Soybean protein adhesive with mildew-proof and flame-retardant properties and preparation method thereof

Abstract

The invention discloses a mildewproof and flame-retardant soybean protein adhesive and a preparation method thereof. The preparation method comprises the following steps: firstly, grafting phytic acid and cinnamyl aldehyde through catalytic esterification reaction, mixing soybean protein isolate and distilled water according to a ratio of 1: 9, mechanically stirring at room temperature for 30 minutes, regulating the pH value to 9-10 by adopting a sodium hydroxide solution in the stirring process, and then adding phytic acid cinnamyl aldehyde with different addition amounts to prepare the modified soybean protein adhesive. According to the invention, cinnamyl aldehyde derived from natural plant cinnamon is used as a modifier, so that the modifier is green, environment-friendly and renewable. The adhesive is high in wet shear strength, good in mildew resistance and flame retardance and simple in production process, and can be used in the field of artificial board manufacturing.

Description

Technical Field

[0001] The invention relates to the technical field of biomass adhesives, and in particular to a soybean protein adhesive with mildew resistance and flame retardancy and a preparation method thereof. Background Art

[0002] At present, the adhesives used in the wood-based panel industry are mainly formaldehyde-based adhesives, which have the problem of formaldehyde release during use. With the improvement of people's environmental awareness, the demand for formaldehyde-free multifunctional biodegradable adhesives has increased significantly. As a natural, low-cost and renewable resource, soy protein has broad application prospects in the research of green adhesives. However, its performance still has certain defects, and the bonding strength, mildew resistance and flame retardancy still need to be improved. At present, the commonly used modification method is chemical cross-linking modification, and the commonly used modifiers are mostly petrochemical products. The modifier only improves one of the properties of water resistance, mildew resistance or flame retardancy. If you want to have the above properties at the same time, you need to use multiple modifiers. Not only is the production process complicated, but the addition of multiple modifiers will also affect the bonding interface of the soy protein adhesive, thereby having a negative impact on the dry and wet shear strength. Therefore, it is of great significance to develop a soy protein adhesive with both mildew resistance and flame retardancy for its promotion and use. Summary of the invention

[0003] In view of the above-mentioned deficiencies of the prior art, the present invention provides a soybean protein adhesive having both mildew resistance and flame retardancy and a preparation method thereof. The preparation method comprises the following steps in sequence: (1) Dissolve 10 g of phytic acid in 50 mL of anhydrous ethanol and slowly add 1 mL of concentrated sulfuric acid. Dissolve 10 g of cinnamaldehyde in 30 mL of anhydrous ethanol and slowly add it to the phytic acid solution under an ice bath. Then maintain the reaction temperature at 60°C for 4 h. Use nitrogen protection to prevent oxidation during the reaction. Stir at 500 rpm during the reaction to ensure adequate mixing.

[0004] (2) After the reaction is completed, the mixed solution is cooled to room temperature and neutralized with saturated sodium bicarbonate solution to a pH of 7. The ethanol is removed by vacuum distillation, and the residue is extracted three times with ether and dried over anhydrous sodium sulfate. The solvent is removed by rotary evaporation to obtain a light yellow viscous liquid, which is cinnamaldehyde-phytic acid complex (CA-PA).

[0005] (3) Soy protein (SPI) was mixed in a ratio of 1:9, that is, 100 g SPI was mixed with 900 g distilled water, and different amounts of CA-PA were added and stirred at room temperature for 30 min. During the stirring process, the pH was adjusted to 9-10 with 1 mol / L NaOH solution to prepare a soybean protein adhesive with mildew resistance and flame retardant properties.

[0006] The beneficial effects of the present invention are as follows: through the acetalization reaction catalyzed by sulfuric acid, the covalent grafting of phytic acid and cinnamaldehyde can be achieved, the aldehyde group of cinnamaldehyde and the hydroxyl oxygen in the phosphate group of phytic acid undergo acetalization reaction to form a stable phosphorus-acetal bond, and the product retains the mildew resistance of the aldehyde group and the flame retardancy of the phosphate group. After CA-PA is added to the soy protein adhesive, its aldehyde group and the hydrophilic amino group in the soy protein undergo Schiff base reaction, the cross-linking density between molecules increases, the molecular structure of the adhesive network becomes more compact, the wet shear strength of the adhesive increases, and the Schiff base has a good antibacterial effect, which can significantly improve the mildew resistance of the adhesive. The phosphate group in CA-PA can promote carbonization, isolate oxygen, and improve the flame retardancy of the adhesive. Compared with the unmodified soy protein adhesive, the dry and wet shear strengths of the soy protein adhesive modified with 2% CA-PA increased by 43.67% and 51.89%, respectively. The mildew-proof period of the uncured adhesive exceeded 30 days, and the mildew-proof period of the cured adhesive exceeded 40 days. The peak heat release rate (PHRR) and total heat release rate (THR) of the modified adhesive were reduced by 55.76% and 29.36%, respectively.

[0007] Based on the above technical solution, the present invention can also be improved as follows: Further, the amount of CA-PA added in step (3) can be 1g, 2g, 3g, 4g or 5g.

[0008] The above parameters are the optimal parameters. Under these parameters, the dry and wet shear strength, mildew resistance and flame retardancy of the modified soy protein adhesive are significantly improved. DETAILED DESCRIPTION

[0009] The specific implementation modes of the present invention are described in detail below.

[0010] In an embodiment of the present invention, a soy protein adhesive having both mildew resistance and flame retardancy and a preparation method thereof are provided, including the synthesis of a modifier CA-PA and the preparation of a modified soy protein adhesive. In this embodiment, the modifier CA-PA is synthesized by sulfuric acid-catalyzed acetalization reaction, and the addition amount is 1-5% of the total mass of the soy protein adhesive. 100g SPI is mixed with 900g distilled water, 1-5% CA-PA is added and stirred at room temperature for 30 minutes, and the pH is adjusted to 10 with a NaOH solution during stirring to prepare a soy protein adhesive having mildew resistance and flame retardancy.

[0011] The soybean protein adhesive prepared by the method has high wet shear strength, good mildew resistance and flame retardancy.

[0012] The following examples are only used to illustrate the present invention in detail and are not intended to limit the scope of the invention in any way. The CA-PA synthesis process is the same in the examples, and only the preparation process of the soybean protein adhesive is listed.

[0013] (1) Embodiment 1 Soy protein (SPI) was mixed in a ratio of 1:9, that is, 100g of soy protein isolate was mixed with 900g of distilled water, and 2% CA-PA was added and stirred at room temperature for 30 minutes. During the stirring process, the pH was adjusted to 10 with 1mol / L NaOH solution to prepare a soy protein adhesive with mildew resistance and flame retardant properties.

[0014] The data of the soybean protein adhesive before and after modification obtained in this embodiment are as follows: Peak heat release rate (W / g) Total heat release rate (kJ / g) Dry shear strength (MPa) Wet shear strength (MPa) Anti-mildew days (days) Unmodified soy protein adhesive 433.1 44.9 1.65 0.84 2 CA-PA modified soybean protein adhesive 236.7 42.5 2.47 1.33 30 and above (2) Embodiment 2 Soy protein (SPI) was mixed in a ratio of 1:9, that is, 100g of soy protein isolate was mixed with 900g of distilled water, and 4% CA-PA was added and stirred at room temperature for 30 minutes. During the stirring process, the pH was adjusted to 10 with 1mol / L NaOH solution to prepare a soy protein adhesive with mildew resistance and flame retardant properties.

[0015] The data of the soybean protein adhesive before and after modification obtained in this embodiment are as follows: Peak heat release rate (W / g) Total heat release rate (kJ / g) Dry shear strength (MPa) Wet shear strength (MPa) Anti-mildew days (days) Unmodified soy protein adhesive 433.1 44.9 1.65 0.84 2 CA-PA modified soybean protein adhesive 212.5 41.5 2.57 1.35 30 and above

Claims

1. Dissolve 10 g of phytic acid in 50 mL of anhydrous ethanol, slowly drop 1 mL of concentrated sulfuric acid, then dissolve 10 g of cinnamaldehyde in 30 mL of anhydrous ethanol and slowly drop it into the phytic acid solution under an ice bath, stir at 500 rpm to ensure full mixing, keep the reaction temperature at 60 ° C, the reaction time is 4 hours, and use nitrogen protection to prevent oxidation. After the reaction is completed, the reaction solution is cooled to room temperature, neutralized with saturated sodium bicarbonate solution to pH 7, and ethanol is removed by vacuum distillation. The residue is extracted with ether 3 times and dried with anhydrous sodium sulfate. The solvent is removed by rotary evaporation to obtain a light yellow viscous liquid, which is cinnamaldehyde-phytic acid complex (CA-PA). Soy protein (SPI) was mixed in a ratio of 1:9, that is, 100g of soy protein isolate (SPI) was mixed with 900g of distilled water, and different amounts of CA-PA were added and stirred at room temperature for 30 minutes. During the stirring process, 1mol / LNaOH solution was used to adjust and control the pH to 9-10 to prepare a soy protein adhesive with mildew resistance and flame retardant properties.

2. The mildew-proof and flame-retardant soybean protein adhesive and its preparation method according to claim 1, characterized in that: The ratios of phytic acid and cinnamaldehyde to anhydrous ethanol were 1:5 and 1:3, respectively.

3. The mildew-proof and flame-retardant soybean protein adhesive and its preparation method according to claim 1, characterized in that: Nitrogen protection is required during the reaction to prevent oxidation.

4. The mildew-proof and flame-retardant soybean protein adhesive and its preparation method according to claim 1, characterized in that: The amount of CA-PA added is 1% to 5% of the mass of soy protein isolate, that is, 10g SPI is mixed with 90g water and 1 to 5g CA-PA is added.