MXPA97007858A - Procedure for material union lignocellulos - Google Patents

Abstract

The present invention relates to a process for joining lignocellulosic material comprising the steps of: a) contacting the lignocellulosic material with an organic polyisocyanate composition, and b) subsequently allowing the material to bind, characterized in that the lignocellulosic material is also put on in contact with a lignin solvent that is a cyclic urea, either simultaneously with, or separately from, the organic polyisocyanate composition.

Description

PROCEDURE FOR THE LIGNOCELLULOSAL M ATERAL UNION P S CRJ PTION OF THE INVENTION This invention relates to a process for the binding of lignocellulosic material using polyisocyanates and to compositions for use in such a process. The molding of lignocellulosic material containing fibers, particles or layers to form composite bodies is well known. The binders, which were normally used, are synthetic resin rubbers such as suspensions of urea-formaldehyde resin or phenol-formaldehyde in water. Bodies containing lignocellulosic compounds produced in this way lack durability and are susceptible to moisture and deterioration conditions in certain construction purposes to which they may be subjected. The organic di- and polyisocyanates as binders for lignocellulosic materials have been proposed and are known to give products of improved stability and mechanical strength. However, even at reduced levels of binder use, the cost of the polyisocyanates compared to the urea-formaldehyde or phenol-formaldehyde resin binders is unfavorable. GB 2096626 discloses polyisocyanate-alkylene oxide adhesive compositions for preparing lignocellulosic composite products.

US 3519581 relates to synthetic lignin-reduced polyisocyanate resin for reacting a polyisocyanate with dissolved lignin. It is an object of the present invention to provide lignocellulosic bodies attached to the polyisocyanate which contain reduced levels of polyisocyanate binder, while retaining the broad equivalent properties. It is another object of the present invention to provide lignocellulosic bodies attached to the polyisocyanate which have improved properties at equivalent charges of the polyisocyanate binder. Therefore, the present invention provides a method for joining a lignocellulosic material comprising the steps of a) contacting the lignocellulosic material with a polyisocyanate composition and b) subsequently allowing such a material to agglutinate, characterized in that the lignocellulosic material is placed in contact with a lignin solvent, either simultaneously with, or in a form separate from, the organic polyisocyanate composition. The advantage of the present invention is that the levels of the polyisocyanate needed to produce a cured lignocellulosic composite body can be substantially reduced, while maintaining the physical properties of the composite material in equivalent or greater form. In addition, at equivalent levels of polyisocyanate, composite bodies having improved physical properties such as strength and swelling are obtained. An improved performance in the release of the compression platens is also observed in some cases, especially in the production of Medium Density Cardboard Fiber. The lignin solvents as used herein, are substances capable of dissolving proto-lignin or lignin of natural existence, as modified by the procedure used to recover it from the lignocellulosic material. Preference is given to reactive lignin solvents without isocyanate. Examples of lignin solvents suitable for use in the process of the present invention include cyclic ureas such as N.N'-dimethylethyleneurea and N, N'-dimethylpropyleneurea, acetol, dioxin, esters such as diethyl sulfate, ethyl oxalate and triethyl phosphate, polyesters, ketone such as acetone, isophorone, mesityl oxide, methyl ethyl ketone and pentanedione, 1,4-dioxane, dioxolane, methylmorpholine, morpholine, propylene oxide, tetrahydrofurfuryl alcohol, tetrahydrofuran, tialdine, acrylonitrile, 2-nitro 2-ethyl-1, 3-propanediol (molten), 2-nitro-2-methyl-1-propanol (molten), dimethylsulfolane, dimethyl sulfoxide, formamide, butyl alcohol and nitroethanol (and mixtures thereof). Of these, N, N'-dimethylethylene urea and N.N'-dimethylpropylene urea are preferred. The use of these two compounds as the lignin solvent has not been described above. Only one of the above lignin solvents can be used in the process of the present invention or mixtures of two or more solvents of such lignin solvents can be used.

Lignin solvents, especially cyclic ureas, are used in the process of the present invention in an amount ranging from 0.1 to 6.0, preferably from 0.3 to 3, and more preferably from 0.5 to 2% by weight based on the polyisocyanate The lignin solvent that will be preferably used and the preferred amount thereof depends on the wood species and can be readily determined by those skilled in the art. Using a lignin solvent in combination with a polyisocyanate in the above amounts, cardboard of physical properties equivalent to a 15 to 20% reduction in polyisocyanate loading is used. The lignin solvent can be either added to the polyisocyanate composition before the composition is contacted with the lignocellulosic material, or the lignin solvent can be added to the lignocellulosic material before or after (preferably before) the add the polyisocyanate. The polyisocyanate compositions containing the above lignin solvents in the above amount are stable. An inert diluent such as a linseed oil, methyl glycol, 2,3-dibenzyltoluene, may be added to such a polyisocyanate composition. Additional reductions in polyisocyanate charges, while maintaining the properties of the board, are possible when both lignin and lignin solvent are added to the lignocellulosic material.

Lignins derived from a wide variety of sources can be used. Examples are lignins resulting from wood and kraft pulping processes, such as alkaline lignins (also called kraft lignin and sulphate lignin), lignins resulting from the process of forming sulfite wood pulp, such as ligninsulfonates, lignins that result from the hydrolysis of wood. Preferred lignins are solvent organ lignin and alkaline lignin. Lignins and hardwood and softwood sources can be used. Instead of the same lignin, lignin models based on units of natural lignin monomer (mainly phenylpropane) can be used. Examples of lignin models include the compounds described by W.E. Collier et al. in Holzforschung, 46 (6), page 523-528 (1992) especially the materials based on CH-R and C4H4 (OCH) R wherein R is CH (OH) CH or CH2CH (OH) CH, the compounds described by L. Eggling in Trends in Biotechnology, 1 (4), page 123-127 (1983) such as dilignoles (two units of phenylpropane), arylglycerol-β-aryl ether, dilignoles of, 2-diarylpropane, and dililolol of phenylcumaran, the compounds described by GE Hawkes et al. in Holzforschung, 47, page 302-312 (1993), such as vanillin, vanillinic acid, acetovainillone, syringaldehyde, 4-hydroxy-3,5-dimethoxybenzoic acid, 4-hydroxybenzaldehyde, 4-hydroxybenzoic acid, 4-hydroxy-3, 5-dimethoxyacetophenone, 4-hydroxycinnamic acid, 3,4-dihydroxycinnamic acid (caffeic acid), 4-hydroxy-3-methoxycinnamic acid (ferulic acid), and 4-hydroxy-3,4-dimethoxycinnamic acid and the compounds described by DK Johnson et al., In "Molecular weight distribution studies using lignin model compounds", chapter 8, page 109-123, edited by W.G. Glasser and S. Sarkanen, ACS Symp. Ser. 397 (1989), ISBN 00-8412-1631 -2. The lignin or lignin model is added in an amount that ranges from 0.1 to 40%, from 1 to 5% by weight based on the polyisocyanate. The lignin or lignin model can be added to the lignocellulosic material separately from the polyisocyanate and the lignin solvent (preferably after the polyisocyanate has been added) or I O can be added simultaneously with the polyisocyanate and / or lignin solvent. If added simultaneously, the preferred method is to first mix the lignin (model) and the lignin solvent and then add the polyisocyanate thereto. Another method involves first adding the lignin (model) to the polyisocyanate and then the lignin solvent. I5 The combination of lignin solvent and lignin (model) can lead to a reduction in polyisocyanate loading of 20 to 40%. The polyisocyanate for use in the process of the present invention may be any organic polyisocyanate compound or mixture of organic polyisocyanate compounds, provided that such compounds have 2 isocyanate groups. Organic polyisocyanates include diisocyanates, particularly aromatic diisocyanates and isocyanates of higher functionality. Examples of organic polyisocyanates, which may be used in the present invention, include aliphatic isocyanates such as hexamethylene diisocyanate; and aromatic isocyanates such as my p-phenylene diisocyanate, 2,4 and 2,6-toluene diisocyanate, 4,4'-diphenylmethane diisocyanate, 2,4-chlorophenylene diisocyanate, 1,5-naphthylene diisocyanate, 4 Diphenylene 4'-diisocyanate, 4,4'-diisocyanato-3,3'-dimethyldiphenyl, 4,4'-3-methyldiphenylmethane diisocyanate and diphenyl ether diisocyanate; and cycloaliphatic diisocyanates such as 2,4 and 2,3-cyclohexane cycloisoxane, 2,4 and 2,6-1-methylcyclohexyl diisocyanate and mixtures thereof, and bis- (isocyanatocyclohexyl) methane and triisocyanates such as 2,4,6 toluene triisocyanate and 2,4,4'-triisocyanatodiphenylethyl ether. Modified polyisocyanates containing isocyanurate, carbodiimide or uretonimine groups can also be used. In addition, blocked polyisocyanates can be used, such as the reaction product of a phenol and an oxime and a polyisocyanate, having an unblocking temperature below the applied temperature when the polyisocyanate composition is used. The organic polyisocyanate may also be an isocyanate end prepolymer made by reacting an excess of a higher functionality diisocyanate or polyisocyanate with a polyol. Water-emulsifiable organic polyisocyanates such as those described in UK Patent No. 1444933, European Patent Publication No. 516361 and PCT Patent Publication No. 91/03082 can also be used. Mixtures of isocyanates, for example, a mixture of isomer of toluene diisocyanate, such as the commercially available mixtures of 2,4 and 2,6-isomers and also mixtures of higher di- and polyisocyanates, produced through the Phosgenation of aniline / formaldehyde condensates. Such mixtures are well known in the art, include the unpurified phosgenation products containing polyphenyl polyisocyanates, bonded with methylene, including diisocyanate, triisocyanate, and higher polyisocyanates together with any byproduct of phosgenation. Preferred isocyanates to be used in the present invention are those in which the isocyanate is a higher functionality aromatic diisocyanate or polyisocyanate, such as a pure diphenylmethane diisocyanate or mixture of methylene-linked polyphenyl polyisocyanates containing diisocyanates, triisocyanates and polyisocyanates of superior functionality. Methylene-linked polyphenyl polyisocyanates are well known in the art. They are prepared through the phosgenation of corresponding mixtures of polyamines obtained with the condensation of aniline and formaldehyde. For convenience, polymer blends of methylene-linked polyphenyl polyisocyanates containing diisocyanate, triisocyanate and polyisocyanate of higher functionality are referred to herein as polymeric MDI. Preferably, the polyisocyanate is liquid at room temperature. The polyisocyanate composition may further comprise conventional additives such as flame retardants, lignocellulosic preservatives, fungicides, waxes, size agents, fillers and other binders such as formaldehyde condensate adhesive resins. The lignocellulosic compounds are prepared by contacting the lignocellulosic parts with the polyisocyanate composition and the lignin solvent by mixing, spraying and / or spraying the polyisocyanate composition and the lignin solvent with / on the lignocellulosic parts and compressing the combination of polyisocyanate composition, lignin solvent and the lignocellulosic parts, preferably by heat compression, usually from 150 ° C to 220 ° C and at a specific pressure of 2 to 6 MPa. Such bonding procedures are commonly known in the art. The lignocellulosic material after the treatment with the composition of polyisocyanate and solvent of lignin is placed on pressing plates made of aluminum or steel, which serve to bring the finish to the press, where it is compressed to the desired degree of a temperature of between 150 ° C and 220 ° C. At the beginning of a manufacturing operation, it may be useful but not essential to condition the compression plates by spraying their surface with an external release agent. The conditioned compression can then be used many times in the process of the invention without further treatment. The process of the present invention can be used in the manufacture of sheet, medium density fibreboard and particleboard (also known as waferboard). In this way, the lignocellulosic material used can include wood filaments, wood wafers, wood fibers, paper cuttings, wood wool, cork, bark, sawdust and similar waste products from the woodworking industry, as well as other materials having a lignocellulosic base such as paper, bagasse, straw, flax, henequen, hemp, copiers, cañuela, rice, pods, grass, walnut shells, and the like. In addition, they can be mixed with lignocellulosic materials, other particulate or fibrous materials such as mineral fillers, glass fiber, mica, rubber, textile waste, such as fabric fibers and plastic. The weight ratio of the polyisocyanate / lignocellulosic material will vary depending on the overall density of the lignocellulosic material employed and the properties required. Therefore, the polyisocyanate compositions can be applied in such amounts to give a weight ratio of polyisocyanate / lignocellulosic material in the range of 0.1: 99.9 to 25:75 and preferably in the range of 0.3: 99.7 to 16: 84 If desired, other conventional bonding agents, such as formaldehyde condensate resins, can be used together with the polyisocyanate composition. More detailed descriptions of methods for making products based on lignocellulosic material are available in the prior art. Techniques and equipment conventionally used can be adapted for use in the method of the present invention. The invention is illustrated, but not limited by the following examples. SUPRASEC is a trademark of Imperial Chemical Industries.

EXAMPLE 1 The lignin solvent was added to the polyisocyanate (SUPRASEC 2185 available from Imperial Chemical Industries) and stirred slowly for about 2 minutes at room temperature. The type and amount (based on the polyisocyanate) of lignin solvent are indicated below in Table 1. The resin was then sprayed onto the wood finish at a 3% load (polyisocyanate + lignin solvent) on a drum mixer with a 0.7 mm nozzle atomized with air. With the sprays of wood sprayed, normal cartons oriented at 30 x 30 x 1 .1 cm were made in a Siempelkamp press. The platens of the press were at a temperature of 200 ° C. The profile of the press used was: closing in 45 seconds at 1 30 bars, closed during 1 76 seconds at 130 bars, the pressure was reduced in 15 seconds from 130 bars to 0 bars. The properties of physics are given in Table 1. The swelling after 24 hours was determined in accordance with DIN 52365, Infernal Bond (IB) was determined in accordance with DIN 52365 for V20 and DIN 68763 and DIN 52365 for V100. Dimethylethylene urea (DMEU) available from Acros Chimica Dimethylpropylene urea (DMPU) available from Acros Chimica Aspen strands obtained from Weyerhaeuser, Drayton Valley Southern Pine strands obtained from Weyerhaeuser, Elkin Table 1 Swelling (%) IB - V20 IB - V100 (kPa ) (kPa) Southern Pine 5 SUPRASEC 2185 33.07 752 / SUPRASEC 2185 + 0.5% DMEU 28.39 844 / SUPRASEC 2185 + 1 .0% DMEU 27.19 1001 / Aspen SUPRASEC 2185 34.28 768 113 the SUPRASEC 2185 + 1 .0% DMPU 27.98 887 219 The results show that even reduced levels of polyisocyanate cartons made in accordance with the invention show improved internal bond strength and swelling. I 5 EXAMPLE 2 Organosolv lignin (available from Repap Technologies Inc. under the name of ALCELL Lignin Powder) (2 ppp per 100 ppi polyisocyanate) was added to the polyisocyanate (SUPRASEC 2185 available from Imperial Chemical Industries) with stirring at room temperature. Subsequently, dimethylurea, lignin solvent (1 ppp per 100 ppp polyisocyanate) was stirred. The resin was then sprayed onto the Aspen wood strands at a charge of 2% (polyisocyanate + lignin solvent + lignin) in a drum mixer with a 0.7 mm nozzle atomized with air. With the sprays of wood sprayed, 30 x 30 x 1 .1 cm oriented strand boards were made on a Siempelkamp press. The platens of the press were at a temperature of 200 ° C. The press profile used was: closing in 45 seconds at 130 bars, closing for 176 seconds at 130 bars, reduction of pressure in 15 seconds from 130 bars to 0 bars. The physical cardboard properties are given in Table 2. The physical cardboard properties of a reference cardboard made with 2% of SUPRASEC 2185 of its property are also presented in Table 2.

Table 2 Inflation IB REFERENCE 42.5 655 SAMPLE 32.5 977 EXAMPLE 3 Dispersions were made by mixing 5 ppp dimethylethylene urea (available from Aldrich) in 93 ppp of polyisocyanate (SUPRASEC 2185 available from Imperial Chemical Industries). While stirring, 2 ppp of lignin was slowly added to this mixture and stirred for 15 minutes.

Individual Aspen bonds of the obtained polyisocyanate compositions were prepared and cured in an oven for 30 minutes at 180 ° C, held in an L-shaped fastener. The joints were constructed using two woods with a cut of 10-12 cm. x 25 mm x 3 mm with an overlap distance of 25 mm. Adhesive was applied to both sides of the overlap (depth of 30 mm) at a load of 12-18 g / m2. The tensile strengths of the joints obtained were measured; 3 mm spacers were used to obtain the resistance in parallel and to minimize the detachment forces. The results are presented in Table 3. The reference used is polyisocyanate (SUPRASEC 2185). The different lignins used are lignin organosolv (available from Repap Technologies), alkaline lignin (available from Aldrich), hydrolytic lignin (available from Aldrich) and sodium lignosulphate (available from Aldrich).

Table 3 Tensile strength (kPa) Reference 2821 Lignin organosolv 31 72 Alkaline lignin 3135 Hydroxylic lignin 3013 Sodium lignosulfonate 2988 EXAMPLE 4 A SUPRASEC 1042 polyisocyanate composition (available from Imperial Chemical Industries) emulsified in water was prepared a ratio of 50:50 and 2% by weight of DMEU were added to it. Fiberboards of the best wood of 18 x 18 x 0.6 cm were made using this polyisocyanate composition at a 6% load (cardboard density 800 kg / m ^). Humidity content of the pre-mat (12%). Temperature of the compression plates: 200 ° C. The release capacity of the cartons of the compression plates was evaluated from 1 to 5; 1 the cardboard being completely glued to the compression plates and 5 being perfectly released from the compression plates. The failure of the wood is also measured as the percentage area of the compression plate covered with wood fibers after taking all the cardboard. The 1 5 results are taken in Table 4. The reference is SUPRASEC 1042 emulsified in water at a ratio of 50:50 Table 4 Release capacity Wood failure 0 REFERENCE 4.5 0.5-1 REFERENCE + 2% DMEU 4.5-5 0 These results show that the release performance was improved by adding a lignin solvent to the polyisocyanate.

Claims (12)

1. A method for bonding lignocellulosic material comprising the steps of a) contacting the lignocellulosic material with an organic polyisocyanate composition and b) subsequently allowing the material to bind, characterized in that the lignocellulosic material is also contacted with a lignin solvent either simultaneously with, or in a form separate from, the organic polyisocyanate composition; The amount of cyclic lignin solvent varies from 0.1 to 6% by weight based on the polyisocyanate.

2. The process according to claim 1, characterized in that the cyclic urea-lignin solvent is N, N'-dimethylethylene urea or N, N'-dimethylpropylene urea.

3. The process according to claim 1 or 2, characterized in that the cyclic urea-lignin solvent is used in an amount ranging from 0.5 to 2% by weight based on the polyisocyanate.

4. The process according to any of the preceding claims, characterized in that the lignocellulosic material is contacted with the lignin or a lignin model based on the monomeric units of natural lignin, either simultaneously with, or in a separate form from the composition of polyisocyanate and / or the cyclic urea-lignin solvent.

5. The process according to claim 4, characterized in that the lignin is organosolv lignin or alkaline lignin.

6. The process according to claims 4 or 5, characterized in that the lignin or the lignin model; based on the units of the natural lignin monomer, it is used in an amount ranging from 1 to 5% by weight based on the polyisocyanate.

7. The process according to any of the preceding claims, characterized in that the organic polyisocyanate is an aromatic polyisocyanate.

8. The process according to claim 7, characterized in that the organic polyisocyanate is polyphenyl polyisocyanate bound by methylene.

9. The process according to any of the preceding claims, characterized in that step b) involves compression by heat of the lignocellulosic material combination, the polyisocyanate composition, the cyclic lignin-urea solvent and optionally the lignin or lignin model.

10. The polyisocyanate composition characterized in that it comprises N, N'-dimethylethylene urea or N, N'-dimethylpropylene urea.

11. The polyisocyanate composition according to claim 10, characterized in that N, N'-dimethylethylene urea or N, N'-dimethylpropylene urea are used in an amount ranging from 0.1 to 6% by weight.

12. The polyisocyanate composition according to claim 11, characterized in that N, N'-dimethylethylene urea or N, N'-dimethylpropylene urea are used in an amount ranging from 0.5 to 2% by weight.