HK1014441A - Process for binding lignocellulosic material - Google Patents

Description

Method for bonding lignocellulosic materials

The present invention relates to a process for bonding lignocellulosic materials using polyisocyanates and compositions for use in the process.

It is known to mold lignocellulosic materials containing fibers, particles or layers into composites. The binder usually used is a suspension of a synthetic resin glue, such as urea-formaldehyde resin or phenol-formaldehyde resin, in water. The lignocellulose-containing composites produced by this method lack durability and are sensitive to humid environments and are prone to deterioration under certain building application conditions.

Organic diisocyanates and polyisocyanates have been reported as binders for lignocellulosic materials and are known to improve product stability and mechanical strength. However, even at reduced binder levels, the cost of the polyisocyanate is still unsatisfactory compared to urea-formaldehyde or phenol-formaldehyde binders.

It is an object of the present invention to provide a lignocellulosic material bonded with polyisocyanate which maintains equivalent board properties at reduced levels of polyisocyanate binder.

It is another object of the present invention to provide a lignocellulosic material bonded with polyisocyanate which has improved properties at equivalent amounts of polyisocyanate.

Accordingly, the present invention provides a process for the production of a bonded lignocellulosic material comprising the steps of:

a) contacting the lignocellulosic material with an organic polyisocyanate composition,

b) and subsequently binding the material, characterized in that the contacting of the lignocellulosic material with the organic polyisocyanate composition and the lignin solvent can be carried out either simultaneously or separately.

An advantage of the present invention is that the amount of polyisocyanate necessary to cure the stamped composite lignocellulosic bodies can be significantly reduced while maintaining equivalent or superior physical properties of the composite board.

Further, the composite having the same amount of polyisocyanate used has improved physical properties such as strength and expansibility. Improved performance on release from the press platen has also been observed in some cases, especially in medium density fiberboard articles.

As used herein, lignin solvents are those substances that can dissolve native raw lignin or can dissolve lignin modified by lignocellulosic material recovery processes. Lignin solvents which do not react with isocyanates are preferred.

Examples of suitable lignin solvents for use in the process of the present invention include cyclic ureas (such as N, N '-dimethylethyleneurea and N, N' -dimethylpropyleneurea), acetomethanol, dihydroxyquinolines, esters (such as diethyl sulfate, ethyl oxalate and triethyl phosphate), polyesters, ketones (such as acetone, isophorone, isopropylideneacetone, methyl ethyl ketone and pentanedione), 1, 4-dioxane, dioxolane, methylmorpholine, morpholine, 1, 2-propylene oxide, tetrahydrofurfuryl alcohol, tetrahydrofuran, thiadine, acrylonitrile, 2-nitro-2-ethyl-1, 3-propanediol (melted), 2-nitro-2-methyl-1-propanol (melted), dimethylthiophenane, dimethyl sulfoxide, formamide, butanol and nitroethanol and mixtures thereof.

Among them, N '-dimethylethyleneurea and N, N' -dimethylpropyleneurea are preferable. The use of these two compounds as lignin solvents has not been described previously.

A single one of the above lignin solvents may be used in the process of the present invention, or a mixture of two or more may be used.

The lignin solvent, especially the cyclic urea, used in the process of the present invention is used in an amount of 0.1 to 6.0%, preferably 0.3 to 3%, most preferably 0.5 to 2% by weight of the polyisocyanate.

The preferred lignin solvent and its preferred amount depend on the wood species, which can be readily determined by one skilled in the art.

The lignin solvent is combined with the polyisocyanate according to the dosage, and the board with the same physical properties can be obtained under the condition that the dosage of the polyisocyanate is reduced by 15-20%.

The lignin solvent can be added to the polyisocyanate composition either before the composition is contacted with the lignocellulosic material or before or after (preferably before) the polyisocyanate is added to the lignocellulosic material.

Polyisocyanate compositions containing the above-mentioned amount of lignin solvent are stable.

Inert diluents, such as linseed oil, methyl oleate and 2, 3-benzhydryltoluene, can be added to such polyisocyanate compositions.

By adding lignin and lignin solvent together to the lignocellulosic material, it is possible to further reduce the amount of polyisocyanate used while maintaining the board properties.

Lignin from various sources can be used. Examples are lignin from kraft and soda wood making processes, such as alkaline lignin (also known as kraft lignin and kraft lignin); lignin such as sulfonated lignin obtained from sulfite wood pulping processes; lignin obtained from wood hydrolysis. Organic soluble lignin and alkali lignin are preferred. Lignin obtained from hardwood and softwood feedstocks may also be used.

In addition to lignin itself, lignin analogs based on natural monolignol units (i.e., phenylpropane) can also be used.

Examples of lignin analogs include: compounds described by Collier et al in Holzforschung (1992, volume 46, pp. 6, 523-528), especially based on C₆H₅R and C₆H₄(OCH₂) R, wherein R is CH (OH) CH₃Or CH₂CH(OH)C₆H₅(ii) a Compounds described by eggling in Trends in biotechnology (1983 vol 1, 123-127), such as bislignin (two phenylpropane units), arylglycerol- β -aryl ethers, 1, 2-diarylpropane bislignin and benzyl coumaran bislignin; e.e. compounds described by hawkes et al in Holzforschung (1993, volume 47, pages 302 to 312), such as vanillin, vanillic acid, acetovanillone, 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; compounds described by johnson et al, see "study of molecular weight distribution using lignin analogs". Chapter 8, pages 109-123, eds W.G.Glasser and S.Sarkanen, ACS Symp Ser.397(1989), ISBN 0-8412-.

The amount of the lignin or lignin analogue added is 0.1-50% by weight of the polyisocyanate, preferably 1-5%.

The lignin or lignin analogue may be added to the lignocellulosic material separately from the polyisocyanate and lignin solvent (preferably after the polyisocyanate has been added), or may be added simultaneously with the polyisocyanate and/or lignin solvent. If added simultaneously, the preferred method involves first mixing the lignin (analog) and lignin solvent and then adding the polyisocyanate thereto. Another method involves adding lignin (an analogue) to the polyisocyanate and then adding the lignin solvent.

The combined use of the lignin solvent and the lignin (analogues) can reduce the usage amount of the polyisocyanate by 20-40%.

The polyisocyanate used in the process of the present invention may be any organic polyisocyanate compound or mixture of organic polyisocyanate compounds as long as it has at least 2 isocyanate groups. Organic polyisocyanates include diisocyanates, especially aromatic diisocyanates, and high functionality isocyanates.

Examples of the organic polyisocyanate usable in the present invention include aliphatic isocyanates such as hexamethylene diisocyanate; aromatic isocyanates such as m-and p-phenylene diisocyanate, xylylene-2, 4-and 2, 6-diisocyanate, diphenylmethane-4, 4 ' -diisocyanate, chlorophenylene-2, 4-diisocyanate, naphthylene-1, 5-diisocyanate, diphenylene-4, 4 ' -diisocyanate, 4, 4 ' -diisocyanate-3, 3 ' -dimethyldiphenyl, 3-methyldiphenylmethane-4, 4 ' -diisocyanate and diphenylether diisocyanate; cycloaliphatic diisocyanates such as cyclohexane-2, 4-and-2, 3-diisocyanate, 1-methylcyclohexyl-2, 4-and-2, 6-diisocyanate and mixtures thereof, bis- (isocyanatocyclohexyl) methane; triisocyanates, such as 2, 4, 6-triisocyanatotoluene and 2, 4, 4-triisocyanatodiphenylether.

Modified polyisocyanates containing isocyanate, carbodiimide or uretonimine groups may also be used. Furthermore, blocked polyisocyanates can also be used, such as the reaction products of phenols or oximes with certain polyisocyanates, which have a deblocking temperature which is lower than the temperature at which the polyisocyanate composition is used.

The organic polyisocyanate may also be an isocyanate-terminated prepolymer prepared by reacting an excess of a diisocyanate or a high functionality polyisocyanate with a polyol.

Water-emulsifiable organic polyisocyanates similar to those described in British patent No. 1444933, European patent application No. 516361 and PCT patent application No. 91/03082 may also be used.

Mixtures of isocyanates may be used, for example mixtures of tolylene diisocyanate isomers such as the commercially available mixtures of 2, 4-and 2, 6-isomers; and mixtures of diisocyanates and high polyisocyanates obtained by phosgenation of aniline/formaldehyde polycondensates. These mixtures are well known in the art and include crude phosgenation products containing methylene-bridged polyphenyl polyisocyanates, including diisocyanates, triisocyanates and higher polyisocyanates as well as all phosgenation by-products.

Preferred isocyanates for use in the present invention are aromatic diisocyanates or high functionality polyisocyanates, such as pure tolylene diisocyanate or mixtures of methylene bridged polyphenyl polyisocyanates containing diisocyanates, triisocyanates and high functionality polyisocyanates.

Methylene-bridged polyphenyl polyisocyanates are well known in the art. They are prepared by phosgenation of the corresponding polyamine mixtures obtained by condensation of aniline and formaldehyde. For convenience, the polymeric MDI will be used hereinafter to refer to the polymeric mixture of methylene-bridged polyphenyl polyisocyanates containing diisocyanates, triisocyanates and high functionality polyisocyanates.

The polyisocyanate is preferably liquid at room temperature.

The polyisocyanate composition may further comprise conventional additives such as flame retardants, ligno-cellulosic preservatives, bactericides, waxes, sizing agents, fillers and other binders such as formaldehyde condensate gluing resins.

Lignocellulosic bodies can be prepared as follows: the lignocellulosic fraction is contacted with the polyisocyanate composition and the lignin solvent by mixing, spraying and/or dispersing the polyisocyanate composition and the lignin solvent in/on the lignocellulosic fraction, and then the combination of the polyisocyanate composition, the lignin solvent and the lignocellulosic fraction is pressurized, preferably hot, typically at 150-220 ℃ and 2-6 MPa. Such bonding methods are well known in the art.

The lignocellulose material treated by the polyisocyanate composition and the lignin solvent is placed on a pad plate disc made of aluminum or steel, and the ingredients are sent into a press by the pad plate to be pressurized to a preset pressure, wherein the temperature is usually 150-220 ℃. It may be useful, but not always necessary, to adjust the press platens at the beginning of the process by spraying a surface release agent on the surface of the caul plate. In the process of the invention, the press can be used several times without further treatment.

The process of the present invention is useful in the manufacture of sheet, medium density fiberboard and particle board (also known as particle board).

Thus, the lignocellulosic materials used may include wood strands, chips, wood fibers, shavings, wood strands, cork, bark, sawdust and similar waste materials from the wood-processing industry, as well as other lignocellulose-based materials such as paper, bagasse, rice straw, flax, sisal, hemp, juncus roe, reeds, chaff, wheat husks, grasses, nut shells and the like. In addition, lignocellulosic materials can be mixed with other particulate or fibrous materials, such as mineral fillers, glass fibers, mica, rubber, textile waste materials such as plastic fibers and fabrics.

The weight ratio of polyisocyanate/lignocellulosic material varies with the bulk density and performance requirements of the lignocellulosic material used. Thus, the polyisocyanate composition may be used in a polyisocyanate/lignocellulosic material weight ratio of from 0.1: 99.9 to 25: 75, preferably in the range of from 0.3: 99.7 to 16: 84.

Other conventional binders, such as formaldehyde condensation-polymerization binder resins, may also be used in conjunction with the polyisocyanate composition, if desired.

A more detailed description of the production of lignocellulose-based products is available from the prior art. Commonly used techniques and apparatus may also be used in the methods of the present invention.

The present invention can be illustrated by the following examples, but is not limited thereto. 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 at room temperature for about 2 minutes. The kind and amount of lignin solvent (based on the amount of polyisocyanate) are shown in table 1.

The resin, formulated to a content of 3% (polyisocyanate + lignin solvent) in a drum mixer, was sprayed onto the wood furnish with an air atomizer having a nozzle orifice of 0.7 mm.

Using the sprayed wood strands, 30X 1.1cm oriented strands were produced in a Siempelkamp press. The press plate temperature was 200 ℃. The general flow of pressing is as follows: the pressure is increased to 130bar by closing the die 45s, the pressure is maintained at 130bar by closing the die 176s, the pressure is reduced, and the pressure is reduced to 0 from 130bar in 15 s.

The physical properties of the wood boards are shown in Table 1. The expansion after 24 hours is determined by standard DIN 52364, the internal adhesion (IB) of V20 is determined according to standard DIN 52365 and V100 is determined according to standards DIN 68763 and DIN 52365.

Dimethylethyleneurea (DMEU) is available from Acros Chimica

Dimethylpropylene Urea (DMPU) was purchased from Acros Chimica

The poplar wood chips were obtained from Weyerhaeuser Drayton Valley

Southern pine wood strips from Weyerhaeuser Elkin

TABLE 1

	Swelling ratio (%)	IB-V20(kPa)	IB-V100(kPa)
				Nardostachys chinensis Franch
SUPRASEC 2185	33.07	752	/
				SUPRASEC 2185+0.5％DMEU	28.39	844	/
SUPRASEC 2185+1.0％DMEU	27.19	1001	/
				White poplar wood
SUPRASEC 2185	34 28	768	113
				SUPRASEC 2185+1.0DMPU	27.98	887	219

The above results show that the panels produced according to the invention show improved expansion and internal bond strength even with reduced amounts of polyisocyanate.

Example 2

Organosoluble lignin (ALCELL brand lignin powder, available from Repap technologies) was slowly added to polyisocyanate (SUPRASEC 2185 available from Imperial Chemical Industries) at room temperature with stirring at a ratio of 2 pbw/100pbw polyisocyanate. The lignin solvent, dimethyl ethylene urea (1 pbw/100pbw polyisocyanate), was then stirred in.

The resin with a content of 2% (polyisocyanate + lignin solvent + lignin) was formulated in a drum mixer and sprayed on poplar with an air atomizer having a nozzle opening of 0.7 mm.

Using the sprayed wood strands, 30X 1.1cm of Oriented Strand plates were produced in a Siempelkamp press at a press temperature of 200 ℃. The general flow of pressing is as follows: closing the mold, rising to 130bar in 45s, closing the mold, and keeping at 176s for 130 bar; the pressure is reduced, and the pressure is reduced from 130bar to 0 in 15 s.

The physical properties of the sheet are shown in Table 2

The reference plate was made from a 2% SUPRASEC 2185 spray and its physical properties are also given in Table 2.

TABLE 2

	Expansion ratio	Internal adhesion
			Reference plate	42.5	655
Sample (I)	32.5	977

Example 3

The coating resin was made from 5pbw of dimethylethylene urea (available from Aldrich) mixed with 93pbw of polyisocyanate (SUPRASEC 2185 available from Imperial Chemical industries). To the mixture was slowly added 2pbw lignin with stirring and stirred for 15 min.

Poplar single lap joints were prepared from the resulting polyisocyanate composition, clamped with an L-clamp and cured in an oven at 180 ℃ for 30 minutes. The lap joint is formed by lapping 2 cut wood chips with the length of 25mm, wherein the cut wood chips are 10-12 cm, 25mm and 3 mm. The binder is 12-18 g/m²The amount of (c) was applied to both sides of the overlapping part (30mm thick).

The tensile strength of the resulting lap joint was measured; to obtain parallel stress and reduce peel force, a 3mm shim was used. The results are shown in Table 3.

The reference used is a polyisocyanate (SUPRASEC 2185). The different lignins used included organosoluble lignin (available from Repap Technologies Inc.), alkaline lignin (available from Aldrich), hydrolyzed lignin (available from Aldrich), and sodium lignosulfonate (available from Aldrich).

TABLE 3

	Tensile Strength (kPa)
		Datum	2821
Organosoluble lignin	3172
		Alkaline lignin	3135
Hydrolyzed lignin	3013
		Sodium lignosulfonate	2988

Example 4

A composition of the polyisocyanate SUPRASEC1042 (available from Imperial Chemical Industries) was emulsified in water in a ratio of 50: 50 and 2% by weight of DMEU was added.

With this content of 6% (board density 800 kg/m)³) The polyisocyanate composition of (2) was prepared into a high-quality wood fiberboard of 15X 18X 0.6 cm. The moisture content of the fibre mat was 12%. The platen temperature was 200 ℃. The dropping capacity of the wood board from the pressing machine is 1-5, and the like. 1, etc. indicates that the board was completely bonded to the press, and 5, etc. indicates that the board was completely removed from the press. The breakage rate of wood is also determined by the percentage of area covered by the press for wood fibres after removal of the board.

The results are shown in Table 4. The reference is SUPRASEC1042 emulsified in water at a 50: 50 ratio.

TABLE 4

	Loosening ability	Breakage rate of wood
			Datum	4.5	0.5-1
Base + 2% DMEU	4.5-5	0

The results show that the addition of lignin solvent to the polyisocyanate improves its release capacity.

Claims (14)

1. A method of bonding lignocellulosic material comprising the steps of:

a) contacting lignocellulosic material with an organic polyisocyanate composition,

b) the material is then allowed to adhere to one another,

characterized in that the lignocellulosic material is contacted with the organic polyisocyanate composition simultaneously or independently with a lignin solvent.

2. The method of claim 1, wherein the lignin solvent is a cyclic urea.

3. The method of claim 2, wherein the lignin solvent is N, N '-dimethylethyleneurea or N, N' -dimethylpropyleneurea.

4. The method of claim 1, 2 or 3 wherein the lignin solvent is present in an amount of 0.1 to 6% by weight of the polyisocyanate.

5. The method of claim 4, wherein the lignin solvent is used in an amount of 0.5 to 2% by weight based on the polyisocyanate.

6. The method according to any one of the preceding claims, wherein the lignocellulosic material is also contacted with lignin or lignin analogues simultaneously or separately with the polyisocyanate composition and/or the lignin solvent.

7. The method of claim 6, wherein the lignin is an organosoluble lignin or an alkaline lignin.

8. A method according to claim 6 or 7, wherein the lignin or lignin analogue is present in an amount of 1 to 5% by weight of the polyisocyanate.

9. The process of any of the preceding claims wherein the organic polyisocyanate is an aromatic polyisocyanate.

10. The process of claim 9 wherein the organic polyisocyanate is methylene bridged polyphenyl polyisocyanate.

11. The method according to any of the preceding claims, wherein step b) comprises a hybrid hot pressing process of lignocellulosic material, polyisocyanate composition, lignin solvent and optionally lignin or lignin analogues.

12. A polyisocyanate composition comprising N, N '-dimethylethylene urea or N, N' -dimethylpropylene urea.

13. A polyisocyanate composition according to claim 12 in which the N, N '-dimethylethylene urea or N, N' -dimethylpropylene urea is used in an amount of 0.1 to 6% by weight.

14. A polyisocyanate composition according to claim 13 in which the N, N '-dimethylethylene urea or N, N' -dimethylpropylene urea is used in an amount of 0.5 to 2% by weight.