NOVEL PROCESS FOR PREPARING A BONDING RESIN

Abstract

The present invention relates to a process for preparing a bonding resin, wherein lignin is provided in the form of an aqueous solution and mixed with one or more of a crosslinker and optionally one or more additives. The bonding resin is useful for example in the manufacture of laminates, mineral wool insulation and wood products such as plywood, oriented strandboard (OSB), laminated veneer lumber (LVL), medium density fiberboards (MDF), high density fiberboards (HDF), parquet flooring, curved plywood, veneered particleboards, veneered MDF or particle boards.

Claims

1. A method for preparing a bonding resin, the method comprising: mixing, to provide a bonding resin, an aqueous lignin solution with one or more crosslinkers selected from a group consisting of 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 or epoxidized plant-based 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 a crosslinker having functional groups selected from a group consisting of 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.

2. The method according to claim 1, wherein the one or more crosslinkers is selected from a group consisting of 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 or epoxidized plant-based 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, and diglycidyl ether of bis-hydroxymethylfuran.

3. The method according to claim 1, wherein the one or more crosslinkers has functional groups selected from a group consisting of glycidyl methacrylate, diglycidyl methacrylate, triglycidyl methacrylate, and polyglycidyl methacrylate.

4. The method according to claim 1, wherein the aqueous lignin solution is an alkali solution.

5. The method according to claim 1, wherein a weight ratio between lignin, calculated on a basis of dry lignin, and a total amount of crosslinker is from 0.1:10 to 10:0.1.

6. The method according to claim 1, wherein the aqueous lignin solution further comprises an additive, and wherein the additive is selected from a group consisting of urea, tannin, surfactant, dispersing agent, filler, coupling agent, a solvent, and combinations thereof.

7. The method according to claim 5, wherein the solvent is glycerol, ethylene glycol, polyethylene glycol, propylene glycol, polypropylene glycol, sorbitol, glycol ethers, alcohol, or a terminal diol having a linear carbon chain of 3-6 carbon atoms.

8. The method according to claim 1, wherein lignin in the aqueous lignin solution is modified by glyoxylation, etherification, esterification or any other method where a lignin hydroxyl content or amine content or thiol content is increased.

9. The method according to claim 1, wherein lignin in the aqueous lignin solution is not chemically modified before being used in the method.

10. A bonding resin obtained by the method of claim 1.

11. The method of claim 1 further comprising: manufacturing a laminate, mineral wool insulation, or wood product with the bonding resin.

12. The method of claim 1 further comprising: providing the bonding resin to a surface in the preparation of a laminate, mineral wool insulation, or wood product, and curing of the bonding resin to form an adhesive when the surface is exposed to pressure and heating.

13. A laminate, mineral wool insulation, or wood product comprising the bonding resin according to claim 10.

14. The method of claim 1 wherein the aqueous lignin solution further comprises an additive.

Description

DETAILED DESCRIPTION

[0010] It is intended throughout the present description that the expression “lignin” embraces any kind of lignin, e.g. lignin originated from hardwood, softwood or annular plants. Preferably the lignin is an alkaline lignin generated in e.g. the Kraft process. Preferably, the lignin has been purified or isolated before being used in the process according to the present invention. The lignin may be isolated from black liquor and optionally be further purified before being used in the process according to the present invention. The purification is typically such that the purity of the lignin is at least 90%, preferably at least 95%. Thus, the lignin used according to the method of the present invention preferably contains less than 10%, preferably less than 5% impurities. The lignin may then be separated from the black liquor by using the process disclosed in WO2006031175. The lignin may then be separated from the black liquor by using the process referred to as the LignoBoost process.

[0011] The epoxidized vanillic acid, epoxidized plant-based phenolic acids, epoxidized soybean oil, tris(4-hydroxyphenyl) methane triglycidyl ether, and a crosslinker having functional groups selected from diglycidyl amide, triglycidyl amide, polyglycidyl amide, diglycidyl ester, triglycidyl ester, polyglycidyl ester, diglycidyl azide, triglycidyl azide, polyglycidyl azide, diglycidyl methacrylate, triglycidyl methacrylate and polyglycidyl methacrylate used according to the present invention acts as a crosslinker. Together with the lignin, it results in an adhesive during curing. Typically, the bonding resin according to the present invention is applied to the surfaces of for example veneers, such as in the manufacture of plywood. When the veneers are pressed together under heating, the crosslinking in the bonding resin takes place, resulting in an adhesive.

[0012] An aqueous solution of lignin can be prepared by methods known in the art, such as by mixing lignin, alkali and water. The pH of the lignin solution is preferably in the range of from 10 to 14. Examples of alkali include sodium hydroxide, potassium hydroxide and mixtures thereof. The amount of alkali in the aqueous solution is preferably from 0.1 wt-% to 15 wt-% of the solution, such as from 0.1 wt-% to 10 wt-% of the solution.

[0013] The weight ratio between lignin (dry weight) and the total amount of a crosslinker selected from 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 a crosslinker having functional groups selected from diglycidyl amide, triglycidyl amide, polyglycidyl amide, diglycidyl ester, triglycidyl ester, polyglycidyl ester, diglycidyl azide, triglycidyl azide, polyglycidyl azide, diglycidyl methacrylate, triglycidyl methacrylate and polyglycidyl methacrylate is preferably in the range of from 0.1:10 to 10:0.1, such as from 1:10 to 10:0.3, such as from 5:10 to 5:0.3, such as from 1:10 to 10:1. The amount of lignin in the bonding resin is preferably from 5 wt-% to 50 wt-%, calculated as the dry weight of lignin and the total weight of the bonding resin.

[0014] The bonding resin may also comprise additives, such as urea, tannin, solvents, surfactants, dispersing agents and fillers.

[0015] The amount of urea in the bonding resin can be 0-40% preferably 5-20% calculated as the dry weight of urea and the total weight of the bonding resin.

[0016] A filler and/or hardener can also be added to the bonding resin. Examples of such fillers and/or hardeners include limestone, cellulose, sodium carbonate, and starch. The bonding resin may also comprise coupling agent. Coupling agents are for example silane-based coupling agents.

[0017] The reactivity of the lignin with the glycidyl ether can be increased by modifying the lignin by glyoxylation, etherification, esterification or any other method where lignin hydroxyl content or carboxylic content or amine content or thiol content is increased. Preferably, the lignin used according to the present invention is not modified chemically.

[0018] Other solvents that can be used in the bonding resins according to the present invention are glycerol, ethylene glycol, polyethylene glycol, propylene glycol, polypropylene glycol, sorbitol and/or any terminal diol having a linear carbon chain of 3-6 carbon atoms.

[0019] The aqueous lignin solution is preferably mixed with the crosslinker at room temperature, such as at a temperature of from 15° C. to 30° C. The mixing is preferably carried out for about 5 minutes to 2 hours. Preferably, the viscosity of the mixture is monitored during mixing, either continuously or by taking samples and determining the viscosity thereof.

[0020] 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.