Demethylated lignin, preparation method thereof and application of the demethylated lignin in phenolic resin adhesive

Abstract

The invention discloses demethylated lignin as well as a preparation method and application thereof in a phenolic resin adhesive. The demethylated lignin is obtained by reacting lignin with laccase ina solvent. The lignin is demethylated through the laccase, so that the content of phenolic hydroxyl groups on lignin molecules is increased, activation sites reacting with formaldehyde in the ligninmolecular structure are increased, the activity is higher, and the reactivity with formaldehyde is higher. Meanwhile, the laccase used in the lignin demethylation process is a biocatalyst, has the advantages of being easy and convenient to operate and environmentally friendly, avoids the use of high-temperature and high-pressure reaction conditions and environment-friendly reagents, and is beneficial to production of downstream phenolic aldehyde adhesives. Moreover, due to the fact that the reaction activity of the demethylated lignin is improved, compared with a phenolic resin adhesive prepared from unmodified lignin, the modified phenolic resin adhesive prepared from the demethylated lignin has the advantages that the gelation time is shortened, the resin activity is improved, the formaldehyde release amount is reduced, and the bonding strength is improved.

Description

technical field [0001] The invention belongs to the technical field of materials, and in particular relates to a demethylated lignin, a preparation method thereof and an application in phenolic resin adhesives. Background technique [0002] Lignin is the most abundant and important natural polymer substance after cellulose in quantity. It is estimated that about 6×10 14 Lignin is a resource with great potential. Since the molecular structure of lignin contains a certain number of active groups such as aromatic groups, alcoholic hydroxyl groups, carbonyl groups, phenolic hydroxyl groups, methoxyl groups, carboxyl groups, ether bonds and conjugated double bonds, lignin can be oxidized, reduced, hydrolyzed, Many chemical reactions, such as alcoholysis, acylation, alkylation, polycondensation or graft copolymerization, can be widely used in the synthesis of biomass-based polymer materials. Moreover, the unsubstituted active hydrogen on the lignin benzene ring structure can un...

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Problems solved by technology

[0005] Purpose of the invention: The technical problem to be solved by this invention is to provide a kind of demethylated lignin and its preparation method in view of the need to use high-pressure equipment and high process requirements in the lignin modification process in the prior art. The lignin is demethylated by laccase under pressure without using toxic reagents and environmentally unfriendly solvents, avoiding the generation of unpleasant odors, and the obtained lignin has increased phenolic hydroxyl content and has a lower Free phenol content and free formaldehyde content can replace phenol to prepare lignin-based phenolic resin adhesives, which are used in various new polymer materials such as adhesives and phenolic plastics

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