CN115558466A

CN115558466A - Lignin-based adhesive

Info

Publication number: CN115558466A
Application number: CN202211221947.6A
Authority: CN
Inventors: 王燕蓬; 刘鲁民
Original assignee: Shandong Baimusheng New Material Technology Co ltd
Current assignee: Shandong Baimusheng New Material Technology Co ltd
Priority date: 2022-10-08
Filing date: 2022-10-08
Publication date: 2023-01-03
Anticipated expiration: 2042-10-08
Also published as: CN115558466B

Abstract

The invention discloses a lignin-based adhesive, which comprises adhesive components of lignin with small condensation degree, wherein the content of the lignin with small condensation degree is 10-67%, and the balance is solvent; the lignin with small condensation degree has the alkylphenol monomer mass yield of more than 10 percent after the depolymerization by hydrogenation. The method utilizes lignin with small condensation degree to prepare the all-lignin-based wood adhesive, the lignin with certain characteristics and an additive are compounded and treated to be directly used as the adhesive, and the lignin is condensed and cured by hot pressing under the acidic condition, so that the wood is bonded together; the invention extracts lignin from the wood biomass and directly uses the lignin as the adhesive, and has the advantages of reproducibility, environmental protection, low price and the like.

Description

Lignin-based adhesive

Technical Field

The invention relates to a lignin-based adhesive, in particular to a lignin-based adhesive directly prepared by directly utilizing lignin with low condensation degree, belonging to the technical field of efficient utilization of lignin.

Background

In nature, lignin, which is the main component of woody biomass, is a natural aromatic high molecular compound and is formed by connecting three precursor units (p-coumarol, coniferyl alcohol and sinapyl alcohol) through various inter-unit C-C and C-O bonds, wherein the C-O bonds mainly comprise beta-O-4, 4-O-5 and the like, the C-C mainly comprises 5-5, beta-beta and the like, and the beta-O-4 is the main bond among the lignin units and accounts for 40-65% of all inter-unit bond types. The synthetic pathway of lignin is shown in fig. 1, and the types of the intercellular bonds of lignin and the contents thereof are shown in table 1. The lignin monomer with phenylpropane structure can be released by breaking the beta-O-4 bond with weaker bond energy. The lignin plays a role in bonding cellulose together in ligneous organisms and improving the rigidity of plants, and is a natural 'adhesive'.

Table 1 shows the types of lignin unit bonds and the contents thereof

On the other hand, in industries currently dominated by cellulose utilization, such as pulp and paper industry and biorefinery industry, lignin utilization is neglected and often used as waste as a low value added fuel, mainly due to: (1) The lignin has a complex structure and cannot be converted into a single product; (2) During the cooking process, lignin is easy to undergo condensation reaction under acid or alkali conditions, namely, a new stable C-C connecting bond is formed between lignin phenol units (as shown in a figure II, a part of possible lignin condensation mechanisms are represented, wherein A is condensation of a lignin side chain and an aromatic ring, and B is aldol condensation of a lignin side chain carbonyl group), the lignin structure becomes more complex, and the utilization difficulty is higher. Therefore, the condensation structure of lignin is mainly composed of the C-C bonds between units formed in the biosynthesis process and the C-C bonds between units formed in the separation process, and the condensation of lignin undoubtedly affects the use scene of lignin.

In the field of adhesives according to the present invention, there is no application in the market that lignin is simply used as a main component and is directly used as an adhesive or a main component of an adhesive without being reacted with aldehydes again. With regard to the role of lignin in adhesives, a great deal of research is currently being focused on the use of industrial lignin (e.g., sodium lignosulfonates, alkali lignin, kraft lignin) instead of phenol to synthesize phenolic resin adhesives. The synthesis of the phenolic resin adhesive mainly comprises the steps of reacting formaldehyde with ortho-para positions of phenolic hydroxyl groups of phenol under an alkaline condition to form a hydroxymethyl structure, and reacting the hydroxymethyl structure with ortho-position and para-position positions of the phenolic hydroxyl groups of the phenol to form a methylene bridging structure, so that a network cross-linking structure is formed by continuously repeating the mechanism. However, the para position of the phenolic hydroxyl group of the phenol unit in lignin is completely occupied by an alkyl side chain, and a part of the ortho position is also occupied by a methoxy group (as shown in fig. 1), thereby resulting in fewer active sites in lignin that can react with formaldehyde under alkaline conditions; in addition, these industrial lignins are heavily condensed during the extraction process, and most of the reaction sites are consumed by the condensation reaction, so that the reactivity of these lignins is further reduced, and finally the synthetic lignin-phenolic resin has low crosslinking activity, is slow to cure, and requires higher hot pressing time and hot pressing temperature. When the ratio of lignin to phenol exceeds about 30%, the performance of the adhesive is obviously reduced. The lignin-phenolic resin adhesive contains a large amount of free formaldehyde, and can release formaldehyde to cause damage to human bodies in the using process and after use. Therefore, the lignin replaces phenol to synthesize the phenolic resin adhesive, and does not show obvious advantages in performance, the wood adhesive in the market still mainly takes petroleum-based aldehyde-containing adhesives such as urea-formaldehyde resin, phenolic resin and the like, and the wood adhesive is not renewable and has large formaldehyde release amount. The formaldehyde-free adhesive mainly comprises MDI (diphenylmethane diisocyanate) and modified soy protein adhesive, but the adhesive is expensive or poor in performance and limited in application.

Disclosure of Invention

The invention aims to solve the technical problem of providing a lignin-based adhesive and a preparation method thereof aiming at the defects in the prior art, the invention selects lignin with small condensation degree to directly prepare a full-lignin-based wood adhesive, directly uses the lignin with certain characteristics and a solvent as the adhesive through compounding treatment, and makes the lignin condensed and solidified through hot pressing under the acidic condition, thereby gluing the wood together; the lignin extracted from the woody biomass can be directly used as an adhesive, and the preparation method has the advantages of simplicity, reproducibility, environmental protection, low price and the like.

In order to achieve the purpose, the invention adopts the following technical scheme:

a lignin-based adhesive, the adhesive component of which is lignin with small condensation degree, is characterized in that: the content of lignin with small condensation degree is 10-67%, and the balance is solvent; the lignin with small condensation degree has the alkylphenol monomer mass yield of more than 10 percent after the hydro-depolymerization. Because lignin needs to be crosslinked again during hot pressing to achieve the effect of the adhesive, not all lignin can be used for preparing the lignin-based adhesive. The lignin is not deeply condensed during the separation and extraction process, and partial condensable active sites still remain, so that the condition that the lignin has recondensation and solidification capacity during hot pressing is necessary. The invention judges the lignin condensation degree by using hydrogenation depolymerized lignin, and hydrogenation can selectively break the beta-O-4 connecting bond with weaker lignin unit inter-bond energy (table 1) and release alkylphenol monomers (figure 3, the monomer types formed by lignin hydrogenation depolymerization). The depolymerization conditions described in the present invention do not have a cleavage effect on the C-C bonds between the units formed during lignin biosynthesis (FIG. 1) and the C-C bonds between the units formed by condensation during isolation and extraction (FIG. 2). After lignin condensation, C-C connecting bonds among lignin internal units are increased, and monomers released after hydrogenation depolymerization are reduced. Therefore, the degree of lignin condensation can be determined by the yield of alkylphenol monomers. In practice, the final use of lignin is not considered in the current industrialized lignin separation technology, in order to rapidly separate lignin, the reaction is usually carried out at high temperature or a large amount of acid or alkali is used as a catalyst, so that the condensation of the separated lignin is serious (such as kraft lignin, alkali lignin and lignosulfonate in the paper industry), and the mass yield of alkylphenol monomers released by the lignin through depolymerization by hydrogenation is often less than 5%. Because of serious condensation and large molecular weight, the lignin can hardly be softened and crosslinked properly again under the hot pressing, and thus the lignin can not play a role in adhering wood or can not well permeate into gaps of an adhesion interface;

in the above technical scheme, the conditions of the depolymerization by hydrogenation are as follows: the reaction temperature is 200 ℃, the reaction time is 6 hours, the hydrogen pressure is 5Mpa, the catalyst is Ru/C (5% ruthenium metal loaded on activated carbon, purchased from Sigma-Aldrich company), and the reaction solvent is methanol; the mass ratio of the methanol to the lignin to the catalyst (Ru/C) is 40. The hydro-depolymerization condition is used as a lignin condensation degree evaluation method, and can selectively break beta-O-4 connecting bonds between lignin units which are not condensed to release lignin monomers. The hydro-depolymerization conditions used in the invention can ensure that the condensation degree of each type of lignin can be evaluated more accurately, and the reaction conditions are slightly changed on the basis, so that the evaluation effect is not greatly influenced.

In the technical scheme, the lignin with small condensation degree can be prepared by organic solvent pretreatment, alkali pretreatment, ionic liquid pretreatment, eutectic solvent pretreatment or organic acid pretreatment. The lignin with small condensation degree used as the adhesive is directly limited from the essence influencing the adhesive performance, namely from the aspects of the quantity of active sites required by condensation retained by the lignin and the height of the condensation degree, so the lignin obtained by various ways is suitable for the application scene of the invention as long as the lignin meets the required conditions of the invention. In practice, pretreatment techniques are widely studied as the primary method for separating the three major components of woody biomass. Wherein the organic solvent pretreatment mainly uses a mixed solvent of low boiling point alcohol (such as methanol, ethanol, butanol and the like) and cyclic ether (such as dioxane, tetrahydrofuran and the like) and water to dissolve out lignin under acidic conditions, and retains cellulose components; the alkali pretreatment is mainly to dissolve out lignin by using an alkali water solution and keep a cellulose component; the ionic liquid and the eutectic solvent have a good dissolving solvent effect on lignin, so that the lignin can be dissolved out, and cellulose components are reserved; the organic acid pretreatment mainly uses high-concentration organic acids (such as formic acid and acetic acid) as solvents to dissolve lignin from the biomass. The various pretreatment methods described above, i.e., methods for extracting and separating lignin, are well known to those skilled in the art. The invention finds that under certain extraction conditions, the pretreatment method can retain uncondensed lignin units with different degrees, and when the conditions are met, the separated lignin has good performance of recondensation crosslinking during hot pressing.

In the technical scheme, the solvent is any one or a mixture of two or more of water, ethanol, dioxane, acetone, tetrahydrofuran and ethyl acetate which are mixed in any proportion; the mass of the solvent is 0.5-9 times of that of the lignin. The lignin is dispersed in the solvent to form uniform liquid, which is beneficial to uniformly applying the adhesive on the surface of the wood to be bonded.

In the above technical solution, the lignin-based adhesive preferably further comprises an auxiliary agent, wherein the auxiliary agent is any one of a cross-linking agent, an acidic catalyst, a thickening agent, and a surfactant, or a mixture of two or more of the cross-linking agent, the acidic catalyst, the thickening agent, and the surfactant, which are mixed in any proportion.

In the technical scheme, the cross-linking agent is any one of hexamethylene tetramine, glyoxal, glutaraldehyde, dialdehyde starch and hydroxymethyl phenol, or a mixture of two or more of hexamethylene tetramine, glyoxal, glutaraldehyde and hydroxymethyl phenol which are mixed in any proportion; the addition amount of the cross-linking agent is 0.1-5% of the weight of the lignin-based adhesive. These cross-linking agents react with the carbonyl and benzene rings in the lignin and the addition of these components contributes to the formation of a more compact cross-linked network and increases the cross-linking strength of the lignin.

In the technical scheme, the acidic catalyst is any one or a mixture of two or more of formic acid, acetic acid, oxalic acid, hydrochloric acid, sulfuric acid, phosphoric acid, ammonium chloride and the like which are mixed in any proportion, and the addition amount of the acidic catalyst is 0.1-10% of the weight of the lignin-based adhesive. Lignin can be condensed under the conditions of acidic catalysts (such as sulfuric acid and ammonium chloride) or high temperature, so that the acidic catalysts are added as auxiliaries in the hot pressing process, the curing and crosslinking of the lignin are facilitated to be accelerated, the hot pressing time is shortened, and the hot pressing temperature is reduced;

in the technical scheme, the thickening agent is any one of starch, protein, defatted soybean powder, cellulose derivatives (such as sodium carboxymethyl cellulose), calcium sulfate, calcium carbonate and condensed lignin, or a mixture of two or more of the starch, the protein, the defatted soybean powder, the cellulose derivatives, the calcium sulfate, the calcium carbonate and the condensed lignin which are mixed in any proportion; the addition amount of the thickening agent is 1-20% of the weight of the lignin-based adhesive. In the actual application process, a thickening agent can be added to adjust the viscosity of the adhesive according to the process requirements.

In the technical scheme, the surface activity is any one of sodium dodecyl sulfate and sodium lignosulfonate, and the addition amount of the thickener is 0.1-5% of the weight of the lignin-based adhesive. Because the lignin is insoluble or has low solubility in water, when water is used as a solvent, a surfactant can be added to improve the dispersion of the lignin in the water, so that a more uniform adhesive liquid is obtained.

The invention also provides a using method of the lignin-based adhesive in wood bonding, wherein the lignin-based adhesive is applied to the surface of wood to be bonded, and the glue application amount is 50-400g/m ² (ii) a And hot-pressing under pressure and temperature to cure the bonded wood. The adhesive disclosed by the invention can be applied to the fields of plywood, fiberboard, shaving board, bamboo and wood composite board and the like, and can be applied to various application scenes which are well known at present. When the glue application amount is low, the viscosity can be adjusted by adding lignin or a thickening agent so as to meet the requirements of use scenes.

In the technical scheme, the hot pressing pressure is 0.5-2.5MPa, and the hot pressing temperature is 100-220 ℃; the lignin can be subjected to condensation reaction under the high-temperature condition. The research of the invention finds that the lignin adhesives with different types and different condensation degrees have different hot pressing temperatures, and the higher the hot pressing temperature is, the easier the lignin adhesives are to crosslink and solidify. The invention also discovers that lignin from the same source can be solidified at lower temperature when the condensation degree of the lignin is small under the same other hot pressing conditions; when the degree of lignin condensation is higher, higher hot pressing temperatures are required to soften and cure the lignin. In practical application, after the hot pressing temperature is selected, the hot pressing time and the hot pressing pressure can be adjusted, so that the bonding strength of the cured and crosslinked lignin can reach the national standard.

Compared with the prior art, the invention has the following beneficial effects:

firstly, lignin separated from woody biomass is directly used as a main component and is compounded with a solvent to obtain an adhesive applicable to wood bonding, so that the adhesive can be called as a full-lignin-based environment-friendly adhesive and does not contain harmful components such as formaldehyde and the like;

secondly, although the prior art can utilize various lignins to prepare the lignin-phenol adhesive, the lignin is mainly used for replacing part of phenol and reacts with formaldehyde to synthesize the adhesive under an alkaline condition, the lignin used as the adhesive in the invention needs to keep a part of uncondensed structures so as to ensure that the uncondensed structures can enable the lignin to have condensation reaction again during hot pressing, thereby playing a role in curing and crosslinking, and the lignin does not need to react with the formaldehyde again, thereby simplifying the preparation process of the adhesive and more fully utilizing the lignin;

thirdly, the invention utilizes the characteristic that lignin has self-crosslinking under acidic condition, and can realize the hot-pressing curing crosslinking of lignin adhesive under the condition of no acid or little acid, while the traditional lignin phenolic resin synthesis and curing are carried out under alkaline condition, and a large amount of alkali is consumed.

Drawings

FIG. 1 shows the synthetic pathway and structure of lignin.

Figure 2 is a partial possible lignin condensation mechanism: a is condensation of lignin side chain and aromatic ring; b is aldol condensation of lignin side chain carbonyl groups.

FIG. 3 is a graph of the types of monomers formed by the hydro-depolymerization of lignin.

FIG. 4 is a formula for calculating the mass yield of lignin monomers and the mass yield of lignin alkylphenol monomers.

Detailed Description

According to the invention, the characteristic that lignin can be condensed at high temperature is utilized, lignin with small lignin separation and condensation degree is selected, the lignin is used as the main component of the adhesive to be coated on the surface of the wood, and the lignin is condensed and crosslinked again through hot pressing, so that the wood can be bonded together. Lignin with small condensation degree is usually small in molecular weight, can be softened under the action of high temperature and can permeate into cell wall gaps and cell cavities to generate mechanical biting force; meanwhile, lignin components in the adhesive can be subjected to the same type of crosslinking condensation with lignin in the wood to form a tight chemical bonding force, and the two bonding forces enable the lignin adhesive to have certain bonding strength.

Therefore, the key point of the technical invention is that the main component lignin used by the adhesive is not subjected to deep condensation reaction in the extraction process, and still remains partial active sites required by condensation, wherein the active sites possibly form condensation crosslinking sites including alpha hydroxyl or ether bonds of lignin side chains, meta-positions of lignin phenol hydroxyl, aldehyde and ketone products formed by lignin hydrolysis and the like; these sites can undergo benzene naphthenation reactions as well as aldol condensation reactions, both of which can form C-C linkages between lignin units, resulting in condensation crosslinking of lignin (FIG. 2).

A more direct method of assessing the degree of lignin condensation is to depolymerize the lignin to lignin monomers, i.e. alkylphenol compounds, by hydrogenation (fig. 3). Hydrogenation can avoid condensation of lignin by acid or alkali, and is a well-established method for splitting lignin into monolignols (see Shuai et al. Formulations catalysis lipids in monomer production polymerization. Science,2016,354, 329-333). After lignin is condensed and crosslinked to form a stable C-C connecting bond between units during separation (figure 2), the yield of lignin monomers generated by lignin depolymerization by hydrogenation is greatly reduced, so that the degree of lignin condensation can be evaluated according to the yield of lignin after depolymerization by hydrogenation, namely the higher the yield of lignin monomers is, the smaller the degree of lignin condensation is; the lower the yield of lignin monomer, the higher the degree of lignin condensation. Since lignin biosynthesis contains 50-60% of the C-C bonds between units (FIG. 1), the beta-O-4 bonds that can be broken under the hydrogenation conditions are only 40-65%. Therefore, a great deal of research has found that the theoretical mass yield of the monomer after the hydro-depolymerization of the primary lignin in the woody biomass is about 13 to 34%. Due to the different types and production places of the woody biomass, the theoretical monomer yield which can be released by the lignin in the hydro-depolymerized woody biomass is slightly different. The mass yield of the monomers released by the hydro-depolymerization of the native lignin in cork is about 13%; the mass yield of the monomers released by the hydro-depolymerizing of the native lignin in the hardwood is about 34%; the mass yield of the monomer released by the primary lignin in the corn straw through hydro-depolymerization is about 30 percent. In the invention, the original structure of part of lignin can be kept to ensure that the lignin can be condensed, cured and crosslinked again in the hot pressing process, so that the yield of the monomer after the lignin hydrogenation for preparing the adhesive can be lower than the theoretical monomer yield of various woods. The invention discovers that when the mass yield of the monomer after the hydrogenation of the lignin is more than about 10 percent (namely accounting for about 30 to 75 percent of the theoretical yield of the monomer), the lignin can be used for preparing the adhesive which has better performance and can be cured under the acidic condition. The mass of the lignin monomer can be calculated after quantification by gas chromatography. The mass yield of lignin monomers and the mass yield of lignin alkylphenol monomers are calculated by the formula shown in FIG. 4.

In order to make the present invention more comprehensible, the technical solutions of the present invention are further described below with reference to specific embodiments, but the present invention is not limited thereto.

Example 1

Extracting and hydrogenating the wood grinding lignin:

vibrating and ball-milling 10 g of 80-mesh eucalyptus wood powder for 24 hours, taking out the ball-milled wood powder, mixing the ball-milled wood powder with 90 ml of dioxane and 10 ml of water, placing the mixture in a reaction kettle, reacting at 90 ℃ for 48 hours to dissolve out lignin in the wood powder, separating the solution, concentrating to about 20 ml, adding 100 ml of water to precipitate the lignin, filtering to obtain a precipitate, and drying the precipitate at 105 ℃ to obtain about 0.7 g of ground wood lignin. Taking part of lignin for hydro-depolymerization under the following conditions: the reaction temperature was 200 ℃, the reaction time was 6 hours, the hydrogen pressure was 5Mpa, the catalyst was Ru/C (5% loading), the reaction solvent was methanol, and the mass ratio of methanol, lignin and catalyst (Ru/C) was 40. The mass yield of the lignin monomer is 26 percent by measurement and calculation.

And uniformly mixing 0.5 g of lignin obtained above and 1.0 g of dioxane to obtain the adhesive. Preparing three-layer plywood by using poplar veneers according to the specification of 4.17 section in GB/T17657-2013 physicochemical property test method for artificial boards and veneers. Measured at a sizing amount of 100g/m ² The plywood prepared under the conditions of hot pressing temperature of 220 ℃, hot pressing pressure of 0.5MPa and hot pressing time of 5 minutes has the bonding strength of 1.2MPa and more than 0.7MPa according to the national standard of II-type plywood measurement method.

Example 2

Extracting and hydrogenating dioxane organic solvent lignin:

mixing 10 g of 80-mesh masson pine wood powder, 90 ml of dioxane and 10 ml of water, placing the mixture into a reaction kettle, adding 400 microliters of hydrochloric acid with the concentration of 37wt%, closing the reaction kettle, reacting at 80 ℃ for 5 hours, separating reaction liquid, concentrating the liquid to about 20 ml, adding 100 ml of water to precipitate lignin, filtering and washing the precipitate until the pH value of the filtrate is neutral, and drying the precipitate at 105 ℃ to obtain about 1.9 g of lignin. A part of lignin is taken to be hydrogenated and depolymerized under the conditions carried by the example 1, and the mass yield of the lignin monomer is 10 percent.

1.5 g of lignin obtained above and 13.5 g of water are mixed uniformly to be used as an adhesive. And (3) preparing a three-layer plywood by using poplar veneers according to the regulations of 4.17 section in GB/T17657-2013 test method for physical and chemical properties of artificial boards and veneers, and testing the strength of the plywood. Measured at a sizing amount of 400g/m ² The plywood prepared under the conditions of hot pressing temperature of 190 ℃, hot pressing pressure of 0.7MPa and hot pressing time of 15 minutes has the bonding strength of 1.0MPa and more than 0.7MPa according to the national standard of II-type plywood measurement method.

Example 3

Extracting and hydrogenating gamma-valerolactone organic solvent lignin:

mixing 10 g of 80-mesh eucalyptus wood powder, 80 ml of gamma-valerolactone and 20 ml of water, placing the mixture into a reaction kettle, adding 500 microliters of hydrochloric acid with the concentration of 37wt%, closing the reaction kettle, reacting at 90 ℃ for 4 hours, adding 400 ml of water to precipitate lignin, filtering, washing the precipitate until the pH value of the filtrate is neutral, and drying the precipitate at 105 ℃ to obtain about 1.6 g of lignin. A part of lignin was subjected to depolymerization by hydrogenation under the conditions as described in example 1, and the yield of monolignol was found to be 11% by mass.

Will be provided withThe obtained 1.5 g of gamma-valerolactone lignin, 3.0 g of water and 50mg of sodium carboxymethylcellulose (thickening agent) are uniformly mixed to be used as an adhesive. The three-layer plywood is prepared by using poplar veneers according to the specification of 4.17 section in GB/T17657-2013 physicochemical property test method for artificial boards and veneers, and the strength of the plywood is tested. Measured at a sizing amount of 100g/m ² The plywood prepared under the conditions of hot pressing temperature of 190 ℃, hot pressing pressure of 0.7MPa and hot pressing time of 10 minutes has the bonding strength of 1.0MPa and more than 0.7MPa according to the national standard of II-type plywood measurement method.

Example 4

Extraction and hydrogenation of ionic liquid lignin:

mixing 10 g of 80-mesh corn straw powder and 100 ml of chlorinated 1-ethyl-3-methylimidazole (ionic liquid), placing the mixture into a reaction kettle, reacting for 6 hours at 120 ℃, separating reaction liquid, adding 500 ml of water to obtain a precipitate, filtering and washing the precipitate until the pH value of the filtrate is neutral, and drying the precipitate at 105 ℃ to obtain about 1.4 g of lignin. The monolignol mass yield was 18% as determined by the hydropolymerisation of a portion of the lignin under the conditions carried out in example 1.

And uniformly mixing 1.0 g of the obtained ionic liquid lignin and 4.0 g of tetrahydrofuran to obtain the adhesive. The three-layer plywood is prepared by using poplar veneers according to the specification of 4.17 section in GB/T17657-2013 physicochemical property test method for artificial boards and veneers, and the strength of the plywood is tested. Measured at a sizing amount of 200g/m ² The plywood prepared under the conditions of hot pressing temperature of 190 ℃, hot pressing pressure of 1.2Mpa and hot pressing time of 10 minutes has the bonding strength of 1.1Mpa and more than 0.7Mpa according to the national standard of II-type plywood measurement method.

Example 5

Extraction and hydrogenation of eutectic solvent lignin:

mixing 10 g of 80-mesh wood flour and 100 ml of choline chloride/lactic acid (molar ratio 1. A portion of the lignin was depolymerized by hydrogenation under the conditions described in example 1, and the monolignol yield was found to be 15% by mass.

And uniformly mixing 1.0 g of the obtained eutectic solvent lignin and 2.0 g of water to obtain the adhesive. The three-layer plywood is prepared by using poplar veneers according to the specification of 4.17 section in GB/T17657-2013 physicochemical property test method for artificial boards and veneers, and the strength of the plywood is tested. Measured at a sizing amount of 200g/m ² The plywood prepared under the conditions of hot pressing temperature of 180 ℃, hot pressing pressure of 1.5Mpa and hot pressing time of 15 minutes has the bonding strength of 1.2Mpa and more than 0.7Mpa according to the national standard of II-type plywood measurement method.

Example 6

Extraction and hydrogenation of maleic lignin:

10 g of 80 mesh wood powder and 100 ml of aqueous solution containing 80wt% of maleic acid are placed in a reaction kettle, reacted at 80 ℃ for 1 hour, 300 ml of water is added into the mixture after the reaction to precipitate lignin, the filtrate is filtered and washed until the pH value of the filtrate is neutral, and the precipitate is dried at 105 ℃ to obtain about 0.7 g of lignin. A portion of the lignin was depolymerized by hydrogenation under the conditions as described in example 1, and the monolignol yield was found to be 23%.

0.5 g of the obtained maleic lignin and 1.5 g of water are uniformly mixed to be used as an adhesive. The three-layer plywood is prepared by using poplar veneers according to the specification of 4.17 section in GB/T17657-2013 physicochemical property test method for artificial boards and veneers, and the strength of the plywood is tested. Measured at a glue application rate of 300g/m ² The plywood prepared under the conditions of hot pressing temperature of 150 ℃, hot pressing pressure of 1.8Mpa and hot pressing time of 10 minutes has the bonding strength of 1.2Mpa and more than 0.7Mpa according to the national standard of II-type plywood measurement method.

Example 7

Extraction and hydrogenation of formaldehyde lignin:

mixing 10 g of 80-mesh eucalyptus wood powder, 90 ml of dioxane and 10 ml of 30% formaldehyde solution, putting the mixture into a reaction kettle, adding 400 ml of 37% hydrochloric acid, closing the reaction kettle, reacting at 100 ℃ for 2 hours, separating reaction liquid, concentrating the liquid to about 20 ml, adding 100 ml of water to precipitate lignin, filtering, washing the precipitate to be neutral, and drying the precipitate at 105 ℃ to obtain about 2.1 g of lignin. The lignin was depolymerized by hydrogenation under the conditions as described in example 1, and the monolignol yield was found to be 48%.

And uniformly mixing 1.0 g of the obtained formaldehyde lignin with 2.0 g of water to obtain the adhesive. The three-layer plywood is prepared by using poplar veneers according to the specification of 4.17 section in GB/T17657-2013 physicochemical property test method for artificial boards and veneers, and the strength of the plywood is tested. The measured glue application amount is 150g/m ² The plywood prepared under the conditions of hot pressing temperature of 190 ℃, hot pressing pressure of 2.0Mpa and hot pressing time of 10 minutes has the bonding strength of 1.4Mpa and more than 0.7Mpa according to the national standard of II-type plywood measurement method.

Example 8

Extraction and hydrogenation of formaldehyde lignin:

1.0 g of formaldehyde lignin obtained in the previous step and 2.0 g of water are uniformly mixed to obtain the adhesive. The three-layer plywood is prepared by using poplar veneers according to the specification of 4.17 section in GB/T17657-2013 physicochemical property test method for artificial boards and veneers, and the strength of the plywood is tested. The measured glue application amount is 150g/m ² The plywood prepared under the conditions of the hot pressing temperature of 100 ℃, the hot pressing pressure of 2.5Mpa and the hot pressing time of 20 minutes has the bonding strength of 0.9Mpa and more than 0.7Mpa according to the national standard of a II-type plywood measuring method.

Example 9

Extracting and hydrogenating acetaldehyde lignin:

mixing 10 g of 80-mesh Ma Weimu wood flour with 90 ml of dioxane and 2 g of paraldehyde, putting the mixture into a reaction kettle, adding 300 ml of 37% hydrochloric acid, closing the reaction kettle, reacting at 120 ℃ for 1 hour, separating reaction liquid, concentrating the liquid to about 20 ml, adding 100 ml of water to precipitate lignin, filtering and washing the precipitate to be neutral, and drying the precipitate at 105 ℃ to obtain about 2.2 g of lignin. The lignin was depolymerized by hydrogenation under the conditions as described in example 1, and the monolignol mass yield was found to be 19%.

The obtained acetaldehyde lignin of 2.0 g is mixed with 1.0 dioxane to form uniform liquid which is used as an adhesive. And (3) preparing a three-layer plywood by using poplar veneers according to the regulations of 4.17 section in GB/T17657-2013 test method for physical and chemical properties of artificial boards and veneers, and testing the strength of the plywood. Measured at a sizing amount of 50g/m ² The plywood prepared under the conditions of the hot pressing temperature of 200 ℃, the hot pressing pressure of 2.0Mpa and the hot pressing time of 10 minutes has the bonding strength of 1.6Mpa and more than 0.7Mpa according to the national standard of a II-type plywood measuring method.

Example 10

The procedure was the same as in example 8, except that 3mg of ammonium chloride was additionally added to the adhesive prepared in example 8. The bonding strength is measured to be 1.1Mpa and is more than 0.7 Mpa.

Example 11

The procedure was as in example 8, except that 300mg of sulfuric acid having a concentration of 98% was additionally added to the adhesive prepared in example 8. The bonding strength is measured to be 1.6Mpa and is more than 0.7Mpa

Example 12

The procedure was the same as in example 7 except that 3mg of hexamethylenetetramine was additionally added to the adhesive prepared in example 7. The bonding strength is measured to be 1.5Mpa and is more than 0.7Mpa

Example 13

The procedure was the same as in example 7, except that 80mg of glutaraldehyde was additionally added to the adhesive prepared in example 7. The bonding strength is measured to be 1.6Mpa and is more than 0.7 Mpa.

Example 14

The procedure was the same as in example 7, except that 150mg of hydroxymethylphenol was additionally added to the adhesive prepared in example 7. The bonding strength is measured to be 1.6Mpa and is more than the national standard of 0.7 Mpa.

Example 15

The procedure was the same as in example 7, except that 3mg of sodium dodecylsulfate was additionally added to the adhesive prepared in example 7. The bonding strength is measured to be 1.4Mpa and is more than the national standard of 0.7 Mpa.

Example 16

The procedure was the same as in example 7, except that 150mg of sodium lignosulfonate was additionally added to the adhesive prepared in example 7. The bonding strength is measured to be 1.5Mpa and is more than the national standard of 0.7 Mpa.

Example 17

The procedure was the same as in example 2, except that 150mg of sodium carboxymethylcellulose was additionally added to the adhesive prepared in example 2. The bonding strength is measured to be 1.4Mpa and is more than 0.7 Mpa.

Example 18

The procedure was the same as in example 2, except that 3g of starch was additionally added to the adhesive prepared in example 2. The bonding strength is measured to be 1.3Mpa and is more than the national standard of 0.8 Mpa.

Comparative example 1

Extraction and hydrogenation of acid lignin

Mixing 10 g of 80-mesh eucalyptus wood powder with 100 ml of water, placing the mixture into a reaction kettle, adding 500 mg of concentrated sulfuric acid with the concentration of 98%, reacting for 1 hour at 160 ℃, and separating and washing the residue to be neutral. Mixing the residue with 200 ml of acetic acid-sodium acetate buffer solution with pH of 5, placing the mixture into a flask, adding 50FPU/g cellulose cellulase to hydrolyze cellulose in the straws, repeatedly hydrolyzing for many times until the content of lignin is about 90% of the residue, filtering and washing the residue to be neutral, and drying to obtain about 1.9 g of enzymatic hydrolysis acid lignin. A portion of the lignin is hydropolymerized under the conditions of claim 4 and a monolignol mass yield of 4% is determined.

1.5 g of the obtained acid hydrolysis lignin is uniformly mixed with 3g of water to be used as an adhesive. The three-layer plywood is prepared by using poplar veneers according to the specification of 4.17 section in GB/T17657-2013 physicochemical property test method for artificial boards and veneers, and the strength of the plywood is tested. The glue application amount is 300g/m ² The adhesive strength was 0 because the plywood was not bonded under the conditions of a hot pressing temperature of 190 ℃, a hot pressing pressure of 2.0Mpa, and a hot pressing time of 10 minutes.

Comparative example 2

Extracting and hydrogenating sulfate lignin:

10 g of industrial kraft lignin separated from the papermaking black liquor was weighed, and a part of the lignin was subjected to the depolymerization by hydrogenation under the conditions described in claim 4, whereby the yield of the lignin monomer was found to be 5% by mass.

2 g of the obtained kraft lignin and 2 g of water are mixed into uniform liquid serving as an adhesive. The three-layer plywood is prepared by using poplar veneers according to the specification of 4.17 section in GB/T17657-2013 physicochemical property test method for artificial boards and veneers, and the strength of the plywood is tested. The glue application amount is 300g/m ² The adhesive strength was 0 because the plywood was not bonded under the conditions of the hot pressing temperature of 190 ℃, the hot pressing pressure of 2.0Mpa, and the hot pressing time of 10 minutes.

From the comparative examples, it can be seen that when the yield of the monomer released after the extracted lignin is subjected to depolymerization by hydrogenation is low, the adhesive prepared by using the lignin of the type cannot be cured and crosslinked under hot pressure. This means that the degree of lignin condensation extracted, i.e. whether the extracted lignin retains sufficient non-condensed structure for secondary condensation crosslinking during lignin hot pressing, is the most essential factor for whether lignin can be used as an adhesive, and whether lignin-based adhesives can have a better adhesive effect.

The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. The lignin-based adhesive comprises a solvent and an adhesive component, and is characterized in that: the adhesive component is lignin, the content of the adhesive component is 10% -67%, and the mass yield of alkylphenol monomers after the lignin is subjected to hydro-depolymerization is more than 10%.

2. The lignin-based adhesive according to claim 1, wherein: the conditions of the hydro-depolymerization are as follows: the reaction temperature is 200 ℃, the reaction time is 6 hours, the hydrogen pressure is 5Mpa, the catalyst is Ru/C (5 percent load), and the reaction solvent is methanol; the mass ratio of the methanol to the lignin to the catalyst (Ru/C) is 40.

3. The lignin-based adhesive according to claim 1, wherein: the lignin is prepared by organic solvent pretreatment, alkali pretreatment, ionic liquid pretreatment, eutectic solvent pretreatment or organic acid pretreatment.

4. The lignin-based adhesive according to claim 1, wherein: the solvent is any one or a mixture of two or more of water, ethanol, dioxane, acetone, tetrahydrofuran and ethyl acetate which are mixed in any proportion; the mass of the solvent is 0.5-9 times of that of the lignin.

5. The lignin-based adhesive according to claim 1, wherein: the lignin-based adhesive also comprises an auxiliary agent, wherein the auxiliary agent is any one or a mixture of two or more of a cross-linking agent, an acid catalyst, a thickening agent and a surfactant which are mixed in any proportion.

6. The lignin-based adhesive according to claim 5, wherein: the cross-linking agent is any one or a mixture of two or more than two of hexamethylenetetramine, glyoxal, glutaraldehyde, dialdehyde starch and hydroxymethyl phenol mixed in any proportion; the addition amount of the cross-linking agent is 0.1-5% of the weight of the lignin-based adhesive.

7. The lignin-based adhesive according to claim 5, wherein: the acid catalyst is any one or mixture of two or more of formic acid, acetic acid, oxalic acid, hydrochloric acid, sulfuric acid, phosphoric acid and ammonium chloride mixed in any proportion; the addition amount of the acidic catalyst is 0.1-10% of the weight of the lignin-based adhesive.

8. The lignin-based adhesive according to claim 5, wherein: the thickening agent is any one or a mixture of two or more of starch, protein, defatted soybean powder, cellulose derivatives, calcium sulfate, calcium carbonate and condensed lignin which are mixed in any proportion; the addition amount of the thickening agent is 1-20% of the weight of the lignin-based adhesive.

9. The lignin-based adhesive according to claim 5, wherein: the surface activity is any one of sodium dodecyl sulfate and sodium lignosulfonate, and the addition amount of the surface active agent is 0.1-5% of the weight of the lignin-based adhesive.

10. A method of using the lignin-based adhesive according to any one of claims 1 to 6 in bonding wood, characterized in that: the lignin-based adhesive is applied to the surface of wood to be bonded, and the glue application amount is 50-400g/m ² (ii) a Hot pressing at 100-220 deg.c and 0.5-2.5MPa to cure the timber.