A chemically activated lignin-modified plant protein adhesive and its preparation method

Abstract

The present invention relates to the technical field of polymer materials, and particularly relates to a chemically activated lignin-modified plant protein adhesive and a preparation method thereof. In the adhesive of the present invention, lignin undergoes chemical activation reactions such as liquefaction and crosslinking with polyurethane prepolymers, and is used to prepare a plant protein adhesive together with camellia seed meal, soybean meal, crosslinking agents, etc. Polyurethane prepolymer is used as a chain extender to chemically activate lignin, forming a bridge between lignin molecules, significantly increasing the molecular weight of the polymer, increasing the viscosity of the system, enabling it to undergo crosslinking reactions with plant proteins such as camellia seed meal and soybean meal, and forming a dense crosslinked network, solving the defects of poor adhesive strength and extensive use of chemical crosslinking agents caused by the low reactivity of lignin at present, and preparing a plant protein adhesive with excellent mechanical properties, good water resistance, and at the same time having mildew-proof performance, meeting the production requirements of the wood-based panel industry.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer materials, and specifically, to a chemically activated lignin-modified plant protein adhesive and a preparation method thereof. Background Art

[0002] Wood materials are widely used as wood-based panels in the furniture and construction industries. However, the adhesives currently used for bonding wood are mainly aldehyde-containing resins, which are toxic, and most of their raw materials come from non-renewable resources. Replacing aldehyde-based adhesives with renewable biomass materials is a trend and challenge in the development of wood-based panels.

[0003] As a degradable biomass material, lignin has attracted people's attention as an alternative to petroleum fossil fuels. Lignin is the second most abundant natural polymer after cellulose, and its structure contains hydroxyl, methoxy, carbonyl, and carboxyl functional groups. In recent years, many studies have synthesized lignin-modified phenolic resin adhesives to replace phenol and formaldehyde, and have overcome high brittleness and high curing temperature. Modified lignin has great potential in the preparation of wood adhesives.

[0004] Currently, the research on lignin in adhesives mainly focuses on lignin-modified aldehyde-containing resin adhesives. For example, in the invention patent with the publication number CN115247040A, a phenolic resin for adhesives is disclosed. The researchers compounded phenolic lignin and litchi enzyme in a ratio of (5-8):3, and the obtained phenolic resin has excellent adhesion performance and remarkable impact toughness, and at the same time, the residue of toxic components is less. In the invention patent with the publication number CN115093522A, a preparation method of tung oil-modified lignin bio-based phenolic resin is invented. The bio-based phenolic resin obtained by adjusting the modification degree at three different temperatures has good acid and alkali resistance and heat resistance. Although the research has reduced the release amount of toxic gases, it still needs to add substances such as formaldehyde-containing aldehydes, resulting in problems such as high cost and environmental pollution.

[0005] In the invention patent with the publication number CN109280537A, the researchers used bio-enzyme to modify lignin and added it to soybean protein adhesive, enhancing its mechanical and heat resistance. In the published patents with the publication numbers CN110835518A and CN10722924A, the researchers used glucose and epichlorohydrin to modify lignin respectively to prepare plant protein adhesives with good wettability and coating performance. The publication number CN114836170A discloses a plant protein adhesive modified by hyperbranched phosphorus and epoxy cross-linking agent lignin, which has high pre-pressing strength and water resistance.

[0006] Although the above research uses lignin-modified plant protein adhesives to solve the problem of formaldehyde release, due to the complex molecular structure and low reactivity of lignin, during the preparation of formaldehyde-free adhesives, there are often problems such as insufficient reactivity and low crosslinking degree. At the same time, there are technical problems such as low strength and poor water resistance caused by unstable bonding, so a large amount of expensive chemical crosslinking agents still need to be added in the current research on lignin-modified plant protein adhesives. Therefore, it is necessary and challenging to develop a lignin-modified plant protein adhesive with high strength, no pollution, and low cost. Summary of the Invention

[0007] In order to solve the defects of poor adhesive strength, extensive use of chemical crosslinking agents, and susceptibility to microbial attack caused by the low reactivity of unmodified lignin, the present invention has studied a plant protein adhesive with excellent mechanical properties, good water resistance, and at the same time having mildew-proof properties. The object of the present invention is to provide a chemically activated modified plant protein adhesive.

[0008] To achieve this object, the present invention uses a polyurethane prepolymer as a chain extender to chemically activate lignin, form a bridge between lignin macromolecules, and enable it to undergo a crosslinking reaction with plant proteins such as camellia seed meal and soybean meal to form a dense crosslinked network, significantly increasing the polymer molecular weight and increasing the system viscosity, so that the adhesive has good mechanical strength and water resistance. The technical solution of the present invention is as follows:

[0009] In the first aspect of the present invention, lignin is chemically activated. After the lignin is liquefied by alkali / urea treatment, a polyurethane prepolymer is added for crosslinking reaction.

[0010] The lignin is one or more of alkali lignin, lignin sulfonate, and enzymatic lignin.

[0011] The alkali / urea liquefaction treatment method is as follows: 15-20 g of sodium hydroxide or potassium hydroxide, 1-3 g of urea, 100-250 g of water, and 70-90 g of lignin are put into a three-necked flask equipped with a stirrer and mixed for 8-12 h. The stirring rate is 200-450 rmp, and the temperature is 30-55 °C to obtain alkali / urea liquefied lignin.

[0012] The polyurethane prepolymer is one or more of terminal isocyanate group polyurethane prepolymer, terminal hydroxyl group polyurethane prepolymer, terminal silyl group polyurethane prepolymer, and terminal acrylate group polyurethane prepolymer.

[0013] The preparation method of the chemically activated lignin is to add the liquefied lignin into the polyurethane prepolymer and react for 4-6 h at 70-90 °C under the condition of introducing nitrogen to obtain chemically activated modified lignin.

[0014] In the second aspect of the present invention, chemically activated lignin is used as a modifier, camellia seed meal and soybean meal are used as main agents, water is used as a dispersion medium, and a cross-linking agent is added appropriately to prepare a chemically activated lignin-modified plant protein adhesive.

[0015] The camellia seed meal is camellia seed meal after removing oil. Using a Soxhlet extractor, with n-hexane, benzene alcohol, petroleum ether, etc. as solvents, extract for 5 - 8 h, and after drying, crush to obtain camellia seed meal powder.

[0016] The protein content of the soybean meal is 40% - 60%.

[0017] The cross-linking agent is one or more of epichlorohydrin, epoxy silane, and diethylenetriamine.

[0018] The preparation method of the chemically activated lignin-modified plant protein adhesive is characterized by including the following steps:

[0019] (1) Add 2 - 15 g of chemically activated modified lignin to 60 - 120 g of water, and stir for 10 - 15 min until the solution becomes uniformly stable;

[0020] (2) Add a certain amount of camellia seed meal and soybean meal to the system, and stir at 30 - 50 °C for 5 - 10 min;

[0021] (3) Continue to add 1 - 6 g of cross-linking agent to the system, and continue to stir for 5 - 20 min to obtain the chemically activated lignin-modified adhesive.

[0022] In the third aspect of the present invention, the chemically activated modified lignin is applied in the field of wood-based panel processing.

[0023] The advantages of the present invention are as follows:

[0024] (1) The present invention uses polyurethane as a chain extender to form a bridge between lignin molecules, effectively improving the cross-linking density of the polymer, reducing the use of expensive chemical cross-linking agents, and reducing production costs.

[0025] (2) The present invention uses waste crops such as lignin and camellia seed meal. The raw material sources are rich and renewable, increasing the added value of agricultural products, meeting the requirements of sustainable development, and having good economic benefits.

[0026] (3) The lignin and camellia seed meal in the present invention contain a large amount of natural polyphenols such as tea saponin, having excellent antibacterial and antifungal advantages, and improving the defect that the plant protein adhesive is vulnerable to microbial attack. Specific embodiments

[0027] Example 1

[0028] The specific steps for preparing a chemically activated lignin-modified plant protein adhesive are as follows:

[0029] (1) Put 10 g of sodium hydroxide, 2 g of urea, 100 g of water, and 70 g of alkali lignin into a three-necked flask equipped with a stirrer and mix for 8 h. The stirring rate is 200 rmp and the temperature is 30 °C to obtain alkali / urea liquefied lignin;

[0030] (2) Add the liquefied lignin to the terminal isocyanate group polyurethane prepolymer and react for 4 h at 70 °C under the condition of introducing nitrogen to obtain chemically activated modified lignin;

[0031] (3) Add 15 g of chemically activated modified lignin to 60 g of water and stir for 10 min until the solution becomes uniformly stable;

[0032] (4) Add 15 g of soybean meal and 15 g of camellia oleifera meal to the system and stir for 5 min at 30 °C;

[0033] (5) Continuously add 1 g of epoxy silane to the system and continue stirring for 20 min to obtain the chemically activated lignin-modified adhesive.

[0034] Example 2

[0035] The specific steps for preparing a chemically activated lignin-modified plant protein adhesive are as follows:

[0036] (1) Put 12 g of potassium hydroxide, 2 g of urea, 150 g of water, and 90 g of alkali lignin into a three-necked flask equipped with a stirrer and mix for 10 h. The stirring rate is 300 rmp and the temperature is 50 °C to obtain alkali / urea liquefied lignin;

[0037] (2) Add the liquefied lignin to the terminal hydroxyl group polyurethane prepolymer and react for 6 h at 90 °C under the condition of introducing nitrogen to obtain chemically activated modified lignin;

[0038] (3) Add 5 g of chemically activated modified lignin to 80 g of water and stir for 15 min until the solution becomes uniformly stable;

[0039] (4) Add 20 g of soybean meal and 10 g of camellia oleifera meal to the system and stir for 10 min at 50 °C;

[0040] (5) Continuously add 3 g of epichlorohydrin to the system and continue stirring for 5 min to obtain the chemically activated lignin-modified adhesive.

[0041] Example 3

[0042] The specific steps for preparing a chemically activated lignin-modified plant protein adhesive are as follows:

[0043] (1) Mix 15 g of sodium hydroxide, 1 g of urea, 120 g of water, and 90 g of alkali lignin in a three-necked flask equipped with a stirrer for 12 h. The stirring rate is 450 rmp, and the temperature is 55 °C to obtain alkali / urea liquefied lignin;

[0044] (2) Add the liquefied lignin to the terminal isocyanate group polyurethane prepolymer and react for 6 h at 70 °C under the condition of introducing nitrogen to obtain chemically activated modified lignin;

[0045] (3) Add 10 g of chemically activated modified lignin to 120 g of water and stir for 15 min until the solution becomes uniformly stable;

[0046] (4) Add 5 g of soybean meal and 25 g of camellia meal to the system and stir for 15 min at 50 °C;

[0047] (5) Continuously add 3 g of epoxy silane to the system and continue to stir for 20 min to obtain a chemically activated lignin-modified adhesive.

[0048] Example 4

[0049] The specific steps for preparing a chemically activated lignin-modified plant protein adhesive are as follows:

[0050] (1) Mix 16 g of sodium hydroxide, 2 g of urea, 200 g of water, and 80 g of alkali lignin in a three-necked flask equipped with a stirrer for 10 h. The stirring rate is 350 rmp, and the temperature is 40 °C to obtain alkali / urea liquefied lignin;

[0051] (2) Add the liquefied lignin to the terminal silyl group polyurethane prepolymer and react for 6 h at 80 °C under the condition of introducing nitrogen to obtain chemically activated modified lignin;

[0052] (3) Add 8 g of chemically activated modified lignin to 80 g of water and stir for 15 min until the solution becomes uniformly stable;

[0053] (4) Add 5 g of soybean meal and 25 g of camellia meal to the system and stir for 10 min at 40 °C;

[0054] (5) Continuously add 2 g of epichlorohydrin to the system and continue to stir for 15 min to obtain a chemically activated lignin-modified adhesive.

[0055] Example 5

[0056] The specific steps for preparing a chemically activated lignin-modified plant protein adhesive are as follows:

[0057] (1) Mix 12 g of potassium hydroxide, 2 g of urea, 150 g of water, and 80 g of alkali lignin in a three-necked flask equipped with a stirrer for 10 h at a stirring rate of 400 rmp and a temperature of 40 °C to obtain alkali / urea liquefied lignin;

[0058] (2) Add the liquefied lignin to the terminal isocyanate acrylate polyurethane prepolymer and react for 6 h at 80 °C under a nitrogen atmosphere to obtain chemically activated modified lignin;

[0059] (3) Add 10 g of chemically activated modified lignin to 100 g of water and stir for 15 min until the solution becomes homogeneous and stable;

[0060] (4) Add 25 g of soybean meal and 5 g of camellia meal to the system and stir for 10 min at 30 °C;

[0061] (5) Continuously add 2 g of diethylenetriamine to the system and continue stirring for 20 min to obtain the chemically activated lignin modified adhesive.

[0062] Example 6

[0063] The specific preparation steps of a chemically activated lignin modified plant protein adhesive are as follows:

[0064] (1) Mix 15 g of sodium hydroxide, 1 g of urea, 160 g of water, and 90 g of alkali lignin in a three-necked flask equipped with a stirrer for 12 h at a stirring rate of 150 rmp and a temperature of 55 °C to obtain alkali / urea liquefied lignin;

[0065] (2) Add the liquefied lignin to the terminal isocyanate group polyurethane prepolymer and react for 6 h at 80 °C under a nitrogen atmosphere to obtain chemically activated modified lignin;

[0066] (3) Add 10 g of chemically activated modified lignin to 110 g of water and stir for 15 min until the solution becomes homogeneous and stable;

[0067] (4) Add 25 g of soybean meal and 5 g of camellia meal to the system and stir for 10 min at 40 °C;

[0068] (5) Continuously add 4 g of epoxy silane to the system and continue stirring for 5 min to obtain the chemically activated lignin modified adhesive.

[0069] Comparative Example 1

[0070] The specific preparation steps of a plant protein adhesive are as follows:

[0071] Add 15 g of soybean meal and 15 g of camellia seed meal to 60 g of water, and stir for 20 min to obtain a plant protein adhesive.

[0072] Comparative Example 2

[0073] The specific steps for preparing an unactivated lignin-modified plant protein adhesive are as follows:

[0074] (1) Add 15 g of unactivated lignin to 100 g of water and stir for 10 min until the solution becomes uniformly stable;

[0075] (2) Add 15 g of soybean meal and 15 g of camellia seed meal to the system and stir at 30 °C for 5 min;

[0076] (3) Continuously add 3 g of epichlorohydrin to the system and continue to stir for 5 min to obtain an unactivated lignin-modified adhesive.

[0077] Comparative Example 3

[0078] The specific steps for preparing an unactivated lignin-modified plant protein adhesive are as follows:

[0079] (1) Add 10 g of unactivated lignin to 60 g of water and stir for 5 min until the solution becomes uniformly stable;

[0080] (2) Add 5 g of soybean meal and 25 g of camellia seed meal to the system and stir at 50 °C for 10 min;

[0081] (3) Continuously add 2 g of epoxy silane to the system and continue to stir for 10 min to obtain an unactivated lignin-modified adhesive.

[0082] Comparative Example 4

[0083] The specific steps for preparing an unactivated lignin-modified plant protein adhesive are as follows:

[0084] (1) Add 6 g of unactivated lignin to 120 g of water and stir for 5 min until the solution becomes uniformly stable;

[0085] (2) Add 10 g of soybean meal and 20 g of camellia seed meal to the system and stir at 50 °C for 10 min;

[0086] (3) Continuously add 2 g of epichlorohydrin to the system and continue to stir for 10 min to obtain an unactivated lignin-modified adhesive.

[0087] Test

[0088] The mechanical properties of the plywood are tested according to the national standard GB / T9846.7-2004. The specimens of Examples 1-6 and Control Examples 1-4 are respectively sawn into 100mm specimens with a size of 100mm, and the glue application amount is 320g / m 2 . Three-layer plywood is prepared under the conditions of a hot pressing temperature of 120°C, a pressure of 1.0 MPa, and a hot pressing time of 6 minutes.

[0089] According to the test method specified for Class II plywood in the country, the sawn specimens are immersed in a water bath at 63±2°C for 3 hours of constant temperature water bath. After being placed at room temperature for 10 minutes, the plywood specimens are tested for bonding strength using an electronic universal mechanical testing machine. The loading speed is 10mm / min, and a load is applied to the specimens at a constant speed until they are damaged to obtain the dry bonding strength and the wet bonding strength.

[0090] The anti-mold test is carried out according to the method of GB 18261-2000-T. Fungi are washed with deionized water in a sterile operating table to prepare a spore suspension. Aspergillus niger is cultured using potato dextrose agar. After inoculating the samples, the samples are cultured in a constant temperature and humidity chamber for 30 days, and the growth state of Aspergillus niger and the state of the adhesive are observed.

[0091] The test results are shown in Table 1

[0092]

[0093] Table 1 Performance indicators of the adhesive

[0094] The experimental results in Table 1 show that the mechanical properties of the chemically activated lignin-modified plant protein adhesive of the present invention are far superior to those of the ordinary plant protein adhesive (Comparative Example 1), and are higher than those of the unactivated lignin-modified plant protein adhesive. It shows that the present invention effectively improves the cross-linking degree of the polymer by using polyurethane to chemically activate lignin, replaces the use of chemical cross-linking agents, and enables the plant protein adhesive to have good water resistance and bonding strength. At the same time, it has excellent anti-mold characteristics compared with the ordinary plant protein adhesive.

[0095] Although the present invention has been described in detail with general descriptions and specific embodiments above, based on the present invention, some modifications or improvements can be made, which are obvious to those skilled in the art. Therefore, these modifications or improvements made without departing from the spirit of the present invention all fall within the scope of protection required by the present invention.

Claims

1. A preparation method of a chemically activated lignin-modified plant protein adhesive, characterized in that, It is divided into the following two steps: (1) After lignin is liquefied, a polyurethane prepolymer is added for cross-linking reaction to obtain chemically activated lignin; (2) Using the chemically activated lignin as a modifier, camellia seed meal and soybean meal as main agents, water as a dispersion medium, and appropriately adding a cross-linking agent to prepare a chemically activated lignin-modified plant protein adhesive.

2. The preparation method of a chemically activated lignin-modified plant protein adhesive according to claim 1, characterized in that The lignin described in step (1) is one or more of alkali lignin, lignin sulfonate, and enzymatically hydrolyzed lignin.

3. The preparation method of a chemically activated lignin-modified plant protein adhesive according to claim 1, characterized in that The liquefaction treatment method in step (1) is as follows: 15 - 20 g of sodium hydroxide or potassium hydroxide, 1 - 3 g of urea, 100 - 250 g of water, and 70 - 90 g of lignin are placed in a three-necked flask equipped with a stirrer and blended for 8 - 12 h. The stirring rate is 200 - 450 rmp, and the temperature is 30 - 55 °C to obtain alkali / urea liquefied lignin.

4. The preparation method of a chemically activated lignin-modified plant protein adhesive according to claim 1, characterized in that The polyurethane prepolymer described in step (1) is one or more of terminal isocyanate group polyurethane prepolymer, terminal hydroxyl group polyurethane prepolymer, terminal silyl group polyurethane prepolymer, and terminal acrylate alkyl ester polyurethane prepolymer.

5. The preparation method of a chemically activated lignin-modified plant protein adhesive according to claim 1, characterized in that The preparation method of the chemically activated lignin in step (1) is to add the liquefied lignin into the polyurethane prepolymer, and react for 4 - 6 h under the condition of introducing nitrogen at 70 - 90 °C to obtain chemically activated modified lignin.

6. The preparation method of a chemically activated lignin-modified plant protein adhesive according to claim 1, characterized in that The camellia seed meal described in step (2) is camellia seed meal after removing oil. Using a Soxhlet extractor, with n-hexane, benzene alcohol, and petroleum ether as solvents, extract for 5 - 8 h, and after drying, crush it to obtain camellia seed meal powder.

7. The preparation method of a chemically activated lignin-modified plant protein adhesive according to claim 1, characterized in that The protein content of the soybean meal described in step (2) is 40% - 60%.

8. The preparation method of a chemically activated lignin-modified plant protein adhesive according to claim 1, characterized in that The cross-linking agent described in step (2) is one or more of epichlorohydrin, epoxy silane, and diethylenetriamine.

9. The preparation method of the chemically activated lignin-modified plant protein adhesive according to any one of claims 6 to 8, characterized in that, It includes the following steps: (1) Add 2 - 15 g of chemically activated modified lignin to 60 - 120 g of water, and stir for 10 - 15 min until the solution is in a uniform and stable state; (2) Add a certain amount of camellia seed meal and soybean meal to the system, and stir for 5 - 10 min at 30 - 50 °C; (3) Continue to add 1 - 6 g of cross-linking agent to the system, and continue to stir for 5 - 20 min to obtain a chemically activated lignin-modified adhesive.

10. Application of the preparation method of the chemically activated lignin-modified plant protein adhesive according to any one of claims 1 - 9 in the field of wood-based panels.

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