CN114736652B

CN114736652B - Method for extracting lignin from woody biomass as adhesive

Info

Publication number: CN114736652B
Application number: CN202210489178.1A
Authority: CN
Inventors: 帅李; 罗小林; 杨光绪
Original assignee: Shandong Baiwo Biotechnology Co ltd
Current assignee: Shandong Baiwo Biotechnology Co ltd
Priority date: 2022-04-28
Filing date: 2022-05-07
Publication date: 2024-05-07
Anticipated expiration: 2042-05-07
Also published as: CN114736652A; WO2023208015A1

Abstract

The invention belongs to the technical field of chemical industry, and particularly relates to a method for extracting lignin from woody biomass and using the lignin as a wood adhesive. The invention creatively adds the modifier in the lignin extraction process, so that the extracted lignin has self-crosslinking performance when in hot pressing and is used as an adhesive. After lignin is modified, the residual modifier in the solvent is removed by utilizing the characteristic that lignin is insoluble in water and adopting steps such as distillation, water separation and the like, so that free modifiers such as formaldehyde and the like are prevented from being released in the crosslinking process of lignin. The method can directly utilize the natural adhesive to replace adhesives from petrochemical sources, such as phenolic resin, urea-formaldehyde resin and the like, solves the key problem that the lignin in the biorefinery industry is difficult to use with high added value, can effectively promote the development of the biomass chemical industry, and provides a brand-new environment-friendly adhesive.

Description

Method for extracting lignin from woody biomass as adhesive

Technical Field

The invention belongs to the technical field of efficient lignin utilization, and particularly relates to a method for extracting modified lignin from woody biomass as an adhesive and the adhesive obtained by the method.

Background

The shortage of fossil resources and the environmental problems caused by fossil-based products have had a non-negligible impact on the sustainable development of human society. Depolymerizing woody biomass into chemicals, fuels, or related renewable materials has become one of the effective ways to alleviate the energy and environmental problems currently faced. Lignin is one of the most abundant aromatic natural polymer compounds on earth as an important constituent of woody biomass. The lignin is used as a natural adhesive, plays a role in binding cellulose together in plants, improves the rigidity of the plants, and has the effect of resisting invasion of external diseases and insect pests due to an aromatic ring structure which is difficult to degrade in the lignin.

Lignin, also called lignin, is a kind of polymer compound with multiple connecting bonds, which is mainly formed by three precursors (p-coumarol, coniferyl alcohol and sinapyl alcohol) through phenol hydroxyl oxidation free radical, free radical delocalization, free radical multistage coupling and other reactions. According to different active radical sites generated by free radical delocalization, two general types of connection bonds of C-O (such as beta-O-4, 4-O-5 and the like) and C-C (such as 5-5, beta-beta and the like) can be formed among lignin units, and the synthesis route, structure and unit connection bond types of lignin are as follows:

In the pulping industry or in the biorefinery process, although acids or bases used in the reaction medium can catalyze the cleavage of C-O bonds to enhance the dissolution rate of lignin in woody biomass, the catalyst or high temperature also promotes the recondensation of lignin degradation products at the same time, so that crosslinking between lignin units generates a new C-C connection structure, resulting in lower lignin activity, which is not directly softened by hot pressing and crosslinked again, which is produced by the prior art.

Thus, the prior art is based primarily on lignin units containing phenol structures, and the use of lignin instead of phenol to synthesize phenolic resin adhesives, and these prior art techniques do not address and exploit the properties of lignin that can self-crosslink. The main synthesis route of phenolic resin adhesives is that phenol and formaldehyde form prepolymer under alkaline condition, namely adhesives, and the reaction mainly involves methylolation of phenol and recondensing of methylol and phenol to form methylene bridging structure among phenol units. Under alkaline conditions, methylolation occurs predominantly in the ortho and para positions of the phenolic hydroxyl groups; in the phenol unit of lignin, the para-position of the phenolic hydroxyl group has been occupied by the alkyl side chain and part of the ortho-position has also been occupied by the methoxy group. Therefore, when lignin is used for replacing phenol to synthesize phenolic resin, the synthesized resin has poor adhesive performance due to a small number of active sites, and when the lignin addition ratio exceeds about 30%, the performance of the synthesized adhesive is drastically reduced. In addition, the condensation of lignin causes low lignin reactivity, and the influence on the properties of the synthetic resin is mainly reflected in high viscosity, obviously increased required hot press curing temperature, long required time, low crosslinking density and the like. In addition, the lignin-phenol-aldehyde resin adhesive contains a large amount of unreacted free formaldehyde, and after the lignin-phenol-aldehyde resin adhesive is used as the adhesive, a large amount of formaldehyde is released, so that the important problems of consumers such as excessive formaldehyde are caused. Thus, despite recent decades of research on lignin-substituted phenol synthesis of lignin-phenol-aldehyde resins, no large-scale production and use of lignin-phenol-aldehyde adhesives is currently seen on the market.

Disclosure of Invention

In order to solve the problems of the lignin synthesized phenolic resin adhesive, the invention provides a method for separating and extracting active lignin from lignin-containing woody biomass to be used as the wood adhesive, in particular to a method for directly using the active lignin as the wood adhesive. The active lignin extracted by the invention can be used as an all-lignin-based adhesive to be glued on the surface of wood after being compounded with a solvent and an auxiliary agent, and the lignin is subjected to condensation crosslinking by hot pressing, so that the wood is bonded together, the economical efficiency of the existing pulping or biorefinery industry is greatly improved, the dependence on traditional aldehyde-containing adhesives such as phenolic resin and urea resin from petroleum base sources is reduced, and a brand new environment-friendly adhesive is provided.

In order to achieve the above purpose, the technical scheme of the invention is as follows:

A method of extracting lignin from woody biomass as an adhesive comprising the steps of:

(1) Mixing lignin-containing woody biomass, a modifier and a first solvent under the condition of pH value of 0-3, heating to 70-180 ℃ for reaction, and separating out an obtained reaction liquid, wherein the modifier is one or more of formaldehyde, trioxymethylene, paraformaldehyde, acetaldehyde, paraldehyde, polyacetaldehyde, propionaldehyde, butyraldehyde, benzaldehyde, furfural, acetone and butanone, and the mass of the added modifier is 0.3-200% of the mass of the woody biomass; carbonyl groups in the modifier can react with phenolic hydroxyl meta-positions in lignin units to form hydroxyalkyl groups, the reaction plays a role in inhibiting self-condensation reaction of lignin in the extraction process by occupying or consuming meta-position sites of the phenolic units, and the formed hydroxyalkyl groups provide new active crosslinking sites for subsequent hot-press crosslinking of lignin;

(2) Adding water into the solution obtained in the step (1) and mixing to obtain a suspension;

(3) Separating the solids in the suspension of step (2);

(4) Mixing the solid obtained in the step (3) with a second solvent to be used as an adhesive.

And (3) uniformly applying the adhesive in the step (4) on the surface of the wood, and performing hot pressing, curing and crosslinking at a certain temperature. The all-lignin-based adhesive can be directly applied to the field of curing and bonding through hot pressing without further reaction or addition of other effective components, and the application is not limited to the preparation of plywood, fiber board, shaving board, bamboo-wood composite board and the like; in practical application, the hot pressing temperature can be adjusted according to practical requirements (such as thickness of the plate, moisture and the like). The hot press curing crosslinking temperature is 100 to 220 ℃, preferably 110 to 200 ℃, more preferably 120 to 180 ℃, more preferably 130 to 170 ℃.

Further, the first solvent in the step (1) is a mixed solvent of an organic solvent and water, wherein the organic solvent is one or more of 1, 4-epoxybutane, 1, 4-dioxane, 4-methyl butyrolactone, 2-methyltetrahydrofuran, methanol, ethanol, propanol, butanol, formic acid, acetic acid, acetone and butanone, and accounts for 40% -95% of the total mass of the first solvent. The organic solvent and water are mixed in proportion to obtain a first solvent, the first solvent is used as an excellent solvent of lignin, and the solvent is used in the lignin extraction process to facilitate dissolution of lignin in woody biomass, so that lignin can react with a modifier in the solvent rapidly, and further, the recondensation of lignin is inhibited.

Further, the first solvent of step (1) is added in an amount of 3-20 times, preferably 4-15 times, more preferably 5-10 times the mass of the woody biomass of step (1); the addition amount is aimed at a batch reactor, and in the practical application process, if a continuous digestion or extraction reactor is adopted, the addition amount can be adjusted according to the requirement.

Further, the second solvent in the step (4) is one or more of water, methanol, ethanol, acetone, butanone, 1, 4-epoxybutane, 2-methyltetrahydrofuran and 1, 4-dioxane, and the effect is mainly that lignin in a solid form obtained by separating in the step (3) is uniformly dispersed, so that the adhesive is uniformly applied to the surface of wood to be bonded. The solvent is added in an amount of 0.5 to 10 times, preferably 1 to 6 times, more preferably 2 to 4 times the dry weight of the solid as described in step (3). The addition amount of the solvent can adjust the sizing amount of the subsequent adhesive; when more solvents are added to prepare the low-concentration adhesive, the sizing amount can be increased to achieve a better adhesive effect, and when less solvents are added to prepare the high-concentration adhesive, the sizing amount can be reduced to achieve a better effect.

Further, in the substance obtained by mixing the solid in the step (4) with the second solvent, an auxiliary agent is also added, wherein the auxiliary agent is one or more of acid, thickener and dispersing agent.

Further, concentrating to remove part or all of the first solvent before adding water and mixing in the step (2); the solvent is removed by concentration, so that the water addition amount can be reduced, and lignin is precipitated into solid suspended matters.

Further, the reaction time of the step (1) is 0.1 to 10 hours. When the use temperature is high, the reaction time is short. When the preferable temperature is 70-80 ℃, the reaction time is 4-10 hours; when the preferable temperature is 81-140 ℃, the reaction time is 0.5-4 hours; when the preferred temperature is 141-180 ℃, the reaction time is 0.1-0.5 hours.

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

Lignin is a natural polymer, and each component unit is mainly connected by a carbon-oxygen bond and a carbon-carbon bond. The lignin undergoes condensation reaction during high temperature or acid-mediated extraction, resulting in the formation of new carbon-carbon bonds between lignin phenol units, which is similar to the curing of most adhesives, e.g. phenolic resins, urea-formaldehyde resins, i.e. carbon-carbon bond cross-linked structures upon hot pressing. Therefore, the invention discovers that the purpose of directly using the separated lignin as the wood adhesive can be achieved by extracting the lignin with low uncondensed or condensed degree from the woody biomass and using the lignin as the adhesive and performing condensation crosslinking in the hot pressing process.

Although the prior art utilizes lignin to replace phenol to synthesize lignin-phenol-aldehyde resin adhesive with formaldehyde under alkaline conditions, the technical route of the invention is obviously different from the thinking of the prior art that lignin is utilized to synthesize the adhesive. Firstly, the prior art mainly utilizes the characteristic that lignin contains a phenol structural unit, and replaces part of phenol and formaldehyde with separated lignin (such as industrial sulfate lignin, sodium lignin sulfonate and the like) to synthesize lignin-phenol-aldehyde resin under alkaline conditions, but because the lignin has a molecular weight larger than that of phenol, fewer active sites on an aromatic ring, low lignin reactivity, high viscosity of an adhesive and the like, the proportion of lignin substituted for phenol is smaller, and the synthesized adhesive has high viscosity and poor performance; secondly, the separated lignin is further polymerized with formaldehyde under alkaline condition to obtain the adhesive in the prior art, and the invention directly extracts the active lignin which can be used as the adhesive under acidic condition in one step; thirdly, the invention utilizes the characteristic that the extracted lignin is insoluble in water under neutral or acidic conditions, and the solid lignin is separated out by adding water so as to remove the residual free modifier (such as formaldehyde and acetone) in the reaction, thereby avoiding the pollution problem caused by the release of the free modifier, which is critical to the requirement that the adhesive is usually required to be used in living scenes and has no pollution, while in the prior art, the lignin is dissolved in an alkaline aqueous solution reaction system and cannot be separated and purified to remove the free formaldehyde; fourth, the lignin purified in the invention can be transported in a solid form, and is compounded when in use, so that the transportation cost and difficulty are reduced; fifthly, the lignin adhesive is cured and crosslinked under the catalysis of acidic conditions (such as self acidic phenolic hydroxyl or acid auxiliary agent), the curing time can be shortened to about 1 minute by adjusting the addition amount of the acid auxiliary agent, the curing temperature can be reduced to about 100 ℃, the synthesis and curing of the traditional lignin phenolic resin are carried out under alkaline conditions, the curing temperature is usually higher than 150 ℃, and the curing time is as long as 15-30 minutes; sixth, the invention can directly use lignin as adhesive, except adding water, etc. as solvent and adding or not adding small amount of thickener and dispersant to facilitate sizing and adhesion, lignin is the main component of adhesive, and lignin-phenol-aldehyde resin synthesized by the prior art only contains part of lignin as substitute of phenol.

The adhesive of the invention greatly improves the economical efficiency of the existing pulping or biorefinery industry, reduces the dependence on traditional aldehyde-containing adhesives such as phenolic resin, urea-formaldehyde resin and the like which are derived from petroleum, and provides a brand new environment-friendly adhesive. In addition, compared with other types of adhesives, such as lignin-phenol-aldehyde resin and phenolic resin, the adhesive provided by the invention can be used for achieving better curing and bonding effects at a lower temperature or in a shorter time, so that the heat energy consumption can be obviously reduced, and the production efficiency can be improved.

Detailed Description

Lignin extraction from woody biomass is achieved primarily by acid-catalyzed hydrolysis of lignin to low molecular weight lignin that is soluble in solvents; however, the leached lignin may undergo recondensation under acid catalysis to form higher molecular weight condensed lignin. In the invention, lignin condensation is inhibited by adding the modifier, and sites available for condensation crosslinking in lignin are reserved, so that the lignin can play a role in adhesion through condensation crosslinking when being used as an adhesive.

The invention discovers that carbonyl groups in the modifier can react with phenolic hydroxyl meta-position in lignin units to form hydroxyalkyl groups, the reaction plays a role in inhibiting the condensation reaction of lignin by occupying or consuming the meta-position of the phenolic units, and the hydroxyalkyl groups provide new active crosslinking sites for subsequent hot-press crosslinking of lignin. Substances which have carbonyl groups and can react with phenolic hydroxyl meta-position in lignin units under acidic conditions can play a role in inhibiting lignin self-condensation to obtain lignin with higher activity, namely can be used as a modifier of the invention, and comprise formaldehyde, trioxymethylene, paraformaldehyde, acetaldehyde, paraldehyde, polyacetaldehyde, propionaldehyde, butyraldehyde, furfural, benzaldehyde, acetone, butanone and the like.

Regarding the theoretical addition amount of the modifier, the addition of aldehyde or ketone with the same molar amount as the phenol unit in the lignin can fully occupy the active site on the lignin phenol unit, thereby achieving the purpose of inhibiting the self-condensation of the lignin. Taking 1g of straw containing 15% lignin, as an example, formaldehyde is added as a modifier, the lignin of the straw has about 0.5 mmol phenol units (with an average molecular weight of 300 g/mol per phenol structural unit) and the required equivalent amount of formaldehyde is 0.5 mmol ×30 mg/mmol=15 mg; thus, the formaldehyde addition was about 15 milligrams of formaldehyde per gram of straw (i.e., the formaldehyde addition was about 1.5% of the straw mass). Considering that only partial lignin condensation needs to be inhibited to retain enough active sites available for curing and crosslinking, the addition amount of formaldehyde can be smaller than the estimated value; experiments show that the lignin separated from the wood biomass with the formaldehyde addition amount of about 0.3% of the mass of the wood biomass can meet the practical requirement for preparing the adhesive, and the formaldehyde with more amount can be added. With the increase of the formaldehyde addition amount, the condensation degree of the extracted lignin is gradually reduced, and the strength of the prepared adhesive is gradually increased; after the formaldehyde addition amount is increased until the extracted lignin is not condensed basically, the performance of the prepared adhesive is gradually stabilized at the optimal level. Preferably, the modifier is added in an amount of 0.3 to 200% by mass of the woody biomass.

The first solvent of the present invention is an excellent solvent for lignin. The lignin contains both hydrophobic groups and hydrophilic groups, so that a proper mixed solvent needs to be prepared to achieve the effect of rapidly dissolving out the lignin. The use of the solvent in the lignin extraction process is beneficial to the dissolution of lignin in the woody biomass, so that the lignin can react with the modifier in the solvent quickly. The first solvent is a mixed solvent of an organic solvent and water, wherein the organic solvent comprises 40% -95% of the total mass of the first solvent, such as 1, 4-epoxybutane, 1, 4-dioxane, 4-methyl butyrolactone, 2-methyltetrahydrofuran, methanol, ethanol, propanol, formic acid, acetic acid and the like.

The thermocompression curing of lignin with a small degree of condensation under acidic conditions, particularly at low temperature, is another point of the present invention different from the prior art. Because of the acidity of the phenolic hydroxyl of lignin, the adhesive prepared by the invention can be subjected to hot press curing crosslinking when no acid is added, namely, under the condition that no acid is added as an auxiliary agent, the actual curing crosslinking still occurs under the acidic condition. The addition of a proper amount of acid can promote the lignin to be condensed and crosslinked more quickly, reduce the hot-pressing temperature and the hot-pressing time, obviously reduce the hot-pressing energy consumption and improve the production efficiency, and is an advantage which is not possessed by the traditional phenolic resin and lignin-phenol-aldehyde resin which are cured under the alkaline high-temperature condition. Therefore, in practical application, a proper amount of acid auxiliary agent can be added according to practical requirements. Acids that may be used as adjuvants in the application of the adhesives of the invention include inorganic acids (e.g., sulfuric acid, hydrochloric acid, phosphoric acid) and organic acids (e.g., formic acid, oxalic acid, methylbenzenesulfonic acid, terephthalic acid, lignin sulfonic acid).

In addition, the adhesive of the invention can also be added with a thickening agent and a dispersing agent. The addition of the thickener is favorable for the uniform sizing of the adhesive, and the thickener capable of achieving the effect comprises carboxymethyl cellulose, starch, flour, protein and the like; the addition of the dispersing agent can more uniformly disperse the solid lignin in water and other solvents, and the dispersing agent capable of achieving the effect is mainly a surfactant, such as sodium dodecyl benzene sulfonate, sodium lignin sulfonate and the like.

In order to make the contents of the present invention more easily understood, the technical scheme of the present invention will be further described with reference to the specific embodiments, but the present invention is not limited thereto.

Example 1

(1) 90 G of 1, 4-dioxane and 10 g of water (first solvent) are added into a 200 ml reaction kettle, the pH is regulated to 0.4 (reaction pH value) by using concentrated hydrochloric acid, then 5g of trioxymethylene (modifier) and 10 g of eucalyptus wood powder (particle size: 80 meshes) are added into the solution, the mixture is stirred and heated to 80 ℃ for reaction for 4 hours (reaction condition), and after the reaction is finished, the reaction solution is obtained by filtration;

(2) 400 ml of water was added to the reaction solution and stirred to obtain a suspension;

(3) Filtration and separation gave a solid (dry weight about 1.5 g);

(4) To this solid was added 3g of water (second solvent) to give a suspension as an adhesive.

Performance evaluation of lignin adhesive:

Plywood was made and tested for strength according to the rules of section 4.17 of GB/T17657-2013 method for testing physicochemical Properties of Artificial Board and veneered Artificial Board. Firstly, a fast-growing poplar veneer is selected to prepare a three-layer plywood, the moisture content of the veneer is 10% -12%, and the length, width and thickness of the veneer are 145 mm, 110 mm and 1.5mm respectively. And (3) sizing the intermediate veneer by adopting the lignin adhesive prepared in the step (3), wherein the sizing mode is double-sided sizing, and the single-sided sizing amount is 100 g/m ². Then, adhering an un-glued veneer on the upper and lower sides of the glued veneer respectively to enable the fiber directions of the adjacent veneers to be perpendicular to each other, placing the combined three-layer veneer on a heating plate of a hot press, wherein the hot pressing temperature is 190 ℃, the hot pressing pressure is 1.5 MPa, and the hot pressing time is 7 minutes. The bonding strength under different application environments is tested according to GB/T9846-2015 standard of common plywood; according to the measurement, the bonding strength of the plywood is 1.5 Mpa according to the measurement method of the class I plywood, the bonding strength of the plywood is 1.5 Mpa according to the measurement method of the class II plywood, and the bonding strength of the plywood is 1.8 Mpa according to the measurement method of the class III plywood, which are all larger than the national standard requirement of 0.7 Mpa.

Example 2

The procedure was the same as in example 1, except that the modifier in step (1) was replaced with 30 mg of paraformaldehyde.

Step (3) is carried out to obtain about 1.4 g of solid dry weight. To this solid was added 1.4 g of water (second solvent) to give a suspension as an adhesive.

Plywood was prepared and its strength was measured as in example 1. The bonding strength under different application environments is tested according to GB/T9846-2015 standard of common plywood; according to the measurement, the bonding strength of the plywood is 0.8 Mpa according to the measurement method of the class I plywood, 0.9 Mpa according to the measurement method of the class II plywood and 1.0 Mpa according to the measurement method of the class III plywood, and the bonding strength is greater than the national standard requirement of 0.7 Mpa.

Example 3

The procedure was as in example 1, except that the modifier in step (1) was replaced with 200 mg of paraldehyde.

Plywood was prepared and its strength was measured as in example 1. The bonding strength under different application environments is tested according to GB/T9846-2015 standard of common plywood; according to the measurement, the bonding strength of the plywood is 1.2 Mpa measured by a class I plywood measurement method, the bonding strength of the plywood is 1.3 Mpa measured by a class II plywood measurement method, and the bonding strength of the plywood is 1.3 Mpa measured by a class III plywood measurement method, which are all larger than the national standard requirements of 0.7 Mpa.

Example 4

The procedure was as in example 1, except that the modifier in step (1) was replaced with 1g of the polyacetaldehyde.

Step (3) is carried out to obtain about 1.5 g of solid dry weight. To this solid was added 1.5 g of water (second solvent) to give a suspension as an adhesive.

Plywood was prepared and its strength was measured as in example 1. The bonding strength under different application environments is tested according to GB/T9846-2015 standard of common plywood; according to the measurement, the bonding strength of the plywood is 1.3 Mpa according to the measurement method of the class I plywood, 1.3 Mpa according to the measurement method of the class II plywood and 1.5 Mpa according to the measurement method of the class III plywood, which are all larger than the national standard requirement of 0.7 Mpa.

Example 5

The procedure was as in example 1, except that the reaction pH in step (1) was changed to 3 using sulfuric acid, the first solvent was changed to 40 g of ethanol and 60 g of water, the reaction conditions were changed to 180℃for 30 minutes, and the reaction solution in step (2) was concentrated to 4 g and then 20 g of water was added.

Step (3) is carried out to obtain about 1.2 g of solid dry weight. To this solid was added 1.5 g of water (second solvent) to give a suspension as an adhesive.

Plywood was prepared and its strength was measured as in example 1. The bonding strength under different application environments is tested according to GB/T9846-2015 standard of common plywood; according to the measurement, the bonding strength of the plywood is 0.8 Mpa according to the measurement method of the class I plywood, the bonding strength of the plywood is 0.8 Mpa according to the measurement method of the class II plywood, and the bonding strength of the plywood is 0.9 Mpa according to the measurement method of the class III plywood, which are all larger than the national standard requirement of 0.7 Mpa.

Example 6

The procedure of example 1 was repeated except that the reaction pH in step (1) was changed to 3 using sulfuric acid, the first solvent was changed to 50 g of acetone and 50 g of water, and the reaction condition was changed to 180℃for 30 minutes.

Step (3) is carried out to obtain about 0.8 g of solid dry weight. To the solid was added 0.8 g of water (second solvent) to give a suspension as an adhesive.

Plywood was prepared and its strength was measured as in example 1. The bonding strength under different application environments is tested according to GB/T9846-2015 standard of common plywood; according to the measurement, the bonding strength of the plywood is 0.9 Mpa according to the measurement method of the class I plywood, 0.8 Mpa according to the measurement method of the class II plywood and 1.1 Mpa according to the measurement method of the class III plywood, and the bonding strength is greater than the national standard requirement of 0.7 Mpa.

Example 7

The procedure was as in example 1, except that the reaction pH in step (1) was changed to 2 using sulfuric acid, the first solvent was changed to 50 g of acetic acid and 50 g of water, the reaction condition was changed to 180℃for 6 minutes, and 10 g of water was added after removing all the solvent to constant weight in the reaction solution in step (2) at 100℃under a pressure of 0.1 bar.

The dry weight of the solid obtained in the step (3) is about 0.6 g. To the solid was added 0.6 g of water (second solvent) to give a suspension as an adhesive.

Plywood was prepared and its strength was measured as in example 1. The bonding strength under different application environments is tested according to GB/T9846-2015 standard of common plywood; according to the measurement, the bonding strength of the plywood is 0.8 Mpa according to the measurement method of the class I plywood, 0.8 Mpa according to the measurement method of the class II plywood and 1.0 Mpa according to the measurement method of the class III plywood, and the bonding strength is greater than the national standard requirement of 0.7 Mpa.

Example 8

The procedure was as in example 1, except that the reaction pH in step (1) was changed to 1 using hydrochloric acid, the reaction conditions were changed to 140℃for 20 minutes, and the modifier was replaced with 10 g of the polymeric aldehyde.

Step (3) is carried out to obtain about 1.4 g of solid dry weight. To this solid was added 2.8 g of water (second solvent) to give a suspension as an adhesive.

Plywood was prepared and its strength was measured as in example 1. The bonding strength under different application environments is tested according to GB/T9846-2015 standard of common plywood; according to the measurement, the bonding strength of the plywood is 1.6 Mpa according to the measurement method of the class I plywood, 1.5 Mpa according to the measurement method of the class II plywood and 1.8 Mpa according to the measurement method of the class III plywood, which are all larger than the national standard requirement of 0.7 Mpa.

Example 9

The procedure of example 1 was repeated except that the reaction pH in step (1) was changed to 0.6 using hydrochloric acid, the reaction conditions were changed to 100℃for 2 hours, and the modifier was replaced with 2g of benzaldehyde.

Step (3) is carried out to obtain about 1.3 g of solid dry weight. To this solid was added 2.6 g of water (second solvent) to give a suspension as an adhesive.

Plywood was prepared and its strength was measured as in example 1. The bonding strength under different application environments is tested according to GB/T9846-2015 standard of common plywood; according to the measurement, the bonding strength of the plywood is 1.4 Mpa according to the measurement method of the class I plywood, 1.5 Mpa according to the measurement method of the class II plywood and 1.7 Mpa according to the measurement method of the class III plywood, which are all larger than the national standard requirement of 0.7 Mpa.

Example 10

The procedure of example 1 was repeated except that the reaction pH in step (1) was changed to 0 using hydrochloric acid, the reaction conditions were changed to 70℃for 10 hours, and the modifier was replaced with 20 g of acetone.

Step (3) is carried out to obtain about 1.6 g of solid dry weight. To this solid was added 3.2 g of water (second solvent) to give a suspension as an adhesive.

Plywood was prepared and its strength was measured as in example 1. The bonding strength under different application environments is tested according to GB/T9846-2015 standard of common plywood; according to the measurement, the bonding strength of the plywood is 1.7 Mpa measured by a class I plywood measurement method, the bonding strength of the plywood is 1.6 Mpa measured by a class II plywood measurement method, and the bonding strength of the plywood is 1.9 Mpa measured by a class III plywood measurement method, which are all larger than the national standard requirements of 0.7 Mpa.

Example 11

The procedure was the same as in example 1, except that 10 mg of carboxymethyl cellulose was additionally added as a thickener in step (4).

Plywood was prepared and its strength was measured as in example 1. The bonding strength under different application environments is tested according to GB/T9846-2015 standard of common plywood; according to the measurement, the bonding strength of the plywood is 1.5 Mpa according to the measurement method of the class I plywood, 1.5 Mpa according to the measurement method of the class II plywood and 1.7 Mpa according to the measurement method of the class III plywood, and the bonding strength is greater than the national standard requirement of 0.7 Mpa.

Example 12

The procedure was the same as in example 1, except that 20 mg of sodium lignin sulfonate was additionally added as a dispersant in step (4).

Plywood was prepared and its strength was measured as in example 1. The bonding strength under different application environments is tested according to GB/T9846-2015 standard of common plywood; according to the measurement, the bonding strength of the plywood is 1.5 Mpa according to the measurement method of the class I plywood, the bonding strength of the plywood is 1.6 Mpa according to the measurement method of the class II plywood, and the bonding strength of the plywood is 1.9 Mpa according to the measurement method of the class III plywood, which are all larger than the national standard requirement of 0.7 Mpa.

Example 13

The procedure was the same as in example 1, except that 3 g of water (second solvent) in step (4) was replaced with 0.75 g of 1, 4-dioxane.

Plywood was prepared and its strength was measured as in example 1. The bonding strength under different application environments is tested according to GB/T9846-2015 standard of common plywood; according to the measurement, the bonding strength of the plywood is 1.8 Mpa measured by a class I plywood measurement method, the bonding strength of the plywood is 1.7 Mpa measured by a class II plywood measurement method, and the bonding strength of the plywood is 2.0 Mpa measured by a class III plywood measurement method, which are all larger than the national standard requirements of 0.7 Mpa.

Example 14

The procedure was the same as in example 1 except that 3g of water (second solvent) in step (4) was replaced with 30 g of acetone, and the single-sided sizing amount of plywood was changed to 300 g/m ².

Plywood was prepared and its strength was measured as in example 1. The bonding strength under different application environments is tested according to GB/T9846-2015 standard of common plywood; according to the measurement, the bonding strength of the plywood is 1.4 Mpa according to the measurement method of the class I plywood, 1.5 Mpa according to the measurement method of the class II plywood and 1.6 Mpa according to the measurement method of the class III plywood, which are all larger than the national standard requirement of 0.7 Mpa.

Example 15

The procedure was the same as in example 1, except that the hot pressing temperature in step (4) was changed to 220 degrees celsius and the hot pressing time was changed to 2 minutes.

Plywood was prepared and its strength was measured as in example 1. The bonding strength under different application environments is tested according to GB/T9846-2015 standard of common plywood; according to the measurement, the bonding strength of the plywood is 1.7 Mpa measured by a class I plywood measurement method, the bonding strength of the plywood is 1.8 Mpa measured by a class II plywood measurement method, and the bonding strength of the plywood is 1.9 Mpa measured by a class III plywood measurement method, which are all larger than the national standard requirements of 0.7 Mpa.

Example 16

The procedure was the same as in example 1, except that the hot pressing temperature was changed to 150 degrees celsius and the hot pressing time was changed to 8 minutes.

Plywood was prepared and its strength was measured as in example 1. The bonding strength under different application environments is tested according to GB/T9846-2015 standard of common plywood; according to the measurement, the bonding strength of the plywood is 1.2 Mpa according to the measurement method of the class I plywood, 1.3 Mpa according to the measurement method of the class II plywood and 1.5 Mpa according to the measurement method of the class III plywood, which are all larger than the national standard requirement of 0.7 Mpa.

The bonding strength of the three-layer plywood was 1.1 Mpa as measured after the glue application and hot pressing.

Example 17

The procedure was the same as in example 1, except that 50 mg of sulfuric acid was additionally added as a curing catalyst in step (4), and the hot pressing time was changed to 1 minute.

Plywood was prepared and its strength was measured as in example 1. The bonding strength under different application environments is tested according to GB/T9846-2015 standard of common plywood; according to the measurement, the bonding strength of the plywood is 1.9 Mpa measured by a class I plywood measurement method, the bonding strength of the plywood is 1.8 Mpa measured by a class II plywood measurement method, and the bonding strength of the plywood is 1.9 Mpa measured by a class III plywood measurement method, which are all greater than the national standard requirements of 0.7 Mpa.

Example 18

The procedure was the same as in example 1, except that 50 mg of sulfuric acid was additionally added as a curing catalyst in step (4), and the hot pressing temperature was changed to 170 degrees celsius and the hot pressing time was changed to 2 minutes.

Plywood was prepared and its strength was measured as in example 1. The bonding strength under different application environments is tested according to GB/T9846-2015 standard of common plywood; according to the measurement, the bonding strength of the plywood is 1.8 Mpa measured by a class I plywood measurement method, the bonding strength of the plywood is 1.8 Mpa measured by a class II plywood measurement method, and the bonding strength of the plywood is 1.8 Mpa measured by a class III plywood measurement method, which are all larger than the national standard requirements of 0.7 Mpa.

Example 19

The procedure was the same as in example 1, except that 50 mg of sulfuric acid was additionally added as a curing catalyst in step (4), and the hot pressing temperature was changed to 140 degrees celsius and the hot pressing time was changed to 7 minutes.

Plywood was prepared and its strength was measured as in example 1. The bonding strength under different application environments is tested according to GB/T9846-2015 standard of common plywood; according to the measurement, the bonding strength of the plywood is 1.4 Mpa measured by a class I plywood measurement method, the bonding strength of the plywood is 1.3 Mpa measured by a class II plywood measurement method, and the bonding strength of the plywood is 1.4 Mpa measured by a class III plywood measurement method, which are all larger than the national standard requirements of 0.7 Mpa.

Example 20

The procedure was the same as in example 1, except that 50mg of sulfuric acid was additionally added as a curing catalyst in step (4), and the hot pressing temperature was changed to 120 degrees celsius and the hot pressing time was changed to 10 minutes.

Plywood was prepared and its strength was measured as in example 1. The bonding strength under different application environments is tested according to GB/T9846-2015 standard of common plywood; according to the measurement, the bonding strength of the plywood is 1.1 Mpa measured by a class I plywood measurement method, the bonding strength of the plywood is 1.0 Mpa measured by a class II plywood measurement method, and the bonding strength of the plywood is 1.2 Mpa measured by a class III plywood measurement method, which are all larger than the national standard requirements of 0.7 Mpa.

Example 21

The procedure was the same as in example 1, except that 100 mg of sulfuric acid was additionally added as a curing catalyst in step (4), and the hot pressing temperature was changed to 100 degrees celsius and the hot pressing time was changed to 15 minutes.

Plywood was prepared and its strength was measured as in example 1. The bonding strength under different application environments is tested according to GB/T9846-2015 standard of common plywood; according to the measurement, the bonding strength of the plywood is 1.0 Mpa measured by a class I plywood measurement method, the bonding strength of the plywood is 0.9 Mpa measured by a class II plywood measurement method, and the bonding strength of the plywood is 0.9 Mpa measured by a class III plywood measurement method, which are all larger than the national standard requirements of 0.7 Mpa.

Example 22

The procedure of example 1 was repeated except that 90 g of 1, 4-dioxane and 10g of water (first solvent) in step (1) were replaced with 60 g of 1, 4-dioxane and 40 g of water.

Step (3) separated to obtain about 0.9 g dry solids. To the solid was added 0.9 g of water (second solvent) to give a suspension as an adhesive.

Example 23

The procedure of example 1 was repeated except that 90 g of 1, 4-dioxane and 10 g of water (first solvent) in step (1) were replaced with 80 g of 1, 4-butylene oxide and 20 g of water.

Step (3) is carried out to obtain about 1.1 g of solid dry weight. To this solid was added 2.2 g of water (second solvent) to give a suspension as an adhesive.

Plywood was prepared and its strength was measured as in example 1. The bonding strength under different application environments is tested according to GB/T9846-2015 standard of common plywood; according to the measurement, the bonding strength of the plywood is 1.3 Mpa according to the measurement method of the class I plywood, 1.4 Mpa according to the measurement method of the class II plywood and 1.5 Mpa according to the measurement method of the class III plywood, which are all larger than the national standard requirement of 0.7 Mpa.

Example 24

The procedure of example 1 was repeated except that 90 g of 1, 4-dioxane and 10 g of water (first solvent) in step (1) were replaced with 95 g of 1, 4-dioxane and 5g of water.

Plywood was prepared and its strength was measured as in example 1. The bonding strength under different application environments is tested according to GB/T9846-2015 standard of common plywood; according to the measurement, the bonding strength of the plywood is 1.3 Mpa according to the measurement method of the class I plywood, the bonding strength of the plywood is 1.3 Mpa according to the measurement method of the class II plywood, and the bonding strength of the plywood is 1.6 Mpa according to the measurement method of the class III plywood, which are all larger than the national standard requirement of 0.7 Mpa.

Example 25

The procedure of example 1 was repeated except that 10 g of eucalyptus powder in step (1) was replaced with 33.3 g of corn stalk powder (particle size: 80 mesh).

Step (3) separated to give about 3.9 g dry solids. To this solid was added 7.8 g of water (second solvent) to give a suspension as an adhesive.

Plywood was prepared and its strength was measured as in example 1. The bonding strength under different application environments is tested according to GB/T9846-2015 standard of common plywood; according to the measurement, the bonding strength of the plywood is 1.6 Mpa measured by a class I plywood measurement method, the bonding strength of the plywood is 1.7 Mpa measured by a class II plywood measurement method, and the bonding strength of the plywood is 1.9 Mpa measured by a class III plywood measurement method, which are all larger than the national standard requirements of 0.7 Mpa.

Example 26

The procedure was the same as in example 1 except that 10 g of eucalyptus powder in step (1) was replaced with 5 g of masson pine wood powder (particle size: 80 mesh).

Step (3) separated to obtain about 0.9 g dry solids. To this solid was added 1.8 g of water (second solvent) to give a suspension as an adhesive.

Comparative example 1

The procedure was the same as in example 8, except that 10 g of the polymer acetaldehyde was not added as a modifier in step (1).

After glue application and hot pressing, the plywood is not bonded, and the bonding strength of the three-layer plywood is 0 Mpa.

As can be seen from comparative example 1 above, lignin extracted under the same reaction conditions of 140 degrees celsius for 20 minutes could not be directly used as an adhesive without adding a modifier such as an aldehyde. The modifier containing carbonyl groups such as formaldehyde, acetaldehyde, acetone and the like and the polymerization inhibitor are added in the extraction process of the step (1), so that the self-condensation of lignin in the extraction process can be inhibited, and the crosslinkable active sites in the lignin are reserved; meanwhile, the modifier can react with the meta-position of lignin phenol to form a hydroxyalkyl group, so that the curing and crosslinking characteristics of lignin under an acidic condition are improved.

The previous description and illustrations of the embodiments are provided to enable those skilled in the art to understand and practice the present invention. The invention is not to be limited to the embodiments described above, and the inventive principles disclosed herein may be implemented in other embodiments without departing from the spirit or scope of the invention, and modifications to such embodiments should be apparent to those skilled in the art to which the invention pertains and yet remain within the scope of this patent.

Claims

1. A method of extracting lignin from woody biomass as an adhesive, characterized by: the method comprises the following steps:

(1) Mixing lignin-containing woody biomass, a modifier and a first solvent under the condition of pH value of 0-3, heating to 70-180 ℃ for reaction, and separating out the obtained reaction liquid, wherein the modifier is one or more of formaldehyde, trioxymethylene, paraformaldehyde, acetaldehyde, paraldehyde, polyacetaldehyde, propionaldehyde and furfural, and the weight of the modifier is 0.3-200% of the mass of the woody biomass;

(2) Adding water into the reaction liquid separated in the step (1) for mixing to obtain a suspension;

(3) Separating the solids in the suspension of step (2);

(4) Mixing the solid obtained in the step (3) with a second solvent to be used as an adhesive;

the first solvent in the step (1) is a mixed solvent of an organic solvent and water, wherein the organic solvent is one or more of 1, 4-epoxybutane, 1, 4-dioxane, 4-methyl butyrolactone, 2-methyltetrahydrofuran, formic acid and acetic acid, and accounts for 40% -95% of the total mass of the first solvent;

the second solvent is one or more of water, acetone and 1, 4-dioxane.

2. The method of extracting lignin from woody biomass as a binder according to claim 1 wherein: the addition amount of the first solvent in the step (1) is 3-20 times of the mass of the woody biomass.

3. The method of extracting lignin from woody biomass as a binder according to claim 1 wherein: the addition amount of the second solvent is 0.5-5 times of the dry weight of the solid in the step (3).

4. The method of extracting lignin from woody biomass as a binder according to claim 1 wherein: and (3) adding an auxiliary agent into the substance obtained by mixing the solid obtained in the step (4) with the second solvent, wherein the auxiliary agent is one or more of acid, thickener and dispersing agent.

5. The method of extracting lignin from woody biomass as a binder according to claim 1 wherein: and (3) adding water to the mixture in the step (2), and concentrating the mixture to remove part or all of the first solvent.

6. The method of extracting lignin from woody biomass as a binder according to claim 1 wherein: the reaction time in the step (1) is 0.1-10 hours.

7. An adhesive obtainable by the process of any one of claims 1 to 6.

8. Use of the adhesive according to claim 7, wherein: the adhesive is directly applied to the surface of the wood, and is hot-pressed and crosslinked at 100-200 ℃ to play a role in bonding the wood.