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CN-121991636-A - Lignin-based formaldehyde-free adhesive, lignin-based plywood and preparation methods and application thereof

CN121991636ACN 121991636 ACN121991636 ACN 121991636ACN-121991636-A

Abstract

The invention relates to the field of refining and application of lignocellulose biomass, and discloses a lignin-based formaldehyde-free adhesive, a lignin-based plywood and preparation methods and application thereof. The lignin-based formaldehyde-free adhesive comprises the components of L-cysteine lignin, wherein the solid content is 10-45wt%. The lignin-based formaldehyde-free adhesive is prepared by mixing an aqueous solution of L-cysteine hydrochloride and lactic acid with raw materials for pretreatment, extracting and vacuum filtering the obtained suspension to obtain dissolved lignin and hemicellulose filtrate, extracting and purifying the filtrate to obtain L-cysteine lignin, and uniformly dispersing the L-cysteine lignin in water. The solvent source used in the invention is green and nontoxic, the hydrated lignin-based adhesive with better fluidity is prepared with lower solid content, and the prepared plywood has excellent dry-wet bonding strength, solvent resistance and weather resistance, and meets the preparation requirements of the national class I plywood.

Inventors

  • YUE FENGXIA
  • ZHOU XIN
  • HU SONGNAN
  • WANG YU

Assignees

  • 华南理工大学

Dates

Publication Date
20260508
Application Date
20241105

Claims (10)

  1. 1. The lignin-based formaldehyde-free adhesive is characterized by having a solid content of 10-45 wt% and comprising L-cysteine lignin.
  2. 2. The lignin-based formaldehyde-free adhesive according to claim 1, wherein the lignin-based formaldehyde-free adhesive is prepared by dispersing L-cysteine lignin in water for 1-4 hours at a stirring speed of 250-1000 rpm/min.
  3. 3. The lignin-based formaldehyde-free adhesive according to claim 1 wherein the β -O-4 content in the L-cysteine lignin is 38.4 to 42.7% calculated based on aromatic rings.
  4. 4. The lignin-based formaldehyde-free adhesive according to claim 1 wherein the L-cysteine lignin is prepared by the following method: s1, mixing raw materials with pretreatment liquid for pretreatment; s2, extracting and vacuum filtering the pretreated suspension to obtain filtrate and filter residues; and S3, extracting and purifying the filtrate to obtain the L-cysteine lignans.
  5. 5. The lignin-based formaldehyde-free adhesive according to claim 3, wherein the pretreatment liquid is obtained by mixing L-cysteine hydrochloride, lactic acid and water in a mass volume ratio of 1g (5-15) mL (2-5) mL.
  6. 6. The lignin-based formaldehyde-free adhesive according to claim 3, wherein the solid-to-liquid ratio of the raw material to the pretreatment liquid is 1 g:12-15 mL, the pretreatment temperature is 80-120 ℃, and the pretreatment time is 1.5-6 h.
  7. 7. Use of a lignin-based formaldehyde-free adhesive according to any one of claims 1 to 6 for gluing wood materials.
  8. 8. A method for preparing lignin-based plywood, which is characterized in that the lignin-based formaldehyde-free adhesive is prepared by using the lignin-based formaldehyde-free adhesive according to any one of claims 1-5.
  9. 9. The method for preparing the lignin-based plywood according to claim 8, wherein the bonding condition of the lignin-based formaldehyde-free adhesive is that the hot pressing temperature is 80-190 ℃, the hot pressing time is 2-8 min, and the hot pressing pressure is 1-1.5 MPa.
  10. 10. A lignin-based plywood characterized by being prepared by the method for preparing the lignin-based plywood according to any one of claims 8-9.

Description

Lignin-based formaldehyde-free adhesive, lignin-based plywood and preparation methods and application thereof Technical Field The invention relates to the field of refining and application of lignocellulose biomass, in particular to a lignin-based formaldehyde-free adhesive, a lignin-based plywood and preparation methods and application thereof. Background In recent years, the development of the wood processing industry in China is rapid, and the dosage of the wood adhesive is greatly improved. Along with the enhancement of environmental protection and health consciousness of people, the requirement of environmental protection value of wood products is higher and higher, and the preparation of low-toxicity adhesive is an important direction of the development of plywood adhesives. Based on the universality of phenolic adhesive application and the difficult substitution of formaldehyde assisted polymerization, researchers are prompted to find green substitutes. The lignin-like phenylpropane structure replaces phenol to carry out polyaddition/polycondensation reaction with monomer at the ortho position of phenolic hydroxyl to prepare lignin-based high polymer. However, due to the structural heterogeneity of lignin after separation, lignin often needs to be further modified after separation to increase active sites to promote adequate reaction of formaldehyde with lignin. The presence of β -O-4 structure in large amounts results in the blocking of phenolic hydroxyl groups in natural lignin in large amounts, so that the natural lignin-like structures represented by organosolv lignin need to be degraded into phenolic oligomers/monomers by protective hydrolysis or reduction to ensure homogeneity, low condensability and high activity (high phenolic hydroxyl group content) of the product. Industrial lignin represented by kraft lignin and lignin sulfonate is often low in purity, wide in molecular weight distribution and high in condensation degree, and reaction sites need to be increased by means of demethylation, methylolation, phenolization and the like so as to improve the performance of the prepolymer after solidification. Although the introduction of modified lignin can replace aldehyde cross-linking agent with higher bonding strength in phenol production to a certain extent, the lignin-based aldehyde adhesive has the defects of darker color, higher viscosity (being unfavorable for large-scale conveying and sizing), more severe curing condition and the like, and the problems of non-mature large-scale sustainable production technology and the like are comprehensively considered, so that the lignin-based aldehyde adhesive with lower cost performance is difficult to be put into large-scale use in the processing field of plywood. The popularization of lignin-based adhesives is limited due to the carcinogenicity of formaldehyde and the defects of lignin-based adhesives in terms of color, viscosity, curing conditions, etc. At present, the existing lignin-based formaldehyde-free adhesive comprises a lignin-furfural and lignin-polyurethane composite system, but the materials are difficult to consider the environmental protection, the adhesive performance (water resistance, weather resistance and solvent resistance) and the cost. From the principle of action of the adhesive, the adhesive force is mainly derived from the attractive force between adhesive interface molecules and the cohesive force of the adhesive itself. The design of high performance lignin-based adhesives requires improved compatibility and diffusivity with wood board interfaces while improving cohesion. In order to solve the problems, shuai Li and the like, a low-condensation lignin aqueous dispersion liquid is developed, and the material forms C-C bond self-crosslinking through acid catalysis in the hot pressing process, so that the cohesive force and the bonding strength are obviously improved. However, the high viscosity of such adhesives remains a challenge for large scale industrial sizing. The formaldehyde system is used as a stabilizing group in lignin separation, and additional acid catalysis is needed to realize the self-crosslinking process of lignin in the hot pressing process, so that the high viscosity of the hydrated adhesive still needs to be further optimized and adapted to industrial sizing. Originally lignin has a relatively large molecular weight and lacks lyophilic groups. Therefore, the development of the lignin hydration adhesive for the high-strength novel plywood is beneficial to realizing the high-value utilization of lignin and can further widen the application field of the plywood. Disclosure of Invention The invention provides a lignin-based formaldehyde-free adhesive for overcoming the defects of formaldehyde dependence, difficult sizing, low adhesive property and the like in the prior art; Another object of the invention is to provide the use of a lignin-based formaldehyde-free adhesive; another object of the present inven