Binder comprising semi-washed lignin

Abstract

The present invention is directed to a process for preparing a binder, wherein semi-washed lignin is mixed with a cross-linker and heated. The invention is also directed a binder obtained according to the process and to the use thereof.

Description

[0001] BINDER COMPRISING SEMI-WASHED LIGNIN

[0002] Field of the invention

[0003] The present invention is directed to a process for preparing a binder, wherein semi-washed lignin is mixed with a cross-linker and heated. The invention is also directed a binder obtained according to the process and to the use thereof.

[0004] Background

[0005] Lignin, an aromatic polymer is a major constituent in e.g. wood, being the most abundant carbon source on Earth second only to cellulose. In recent years, with development and commercialization of technologies to extract lignin in a highly purified, solid and particularized form from the pulp-making process, it has attracted significant attention as a possible renewable substitute to primarily aromatic chemical precursors currently sourced from the petrochemical industry.

[0006] Lignin has been extensively investigated as suitable substitute for phenol during production of phenol-formaldehyde binders for production of panel boards such as plywood, hard board, medium density fiberboard or particle boards.

[0007] Lignin is an amorphous and highly branched polymer. Lignin comprises three different units: p-coumaryl alcohol, coniferyl alcohol and sinapyl alcohol. The units are connected to each other by carbon-carbon or ether bonds to a three- dimensional heterogenous structure. The relatively low reactivity of lignin is an obstacle towards implementing lignin-based binders in applications wherein a high reactivity and good strength properties products produced is required, such as in production of engineered wood products.

[0008] Summary of the invention

[0009] The present invention provides a solution to one more of the problems of the prior art. A particular advantage of the process according to the present invention is that reactivity of the lignin can be increased, which is particularly desirable for certain areas of application.

[0010] Semi-washed lignin is easier to prepare than for example lignin produced in the Lignoboost process. When preparing semi-washed lignin, only one single filter is used. Thus, the production of semi-washed lignin starts from black liquor from the Kraft process, optionally oxidized, to which carbon dioxide and / or acid is added to precipitate lignin, followed by filtration with a single filter setup. Contrary to for example the Lignoboost process, only one filter is used when preparing semi-washed lignin. The precipitated lignin may optionally be washed.

[0011] Surprisingly, it has been found that the semi-washed lignin is more reactive towards epoxy-based crosslinkers than lignin produced in the Lignoboost process. More specifically, the combination of semi-washed lignin with epoxybased crosslinkers leads to improved strength properties of engineered wood products.

[0012] The present invention is directed to a process for preparing a binder, wherein semi-washed lignin is used in the production of a binder. Thus, the present invention is directed to a process for production of a binder, comprising the steps of a) providing semi-washed lignin generated in the Kraft process, which has been precipitated from black liquor and subjected to filtration employing one single filter, and wherein the lignin has not been subjected to heat treatment above 150°C; b) mixing semi-washed lignin from step a), in the absence of aminated lignin, with an epoxy-based crosslinking agent and optionally additives and heating the mixture to a temperature in the range of from 30 to 220°C to react the semi-washed lignin and the epoxy-based crosslinking agent to obtain a binder.

[0013] The present invention is also directed to a binder obtained according to the process of the invention. The present invention is also directed to the use of the binder in the production of engineered wood products such as plywood, hard board, medium density fiberboard or particle boards.

[0014] Description of the figures

[0015] Figure 1 shows shear strength versus press time for the samples of Example 1. Figure 1 illustrates the difference between the use of semi-washed lignin and a reference lignin extracted using the Lignoboost process.

[0016] Detailed description

[0017] It is intended throughout the present description that the expression "lignin" embraces lignin originating from any type of plants, e.g. lignin originated from hardwood, softwood or annual plants. The lignin is an alkaline lignin generated in the Kraft process. The term “semi-washed lignin” used herein refers to lignin that has been generated in the Kraft process and which has been precipitated from black liquor and subjected to filtration employing a single filter setup. Thus, the filtration is not carried out in multiple steps, but in one step only. The lignin may be purified or isolated before being used in the process according to the present invention. The ash content of the semiwashed lignin is in a range of from 1 weight-% to 10 weight-%. Thus, the lignin used according to the process of the present invention preferably contains less than 10% impurities by weight. The semi-washed lignin may be provided in the form of particles, such as particles having an average particle size of from 20 micrometers to 5 mm. Preferably, the semi-washed lignin used according to the present invention is not modified chemically after its extraction from wood and isolation before being used according to the present invention. The semi-washed lignin is not aminated, i.e. it is not aminated and it does not comprise aminated lignin. The semi-washed lignin has not been subjected to any heat treatment above 150°C. The pH of the semi-washed lignin is preferably in a range of from 4 to 9, measured on a slurry.

[0018] The semi-washed lignin to be used according to the present invention is preferably provided in the form of a solution or dispersion. The solution or dispersion may be prepared by dissolving or dispersing semi-washed lignin in an aqueous medium. The pH of the aqueous medium may be adjusted by addition of acid or base. The medium in which the semi-washed lignin is dispersed or dissolved may also contain additives, such as solvents, surfactants, dispersing agents, surfactants, coupling agents, plasticizers and fillers.

[0019] Examples of fillers and / or hardeners include limestone, cellulose, sodium carbonate, and starch. Coupling agents are for example silane-based coupling agents.

[0020] If the semi-washed lignin is provided in the form of an aqueous solution of lignin, the solution may be obtained by dissolving lignin in water and alkali. Alternatively, the semi-washed lignin may be dissolved in a solution comprising water and ammonia and / or an organic base, which can be prepared by methods known in the art, such as by mixing semi-washed lignin and ammonia and / or organic base with water. The pH of the aqueous solution of semi-washed lignin is preferably in the range of from 10 to 14. Examples of organic bases include amines, such as primary, secondary and tertiary amines and mixtures thereof. Preferably, the organic base is selected from the group consisting of methylamine, ethylamine, propylamine, butylamine, ethylenediamine, methanolamine, ethanolamine, aniline, cyclohexylamine, benzylamine, dimethylamine, diethylamine, dipropylamine, dibutylamine, dimethanolamine, diethanolamine, diphenylamine, phenylmethylamine, phenylethylamine, dicyclohexylamine, piperazine, imidazole, 2- methylimidazole, 2-ethylimidazole, 2-ethyl-4-methylimidazole, 2- isopropylimidazole, 2- phenylimidazole, 2-methylimidazoline, 2- phenylimidazoline, trimethylamine, triethylamine, dimethylhexylamine, N- methylpiperazine, dimethylbenzylamine, aminomethyl propanol, tris(dimethylaminomethyl)phenol and dimethylaniline or mixtures thereof. The total amount of ammonia and / or organic base in the aqueous solution is preferably in the range of from 0.1 wt-% to 20 wt-%, preferably 0.1 wt-% to 10 wt-%, of the total weight of the aqueous solution comprising water, lignin and ammonia and / or an organic base. The amount of semi-washed lignin in the aqueous solution of lignin comprising ammonia and / or an organic base is preferably from 1 wt-% to 60 wt-% of the solution, such as from 10 wt-% to 30 wt-% of the solution.

[0021] The semi-washed lignin is used in combination with an epoxy-based crosslinker, to prepare a binder. Such binders may be used for example in the production of insulation or engineered wood products, such as plywood, oriented strandboard (OSB), laminated veneer lumber (LVL), medium density fiberboard (MDF), high density fiberboard (HDF), parquet flooring, curved plywood, veneered particleboard, veneered MDF or particle board.

[0022] For the preparation of a binder, the semi-washed lignin can be mixed with other, non-semi-washed lignin, such as lignin originating from black liquor from the Kraft process and extracted using for example the LignoBoost process, to provide a mixture of semi-washed and non-semi-washed lignin. Such a mixture may comprise 1-99 wt-% of semi-washed lignin and 1-99 wt- % non-semi-washed lignin, the combined amount thereof being 100 wt-%.

[0023] There are several methods for preparing binders, wherein an epoxy-based crosslinking agent is mixed with semi-washed lignin. According to the present invention, the mixture of semi-washed lignin and epoxy-based crosslinking agent is preferably heated to a temperature in the range of from 30 to 220°C to react the semi-washed lignin and the epoxy-based crosslinking agent to obtain a binder. The reaction time is preferably short to allow high production efficiency. Alternatively, a binder can be prepared by dissolving the semiwashed lignin in an aqueous solution, preferably having a pH in the range of from 10 to 14, and mixing with an epoxy-based crosslinking agent according to methods known in the art, followed by heating.

[0024] Epoxy-based crosslinking agent is an agent which functions as a crosslinker and wherein the crosslinking takes place by reaction involving the epoxy group. Examples of epoxy-based crosslinkers include glycerol diglycidyl ether, polyglycerol diglycidyl ether, polyglycerol polyglycidyl ether, glycerol triglycidyl ether, sorbitol polyglycidyl ether, alkoxylated glycerol polyglycidyl ether, trimethylolpropane triglycidyl ether, trimethylolpropane diglycidyl ether, polyoxypropylene glycol diglycidylether, polyoxypropylene glycol triglycidyl ether, diglycidylether of cyclohexane dimethanol, resorcinol diglycidyl ether, isosorbide diglycidyl ether, pentaerythritol tetraglycidyl ether, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether having 2-9 ethylene glycol units, propylene glycol diglycidyl ether having 1-5 propylene glycol units, diglycidyl-, triglycidyl- or polyglycidyl- ether of a carbohydrate, diglycidyl-, triglycidyl- or polyglycidyl-ester of a carbohydrate, diglycidyl-ether or diglycidyl ester of salicylic acid, vanillic acid, or 4-hydroxybenzoic acid, an epoxidized or glycidyl substituted plant-based phenolic compound (such as tannin, cardanol, cardol, anacardic acid) or epoxidized plant-based oil (such as rapeseed oil, linseed oil, soy bean oil), tris(4-hydroxyphenyl) methane triglycidyl ether, N,N-bis(2,3-epoxypropyl)aniline, p-(2,3-epoxypropoxy-N,N- bis(2, 3-epoxypropyl)aniline, diglycidyl ether of bis-hydroxymethylfuran, and / or diglycidyl ether of terminal diol having a linear carbon chain of 3-6 carbon atoms, and a crosslinker having functional groups selected from glycidyl amine, diglycidyl amine, triglycidyl amine, polyglycidyl amine, glycidyl amide, diglycidyl amide, triglycidyl amide, polyglycidyl amide, glycidyl ester, diglycidyl ester, triglycidyl ester, polyglycidyl ester, glycidyl azide, diglycidyl azide, triglycidyl azide, polyglycidyl azide, glycidyl methacrylate, diglycidyl methacrylate, triglycidyl methacrylate, or polyglycidyl methacrylate. Glycidyl ethers with more functional epoxide groups are further examples, such as glycerol diglycidyl ether, glycerol triglycidyl ether and sorbitol polyglycidyl ether. Other glycidyl ethers having two to nine alkylene glycol groups (such as 2-4 alkylene glycol groups or 2-6 alkylene glycol groups) are further examples, such as diethylene glycol diglycidyl ether, triethylene glycol diglycidyl ether, dipropylene glycol diglycidyl ether and tripropylene diglycidyl ether. Other epoxy-based crosslinkers include crosslinkers having functional groups selected from glycidyl amine, diglycidyl amine, triglycidyl amine, polyglycidyl amine, glycidyl amide, diglycidyl amide, triglycidyl amide, polyglycidyl amide, glycidyl ester, diglycidyl ester, triglycidyl ester, polyglycidyl ester, glycidyl azide, diglycidyl azide, triglycidyl azide, polyglycidyl azide, glycidyl methacrylate, diglycidyl methacrylate, triglycidyl methacrylate and polyglycidyl methacrylate.

[0025] When preparing the binder, the amount of semi-washed lignin in the binder is preferably from 1 wt-% to 45 wt-%, calculated as the dry weight of semiwashed lignin and the total weight of the binder. More preferably, the amount of semi-washed lignin in the bonding resin is from 5 wt-% to 30 wt-%, calculated as the dry weight of semi-washed lignin and the total weight of the binder.

[0026] The binder used when producing engineered wood is typically an aqueous solution containing from 1% to 80% by weight of binder. In one embodiment of the present invention, the resin solution contains from 10% to 40% of bonding resin, but also higher concentrations can be used, such as an aqueous solution containing 40-80% by weight of bonding resin. The pH of the bonding resin solution is generally above pH 9, preferably above pH 10, more preferably in the range of from pH 10 to pH 13. The bonding resin solution may optionally contain additional components such as pigments, surfactants, curing agents, pH stabilizers and fire retardants.

[0027] The quantity of binder applied on a surface when producing engineered wood products can be for example 10-400 g / m2, advantageously 10-150 g / m2, preferably 30-100 g / m2and most advantageously about 50 g / m2, when calculated as hardened binder compared to dry product produced.

[0028] Examples

[0029] Example 1

[0030] The NaOH (reagent grade) and the Glycerol diglycidyl ether (GDE, technical grade) were purchased from Sigma Aldrich.

[0031] Dissolution of lignin

[0032] Water (95.15 g) and NaOH (13.8 g, 50 wt%) was added to semi-washed Kraft lignin (28.0 g, S.C 97.75%). The solution was stirred over night with a magnetic stirrer at 600 RPM.

[0033] Evaluation of the semi-washed lignin

[0034] The reactivity was evaluated using an Automated Bonding Evaluation System (ABES) provided by Adhesive Evaluation Systems. A sample of the semi-washed lignin solution (5 g) was mixed with GDE (0.75 g) for 1 minute. The binder mixture was then tested according to the following method:

[0035] Sliced beech veneers (cut with the pneumatic cutter to a size of 117 mm long, 20 mm wide and 0.6 mm thick) conditioned at 23 °C and 50% R.H were used. The binder mixture was applied on the outer section of 5 x 20 mm (100 mm2) of a veneer using a pipette. The binder amount was then adjusted using a wire bar applicator (150 microns, from neurtek) to create an even amount of applied binder.

[0036] The veneer was pressed against a second veneer with a press temperature of 105 °C, for 10 - 90 seconds followed by an air-cooling step of 3 seconds and a pulling step of 4 seconds.

[0037] As reference a Lignoboost Kraft Lignin was used. The reference lignin was dissolved in the same ratios as the semi-washed lignin.

[0038] The shear strength versus press time is illustrated in Figure 1.

[0039] In view of the above detailed description of the present invention, other modifications and variations will become apparent to those skilled in the art. However, it should be apparent that such other modifications and variations may be effected without departing from the spirit and scope of the invention.

Claims

Claims1. A process for production of a binder, comprising the steps of a) providing semi-washed lignin generated in the Kraft process, which has been precipitated from black liquor and subjected to filtration employing one single filter, and wherein the lignin has not been subjected to heat treatment above 150°C; b) mixing semi-washed lignin from step a), in the absence of aminated lignin, with an epoxy-based crosslinking agent and optionally additives and heating the mixture to a temperature in the range of from 30 to 220°C to react the semi-washed lignin and the epoxy-based crosslinking agent to obtain a binder.

2. The process according to claim 1 , characterized in that the ash content of the semi-washed lignin is in a range of from 1 weight-% to 10 weight-%.

3. The process according to claim 1 or 2, wherein the semi-washed lignin is provided in the form of a dispersion or in the form of an aqueous solution.

4. The process according to claim 3, wherein the semi-washed lignin is provided in the form of a solution.

5. The process according to claim 4, wherein the aqueous solution has a pH in the range of from 10 to 13.

6. A process according to any one of claims 1-5, wherein the epoxybased crosslinking agent is selected from glycerol diglycidyl ether, polyglycerol diglycidyl ether, polyglycerol polyglycidyl ether, glycerol triglycidyl ether, sorbitol polyglycidyl ether, alkoxylated glycerol polyglycidyl ether, trimethylolpropane triglycidyl ether, trimethylolpropane diglycidyl ether, polyoxypropylene glycol diglycidylether, polyoxypropylene glycol triglycidyl ether, diglycidylether of cyclohexane dimethanol, resorcinol diglycidyl ether, isosorbidediglycidyl ether, pentaerythritol tetraglycidyl ether, ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether having 2-9 ethylene glycol units, propylene glycol diglycidyl ether having 1-5 propylene glycol units.

7. A process according to any one of claims 1-6, wherein the semiwashed lignin is mixed with non-semi-washed lignin before step b).

8. A process according to any one of claims 1-6, wherein the semiwashed lignin is not modified chemically after its extraction from wood and isolation before step b).

9. Binder obtainable according to the process of any one of claims 1 to 8.

10. Engineered wood product produced using a binder according to claim 9.

11. Engineered wood product according to claim 10, wherein said engineered wood product is plywood, oriented strandboard (OSB), laminated veneer lumber (LVL), medium density fiberboard (MDF), high density fiberboard (HDF), parquet flooring, curved plywood, veneered particleboard, veneered MDF or particle board.

12. Insulation product produced using a binder according to claim 9.

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