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EP-4739745-A1 - BINDER COMPRISING MODIFIED LIGNIN

EP4739745A1EP 4739745 A1EP4739745 A1EP 4739745A1EP-4739745-A1

Abstract

The present invention is directed to a process for preparing a binder, wherein lignin is subjected to demethylation whereby methoxy groups of lignin are converted to hydroxy groups. The demethylated 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.

Inventors

  • EKSTRÖM, Jesper
  • ARESKOGH, DIMITRI

Assignees

  • Stora Enso Oyj

Dates

Publication Date
20260513
Application Date
20240704

Claims (12)

  1. 1. A process for production of a binder, comprising the steps of a) providing lignin generated in the Kraft process, wherein the lignin contains less than 10% impurities; b) subjecting the lignin from step a) to a demethylation reaction whereby methoxy groups of lignin are converted to hydroxy groups, wherein the demethylation reaction is carried out until at least 10% of the methoxy groups of the lignin have been converted to hydroxy groups; c) mixing the modified lignin obtained in step b) with a crosslinking agent and optionally additives and heating the mixture to a temperature in the range of from 30 to 220°C to react the modified lignin and the crosslinking agent to obtain a binder.
  2. 2. The process according to claim 1 , characterized in that the demethylation reaction in step b) is carried out until at least 15% of the methoxy groups of the lignin have been converted to hydroxy groups.
  3. 3. The process according to claim 1 or 2, wherein the lignin is provided in the form of an aqueous solution.
  4. 4. The process according to claim 3, wherein the aqueous solution has a pH in the range of from 10 to 13.
  5. 5. A process according to any one of claims 1-4, wherein the crosslinking agent is an epoxy-based crosslinker.
  6. 6. A process according to any one of claims 1-4, wherein the crosslinking agent is an aldehyde and wherein phenol is also added in step c).
  7. 7. A process according to any one of claims 1-4, wherein the crosslinking agent is an amine.
  8. 8. A process according to any one of claims 1-8, wherein the modified lignin is mixed with lignin which has not been modified before step c).
  9. 9. Binder obtainable according to the process of any one of claims 1 to 8.
  10. 10. Engineered wood product produced using a binder according to claim 9.
  11. 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. 12. Insulation product produced using a binder according to claim 9.

Description

BINDER COMPRISING MODIFIED LIGNIN Field of the invention The present invention is directed to a process for preparing a binder, wherein lignin is subjected to demethylation whereby methoxy groups of lignin are converted to hydroxy groups. The demethylated lignin is mixed with a crosslinker and heated. The invention is also directed a binder obtained according to the process and to the use thereof. Background 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. 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. 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 a major obstacle towards implementing higher substitution levels. Modification of lignin is known in the art. For example, depolymerization, pyrolysis and solvolysis has been described, all of which lead to depolymerization of lignin. Oxidation of lignin has also been evaluated, to obtain various phenolic derivatives. Functionalization of hydroxyl groups on lignin has also been explored, such as by etherification, esterification, oxidation, phenolation, silylation and esterification. Summary of the invention 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. The present invention is directed to a process for preparing a binder, wherein lignin is subjected to a demethylation process whereby methoxy groups of lignin are converted to hydroxy groups. The modified lignin is then used in the production of a binder. The modified lignin can also be mixed with lignin which has not been modified, before the preparation of the binder. By mixing modified and unmodified lignin a mixture having an adapted degree of reactivity can be obtained. Thus, the present invention is directed to a process for production of a binder, comprising the steps of a) providing lignin generated in the Kraft process, wherein the lignin contains less than 10% impurities; b) subjecting the lignin from step a) to a demethylation reaction whereby methoxy groups of lignin are converted to hydroxy groups, wherein the demethylation reaction is carried out until at least 10% of the methoxy groups of lignin have been converted to hydroxy groups; c) mixing the modified lignin obtained in step b) with a crosslinking agent and optionally additives and heating the mixture to a temperature in the range of from 30 to 220°C to react the modified lignin and the crosslinking agent to obtain a binder. 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. Description of the figures Figure 1 shows shear strength as a function of time from starting to mix a 20% lignin solution with Glycerol diglycidyl ether until the press in an Automated Bonding Evaluation System is closed. Detailed description 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. 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 may 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 process 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 W02006031175. The lignin may be provided in the form of particles, such as particles having an average particle size of from 20 micrometers to 5 mm.