阅读说明：本技术 一种全生物基双组分大豆胶粘剂、制备方法及其应用 (Full-bio-based bi-component soybean adhesive, preparation method and application thereof ) 是由 孙理超 刘涛 赵欣桐 刘珍珍 王清文 欧荣贤 郝笑龙 于 2021-07-19 设计创作，主要内容包括：本发明公开了一种全生物基双组分大豆胶粘剂、制备方法及其应用,属于木材胶粘剂制备技术领域,其中包括大豆蛋白混合主剂A和交联固化剂B,按照重量份数计,所述大豆蛋白混合主剂A包括大豆蛋白粉20-30份、去离子水40-70份、碱2-5份、植酸4-10份,所述交联固化剂B包括生物基交联固化剂70-100份、去离子水0-30份。通过该方法制备的胶粘剂粘度适中,在木材表面具有良好浸润性,继而固化后在粘接面能形成强大致密的交联结构,该胶粘剂的干/湿胶接强度高,热稳定性好,采用本胶粘剂制备的人造板的阻燃和耐水性能显著提升,提高了大豆蛋白胶粘剂的实际应用性能。(The invention discloses a full-bio-based bi-component soybean adhesive, a preparation method and application thereof, and belongs to the technical field of wood adhesive preparation, wherein the full-bio-based bi-component soybean adhesive comprises a soybean protein mixing main agent A and a crosslinking curing agent B, the soybean protein mixing main agent A comprises 20-30 parts by weight of soybean protein powder, 40-70 parts by weight of deionized water, 2-5 parts by weight of alkali and 4-10 parts by weight of phytic acid, and the crosslinking curing agent B comprises 70-100 parts by weight of a bio-based crosslinking curing agent and 0-30 parts by weight of deionized water. The adhesive prepared by the method has moderate viscosity, good wettability on the surface of wood, and a strong and compact cross-linking structure can be formed on the bonding surface after curing, the dry/wet bonding strength of the adhesive is high, the thermal stability is good, the flame retardance and the water resistance of the artificial board prepared by the adhesive are obviously improved, and the actual application performance of the soybean protein adhesive is improved.)

1. The full-bio-based bi-component soybean adhesive is characterized by comprising a soybean protein mixed main agent A and a cross-linking curing agent B, wherein the soybean protein mixed main agent A comprises 20-30 parts by weight of soybean protein powder, 40-70 parts by weight of deionized water, 2-5 parts by weight of alkali and 4-10 parts by weight of phytic acid, and the cross-linking curing agent B comprises 70-100 parts by weight of a bio-based cross-linking curing agent and 0-30 parts by weight of deionized water.

2. The two-component soy adhesive based on total biology as claimed in claim 1, wherein the soy protein powder comprises soy protein concentrate powder, soy tissue protein powder, soy protein isolate powder or their mixture.

3. The all bio-based two component soy adhesive of claim 1 wherein said base comprises an aqueous solution of sodium hydroxide, potassium hydroxide or mixtures thereof.

4. The full bio-based bi-component soybean adhesive according to claim 1, wherein the bio-based crosslinking curing agent comprises furfuryl alcohol, or a mixture of furfuryl alcohol and one or more of furfural, 5-hydroxy furfuryl alcohol and 5-hydroxy furfuryl aldehyde.

5. The fully bio-based two-component soy adhesive of claim 1, wherein said adhesive has a solids content of 20-50%.

6. A method of preparing a full bio-based two component soy adhesive as defined in any of claims 1 to 5, comprising the steps of:

(1) according to the weight parts, 40-70 parts of soybean protein powder and deionized water are stirred and mixed, then alkali is added, the pH of the mixed solution is adjusted to 9-12, the temperature is raised to 40-80 ℃, after stirring and reacting for 1-3h, phytic acid is added to adjust the pH to 2-5, and cooling is carried out, thus obtaining a soybean protein mixed main agent A;

(2) stirring and mixing the bio-based crosslinking curing agent and 0-30 parts of water according to the parts by weight to obtain a crosslinking curing agent B;

(3) adding the crosslinking curing agent B into the soybean protein mixed main agent A in parts by weight, uniformly stirring and mixing, and discharging to obtain the full-bio-based bi-component soybean adhesive.

7. The preparation method according to claim 6, wherein the weight ratio of the crosslinking curing agent B to the soybean protein mixed main agent A in the step (3) is (1-5): 20.

8. the use of the full bio-based two-component soybean adhesive according to any one of claims 1 to 5, wherein the full bio-based two-component soybean adhesive is used for gluing of an artificial board, wherein the artificial board is one of plywood, particle board or fiber board.

9. The use of claim 8, wherein when the all bio-based two-component soy adhesive is used in plywood gluing, the application method is as follows: coating the full-bio-based bi-component soybean adhesive on a veneer, then assembling the veneer blank coated with the adhesive, standing at a closed opening at normal temperature, and finally performing hot-pressing curing molding on the plywood at the temperature of 170-190 ℃.

10. The use as claimed in claim 9, wherein the sizing amount is 150-170g/m²The time of closed-mouth aging is 15-20min, the hot-pressing pressure is 1-2MPa, and the hot-pressing temperature is 180 ℃.

Technical Field

The invention relates to the technical field of wood adhesive preparation, in particular to a full-bio-based bi-component soybean adhesive, a preparation method and application thereof.

Background

With the continuous popularization and deepening of sustainable development and green environmental protection concept, the bio-based adhesive prepared by taking natural renewable biomass as a raw material and the bonding application of artificial boards and furniture thereof are attracted by wide attention. Various biomass resources, including cellulose, lignin, starch, soy protein, chitin, tannin, etc., have been used as renewable raw materials in the field of processing and manufacturing of artificial boards.

The method for preparing the wood adhesive by using the soybean protein as the raw material has the advantages of reliability, richness, low cost, simple and convenient operation, environmental friendliness and the like. Therefore, the soy protein adhesive is evaluated as a novel environment-friendly adhesive which is expected to replace the existing formaldehyde-based thermosetting adhesive. However, the existing soybean protein adhesive generally has the problems of poor water resistance, poor bonding strength, slow curing speed and the like, and the application of the soybean protein adhesive is limited.

In recent years, researchers in the industry have solved the above problems by various methods such as physical, chemical, biological, and the like. In order to achieve both good adhesive bonding performance and water resistance, a crosslinking agent and an additive which are not renewable and petrochemical are added into the formula, so that the degradation performance and the environmental friendliness of the soybean protein adhesive are reduced. Meanwhile, in view of the application of the soybean protein glue in the industries of artificial boards and furniture, the fire safety of the product is also a key performance which needs to be solved urgently at present.

Therefore, how to prepare the high-adhesion-strength, flame-retardant and water-resistant all-bio-based soy protein-based adhesive in a simple and green manner is a great challenge in practical application.

Disclosure of Invention

The invention provides a full-bio-based bi-component soybean adhesive, a preparation method and application thereof, aiming at the problem that the existing adhesive preparation technology cannot give consideration to both flame retardance and water resistance and the practicability and environmental protection of full bio-based.

In order to achieve the purpose, the invention provides the following scheme:

the technical scheme is as follows:

the invention provides a full-bio-based bi-component soybean adhesive, which comprises a soybean protein mixed main agent A and a cross-linking curing agent B, wherein the soybean protein mixed main agent A comprises 20-30 parts by weight of soybean protein powder, 40-70 parts by weight of deionized water, 2-5 parts by weight of alkali and 4-10 parts by weight of phytic acid, and the cross-linking curing agent B comprises 70-100 parts by weight of bio-based cross-linking curing agent and 0-30 parts by weight of deionized water.

Preferably, the soy protein powder comprises soy protein concentrate powder, soy tissue protein powder, soy protein isolate powder or a combination thereof. More preferably, the soybean protein powder is soybean protein isolate powder, the particle size is 150-200 meshes, and the protein content is more than or equal to 90 percent.

Preferably, the base comprises an aqueous solution of sodium hydroxide, potassium hydroxide, or a mixture thereof.

Preferably, the bio-based crosslinking curing agent comprises furfuryl alcohol, or a mixture of furfuryl alcohol and one or more of furfural, 5-hydroxy furfuryl alcohol and 5-hydroxy furfuryl aldehyde. More preferably, the bio-based crosslinking curing agent is furfuryl alcohol.

Preferably, the solids content of the adhesive is 20-50%.

The invention provides a simple preparation method of a full-bio-based chemically crosslinked flame-retardant water-resistant bi-component soybean protein adhesive, wherein the adhesive comprises the following raw materials: soy protein, phytic acid, furfuryl alcohol, and the like. The soybean protein-based adhesive disclosed by the invention comprises two components, namely a soybean protein mixed main agent A and a crosslinking curing agent B. Wherein, the furfuryl alcohol is used as a bio-based cross-linking agent to form chemical cross-linking in the soybean protein glue, thereby remarkably improving the bonding property and the water resistance of the prepared soybean glue; the phytic acid can be used as a furfuryl alcohol crosslinking promoter, can be used as a flame retardant due to the fact that the phytic acid contains a large amount of phosphorus elements, and can form a nitrogen and phosphorus synergistic flame retardant system with an excellent flame retardant effect with a large amount of nitrogen elements contained in the soybean protein, so that the thermal stability and the flame retardance of the prepared soybean gum are remarkably improved.

Preferably, the sodium hydroxide solution is used as an alkali treatment agent, which is helpful for protein molecule depolymerization to become loose, molecular chain to become stretched, and polar and nonpolar groups to react with wood. The chance of intermolecular binding is increased during heating. The optimal conditions for alkali treatment of the isolated soy protein are as follows: the temperature was 50 ℃ and the pH was 10.0. After modification, more active groups are exposed to react with the cross-linking agent, so that the water resistance is improved.

The phytic acid in the invention is a cross-linking promoter and a flame retardant, is a natural renewable organic compound, is natural and nontoxic, and is derived from the rhizome of grains and beans. In addition, the unique phosphate-rich group in the phytic acid is beneficial to improving the thermal stability and the flame retardance of a system, and meanwhile, a metal coordination network can be formed to form physical crosslinking, so that the bonding strength of the soybean gum is improved.

The furfuryl alcohol is a cross-linking curing agent, is an alcohol heterocyclic compound of biological origin, is usually derived from agricultural residues rich in pentose, such as rice husks, bagasse and corncobs, has strong polarity and good corrosion resistance and water solubility, can form polyfurfuryl alcohol, and is a biological-based cross-linking agent with great potential.

The second technical proposal is that:

the invention also provides a preparation method of the full-bio-based bi-component soybean adhesive, which comprises the following steps:

(1) according to the weight portion, 40-70 portions of soybean protein powder and deionized water are stirred and mixed, alkali is added, the pH of the mixed solution is adjusted to 9-12, preferably to 10, the temperature is raised to 40-80 ℃, after stirring and reaction for 1-3 hours, phytic acid is added to adjust the pH to 2-5, preferably phytic acid is added to adjust the pH of a system to 3.5-4, and cooling is carried out, so as to obtain a soybean protein mixed main agent A;

(2) stirring and mixing 100-70 parts of bio-based crosslinking curing agent and 0-30 parts of water according to parts by weight to obtain crosslinking curing agent B;

(3) adding the crosslinking curing agent B into the soybean protein mixed main agent A in parts by weight, uniformly stirring and mixing, and discharging to obtain the full-bio-based bi-component soybean adhesive.

Preferably, the weight ratio of the crosslinking curing agent B to the soybean protein mixed main agent A in the step (3) is (1-5): 20.

the third technical scheme is as follows:

the invention also provides an application of the full bio-based bi-component soybean adhesive, wherein the full bio-based bi-component soybean adhesive is used for gluing an artificial board, and the artificial board is one of plywood, flakeboard or fiberboard.

Preferably, when the full bio-based two-component soybean adhesive is used for plywood gluing, the application method is as follows: coating the full-bio-based bi-component soybean adhesive on a veneer, then assembling the veneer blank coated with the adhesive, standing at a closed opening at normal temperature, and finally performing hot-pressing curing molding on the plywood at the temperature of 170-190 ℃.

Preferably, when the all-biobased two-component soybean adhesive is used for gluing plywood, the glue application amount is 150-170g/m²The time of closed-mouth aging is 15-20min, the hot-pressing pressure is 1-2MPa, and the hot-pressing temperature is 180 ℃.

Preferably, when the all-bio-based two-component soybean adhesive is used for particle board gluing, the application method is as follows: spraying the adhesive by using a high-pressure atomizing nozzle to uniformly mix the adhesive, manually assembling the blank, performing hot-pressing molding at the hot-pressing pressure of 1-3MPa and the hot-pressing temperature of 160-180 ℃ for 5-8min, wherein the viscosity of the adhesive is 200-1000mPa & s, and the density of the shaving board is 0.7-0.8g & cm^-3(ii) a The mass ratio of the wood shavings of the surface layer is 4:5, and the glue application amount is 12-18% (accounting for the mass of the absolutely dry wood shavings).

The invention discloses the following technical effects:

1) the invention adopts two components, namely the soybean protein mixing main agent and the crosslinking curing agent, and the components are mixed immediately after use, thus the operation is simple and the implementation is easy;

2) the adhesive has moderate viscosity and good wettability on the surface of the wood to be bonded;

3) the soybean protein adhesive prepared by the invention does not contain harmful substances, all raw materials are derived from biomass, and the soybean protein adhesive is a full-bio-based soybean protein adhesive in the true sense;

4) the soybean protein adhesive has the advantages of good water retention, high solubility, high curing speed, good toughness and water resistance after curing, large crosslinking density and stable performance, and the prepared plywood product has stable quality and good tri-state comprehensive bonding strength of dry, wet and boiling water; the prepared shaving board has good thermal stability and flame retardance, and the room-temperature storage period of the adhesive is 15-30 days;

5) the adhesive prepared by the method has moderate viscosity, good wettability on the surface of wood, and a strong and compact cross-linking structure can be formed on the bonding surface after curing, the dry/wet bonding strength of the adhesive is high, the thermal stability is good, the flame retardance and the water resistance of the artificial board prepared by the adhesive are obviously improved, and the actual application performance of the soybean protein adhesive is improved.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings needed to be used in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings without inventive exercise.

FIG. 1 is a schematic representation of a sample of plywood made with the soy protein adhesive of the present invention;

FIG. 2 is an infrared spectrum of a cured adhesive prepared in examples 1 to 6 of the present invention and comparative examples 1 to 4;

FIG. 3 is a result of sol-gel test of cured adhesives prepared in examples 1 to 6 of the present invention and comparative examples 1 to 4, in which the soluble fraction is shown on the left side and the swelling ratio is shown on the right side;

FIG. 4 is a TG curve of cured adhesives prepared in examples 1 to 6 of the present invention and comparative examples 1 to 4;

FIG. 5 is a DTG curve (N) of the cured adhesives obtained in examples 1-6 of the present invention and comparative examples 1-4₂Under the action of the air);

FIG. 6 is a graph showing the effect of water contact angle of a pressed film of a cured adhesive prepared according to examples 1 to 6 of the present invention and comparative examples 1 to 3;

FIG. 7 is a scanning electron microscope image of the surface of a cured adhesive prepared in examples 1 to 6 of the present invention and comparative examples 1 to 3;

FIG. 8 is a sectional scanning electron microscope image of cured adhesives prepared in example 1, comparative example 1 and comparative example 3 of the present invention;

FIG. 9 is a graph of cone calorimetry results for particle boards made with the adhesives prepared in accordance with example 1 of the present invention, wherein a is the total heat release value, b is the total smoke release value, c is the peak heat release rate, and d is the peak smoke release rate.

Detailed Description

Reference will now be made in detail to various exemplary embodiments of the invention, the detailed description should not be construed as limiting the invention but as a more detailed description of certain aspects, features and embodiments of the invention.

It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. Further, for numerical ranges in this disclosure, it is understood that each intervening value, between the upper and lower limit of that range, is also specifically disclosed. Every smaller range between any stated value or intervening value in a stated range and any other stated or intervening value in a stated range is encompassed within the invention. The upper and lower limits of these smaller ranges may independently be included or excluded in the range.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference herein for the purpose of disclosing and describing the methods and/or materials associated with the documents. In case of conflict with any incorporated document, the present specification will control.

It will be apparent to those skilled in the art that various modifications and variations can be made in the specific embodiments of the present disclosure without departing from the scope or spirit of the disclosure. Other embodiments will be apparent to those skilled in the art from consideration of the specification. The description and examples are intended to be illustrative only.

As used herein, the terms "comprising," "including," "having," "containing," and the like are open-ended terms that mean including, but not limited to.

The percent symbols "%" referred to in the present invention mean weight percentages based on the total weight, unless otherwise specified. But the percentage of the solution, unless otherwise specified, means that 100mL of the solution contains several grams of solute; the percentage between the liquids refers to the ratio of the volumes at 20 ℃.

The experimental procedures used in the following examples are all conventional procedures unless otherwise specified.

Materials, reagents and the like used in the following examples are commercially available unless otherwise specified.

The examples in the drawings in the specification of the invention are the examples, such as example 1 is example 1, and the comparison example is the comparative example.

The detection method in the embodiment of the invention is as follows:

fourier infrared (FTIR) measurements: PerkinElmer Spectrum 100FTIR spectrometer and Nicolet nexus470 FTIR spectrometer using potassium bromide tabletting technique at 4000-^-1Scanning in range with resolution of 4cm^-1FTIR spectra of different cured adhesives were tested.

Sol gel test: the cross-linking degree of different soy protein-based adhesives was studied by a sol-gel method. The prepared adhesive is completely cured and dried to constant weight (M)₀). The samples were then soaked in boiling water for 4h (M)₁) Drying at 103 + -3 deg.C to obtain stable mass (M)₂). Sol fraction of (M)₀-M₂)/M₀X 100%, swelling ratio of (M)₁-M₂)/M₂X 100%. Five replicates of each sample were tested,and the average was recorded.

Thermogravimetric (TGA) analysis determination: the test was carried out using a thermogravimetric analyzer of the type TG 209F1 Libra TM analyzer, Netzsch, Germany, weighing approximately 5mg each, heated under nitrogen in linear increments from 35 ℃ to 600 ℃ at a heating rate of 10 ℃/min. The thermogravimetric curve of the sample and its differential thermogravimetric analysis (DTG) were recorded by experiment.

Water Contact Angle (WCA): the static contact angle of water was measured by the sitting drop method on a DSA100 instrument (KRUSS) at 28 ℃ and 65% relative humidity. mu.L of deionized water was dropped on the surface of the sample. The fall angle was recorded at 0.1s intervals for a total duration of 30 s. Each specimen was replicated 6 times at different locations.

Scanning Electron Microscope (SEM): the adhesive was fully cured in an oven and then broken into small pieces. The broken and surface glue samples were gold sprayed and then observed for morphological changes using a scanning electron microscope (ZEISS EVO18 SEM, germany).

Bonding strength: and (3) placing the hot-pressed plywood at room temperature for at least one day, and then carrying out a bonding strength test. The dry and wet shear strength (type II plywood) and the aged bond strength (type I plywood) were tested according to the standard GB/T9846-2015, respectively, using a universal tester (strain rate 10mm/min, Qingdao). 8 plywood test pieces (25 mm. times.100 mm) were cut from the centre of each panel, the plywood area being 25X 25mm². Preparation of plywood samples and the direction of force loading are shown in figure 1. In the wood breakage rate test, a digital camera is used for detecting the adhesive area shape of the plywood test piece after the dry shear strength test, and 8 test pieces are observed visually to obtain the average wood breakage rate.

CONE calorimeter test (CONE):

the total heat release, total smoke release rate, peak heat release rate and peak smoke release rate of particle boards prepared from the all-bio-based flame-retardant water-resistant bi-component soybean adhesive were determined using a cone calorimeter (mo-diske combustion technology instruments ltd, kun-shan, china) according to ISO5660-1(2015) standard. The edges of the samples were protected using a standard metal frame and aluminum foil to coat the surfaceExposed to fire. All dimensions being 100X 10mm³All the test pieces are 50kW/m²The test was performed under horizontal exposure to heat flow conditions. Each sample treatment was 3 replicates.

Example 1

Adding 22.2g of isolated soy protein powder (the weight percentage of protein is more than or equal to 90%) and 65.3g of deionized water into a 250mL beaker, uniformly stirring and mixing, adding 3.3g of sodium hydroxide (20 wt% aqueous solution), adjusting the pH value to 10.5, heating to 60 ℃, reacting for 2 hours under mechanical stirring at 400r/min, adding 5.5g of phytic acid (70 wt% aqueous solution), and measuring the pH value to be 4.0 to obtain a soy protein mixed main agent A; then adding 3.7g of furfuryl alcohol as a crosslinking curing agent B into the soybean protein mixed main agent A, and continuously stirring for 15 minutes to obtain the target soybean protein adhesive, which is recorded as P4F16.7.

Example 2

Adding 23.6g of soybean protein powder (the weight percentage of protein is more than or equal to 90%) and 65.0g of deionized water into a 250mL beaker, stirring and mixing, adding 3.2g of 20 wt% sodium hydroxide solution, adjusting the pH value to 10.0, heating to 40 ℃, reacting for 1h under mechanical stirring at 400r/min, adding 7.0g of phytic acid (70 wt% aqueous solution), and obtaining a soybean protein mixed main agent A, wherein the pH value is 3.5; then adding a mixture B1.2g of a cross-linking curing agent furfuryl alcohol and furfural into the soybean protein mixed main agent A, wherein the mass ratio of furfuryl alcohol to furfural is 1: 1, stirring for 15 minutes to obtain the target soybean protein adhesive, which is recorded as P3.5F5.

Example 3

Adding 23.3g of soybean protein powder (the weight percentage of protein is more than or equal to 90%) and 64.0g of deionized water into a 250mL beaker, stirring and mixing, adding 2.7g of 20 wt% sodium hydroxide solution, adjusting the pH value to 9.5, heating to 70 ℃, reacting for 3 hours under the mechanical stirring of 400r/min, adding 7g of phytic acid (70 wt% aqueous solution), and measuring the pH value to be 3.0 to obtain a soybean protein mixed main agent A; then 3g of bio-based cross-linking curing agent furfuryl alcohol and 3g of water are stirred and mixed to obtain a cross-linking curing agent B, 3g of the cross-linking curing agent B is added into the soybean protein mixing main agent A, and stirring is continued for 15 minutes to obtain the target soybean protein adhesive, which is recorded as P3.5F10.

Example 4

Adding 22g of soybean protein powder (the weight percentage content of protein is more than or equal to 90 percent), 66.4g of deionized water and 1.8g of 20 wt% sodium hydroxide solution into a 250mL beaker, adjusting the pH to 8.9, heating to 80 ℃, reacting for 2 hours under mechanical stirring at 400r/min, adding 6.6g of phytic acid (70 wt% aqueous solution), and obtaining a soybean protein mixed main agent A, wherein the pH value is 2.5; then adding 3.2g of a mixture of furfuryl alcohol and 5-hydroxyl furfuryl alcohol of a crosslinking curing agent B into the soybean protein mixed main agent A, wherein the mass ratio of furfuryl alcohol to 5-hydroxyl furfuryl alcohol in the mixture is 1: 1, stirring for 15 minutes to obtain the target soybean protein adhesive, which is recorded as P3.5F15.

Example 5

Adding 21g of soybean protein powder (the weight percentage content of protein is more than or equal to 90 percent), 65.2g of deionized water and 3.2g of 20 wt% sodium hydroxide solution into a 250mL beaker, adjusting the pH to 10.0, heating to 60 ℃, reacting for 1h under mechanical stirring at 400r/min, adding 6.4g of phytic acid (70 wt% aqueous solution), and measuring the pH value to be 3.5 to obtain a soybean protein mixed main agent A; then adding 4.2g of furfuryl alcohol of a crosslinking curing agent B into the soybean protein mixed main agent A, and continuously stirring for 15 minutes to obtain the target soybean protein adhesive, which is recorded as P3.5F20.

Example 6

Adding 20.2 g of soybean protein powder (the weight percentage of protein is more than or equal to 90 percent), 65.5g of deionized water and 3.1g of 20 wt% sodium hydroxide solution into a 250mL beaker, adjusting the pH value to 9.8, heating to 60 ℃, reacting for 1h under mechanical stirring at 400r/min, adding 6.1g of phytic acid (70 wt% aqueous solution), and obtaining a soybean protein mixed main agent A, wherein the pH value is 3.5; then, 5.1g of furfuryl alcohol as a crosslinking curing agent B is added into the soybean protein mixed main agent A, and the mixture is continuously stirred for 15 minutes to obtain the target soybean protein adhesive, which is recorded as P3.5F25.

Comparative example 1

Adding 23.0g of isolated soy protein powder (the weight percentage of protein is more than or equal to 90 percent), 67.7g of deionized water and 3.5g of sodium hydroxide (20 wt% aqueous solution) into a 250mL beaker, adjusting the pH to 10.5, heating to 60 ℃, adding 5.8g of phytic acid (70 wt% aqueous solution) after reacting for 2 hours under mechanical stirring at 400r/min, and obtaining a soy protein mixed main agent when the pH value is 4.0; stirring is continued for 15 minutes to obtain the target soybean protein adhesive which is marked as P4.

Comparative example 2

Adding 21.4g of soybean protein powder (the weight percentage of protein is more than or equal to 90 percent), 68.9g of deionized water and 3.3g of 20 wt% sodium hydroxide solution into a 250mL beaker, adjusting the pH value to 9.8, heating to 60 ℃, adding 6.4g of phytic acid (70 wt% aqueous solution) after reacting for 1h under mechanical stirring at 400r/min, measuring the pH value to be 3.5 to obtain a soybean protein mixed main agent, and continuously stirring for 15 minutes to obtain a target soybean protein adhesive, which is marked as P3.5.

Comparative example 3

30g of soybean protein powder (the weight percentage of protein is more than or equal to 90 percent) and 70g of deionized water are added into a 250mL beaker, the temperature is raised to 60 ℃, and the unmodified soybean protein adhesive is obtained after reaction for 1h under the mechanical stirring of 400r/min, and is recorded as SPI.

Comparative example 4

Adding 22.2g of isolated soy protein powder (the weight percentage of protein is more than or equal to 90 percent), 70.8g of deionized water and 3.3g of sodium hydroxide (20 wt% of aqueous solution) into a 250mL beaker, adjusting the pH to 10.5, heating to 60 ℃, and reacting for 2 hours under mechanical stirring at 400r/min to obtain a soy protein mixed main agent A; then adding 3.7g of furfuryl alcohol of a crosslinking curing agent B into the soybean protein mixed main agent A, and continuously stirring for 15 minutes to obtain the target soybean protein adhesive.

Examples 1-6 compare comparative examples 1-4, respectively, comparative example 1 and comparative example 2 without the addition of the crosslinking curing agent furfuryl alcohol; comparative example 3 is a blank comparative example, i.e., an unmodified soy protein adhesive, and comparative example 4 has no added phytic acid.

FIG. 2 is an infrared spectrum of the cured adhesives obtained in examples 1 to 6 of the present invention and comparative examples 1 to 4, showing that the modification is effective from the change of the characteristic infrared peak. Comparison of the spectra of the adhesives modified to different degrees shows that the thickness of the adhesive in example 1 is 1240cm^-1The characteristic peak value of the formed C-N group (amide III band) is weakened; approximately 1386cm^-1The absorption peak of (2) is assigned to the nearby carboxyl group (COO b-doping), and almost disappears in the spectrum of comparative example 1. These changes indicate HPO of phytic acid₄ ^2-And NH₂and/OH and possibly a covalent crosslinking with furfuryl alcohol as a crosslinking agent. Supposing that it is soybeanThe condensation of the functional group of furfuryl alcohol with the carboxyl group of the reactive group in the protein to form an alcoholic hydroxyl group or ester linkage results in a decrease in the intensity of the absorption peak in the spectra of examples 1-6. At 1049cm^-1There was a distinct absorption peak, which was considered to be an asymmetric stretching vibration of C-O-C, indicating that there were more methylene ether linkages (C-O-C) in the adhesives of examples 1-6, which is also one of the characteristics of furfuryl alcohol participating in the reaction. In comparative example 4, the feature that furfuryl alcohol takes part in the reaction was not found.

FIG. 3 shows the results of sol-gel tests of cured adhesives prepared in examples 1 to 6 of the present invention and comparative examples 1 to 4. According to the sol-gel test results in fig. 3, since comparative example 3 has high hydrophilicity, it is easily dissolved after 4 hours in boiling water (sol fraction < 50%). The sol fraction of comparative example 1 was reduced from 63.1% to 39.2% and the swelling ratio was significantly reduced by half compared to comparative example 3. The sol fraction and swelling ratio of example 1 were low. From comparative example 4, it can be seen that the soy protein adhesive that was not acid cured was minimally crosslinked. Based on the sol-gel test, the modified soybean protein adhesive reduces the polar groups of the protein chain, increases the crosslinking degree, is beneficial to forming a more compact three-dimensional network, and endows the soybean protein adhesive with better swelling resistance and solubility.

FIGS. 4 to 5 are graphs showing the results of thermogravimetric analysis tests of the cured adhesives prepared in examples 1 to 6 and comparative examples 1 to 4 of the present invention, in which FIG. 4 is a TG curve and FIG. 5 is a DTG curve (N)₂Under the action). As can be seen from fig. 4 and 5, the residual ratio of comparative example 1 at 600 c was 42.64%, which is an increase of 59.64% compared to comparative example 3. In contrast, examples 1-6, after further crosslinking modification, had higher residual rates at high and low temperatures. Likewise, the maximum degradation temperature peak (Tmax) trend of the DTG curve is consistent with the above analysis. The modified soy protein adhesive can form high-density hydrogen bonds or other interactions, so that a cross-linked network is strengthened, a heat stable bonding structure is formed, and the heat stability of the adhesive is improved.

The wood breakage rate is consistent with the analysis result of the bonding strength, and the adhesive has good bonding strength.

In view of the above characterization, comparative example 4 has not undergone phytic acid curing, hardly causes furfuryl alcohol to crosslink with the system, and has poor performance, which is not included in the following experiments.

FIG. 6 is a graph showing the effect of water contact angle on the pressed films of the cured adhesives obtained in examples 1 to 6 of the present invention and comparative examples 1 to 3. It can be seen that the modified soy protein adhesive shows superior swelling and wetting properties compared to the unmodified soy protein adhesive. After 30s of test, the liquid drop on the sample can keep the shape, which shows that the sample has good hydrophobic stability, thereby improving the water resistance to a certain extent.

FIG. 7 is a scanning electron microscope image of the surface of the cured adhesive prepared in examples 1 to 6 of the present invention and comparative examples 1 to 3. As can be seen from fig. 7, the surface of the modified soy protein adhesive is compact and uniform, has no holes or gaps, and shows good toughness under microscopic morphology observation.

FIG. 8 is a scanning electron microscope cross-sectional view of a cured adhesive prepared in example 1 of the present invention and in comparative examples 1 and 3. As can be seen from FIG. 8, under the observation of microscopic morphology, the cross section of the modified soy protein adhesive is neat and compact, and excellent dispersibility and compatibility are shown.

FIG. 9 shows cone calorimetry results of particle boards made with the adhesive prepared in example 1 according to the present invention with modifications. As can be seen from fig. 9, the total heat release amount and the heat release rate of the modified soybean protein adhesive particle board are reduced, and the combustion performance of the prepared flame-retardant particle board is improved, compared with the commercial adhesive.

Bond Strength test

Carrying out a bonding strength test: the preparation method comprises the steps of taking poplar veneers, respectively coating 2 surfaces of the veneers with the veneers of examples 1-6 and comparative examples 1-4 to obtain coated veneers (the glue application amount is the same), vertically and respectively placing the poplar veneers which are not coated with glue on two surfaces of the coated veneers according to wood grains, then closing the openings at room temperature for standing for 15min, finally pressing the poplar veneers into three-layer plywood at 180 ℃ and 1.5MPa, and placing the poplar veneers at room temperature for 3 days to obtain the plywood. Type II wet shear strength test the plywood test pieces were immersed in tap water at 63 ± 3 ℃ for 3h, then cooled at room temperature for 10min and tested. The plywood samples for type I wet shear strength (aged bond strength) were subjected to 28h boiling-dry-boiling damp heat treatment (4h boiling, drying at 63 ± 3 ℃, 4h boiling), then cooled at room temperature for 10min and tested. Three bond strengths were tested per set of plywood according to the method of GB/T9846-2015, taking the average of the bond strengths of 20 replicates per bond strength test. The results are shown in Table 1.

Poplar veneer: the water content is 8%; size 40cm by 0.15 cm.

The preparation method comprises the following normal preparation processes: sizing: the glue coating amount is 340g/m²。

Hot pressing for 5min, and cold pressing for 3 min.

TABLE 1 comprehensive mechanical Properties data for the soy protein adhesives prepared in examples 1-6 and comparative examples 1-4

The results of plywood bonding strength experiments in Table 1 show that the soybean protein adhesive can effectively improve the water-resistant bonding performance of the prepared plywood, and the bonding strength can reach 1.47MPa and the dry strength of 1.61MPa according to the detection of II-type plywood, and even reach the strength standard of I-type plywood. This shows that the stability of the adhesive is obviously improved and the reinforcing effect is obvious.

The above-described embodiments are merely illustrative of the preferred embodiments of the present invention, and do not limit the scope of the present invention, and various modifications and improvements of the technical solutions of the present invention can be made by those skilled in the art without departing from the spirit of the present invention, and the technical solutions of the present invention are within the scope of the present invention defined by the claims.