MXPA99005072A - Method for use of recycled lignocellulosic composite materials - Google Patents

Abstract

Materials for use in forming composite products are prepared from recycled composite materials and treated by hydrothermal treatment at 40°C to 120°C along with or followed by high shear treatment. The process enables the use of recycled materials not hitherto usable successfully and it is possible to form composite products with less or no additional bonding resin.

Description

METHOD FOR THE USE OF COMPOUNDED LIGNOCELLULOSIC MATERIALS This invention relates to the production of lignoceiulosic particles or fibers and the formation of composite materials therefrom. It particularly relates to the production of such particles or fibers from recycled composites and binding with synthetic binders in composite materials. Never before has there been so much demand placed on the fiber source of the world. Growth and economic development throughout the world have created needs for converted forest products. Congruently, the energy needs of developing countries are generating growing demands for fuelwood, which now accounts for 50% of the total consumption of wood fibers. At the same time, global fiber production systems, in total, are demonstrating the capacity to meet these demands. Regardless of the enormous pressures of fiber sources, there is no scarcity or crisis of fibers globally. However, there are some serious local and regional fiber deficits and resource management conflicts that will play a critical role in the immediate and long-term future. Composite materials such as particle boards, medium and high density fiber boards are mainly made of wood using binders such as acid curing urea-formaldehyde resins, alkaline-curing phenol-formaldehyde resins, as well as polyisocyanate adhesives. The medium density fiber boards are fiber boards prepared using a dry technique as follows: wood or any other lignocellulosic materials are subjected to conversion to thermomechanical pulp at a temperature of about 160 to 180 ° C, then mixed with the resin and they dry. Then mats are formed from the fibers and pressed to form fiber boards. Particle tables, on the other hand, can be prepared from chip that is mixed with resins and the gummed particles are watered on the mats and pressed at high temperature to obtain particle tables. The medium density fiber boards cover a wide range of densities between 0.6 and 0.8 g / cm3 depending on their thickness and field of application. Tables with density less than 0.5 g / cm3 are not common, but can be produced. The quality required depends on the field of application of the table and its thickness: Thickness For > 6-12 mm To > 12-19 mm Internal connection (U l), N / mm2 0.65 0.60 Flexural strength (MOR), N / mm2 35 30 The particle tables are prepared in the density range from 0.4 to 0.85 g / cm3 depending on their field of application and thickness. Tables with density less than 0.5 g / cm3 are of medium density and other than 0.7 g / cm3 are high density tables. Also in the case of particle tables, the requirements depend on the field of application and thickness of the tables: Thickness For > 6-13 mm For > 13-20 mm Internal connection (U l), N / mm2 0.4 0.35 Resistance to bending (MOR), N / mm2 17 15 The conventional process for making composite panel products from lignocellulosic materials depends exclusively on the synthetic resin binders to join them. Since synthetic resins, such as phenol- and urea-formaldehyde, are expensive, they usually make up a large portion of the production cost for conventional panel products, such as particle boards, layer tables and medium density fiberboards. . This is especially true in the case of agricultural waste. Due to their physical nature, a relatively high content of resin binders is required to be manufactured, resulting in an expensive panel product. Therefore, greater attention has been paid to induce the union between lignocellulosic surfaces by creating surface-to-surface bonds without the use of any adhesive. Thus, there is some need to economize in amounts of bonding agent, used in composite materials for economic reasons and to minimize possible contamination. The literature that is relevant to this publication is: Brink, D. L.; Collett, B.M.; Pohlman, A. A.; Wong, A. F.; Philippou, J.; In wood technology; Chemical Aspects, Goldstein, I .S. , Ed .; ACS Symposium Series, no. 43; ACS Washington, D.C. , 1977, p. 169. Brink, D. L.; Johns, E. E.; Zaverin, E.; Kuo, M. L.; Nguyen, T.; Layton, D.; Wong, A.; Bimbach, M.; Merriman, M. M.; Breiner, T.; Grozdits, G.; Wu, K.T .; University of California, Forest Products Laboratory, Techn.

Rep.36.01.108, 1977-80. Collett, B.M .; Thesis, University of California, Berkeley, 1973. Linzell, H.K .; U.S. Patent 2,388,487, 1945. Philippou, J.L .; Wood Chem. Technol., 1981, 1, 199. Philippou, J.L .; Johns, W.E .; Nguyen, T .; Holzforschung, 1982.36,37. Philippou, J.L .; Johns, W.E .; Zavarin, E .; Nguyen, T .; Forest Products Journal, 1982, 32, 3, 27. Philippou, J.L .; Zavarin, E .; Johns, W.E .; Nguyen, T .; Forest Products Journal, 1982, 32 5 55. Pohlman, A. A .; M.S. dissertation, Berkeley, California, 1874. Roffael, E .; Dix, B .; Lighin und Ligninsulfonate in non-conventional bonding - an overview. Holz ais Roh- und Werkstoff 49, 199, 205. Roffael, E .; Schaller, K .; Elnfiuß thermischer Behandiuing auf Cellulose. Holz ais Roh- und Werkstoff 29, 275-278. Schorning, P .; Roffael, E .; Stegmann, G .; Holz ais Roh- und Werkstoff, 1972, 30, 253. Troughton, G.E .; Chow, S.-Z .; Wood Science, 1971, 3, 129. The first attempts to create covalent bonds between two surfaces dates back to 1945, when Linzell patented a process to make fiber products by compressing and heating a mixture of lignocellulosic fibers and ferric compounds as an oxidizing agent (Patent from E.U., US-A-2,388,487). Stafko and Zavarin (U.S. Patent, US-A-4,007,312) used oxidation coupling to include wood-to-wood bonds (Philipou et al., 1981, 1982).

The covalent joining of wood by means of bifunctional molecules seems to offer additional possibilities through more efficient bridging of the spaces between the wooden surfaces, that is to say, the wooden surfaces do not need to be as close as about a joint length as in the case of direct union, otherwise they could be separated by spaces of several lengths of ligature. Schorning et al., (1972) attempted to make particle tables using ethylenediamine and 1,6-hexanediamine as binding agents. These amines are known to interact with wood surfaces by condensation with lignin. The addition of 15% of ethylenediamine imparted remarkable resistance to the particle board, which was insufficient even for commercial considerations. 1,6-Hexenediamine was more efficient with the particle board having a flexural strength of 6.5 N / mm2 at 7% addition (density, 0.85 g / cm2, pressed at 14 ° C for 12 minutes); however, the water resistance was low. The best results obtained with 1, 6-hexanediamine can be explained by the more efficient bridging ability of the amine. Here the internal bonding strength was 0.3 N / mm2 at 7% addition and the flexural strength at 16.6 N / mm2. Here again, the thickness bulge was more than about 100%. Collett (1970) and Brink (1977) attempted to improve the method of Schorning et al. By pre-oxidizing wood particles with either HN 03 in the presence of oxygen, or with nitrogen oxides in the presence of oxygen under controlled conditions of time and temperature. The bifunctional agents 1, 6-hexenediamine, ethylenediamine, phenylenediamine, ethylene glycol, and 1,6-hexanediol as well as the monofunctional ammonia were used. Above all, the diamines gave the best IB values, followed by ammonia, and the glycols behaved poorly. As with Schorning and co-workers, 1,6-hexanediamine proved to be better than ethylenediamine. At densities of 0.81 -0.88 g / cm3, the table of 1,6-hexanediamine with 10% dry wood base gave internal union (IB) values (measured in Kp / cm2) appreciably above the values reached by Schorning and collaborators, which demonstrated the value of pre-oxidation. The binding properties were very low even compared to technical products. The increased pre-oxidation with nitrous gases or higher amine levels resulted in less bulking and an increase in I B. The results suggest the formation of covalent bonds resistant to water. The formation of amide and ester ligatures was used to explain the formation of bonds (Patent of EU-US-A-3, 900,334). Bifunctional molecules were studied (Brink '1977, Pohiman, 1974), including maleic anhydride, maleic acid, succinic anhydride, and saccharinic acid as cross-over agents, in combination with surface activators including HCl, hydrobromic acid, perchloric acid, H2SO4, ferric chloride, zinc chloride, ferric nitrate, oxalic acid, and formic acid. Although superior in water resistance, especially the table was appreciably lower than the phenol-formaldehyde table. Extraction experiments indicated that between 97 and 99% of monomers interacted with the surface.

Under aggressive acid conditions, carbohydrates, especially hemicelluloses, undergo degradation leading to the formation of monomeric sugars, which can undergo transformation after furfural and furfural derivatives. Thus, sugar monomers can intertwine wooden surfaces. In EP 0, 161, 768 B1, a process is described, in which lignocellulosic materials are converted to reconstituted composite materials by packing the lignocellulosic material in a container and applying steam at elevated pressure to heat a cellulosic material. Hemicelluloses are degraded under the action of hydrothermal treatment. The lignocellulosic materials can then be pressed into a reconstituted panel without adding any additional common adhesive such as urea-formaldehyde or phenol-formaldehyde resins or by adding less than what could be added usually taking into account the fibrous or particulate content. However, this process is applicable only in lignocellulosics with a relatively high hemicelluloses content. Many patent applications were dedicated to the adhesive properties of hemicellulosic substances derived from wood or any other lignocellulosic material. In the Patent of E. U. , US-A-2,224, 135 The water-soluble compounds of the board manufacturing process were separated and treated as an adhesive. However, the adhesive bonds created by hemicelluloses and their degradation products are of poor stability and have limited commercial applications. In the Patent of E. U. , US-A-5,01 7,319 describes a method for creating wood-to-wood joints by a three-step process: In the first step the wood material is hydrolyzed by the action of steam. In the second step the lignocellulosic raw material is kept in contact with the hemicelluloses released for a sufficient time for the non-catalytic decomposition of the hemicelluloses to low molecular weight carbohydrates. In the last step the lignocellulosic material is pressed without any washing of the degradation product. However, this method requires a high energy treatment and a special apparatus to carry out the steam application process. Another concept to increase the wood-to-wood bond is to activate the surface of wood particles or wood veneers by various mechanisms including oxidation, free radical formation and identification. A journal on the literature of this subject has been published by Roffael and Dix (1990). However, all the tests to increase the bond strength were traditionally economically unfavorable. Therefore, no industrial interest has been directed towards this method. In our applications U K-9607566.8 and a corresponding EU application both filed on April 12, 1996 and our PCT application filed on April 10, 1997, a method to improve the ability to bind annual plant fibers by attaching such fibers is described. from plant to treatment with water or steam (hydrothermal treatment) from 40 to 120 ° C accompanied or followed by a treatment with high cutting forces that defibrate the plant fibers. The resulting treating fibers can be formed into compounds for example fiber board or particle board by bonding with synthetic resins. The extent of the high cut treatment required may depend on the type of compound to be produced. The compounds are linked with synthetic resins such as urea-formaldehyde resins, melamine resins, or polyisocyanate resins. Optionally the process can be improved by treatment with a dilute alkaline solution, for example a sodium hydroxide solution. As established by the treatment process with water or steam / high cut treatment can be carried out simultaneously or in sequence. The mixing with bonding resin can be carried out in the high cutting machine. Now it has been found that this hydrothermal treatment / high shear treatment process can be used to convert composite table materials, for example particle and fiber boards, that is, composite materials bonded with synthetic resins in products for the manufacture of composite products. In one embodiment of the invention the waste or recycled composite product will be bonded in a composite material with the addition of less binding resin than would normally be required. Thus, the process of the invention will result in resin savings. Although the fibrous lignocellulosic materials / particles have been treated by water / steam treatments with simultaneous or subsequent elevated cutting treatment, the use of these lower temperatures has only been in the context of treatments for the manufacture of paper or similar materials and has not There was a suggestion that this treatment when applied to lignocellulosic materials in the context of producing compounds would increase the fibrous material or particles to form it into composite material. The process of the invention is also distinguished from the production of composite materials from lignocellulosic materials in which there is an initial treatment at an elevated temperature of at least 150 ° C, usually 150 ° C to 170 ° C followed by defibration. Thus, DE-A-3609506 refers to a treatment of raw wood chips with steam in which a mixture of glue is added under specific conditions. High pressure steam is used. Similar technique is WO91 / 12367, WO93 / 25358, EPO664191A1, US-A-3843431, DE421 1888A1, EPO292584A1 and EPO373725. According to the invention, therefore, there is provided a method for producing fibrous or particulate material to make composite materials from recycled composite material wherein the recycled material is subjected to treatment with water or steam from 40 ° to 120 °. C and is subjected simultaneously or subsequently to a high shear treatment. The product can then be formed into a composite material. The invention also relates to a lignocellulosic material that has been subjected to such water / steam treatment and high shear treatment and is in a form suitable for binding to a compound. The initial material is then fibrous or particulate material derived from recycled composites (waste). Thus, one can prepare fibers with high self-adhesion properties by hydrothermomechanical treatment of waste particle boards or boards of waste fibers bonded with aminoplast resins such as urea-formaldehyde resins, melamine urea-formaldehyde resins or any other hydrolysable resin . This result was unexpected due to the following reasons: 1. Lignocellulosics, such as tables of waste particles have been thermally treated under acidic conditions during the drying and pressing process. Under such conditions the lignocelluloses undergo a so-called "irreversible hornification" (Roffael and Schaller, 1971). Due to such a process the ability of lignocellulosics to rejoin and gather is considerably diminished. 2. The firing process is increased in the presence of acid medium by the hardeners in the particle board. It may be possible to form the composite product with less or without the use of any additional binder. The invention also includes the process for forming the hydrothermal treated / cut material into a composite material with bonding by the addition of bonding resin or, possibly with less bonding material or without the addition of bonding resin. Preferably the process involves the treatment of recycled composite materials from 50 ° C to 120 ° C. The term recycled composites covers all materials that comprise fibers or particles of lignocellulosic materials that have been bound with synthetic resins.

The final composites can be panel products, reconstituted wood products and molded articles including particle board, layer board and fiber board. In a specific embodiment of the present invention, the invention relates to a process for converting such recycled lignocellulosic materials into composite products such as panel products, etc. This aspect of the invention relates to a process for converting particle and fiber boards into composite products. This invention relates particularly to a process for converting such recycled lignocellulosic materials into composite products such as panel products, reconstituted wood and molded articles, possibly without the use of any additional adhesive binders which are an essential part of the conventional drying process for manufacture composite materials, such as wood-based particle boards, layer tables and medium density fiber boards. Hydrothermomechanical treatment can be carried out on any high cutting device such as a twin screw extruder or grinding mill. The treatment according to the invention is thus conducted in a high cut machine under conditions that result in breaking and disintegration of recycled material to increase its accessibility to the joint. The extrusion regime depends on the conditions used and also on the type of the machine applied and can differ 5 kg / h to 20 kg / h. the use of BIVIS extruder according to a preferred embodiment of the invention the high cut treatment requirement. Other high cut machines, which can be used are, v. g. , Ultra Turrax mixers, which through their mechanical design are capable of disrupting the morphological structure of recycled material. "The cutting forces to be applied depend on the raw material used and whether or not chemicals are added to the substrate." The hydrothermomechanical treatment can be carried out at a temperature from 50 ° C to 120 ° C. Furthermore, chemicals such as diluted acids, diluted alkali or even chemicals with high affinity for lignin such as sodium sulfite, sulfur dioxide, can be added to increase the defibration of waste lignocellulosic material. Thus the properties of the boards made of recycled material can be further improved if the material is treated with various chemicals. These reagents can be used either alone or in combinations and include metal hydroxides, such as lithium hydroxide, sodium, potassium, magnesium, aluminum, etc. , organic and inorganic acids, such as phosphoric, hydrochloric, sulfuric, formic, acetic acids, etc. , salts, such as sodium sulfate, sodium sulfite, sodium tetraborate, etc. , oxides, such as aluminum oxide, etc. , several amines and urea, ammonia, as well as ammonium salts. The above reagents are used in the form of a solution in water or suspension in amounts between 0.01 -10% based on the dry material. The chemical treatment and the defibration can be carried out in one step, holding the recycled material to a stream of water during the high-cut stage, containing the amount of chemical needed to increase the properties of the boards bound with amino resin. After defibration, the fibers produced can be dried using conventional dryers used in particleboard factories, v. g. , a drum dryer or a tube dryer, such as that used in medium density fiberboard mills. Thereafter, the dry fibers follow the conventional procedure for the production of particle tables or medium density fiber boards. However, the addition of such chemical products is not mandatory since applying the hydrothermal mechanical treatment produces fibers with high self-adhesion properties. The starting material can be obtained by mechanically disintegrating a composite material, for example, particle board to chips. A lignocellulose modifying agent can be added, for example a metal hydroxide, an organic or inorganic acid, an oxide, an amine, ammonia or an ammonium salt. Also standard components of a binding agent such as formaldehyde scavengers, catalysts and extenders can be added if additional binding material is added. Thus the process can be carried out possibly in the presence of 0.01 to 0.4% by weight of sodium sulfate alone or with 0.01 to 0.4% by weight of sodium hydroxide. The original or disintegrated product can be treated with 0.01 to 0.4% by weight of sulfuric acid. The main advantage of the process is that fibers can be produced from one-step waste particle tables. Therefore, the process is totally different from the process to make medium density fibreboard from lignocellulosic materials, in which the lignocellulosic material is impregnated in the first step with water or chemical products at an elevated temperature of approximately 150 ° C. at 179 ° C and then defibrated in a refiner with one or two discs. In the process described by the invention there is no need to treat the table of waste particles or the mechanical disintegration products therefrom at such a high temperature. The treatment with water at 50 ° C under high-cut mechanical grinding is sufficient to disintegrate particle boards to fibers with high self-adhesive behavior. It was found that although the boards disintegrated and converted to fibers, the resin degradation products still cover the surface of the fibers. The resin on the surface of the fiber can be the main reason why the fibers have high self-adhesive properties. During the heat treatment, for example, a twin-screw extruder the disintegration products of the recycled material can be collected or left in the fibers to further increase the bonding capacity.

The resulting hydrothermally treated material is preferably combined with the same adhesive as the recycled material. Typical bonding resin materials that can be used include urea-formaldehyde resins (UF resins), melamine-urea-formaldehyde resins (MUF resins), melamine resins (MF resins), phenol-formaldehyde resins (PF resins) , resorcinol-formaldehyde resins (RF resins), tannin-formaldehyde resins (TF resins), polymeric isocyanate binders (PMDI) and their mixtures. The resins can be added in the amount of 5-15% based on the dry lignocellulose material. It is also one of the embodiments of this invention to mix the recycled material with the binder mixture already in the high cut machine. Resins U F, MUF, MF, PF, RF, and TF can be used for this purpose. In the case of amino resins, the adhesive can be added in a pre-catalyzed or late catalyzed or uncatalyzed state. A catalyst can also be added separately in the high shear stage. Resin mixtures such as UF-polyisocyanates can also be used in the same manner. The addition of a sizing agent is not mandatory. However, it can be added if necessary, either on the high cutting machine or separately. Other components of a standard adhesive mixture such as formaldehyde scavengers, extenders, etc., can also be added in the same manner. If residues are removed from the binding resin materials derived from the original recycled composite material then additional binding resin may have to be added in the final formation of the composite material but the invention is still advantageous in that one has the desirable ability to use recycled materials that until now have proven difficult to recycle and train them into new composite products. Modes of the invention will now be illustrated in the following examples. EXAMPLE 1 Tables of waste particles - were mechanically disintegrated and subsequently treated in a twin screw extruder device injecting water solutions of 0.01% H2S02 or 1.0% NaOH at 1 00 ° C and 1.0% NaOH at 50 ° C. The fibers produced were used for the production of 16 mm boards at lab scale after mixing with resin U F. The resin level used was 10%, the compression temperature was 180 ° C and the press pressure was 35 kg / cm2. Three replica tables were produced in each case and their properties were determined subsequently. The average values of table properties are presented below: 0. 01% H2SO 1 .0% NaOH 1.0% NaOH 100 ° C 100 ° C 50 ° C IB, N / mm2 0.21 0.39 0.46 MOR, N / mm2 12.7 10.1 13.1 24h bulge,% 22.5 20.4 23.5 HCHO, mg / 100 g table 21 .4 1 3.5 16.3 The formaldehyde emission (HCHO) was determined using the Perforator method. As can be seen from the previous test, treatment with NaOH solution gave the best results. The treatment at 50 ° C gave an improvement of the values of the Bonding strength (I B) and resistance to bending (Modulus of Rupture, MOR), but increased the values of bulking and emission of formaldehyde. Treatment with NaOH at 100 ° C gave better results.

EXAMPLE 2 Wood chips and particle boards produced from these were treated separately in a twin screw extruder device by injecting an aqueous solution of 0.04% H2SO at 100 ° C. 8 mm tables were produced at lab scale from their fibers using levels of 0, 2, 4, 6 and 8% UF resin. The production parameters of the rest were the same as before. The average values of table properties are presented in the following table: IB MOR HCHO level 24 h Resin N / mm2 N / mm2 mg / 100 g table swelling% 0 0.05 5.3 1 .3 121 .6 2 0.13 7.5 5.0 70.1 Wood chips 4 0.17 8.0 6.0 60.2 6 0.23 1 1 .6 8.3 47.7 8 0.29 13.3 10.5 35.3 0 0.07 6.5 10.8 88.5 2 0.22 8.5 9.7 68.2 Table of particles 4 0.33 9.2 9.6 56.5 6 0.35 12.3 10.2 41 .4 8 0.41 1 8.4 15.0 28.1 From the results of the above table, it is obvious that a significant reduction in resin consumption can be achieved by using fibers produced from waste particle boards treated according to the process of the invention.

Claims (9)

1. REIVI NDICATIONS 1. A method for producing fibrous or particulate material for manufacturing composite materials from recycled composite material wherein the fibrous or particulate recycled composite material is subjected to treatment with water or steam of 40 ° to 120 ° C and subject to shear treatment elevated simultaneously or subsequently.
2. 2. A process for forming a composite material by holding the fibrous or particulate material according to claim 1 for heating and pressing in the presence of a binding resin agent.
3. 3. A modification of the process of claim 2 in which the final composite material is formed without addition of binding resin or with less binding resin than would normally be employed for the formation of the desired compound taking into account the amount of fibrous or particulate material used.
4. 4. A method according to claim 1 wherein the hydrothermal treatment is at a temperature of 50 ° C to 120 ° C.
5. 5. A method according to any one of claims 1 to 4 wherein the high shear treatment is in a twin screw extruder.
6. 6. A method according to any one of claims 1 to 5 in which a waste composite board is mechanically disintegrated into chips prior to the hydrothermal treatment.
7. 7. A method according to any one of claims 5 or 6 wherein composite waste boards or disintegrating products thereof are treated with 0.01 -0.4% sulfuric acid as a catalyst.
8. 8. A method according to any of claims 6 or 7 wherein the composite waste boards are disintegrated in the presence of 0.01 -0.4% sodium sulfite as a catalyst.
9. 9. A method according to any of claims 6 or 7 wherein the composite waste boards are disintegrated in the presence of 0.01-0.4% by weight of sodium sulfite and 0.01-0.4% by weight of sodium hydroxide.