaldehyde from plant parts. After hydrolysis of wood particles and separa-tion of furylaldehyde, residues with residual binding com-ponents can be pressure moulded to obtain a useful product.
To attain better properties, further furan binder or further activated particles of a plant origin can be added to the residual material. In this way, furylaldehyde is obtained from the whole volume of each particle, a small part of which is returned into the composite material in the form of a component of furan binder applied to the sur-face of remaining particles. Mutual connection of the binder with the original material of untreated particles is advantageously achieved by formation of linkages between the active ends of original structure and the chains of newly formed polymer from the binder. The furan binder has to be understood as a binder based in particular on furyl-alcohol or furylacetone which contains furylaldehyde at least in a small amount.
The binding effect of the binder generated from a lignocellulose material may be increased by addition of some derivative of phenol, which partly gives the rise to a furylaldehyde resol curable by heating to resin.
Pressure moulding of products from the particles is carried out in such a way, that the particles are com-pressed together by the moulding pressure of 0.2 to 10 MPa at temperature of 80C to 200C, whereas the moulding pressure acts for 5 to 300 seconds.
The method according to the invention can be advantageously adapted by applying a catalyst, which facilitates the hydrolysis of original material, on the contact surfaces. Such catalysts are, e.g., potassium permanganate, aluminium, zinc, metallic hydrides.
The composition and manufacturing of the com-posite material according to the invention is illustrated by means of the following examples, which, however, do not limit the scope of invention by any means.
Example 1 To prepare a product from the composite material according to the invention, 100 weight parts of spruce-wood chips was fed into a drum blender and a fog of concentrated sulfuric acid in air was applied on the chips by means of a spraying equipment. Total amount ox applied sulfuric acid was 3 weight parts. Then, 6 weight parts of powdered urea was added and mixed with the chips and sulfuric acid to form a moulding mixture. The original polymer on the sur-face of chips was activated or transferred to a monomer by action of sulfuric acid and the excess of sulfuric acid was neutralized in the subsequent step by the added powdered urea. The moulding mixture was then pressure moulded at temperature of 180C and closing pressure of 8.0 MPa for 5 minutes. The product which was removed from a press after 5 minutes exhibited bending strength of 12.0 MPa and volume weight of 950 kg/m3.
Example 2 Crushed residues of dry corn stalks were fed into a drum blender in the amount of 100 weight parts and 5 weight parts of 96 sulfuric acid was added by spraying homogeneously as much as possible on the surface of stalks.
Then, 7 weight parts of powdered urea was admixed and the prepared mixture was pressure moulded at temperature of 160C and closing pressure of 8.0 MPa. Final properties were attained after 4 minutes under pressure, when the activated monomer crosslinked on the particle surface giving virtually the same kind of polymer as was the polymer of starting material; i.e. the bending strength of at least 1.2 MPa at the volume weight 700 kg/m3.
Example 3 A mixture of wood chips and saw dust in the ratio

3:1 was charged into a drum blender in the total amount of 100 weight parts. Sulfuric acid was evenly applied on the surface of particles in the form of aerosol in the amount of 4 weight parts. Then, 6 weight parts of powdered urea was added and the mixture was thoroughly mixed. The mould-ing mixture was pressure moulded in a press under final pressure of about 2.0 MPa at temperature of 170C for 6 lZ419~0 minutes. The product attained bending strength of at least 10 MPa at the volume weight above 800 kg/m3.
Example 4 Chips of birch wood (100 wt. parts) were mixed S in a blender with 8 wt. parts of powdered urea. Then, 6 wt. parts of 80 phosphoric acid was dispersed by means of a spraying equipment. The prepared mixture was pressure moulded at temperature of 170C and pressure of 8 MPa for 6.5 min. The resulting product had density of 0.65 g/cm3 and bending strength of at least 1.5 MPa.
Example 5 Chips of coniferous wood (100 wt. parts) were mixed with 6.25 wt. parts of powdered urea and then 6.25 parts of 65 nitric acid was spread in the mixture. The material resulting from pressure moulding of the mixture at pressure of 8 MPa and temperature of 170C for 7 min.
had density of 0.65 g/cm3 and tensile and bending strengths o at least 1.5 MPa.
Example 6 Chips of spruce wood (100 wt. parts) were mixed in a blender with 4 wt. parts of powdered urea and 3 wt.
parts of potassium permanganate as a catalyst which accel-erates the activation of binding compounds. Then, 4 wt.
parts of 96 % sulfuric acid was added to the mixture as a fine fog with air. The mixture was pressure moulded at temperature of 150C and pressure of 10 MPa for 2 min. The product had density of 0.95 g/cm3 and bending strength of 15 MPa. '' Example 7 The same mixture as in example 1 was pressure moulded under the same pressure at temperature of 80C for 10 min. Properties of the product were the same.
Example 8 The surface of veneers, which form layers of a , manufactured plywood, were coated by brush or spraying with a concentrated or diluted acid, particularly sulfuric acid, to initiate superficial hydrolysis of wood on the contact surface of veneers, which gives arl active monomer by hydrolytic degradation of the original polymer. To neu-tralize the excess of sulfuric acid, if any, powdered urea was dusted on the contact surface of veneers. The veneers were then laminated, inserted into a press, and loaded with pressure of 2.0 MPa at temperature~of 160C for 15 seconds.
The active monomer was transformed by pressure and heat into a regenerated polymer, the macromolecules of which are linked together, on one hand, and anchored in the original material of veneers, on the other. A strong-mutual bonding of contact surfaces occurs in this way and the product is finished after removing from the press.
Example 9 To form an adhesive binding of two wooden and/or lignocellulose elements with the thickness of 5 to lO mm, for example, of a mortise-and-tenon joints, halved friezes, or corner connections of dovetail males, a concentrated acid, in particular sulfuric acid, was applied on the contact surface of linked parts by brush or spraying, to generate an activated monomer on the contact surfaces of joined parts from their material by acid hydrolysis. The contact surfaces were then put together, the joined elements were inserted into a press where the contact surfaces were compressed by pressure of 6.0 MPa at temperature of 180C
for 180 seconds. The joint was finished after removing from the press.
Example lO
In the manufacturing of jacketed chipboard, chips of spruce wood were first prepared, then charged into a drum blender in the amount of lO0 weight parts, and there coated with 5 weight parts of 96 % sulfuric acid by means lZ41900 of a spraying equipment. To neutralize the excess of unreacted sulfuric acid, 7 weight parts of powdered urea was spread into the mixture. The mixture prepared in this way was transferred into a mould with one of jacket layers, e.g., a wooden veneer or plywood or a fibreboard, placed on its bottom. The surface of this layer was previously furnished also with a coating of sulfuric acid to induce the superficial hydrolysis. An upper jacket layer, e.g.
also wooden veneer, plywood or fibreboard, the contact surface of which was furnished with a coating of sulfuric acid, was then placed on the surface of layer of the activated wooden chips. The mould was then closed and the content was moulded at the closing pressure of 8.0 MPa at temperature of 180C, which were kept for 5 minutes. The laminated board with a chipboard core was thus made in a single process and had volume weight of 950 kg/m3 and bending strength higher than 12.0 MPa.
Example 11 Wooden chips (300 g) were mixed in a drum blender with 10 g of phosphorus pentoxide added. This mixture was pressure moulded at pressure of 1 MPa and temperature of 1~0C for 2 min. The obtained material in the form of a board has bending strength of 11.0 MPa.
Example 12 Wooden chips (300 g) were mixed in a drum blender with 30 g of ammonium hydrogensulfate. The mixture was pressure moulded at temperature of 180C for 7 min. The resulting material in the form of a board exhibited bending strength of 18.0 MPa.
Example 13 A fog of 80 % aqueous solution of urea sulfate was applied in the amount of 38 g on the surface of 300 g wooden chips in a drum blender. The mixture was pressure moulded at temperature of 180C for 3 minutes and gave the ., .

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lZ41900 product in the form of a board, which attained bending strength of 18,6 MPa.
Example 14 Wooden chips (250 g) with applied acid catalyst were mixed in a drum blender with the mixture comprising 150 g of wooden chips 34 g of urea sulfate 20 g of furylalcohol 10 g of furylaldehyde.
The mixture was moulded by pressure of 0,80 MPa at temperature of 80C for 8 hours. The resulting material in the form of a cube exhibited compression strength of 44,5 MPa.
Example 15 Sawdust (300 g) and 14 g of ammonium hydrogen-sulfate were mixed in a drum blender and then 20 g of furyl-alcohol and 10 g of furylaldehyde were applied on this mixture. The blend was moulded under pressure of 0,8 MPa at temperature of 80C for 8 hours. The moulding, having the form of a cube, exhibited compression strength of 23,8 MPa.
Example 16 To the same mixture as in example 1 was added 5 weight parts of emulsion polyvinylchloride and then the mixture was pressure moulded at temperature of 180C and pressure of 2 MPa for 5 minutes. The resulting material had flexural strength of 21,96 MPa and it was water-resis-tant without change of its volume.
Example 17 To a mixture as in example 1, neutralized by a mixture of urea and ammoniumsulphate was added a powder mix of polyvinylchloride and chlorinated polyethylene in the weight ratio of 1:1. The resulting blend was pressure moulded at temperature of 180C and pressure of 6 MPa for ~2419(~0 six minutes. The resulting material had flexural strength of 19,6 MPa and it was water-resistant without change of its volume.
' Example 18 To as mixture as in example 3 was added powdered polypropylene and it was pressure moulded at temperature of 180C and pressure of 1,9 MPa for 5 minutes. Resulting composite material had flexural strength of 22,3 MPa and good water-resistance.

Claims (7)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method of manufacturing a composite material from particles of a polymeric lignocellulose material, comprising the steps of:
- contacting surface portions of at least one part of the lignocellulose material particles with an activation agent selected from the group consisting of concentrated H2SO4, concentrated H3PO4, HNO3, urea sulfate, ammonium bisulfate, concentrated P2O5 and mixtures thereof, to depolymerize only said surface portions of said at least one part of the lignocellulose material and form a monomeric or oligomeric binding agent therefrom; and - heating and compressing said lignocellulose material particles and said monomeric binding agent for a time and under a temperature and a pressure sufficient to cause the said surface portions of said at least one part of the lignocellulose material particles to incorporate the said monomeric or oligomeric binding agent therein and repoly-merize to form a hardened mass with cohesion bonds among particles.

2. The method of claim 1, wherein the activation agent is applied on the particles in the form of an aerosol.

3. The method of claim 1, wherein the activation agent is concentrated H2SO4.

4. The method of claim 1, 2 or 3, comprising the additional step of combining with the said polymeric lignocellulose material particles a component selected from the group consisting of polyvinylchloride, chlorinated polyethylene, polypropylene and mixtures thereof, prior to the heating and compressing step.

5. The method of claim 1, 2 or 3, wherein a furan binder selected from the group consisting of furylalcohol, furylaldehyde, and combinations thereof, is applied to said particles prior to the heating and compressing step.

6. The method of claim 1, 2 or 3, wherein the activation agent is neutralized with powdered urea after the surface portions have depolymerized to a polymerizable monomer but before the heating and compressing step.

7. The method of claim 1, 2 or 3, wherein the lignocellulosedepolymerizing effect of the activation agent is enhanced by further including with said activation agent in said contacting step a catalyst selected from the group consisting of potassium permanganate, aluminium, zinc and metallic hydrides.