FR2536334A1 - Lignocellulosic composite material prodn. - Google Patents

Abstract

A composite material is obtd. from lignocellulosic particles which are bound together by a polymer which is derived from the initial polymer of the starting lignocellulosic material by converting, through actuation, of the initial polymer into reactive cpds. (I), partic. into monomers, which are converted into the final polymer by subsequent crosslinking. Pref. the composite material comprises a mixt. of constituents modified by activation, contg. a monomer or another active cpd. and converted into the final polymer by crosslinking, and constituents which are not modified by activation. In a variant the composite material comprises at least 2 layers having different characteristics and comprising constituents different from the raw material. The material is free from such binders as urea-formaldehyde resins and contains a binder obtd. directly from the raw material by means of an activation agent, e.g. H2SO4, applied on the surface of the particles. Articles obtd. from the composite material, e.g. panels for buildings, are therefore harmless w.r.t. health and are relatively cheap since expensive binders are not involved.

Description

 The invention relates to a composite material formed from particles of plant origin, based on lignocellulosic material, linked to each other by a polymer compound obtained from an initial polymer of starting material by activating the initial polymer into active compounds. The invention also relates to a process for manufacturing such a composite material.

 Composite materials based on vegetable raw materials are produced at the present time, in particular based on wood such as fibers, shavings, planures, sawdust and the like by mixing dry and hydrophobic particles with various binders, mainly thermosetting binders, by example with a urea-formaldehyde resin, then transformation by subsequent molding at a temperature exceeding 130 C into building elements of desired shape, mainly planks. We manufacture many varieties of these materials, differing from each other by the type of material of departure, type of binder, molding pressure and temperature. These materials have a main common drawback; they give rise for a long time to the detachment of fragments of the resinous binder, namely formaldehyde, urea and formaldehyde oligomers, or phenol, which.

have carcinogenic or other undesirable metabolic effects on the human body. Considering that these materials, in particular chip-based boards, have recently taken on an increasing importance in the construction of dwellings, the aforementioned drawback of known composite materials based on plant fragments or particles has become very serious. . It is necessary to prohibit by various measures the penetration of these products inside buildings, which increases the construction costs.

 Until now, wooden elements have been bonded using adhesives of various kinds, which are applied to the surfaces in contact with the linked elements. In addition to the need to apply a layer of adhesive on the surface of the formed joint, which is done either cold or hot depending on the type of adhesive used, the joint must be left to stand for a time. long enough to ensure the evaporation of water from aqueous adhesives, or solvents from solvent adhesives, or even to allow the polymerization of monomer adhesives, in some cases at high temperature and high pressure.

Certain adhesives are harmful to health during their preparation or also during the use of the parts linked to the adhesive. This is particularly the case with adhesives containing formaldehyde which exert on human beings carcinogenic or other blue undesirable metabolic effects. In addition, the bonding of wood-based and lignocellulose materials to the adhesive takes time and, in many cases, also involves high energy consumption, in particular for the manufacture of composite elements with large interfaces; namely plywood and veneers based on wood or lignocellulose.

 Another disadvantage of these composite materials according to the prior art lies in the complexity of the manufacturing process, comprising the preparation of a precondensate and the strict observance of a technological protocol, necessary for obtaining products of required quality. Therefore, it is not possible for these materials to increase productivity by shortening the manufacturing cycle. During the manufacturing process, i.e. during die-casting, harmful reaction products, with a high formaldehyde content, are released in a high concentration by the molded material. Another disadvantage is the high cost of the articles produced. from the aforementioned prior materials, which results from the fact that the doses of binder present in the articles are relatively large, reaching as a rule 10 to 30% by weight.

 These drawbacks are eliminated by virtue of the composite material formed of elements of plant origin based on lignocellulose according to the invention, in which the individual elements are linked to each other by a polymer compound obtained from the initial polymer of the material. starting lignocellulosigue by activating transformation of the initial polymer into active compounds capable of reacting, themselves transformed by crosslinking into a final polymer material.

 The invention also relates to a process for manufacturing the composite material, according to which elements of plant origin based on lignocellulosic material are formed in coherent form by bonding with a binder by a process consisting in exposing the surface of a part. at least one of said elements with the degrading effect of an activating agent, an effect which can be increased by a catalyst or canceled out by a neutralizing agent, by adding at least one compound chosen from furyl alcohol, acetone furyl, furyl aldehyde, phenols and phenolic precondensates and thermoplastics, if such addition is desirable, and joining the elements together by pressure molding with heating and curing.

 The main advantage of the material: composite according to the invention resides in that the binder necessary to bind the individual juxt @ elements placed is formed directly from the material of these elements by means of an activating agent, for example acid. sulfur, applied to the surface of said particles. The articles of the composite material according to the invention contain exclusively the starting material and a small quantity of deactivating agents, absolutely-harmless for health, and in addition the costs of preparing relatively expensive binders are eliminated. . The preparation of the material before the pressure molding takes place in a single step and lies in the application of the activating agent on the surface of elements of plant origin.

 Another advantage of the process according to the invention is the possibility of using an almost waste material, for example bark simultaneously. It is not necessary to reduce the water content of the elements, as required by the prior processes. known, so that the energy necessary for drying the starting material is saved.

 The manufacture of the composite material according to the invention consists in causing an activating agent to act on elements of the starting material of plant origin in order to degrade the initial high molecular weight polymeric binder of the starting material into a monomer. , then neutralize, if it is desirable, the excess activating agent and subject the elements which are at least partly coated on the surface with a layer of monomer to an application of heat and pressure, to cause polymerization of the monomer into a polymer derivative, which binds to each other the individual elements of the material.

 An activating agent can be added to only part of the starting elements of vegetable chlorine, then mix this part with the rest of the elements and make an article from this mixture in coherent form.

 The starting material used for the manufacture is formed of elements of Vegetable origin which contain lignocellulosic material comprising polysaccha rider of lignin, tannins, essential oils, etc., for example wood fragments, shavings, sawdust , planures, stalks and dry stalks of mals in the ground state and various fibers The resulting material is coherent and is given by pressure molding a shape, in particular, that of boards, blocks etc. whose strength and other mechanical properties, as well as other parameters, depend very much on the starting material and the manufacturing method.The resulting material can be used in the form of boards, blocks and other moldings obtained under pressure in construction parts of buildings or furniture, for insulation purposes, etc.

The hydrolysis effect exerted by acids is used in the manufacturing process to liberate furyl aldehyde and its derivatives and activate the lignocellulosic substances. The active monomeric compounds thus released are transformed by reverse process, in acidic medium and by application of temperature. and high pressure, in a crosslinked polymer with a structure similar to that of the initial phytomass. The amount of monomer released by the degree of activation and determines, together with the molding pressure, the properties of the product However, this does not exclude no possibility to modify the properties of the product by adding appropriate mixtures, including furan-type binders
Another possible procedure consists in adding a strong mineral acid or a compound releasing such an acid, a Lewis acid, or their mixtures, to at least part of the starting materials. Concentrated sulfuric acid, gaseous hydrochloric acid, ammonium bisulfate, amine sulfates, or mixtures of these compounds can be added to the elements as an activating agent. By "Lewis acid" is meant a compound capable of accepting a pair of electrons.

The excess activating agent present in mixture with the elements is neutralized, before pressure molding, by addition of basic agents, in particular urea, urea with ammonium sulphate, alkaline soaps or Lewis bases, or their mixtures. By "Lewis base" is meant here a compound capable of restoring a pair of electrons. The activating agent is applied to the elements in the form of gas, aerosol or solution, possibly in the diluted state. by inert solvents. The starting materials are left with the moisture content they had before use or, optionally, a hydrophobic coating can be applied to their surface.

 Before pressure molding, the elements are heated enough to bring their temperature between 80 and 2000C, - then the elements are then compressed, comprising the activated monomer on at least part of their surface, in a mold generating a closing pressure of 0.2 to 10 Pa. The properties of the resulting material depend on the molding pressure and also on the quantity and nature of the activating agent.

 Another possible procedure consists in depositing at least partially activated surface elements in layers, at least two layers containing deposited particles mixed with different quantities or different kinds of activating agent or neutralization.

 The method according to the invention also makes it possible to carry out the adhesive bonding of wooden or lignocellulose parts without using any particular adhesive, because the necessary bonding structure is created directly on the surfaces in contact with the parts joined together from the material of these parts. Wood and lignccellulose materials contain polysaccharides, lignin, tannins, essential oils and the like.

By initiating a surface hydrolysis, by means of acidic agents or by enzymatic way, on the surface of wood or similar material, one generates in wood adhesive compounds which make it possible to obtain a junction in one piece because they give, after application of pressure, through molecules of a newly formed polymer, partly located in the initial particles in the structural network of the two parts together.

 There is no need for expensive or harmful adhesives for the creation of an adhesive bond, which then contains exclusively compounds having virtually the same composition as the initial material. The main advantage is that the manufacturing process is then much easier, less expensive and faster.

 The method according to the invention can be used to manufacture plywood, to glue veneers on various lignocellulose supports, and to produce various articles in laminated wood. Such an embodiment of a laminated article is particularly advantageous when a central core is formed from particles of pressure molded wood bonded to each other by a regenerated polymeric material and when the core of wood is coated on both. faces of veneer or plywood also glued with regenerated active material.

The pressure molding of the particles in the presence of binding compounds based on furan binder and of activated binding compounds of the phytomass is carried out by bringing the particles to a temperature of 120 to 2000 ° C. in the mold, including the closing pressure. is 1 to 10
MPa. The properties of the final products depend on the molding pressure and the quantity of binder present on the contact surfaces of the molded particles, and can be the same throughout the thickness of the product or vary from one layer to another of the product.The products made of the composite material are mainly in the form of boards, blocks and other molded articles and can be used in the building, in insulation or for other purposes
The process according to the invention makes it possible to manufacture interesting products also from practically waste materials originating from the manufacture of furyl aldehyde from plant elements. After hydrolysis of wood particles and separation of the furyl alpine, the residues containing residual binding components can be pressure molded to obtain a useful product. To obtain better properties, furan binder or other activated particles of plant origin can be added to the residual material. In this way, furyl aldehyde is obtained from the entire volume of each particle. a small part of which is returned to the composite material in the form of a furan binder compound applied to the surface of the remaining particles
A mutual bond between the binder and the initial material of the untreated particles is advantageously obtained by forming bonds between the active ends of the initial structure and the newly formed polymer chalnes from the binder. By furan binder "means a binder based in particular on furfuryl alcohol or furylacetone which contains furyl aldehyde at least in small proportion.

 The binding effect of the binder generated from lignocellulosic material can be increased by adding some phenolic derivative by adding some phenolic derivative, which in part gives rise to a resol of furfuryl aldehyde crosslinkable by heating.

The particles are transformed by pressure molding into products by uniting the particles together under the effect of the molding pressure of
C, 2 to 10 MPa at a temperature of 80 to 2000C, the molding pressure acting for 5 to 300 seconds
The process according to the invention can advantageously be adapted by applying a catalyst to the surfaces in contact, which facilitates the hydrolysis of the initial material. Such catalysts are, for example, potassium permanganate, aluminum, zinc, metal hydrides
The composition and manufacture of the composite material according to the invention are illustrated by the following examples, which are however not limiting in any way.

Example 1
To prepare a product from the composite material according to the invention, 100 parts by weight of spruce chips are brought into a drum mixer and a concentrated sulfuric acid mist is applied to the chips. spraying equipment. Sulfuric acid is applied at a total of 3 parts by weight. 6 parts by weight of powdered urea are then added which are eaten with the shavings and sulfuric acid to form a molding mixture. An initial polymer present on the surface of the shavings is activated or transformed into monomer under the action of sulfuric acid, the excess of which is neutralized in the next step by the powdered urea added
The molding mixture is then molded under pressure at a temperature of 180 ° C. and under a closing pressure of 8.0 MPa for 5 minutes The product removed from the molding press after 5 minutes has a flexural strength of 12 , 0 MPa and a density of 0.950.

Example 2
Crushed residues of dry corn stalks are brought into a drum mixer at the rate of 100 parts by weight and 5 parts by weight of 96% sulfuric acid are added by spraying as homogeneously as possible onto the surface of the stems. Then, by stirring, 7 parts by weight of pulverulent duration are incorporated and the mixture prepared under pressure is the mixture prepared at a temperature of 1600 ° C. and under a closing pressure of 8.0 MPa. The final characteristics are obtained after 4 minutes of keeping under pressure, when the activated monomer crosslinks on the surfaces of the particles, giving a polymer practically of the same nature as that of the starting material g the flexural strength is then at least 1.2 MPa for a density of 0.700
Example 3
A mixture of wood shavings and sawdust in a ratio of 3: 1 is loaded into a drum mixer at a total of 100 parts by weight. Particular sulfuric acid is regularly applied to the surface in the form of aerosol at the rate of 4 parts by weight 6 parts by weight of powdered urea are then added and the mixture is thoroughly stirred. The molding mixture is pressure molded in a press under a final pressure of about 2.0 MPa at a temperature of 1700C for 6 minutes The product has a flexural strength of at least 10 MPa for a density exceeding 0.800.

Example
Birch chips (100 parts by weight) are mixed in a mixer with 8 parts by weight of pulverulent urea. 6 parts by weight of 80% phosphoric acid are then dispersed using a spraying apparatus. the mixture prepares at a temperature of 1700C and under a pressure of 8 MPa for 6.5 minutes The resulting product has a density of 0.65 and a flexural strength of at least 1.5 MPa.

Example 5
Shavings of this coniferous wood (100 parts by weight) are mixed with 5.25 parts by weight of pulverulent urea, then 6.25 parts of 65% nitric acid are sprayed into the mixture. The material obtained by molding the mixture under pressure at a pressure of 8 MPa and at a temperature of 170 C has a density of 0.65 and tensile and flexural strengths of at least 1.5 MPa
Example 6
Spruce wood shavings (100 parts by weight) are mixed in a mixer with 4 parts by weight of powdered urea and 3 parts by weight of potassium permanganate as a catalyst accelerating the activation of the binding compounds Next, 4 parts by weight of 96% sulfuric acid in fine mist in air are added to the mixture. The mixture is molded under pressure at a temperature of 150 ° C. and under a pressure of 10 MPa for 2 minutes. The product has a density of 0.95 and a flexural strength of 15 MPa.

Example 7
The same mixture as in Example 1 is subjected to a molding under the same pressure at a temperature of 80 ° C. for 10 minutes. The product features are the same.

Example 8
The surface of veneer slats forming a layer of plywood made with concentrated or diluted acid, in particular sulfuric acid, is coated or sprayed on in order to initiate a surface hydrolysis of the wood on the surface of the blades, which gives an active monomer due to the degradation by hydrolysis of the initial polymer. To neutralize any sulfuric acid, the contact surfaces of the blades are sprinkled with urea. The slides are then superimposed, they are inserted in a press and a pressure of 2.0 MPa is applied to them at a temperature of 1600C for 15 seconds. The pressure and the heat transform the active monomer into a regenerated polymer whose macromolecules are, on the one hand, linked together and, on the other hand, anchored in the initial material of the blades. It thus appears a strong bond between the surfaces in contact and the product is finished once extracted from the press.

Example 9
To ensure the adherent connection of two wooden elements and / or lignocellulose of 5 to 10 mm thick belonging for example to a tenon and mortise joint, to half-friezes or to an angle connection of elements with tail male dovetails, a concentrated acid, in particular sulfuric acid, is applied to the contact surfaces of the parts to be connected, by brushing or spraying, in order to generate an active monomer on these surfaces, from their constituent material, by acid hydrolysis. The contact surfaces are assembled and the assembled elements are inserted in a press where a pressure of 6.0 MPa is applied to the contact surfaces at a temperature of 1800C for 1.80 seconds.

The joint is finished once extracted from the press.

Example 10
To make a clad chipboard, spruce wood chips are first prepared, then loaded into a drum mixer at the rate of 100 parts by weight and coated with 5 parts by weight. sulfuric acid 96% by means of a spraying apparatus, To neutralize the excess unreacted sulfuric acid, 7 parts by weight of pulverulent urea are dispersed in the mixture. The mixture is then transferred as prepared in a mold on the bottom of which is placed one of the veneer layers, for example a wooden strip or counterplate or hard cardboard. The surface of this layer of sulfuric acid was previously also coated to cause a superficial hydrolysis. then an upper layer of veneer, which can also be, for example, a wooden strip, plywood or hard cardboard, with contact surface coated with sulfuric acid, on the surface of the layer of activated wood chips We then close the mold and we soft the contents under the closing pressure of 8.0 MPa and at a temperature of 1800C, maintained for 5 minutes. The laminated core board of chipboard is thus obtained by a single process and has a density of 0.950 and a flexural strength exceeding 12.0 MPa.

Example 11
Wood shavings (300 g) are mixed in a drum mixer with 10 g of lighthouse phos pentoxide. This mixture is molded under a pressure of 1 MPa and at a temperature of 1800 ° C. for 2 minutes. The material obtained in the form of a plank has a flexural strength of 11.0 MPa.

Example 12
Wood shavings (300 g) are mixed in a drum mixer with 30 g of diammonium acid sulfate. The mixture is pressure molded at a temperature of 180 ° C. for 7 minutes. The resulting plank material has a flexural strength of 18.0
MPa.

Example 13
A mist of an aqueous solution of 80% urea sulfate, in an amount of 38 g, is applied to the surface of 300 g of wood chips, in a drum mixer.

The mixture is pressure molded at a temperature of 160 ° C. for 3 minutes and a product is obtained in the form of a board, with a flexural strength reaching 18.6 MPa.

Example 14
Wood shavings (250 g) coated with acid catalyst are mixed in a drum mixer with a mixture comprising
150 g of wood chips,
34 q of urea sulfate,
20 g of furyl alcohol,
10 g of furyl aldehyde.

 The mixture is molded under pressure of 0.80 MPa and at a temperature of 800C for 8 hours. The resulting material, in the form of a cube, has a compressive strength of 44.5 MPa.

Example 15
Sawdust (300 g) and 14 g of ammonium acid sulphate are mixed in a drum mixer, then 20 g of furyl alcohol and 10 g of furyl aldehyde are applied to this mixture. The mixture is molded under 0.8 MPa at a temperature of 800C for 8 hours. The cube-shaped molding has a compressive strength of 23.8 MPa.

Example 16
To the same mixture as in Example 1, 5 parts by weight of polyvinyl chloride in emulsion are added, then the mixture is pressure molded at a temperature of 1800C and under a pressure of 2 MPa for 5 minutes.

The resulting material has a flexural strength of 21.96 MPa and is water resistant without undergoing any change in volume.

Example 17
To the mixture according to Example 1, neutralized by a mixture of urea and ammonium sulphate, a powder mixture of polyvinyl chloride and chlorinated polyethylene is added in a weight ratio of 1: 1. The resulting mixture is pressure molded at a temperature of 180 ° C. and at a pressure of 6 MPa for six minutes. The resulting material has a flexural strength of 19.6 MPa and resists water without undergoing any change in volume.

Example lb
To the mixture according to Example 3, polypropylene powder is added and it is molded under pressure at a temperature of 1800 ° C. and under pressure of 1.9 MPa for 5 minutes. The resulting composite material has a flexural strength of 22.3 MPa and good water resistance.

Claims (25)

 1. Composite material formed from elements of plant origin based on lignocelluloseg the elements being independent or linked to each other, characterized in that the elements are linked to each other by means of a polymer compound obtained from initial polymer of the starting material by transforming, by activation, the initial polymer into active compounds capable of reacting, in particular monomers, which are transformed into the final polymer compound by subsequent crosslinking.  2. Composite material according to claim 1, characterized in that it is composed of a mixture of elements modified by activation, carrying a monomer or other active compound transformed by crosslinking into the final polymer and of particles not modified by activation.  3. Composite material according to claim 1 characterized in that it is composed Vau at least two layers with different parameters formed of elements in different starting materials.  4. Composite material according to claim 1 or 2, characterized in that it is formed from a bonded mixture of unmodified elements of plant origin and plant elements modified by activation which are bonded by means of a mixture formed of a polymer compound obtained "by transforming, by activation, the initial polymer of, the starting material of vegetable origin into active compounds which are capable of reacting, and a binder of furan added  5. Composite material according to any one of Claims 1 to 4, characterized in that it is linked by means of a polymer compound obtained from the initial polymer, and in that active compounds formed from the initial polymer are enriched by at least one phenolic derivative.  6. Composite material according to any one of claims 1 to 5, characterized in that it is linked by means of a polymer compound derived from the initial polymer and in that active compounds capable of reacting formed from the initial polymer are enriched with urea.  7. Composite material according to any one of claims 1 to 6, characterized in that it is linked by means of a polymer compound derived from the initial polymer and in that active compounds capable of reacting formed from the initial polymer are enriched with at least one thermoplastic.  8. A method of manufacturing the composite material according to claim 1, characterized in that the elements of plant origin based on lignocellulose by means of a binder to put them in coherent form, the surface is subjected to. at least part of the elements with the decomposition effect of an activating agent, an effect which can be increased by a catalyst or canceled out by a neutralizing agent, then a compound chosen from furfuryl alcohol is optionally added, l furyl acetone, furyl aldehyde, phenols, and their precondensates, and thermoplastics, and the particles are compressed by heating and cured.  9. Process according to claim 8, characterized in that the elements are subjected to the decomposition effect of an activating agent, a neutralizing agent is added to remove the residual acidity, then the particles are combined by compression with heating and they harden.  10. Method according to claim 9, characterized in that the elements are first mixed with a mixture of neutralizing agent and catalyst, the modified elements are then subjected to the action of an activating agent, then they are brought together by compression and hardened.  11. Method according to claim 8 or 9, characterized in that an activating agent is added to a fraction of elements in starting material of vegetable origin, the fraction of elements thus modified is then mixed with another fraction of elements, not modified by activation, then the elements are brought into mutual contact by pressure and hardened by heating  12. The method as claimed in claim 8, characterized in that an activating agent is applied to the contact surface of at least one element to cause the surface hydrolysis of the initial material of linked parts t to release adhesive compounds present in the initial material, then the bonded particles are combined by heating, and hardened  13. The process as claimed in claim 8, characterized in that an activating agent is first applied to the surface of lignocellulose particles, in particular chips, a layer of the particles is formed; a continuous layer of lignocellulosic material is placed on at least one side of this layer, after prior modification of the contact surface by an activating agent, then the layers are combined by compression at high temperature and hardened  14. Method according to any one of claims 8 to 13, characterized in that elements of plant origin are subjected to the action of a deactivation agent, the excess of which can be made inactive at Using a neutralizing agent, furan binder-generating compounds are added, then the elements are pressed together with heating and hardened.  15 Method according to any one of claims 8 to 14, characterized in that elements of plant origin are subjected to the action of an activating agent, or added at least one phenolic derivative, then we. brings the elements together by compression and hardens  16. Method according to any one of claims 8 to 12 or 14 or 15, characterized in that the elements of vegetable origin based on lignocellulose are, for example, wood chips or fibers, flax husk, stalks of crushed males and chopped straw.  17 Method according to any one of claims 8 to 12 or 14 or 15, characterized in that the elements of plant origin based on lignocellu losic material are elements, for example veneer blades and plywood, of material of the type wood.  18. Method according to any one of claims 8 to 15, characterized in that the activating agent is at least one compound chosen by strong mineral acids, the compounds releasing such acids and Lewis acids.  19. The method of claim 18, characterized in that the activating agent is sulfuric acid.  20 Method according to any one of claims 8 to 11 or 14 or 15, characterized in that the neutralizing agent is at least one compound chosen from Lewis bases and metallic soaps  21. The method of claim 20 characterized in that the neutralizing agent is urea.  22. Method according to claim 8 to 10, characterized in that the catalyst is potassium permanganate.  23 Method according to any one of claims 9 to 15, characterized in that the particles are brought together by compression under pressure from 0.2 to 10 MPs.  24. Method according to any one of claims 8 to 15, characterized in that the elements are combined by compression at a temperature of 80 to 200 C.  25. The method of claim 9, characterized in that the thermoplastic is polyvinyl chloride.