A kind of biodegradable hot melt adhesive and preparation method thereof

Abstract

The invention discloses a biodegradable bio-based hot melt adhesive and a preparation method thereof. The method comprises the following steps: dissolving and mixing epoxy fatty acid, protein-based adhesive, L-glutamic acid, maleic anhydride and tetrabutylammonium iodide in toluene, stirring and reacting, adding a silane coupling agent and bio-based silica gel, rotary evaporating the solvent, and evacuating until there are no bubbles to obtain the biodegradable bio-based hot melt adhesive. The biodegradable bio-based hot melt adhesive prepared by the invention is prepared from bio-based materials and has good degradability. The wet adhesion ability is improved by polylactic acid and polymethyl methacrylate, the initial adhesion strength of the biodegradable bio-based hot melt adhesive is improved by hydrogen bonds formed by polyethylene glycol and nano-silica, the wet adhesion is improved by hydrophilic groups, the hydrogen bonds are oxidized into coordination bonds after thermal curing, and the bonding strength is improved. The bonding strength and water resistance of the biodegradable bio-based hot melt adhesive are improved by cross-linking reaction between epoxy fatty acid and protein-based adhesive.

Description

Technical Field

[0001] The present invention belongs to the technical field of hot melt adhesives, and in particular relates to a degradable bio-based hot melt adhesive and a preparation method thereof. Background Art

[0002] Thermoplastic polymers commonly used in hot melt adhesives are mainly made of polyolefins and ethylene-vinyl acetate mixed with tackifiers such as C5 resin, C9 resin, terpene resin and wax. However, these compositions are made from petroleum-based sources, are difficult to degrade, and are not environmentally friendly. Bio-based degradable materials have the characteristics of environmental friendliness, renewable and biodegradable that traditional petroleum-based polymer materials do not have, which can increase the degradability of hot melt adhesives. Reactive polyurethane hot melt adhesives are a kind of -NCO group-terminated prepolymers with corresponding molecular weights prepared with polyols and polyisocyanates as the main raw materials and various additives under specific temperature, pressure and catalyst conditions. The polyols and polyurethane additives can be replaced by plant-based polyols and bio-based aliphatic isocyanates to obtain easily degradable bio-based hot melt adhesives, reducing the pollution of difficult-to-degrade hot melt adhesives to the environment.

[0003] Patent CN113336911 A discloses a bio-based water-based polyurethane hot melt adhesive and its preparation method and application. The water-based polyurethane hot melt adhesive is prepared by bio-based isocyanate, bio-based macromolecular polyol and hydrophilic chain extender. The hot melt adhesive has excellent peel strength, biodegradability and biocompatibility. However, this solution requires water as a solvent, does not have waterproof properties, and has poor bonding properties in a water environment.

[0004] Patent CN116478653A discloses a bio-based degradable moisture-curing polyurethane hot melt adhesive and a preparation method thereof. A bio-based polyester diol is prepared using bio-based raw materials and applied to the moisture-curing polyurethane hot melt adhesive to obtain a moisture-curing polyurethane hot melt adhesive with excellent adhesion, excellent flexibility and biodegradability under the action of microorganisms. However, in this scheme, the hot melt adhesive needs to be cured in a constant temperature and humidity environment, and the bonding effect is poor in a water environment.

[0005] Therefore, there is a need for a biodegradable bio-based hot melt adhesive that uses bio-based materials as raw materials, is easy to degrade, has good bonding properties, and has certain waterproof properties so as to be suitable for applications in a variety of environments. Summary of the invention

[0006] The purpose of the present invention is to solve the problem of how to improve the degradability and waterproof performance of a bio-based hot melt adhesive, and to provide a degradable bio-based hot melt adhesive and a preparation method thereof.

[0007] The purpose of the present invention can be achieved through the following technical solutions:

[0008] A method for preparing a degradable bio-based hot melt adhesive comprises the following steps:

[0009] In a reactor, epoxy fatty acid, protein-based adhesive, L-glutamic acid, maleic anhydride and tetrabutylammonium iodide are dissolved and mixed in toluene under nitrogen protection, stirred and reacted at 80-120° C. for 2-3 hours, cooled to 60-70° C., silane coupling agent and bio-based silica gel are added, stirred and reacted for 0.5-1 hour, the solvent is rotary evaporated, and vacuum is evacuated until there are no bubbles to obtain a degradable bio-based hot melt adhesive.

[0010] Furthermore, the usage ratio of epoxy fatty acid, protein-based adhesive, L-glutamic acid, maleic anhydride, tetrabutylammonium iodide, toluene, silane coupling agent and bio-based silica gel is 10-20g: 15-25g: 1.2-1.5g: 3-4g: 1.5-1.8g: 100-150mL: 2-4g: 35-45g.

[0011] Further, the epoxy fatty acid is prepared by the following steps:

[0012] Dissolve the esterified linoleic acid in dichloromethane in a reaction kettle, slowly add cyclohexanone peroxide into the reaction kettle under an ice bath, raise the temperature to 20-25°C and stir to react for 16-18h, wash with 1M sodium hydroxide solution, separate the organic layer after stratification, dry and vacuum evaporate to remove the solvent to obtain epoxy fatty acid.

[0013] Furthermore, the usage ratio of esterified linoleic acid, dichloromethane and cyclohexanone peroxide is 8-12 g: 100-150 mL: 10-15 g.

[0014] Further, the esterified linoleic acid is prepared by the following steps:

[0015] In a reaction kettle, linoleic acid, ethanol and p-toluenesulfonic acid monohydrate are added to toluene, heated to 60-70° C. and refluxed for reaction for 4-5 hours, and the solvent is removed under reduced pressure to obtain esterified linoleic acid.

[0016] Furthermore, the usage ratio of linoleic acid, ethanol, p-toluenesulfonic acid monohydrate and toluene is 20-40 g: 4-6 mL: 0.2-0.3 g: 200-250 mL.

[0017] Further, the protein-based adhesive is prepared by the following steps:

[0018] In a reactor, the soy protein isolate is dissolved in deionized water, maleic anhydride is added, the temperature is raised to 50-60°C for reaction for 2-2.5 hours, and then hexamethylenediamine is added, the temperature is raised to 85-95°C for reaction for 2-2.5 hours, and after cooling, the water is removed by rotary evaporation for 1-1.5 hours to obtain a protein-based adhesive.

[0019] Furthermore, the usage ratio of soy protein isolate, deionized water, maleic anhydride and hexamethylenediamine is 25-30 g: 120-150 mL: 15-17 g: 30-35 g.

[0020] Further, the bio-based silica gel is prepared by the following steps:

[0021] Dissolve polylactic acid in triethylene glycol divinyl ether in a reaction kettle, heat to 90-100° C. and stir to dissolve the polylactic acid, add nano-silica, stir and mix, then add polymethyl methacrylate and polyethylene glycol, stir at 65-75° C. for 1-2 hours, and vacuum dry to obtain bio-based silica gel.

[0022] Furthermore, the usage ratio of polylactic acid, triethylene glycol divinyl ether, nano silicon dioxide, polymethyl methacrylate and polyethylene glycol is 40-60g: 500-600g: 20-30g: 150-200g: 30-40g.

[0023] Beneficial effects of the present invention:

[0024] (1) The biodegradable bio-based hot melt adhesive prepared by the present invention is made of bio-based materials and has good biodegradability. The adhesion ability of the biodegradable bio-based hot melt adhesive to the surface of the substrate in a humid environment is improved by polylactic acid and polymethyl methacrylate. The hydrogen bonds formed by polyethylene glycol and nano-silica are used to improve the initial adhesion strength of the biodegradable bio-based hot melt adhesive. The hydrophilic group improves the adhesion to the surface of the substrate in a humid environment. After thermal curing, the hydrogen bonds are oxidized into coordination bonds to improve the bonding strength of the biodegradable bio-based hot melt adhesive. The cross-linking reaction of epoxy fatty acids and protein-based adhesives is used to improve the bonding strength and water resistance of the biodegradable bio-based hot melt adhesive.

[0025] (2) The preparation method of the present invention disperses nano-silicon dioxide through the cross-linking effect of polyethylene glycol and polymethyl methacrylate, and obtains sticky soy protein isolate polyamide through soy protein isolate, which forms a cross-linking network during thermal curing to improve the bonding strength. The fatty acid is epoxidized and then compounded with a protein-based adhesive, and the bonding strength and water resistance are improved by the reaction between the epoxy group and the amino group. The synergistic effect with the fatty acid makes the prepared biodegradable bio-based hot melt adhesive have higher bonding strength and waterproof performance. DETAILED DESCRIPTION

[0026] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] Embodiment 1: A method for preparing a biodegradable bio-based hot melt adhesive, comprising the following steps:

[0028] S1. Dissolve 40 g of polylactic acid in 500 g of triethylene glycol divinyl ether in a reactor, heat to 90° C. and stir to dissolve the polylactic acid, add 20 g of nano-silica, stir and mix, then add 150 g of polymethyl methacrylate and 30 g of polyethylene glycol, stir at 65° C. for 1 h, and vacuum dry to obtain bio-based silica gel.

[0029] S2. Dissolve 25 g of soy protein isolate in 120 mL of deionized water in a reactor, add 15 g of maleic anhydride, heat to 50 °C and react for 2 h, then add 30 g of hexamethylenediamine, heat to 85 °C and react for 2 h, cool and evaporate for 1 h to remove moisture to obtain a protein-based adhesive.

[0030] S3. In a reactor, 0.2 g of p-toluenesulfonic acid monohydrate was dissolved in 4 mL of ethanol, and then added with 20 g of linoleic acid into 200 mL of toluene. The mixture was heated to 60° C. and refluxed for 4 h. The solvent was removed under reduced pressure to obtain esterified linoleic acid. 8 g of esterified linoleic acid was dissolved in 100 mL of dichloromethane in a reactor. 10 g of cyclohexanone peroxide was slowly added into the reactor under an ice bath. The mixture was heated to 20° C. and stirred for 16 h. The mixture was washed with 1 M sodium hydroxide solution. The organic layer was separated after stratification. The solvent was removed by vacuum rotary evaporation after drying to obtain epoxy fatty acid.

[0031] S4. In a reactor under nitrogen protection, 10 g of epoxy fatty acid, 15 g of protein-based adhesive, 1.2 g of L-glutamic acid, 3 g of maleic anhydride and 1.5 g of tetrabutylammonium iodide were dissolved and mixed in 100 mL of toluene, stirred and reacted at 80 ° C for 2 h, cooled to 60 ° C, 2 g of KH560 and 35 g of bio-based silica gel were added, stirred and reacted for 0.5 h, the solvent was rotary evaporated, and vacuum was evacuated until there were no bubbles to obtain a degradable bio-based hot melt adhesive.

[0032] Embodiment 2: A method for preparing a biodegradable bio-based hot melt adhesive, comprising the following steps:

[0033] S1. Dissolve 50 g of polylactic acid in 550 g of triethylene glycol divinyl ether in a reactor, heat to 95°C and stir to dissolve the polylactic acid, add 25 g of nano-silica, stir and mix, then add 175 g of polymethyl methacrylate and 35 g of polyethylene glycol, stir at 70°C for 1.5 h, and vacuum dry to obtain bio-based silica gel.

[0034] S2. Dissolve 27.5 g of soy protein isolate in 135 mL of deionized water in a reactor, add 16 g of maleic anhydride, heat to 55 °C and react for 2.25 h, then add 32.5 g of hexamethylenediamine, heat to 90 °C and react for 2.25 h, cool and evaporate for 1.25 h to remove moisture to obtain a protein-based adhesive.

[0035] S3. In a reactor, 0.25 g of p-toluenesulfonic acid monohydrate was dissolved in 5 mL of ethanol, and then added with 30 g of linoleic acid into 225 mL of toluene. The mixture was heated to 65° C. and refluxed for 4.5 h. The solvent was removed under reduced pressure to obtain esterified linoleic acid. 10 g of esterified linoleic acid was dissolved in 125 mL of dichloromethane in a reactor. 12.5 g of cyclohexanone peroxide was slowly added into the reactor under an ice bath. The mixture was heated to 22.5° C. and stirred for 17 h. The mixture was washed with 1 M sodium hydroxide solution. The organic layer was separated after stratification. The solvent was removed by vacuum rotary evaporation after drying to obtain epoxy fatty acid.

[0036] S4. In a reactor under nitrogen protection, 15 g of epoxy fatty acid, 20 g of protein-based adhesive, 1.35 g of L-glutamic acid, 3.5 g of maleic anhydride and 1.65 g of tetrabutylammonium iodide were dissolved and mixed in 125 mL of toluene, stirred and reacted at 100 °C for 2.5 h, cooled to 65 °C, 3 g of KH560 and 40 g of bio-based silica gel were added, stirred and reacted for 0.75 h, the solvent was rotary evaporated, and vacuum was evacuated until there were no bubbles to obtain a degradable bio-based hot melt adhesive.

[0037] Embodiment 3: A method for preparing a degradable bio-based hot melt adhesive, comprising the following steps:

[0038] S1. Dissolve 60 g of polylactic acid in 600 g of triethylene glycol divinyl ether in a reactor, heat to 100° C. and stir to dissolve the polylactic acid, add 30 g of nano-silica, stir and mix, then add 200 g of polymethyl methacrylate and 40 g of polyethylene glycol, stir at 75° C. for 2 h, and vacuum dry to obtain bio-based silica gel.

[0039] S2. Dissolve 30 g of soy protein isolate in 150 mL of deionized water in a reactor, add 17 g of maleic anhydride, heat to 60 °C and react for 2.5 h, then add 35 g of hexamethylenediamine, heat to 95 °C and react for 2.5 h, cool and evaporate for 1.5 h to remove moisture to obtain a protein-based adhesive.

[0040] S3. In a reactor, 0.3 g of p-toluenesulfonic acid monohydrate was dissolved in 6 mL of ethanol, and then added with 40 g of linoleic acid into 250 mL of toluene. The mixture was heated to 70° C. and refluxed for 5 h. The solvent was removed under reduced pressure to obtain esterified linoleic acid. 12 g of esterified linoleic acid was dissolved in 150 mL of dichloromethane in a reactor. 15 g of cyclohexanone peroxide was slowly added into the reactor under ice bath. The mixture was heated to 25° C. and stirred for 18 h. The mixture was washed with 1 M sodium hydroxide solution. The organic layer was separated after stratification. The solvent was removed by vacuum rotary evaporation after drying to obtain epoxy fatty acid.

[0041] S4. In a reactor under nitrogen protection, 20 g of epoxy fatty acid, 25 g of protein-based adhesive, 1.5 g of L-glutamic acid, 4 g of maleic anhydride and 1.8 g of tetrabutylammonium iodide were dissolved and mixed in 150 mL of toluene, stirred and reacted at 120 ° C for 3 h, cooled to 70 ° C, 4 g of KH560 and 45 g of bio-based silica gel were added, stirred and reacted for 1 h, the solvent was rotary evaporated, and vacuum was evacuated until there were no bubbles to obtain a degradable bio-based hot melt adhesive.

[0042] Principle of the invention: By blending plant-derived polylactic acid with nano-silica, the nano-silica is dispersed through the cross-linking effect of polyethylene glycol and polymethyl methacrylate. Polylactic acid not only improves the adhesion of bio-based silica gel, but also helps to break the water film on the surface of the substrate in a humid environment, thereby improving the adhesion of the degradable bio-based hot melt adhesive in a humid environment. Polymethyl methacrylate has a certain hydrophobic ability, and synergizes with polylactic acid to break the water film on the surface of the substrate, thereby helping to improve the wet adhesion of the degradable bio-based hot melt adhesive.

[0043] The hydroxyl groups on the surfaces of polyethylene glycol and nano-silica can form hydrogen bonds. A high content of hydrogen bonds helps to improve the initial adhesion strength of the biodegradable bio-based hot melt adhesive. At the same time, hydrogen bonds have a strong affinity for the surface of the substrate containing water. The hydrophilic unit can promote the adhesive to fully contact with the substrate surface in a wet environment and improve the adhesion to the surface of the substrate containing water. After thermal curing, the hydrogen bonds are oxidized to coordination bonds, further improving the bonding strength of the biodegradable bio-based hot melt adhesive. Maleic anhydride reacts with the amino acids in the soybean protein molecules and then reacts with hexamethylenediamine to form a polyamide with a carbamate structure, which can form a network during the curing process and improve the bonding performance of the biodegradable bio-based hot melt adhesive. By adding bio-based lipids The fatty acid linoleic acid is esterified and then epoxidized with cyclohexanone peroxide to obtain epoxidized fatty acids. The epoxy fatty acids are cross-linked with protein-based adhesives under the promotion of amino acids, maleic anhydride and tetrabutylammonium iodide, so that the protein-based adhesive reacts with the epoxy groups in the epoxy fatty acids to improve the bonding strength and water resistance of the protein-based adhesive. At the same time, the introduced fatty acids can effectively improve the water resistance of the protein-based adhesive, which is beneficial to improving the waterproof ability of the degradable bio-based hot melt adhesive. The bio-based silica gel formed by the bio-based protein-based adhesive, epoxy fatty acids and polylactic acid makes the degradable bio-based hot melt adhesive have excellent degradability while maintaining high bonding strength and waterproof properties.

[0044] Comparative Example 1: The difference from Example 1 is that no bio-based silica gel is added to prepare a degradable bio-based hot melt adhesive.

[0045] Comparative Example 2: The difference from Example 1 is that in S4, the protein-based adhesive is replaced by an equal mass of isocyanate to prepare a degradable bio-based hot melt adhesive.

[0046] Comparative Example 3: The difference from Example 1 is that in S4, an equal mass of epoxy soybean oil is used to replace epoxy fatty acid to prepare a degradable bio-based hot melt adhesive.

[0047] The performance test of the biodegradable bio-based hot melt adhesive prepared in Examples 1 to 3 and Comparative Examples 1 to 3 was carried out using a 200×200×5 mm poplar board with a coating amount of 250 g / m 2 , hot pressing curing for 5 minutes, hot pressing temperature of 200℃, hot pressing pressure of 1.5Mpa, the bonding strength of the poplar board dry board bonding and the wet board bonding obtained after soaking in water for 24 hours were tested respectively;

[0048] Apply biodegradable hot melt adhesive on high temperature resistant release paper with a coating amount of 250g / m 2 , hot pressing curing for 5 minutes, the hot pressing temperature is 200℃, the hot pressing pressure is 1.5Mpa, after hot pressing curing, remove the release paper, cut the hot melt adhesive sheet into 50×50mm square pieces and weigh them, bury them in the soil, the burial depth is 1m, dig out, clean and dry them every month, and weigh them to calculate the degradation rate.

[0049] The results are shown in Table 1:

[0050] Table 1: Test results of bonding performance and degradation performance of biodegradable hot melt adhesive

[0051]

[0052] As can be seen from Table 1, the biodegradable bio-based hot melt adhesive prepared by the present invention has high bonding strength on dry plates and wet plates, a small difference in bonding strength between dry plates and wet plates, good waterproof ability and wet plate bonding ability, and a degradation rate of more than 50% after 3 months of degradation, which has excellent degradation ability and is environmentally friendly.

[0053] Since no bio-based silica gel was added to Comparative Example 1, the viscosity was poor and the wet adhesion ability was reduced, so the wet board bonding strength was low.

[0054] In Comparative Example 2, since isocyanate is used to replace the protein-based adhesive, the cross-linking density of isocyanate with epoxy and polyol is better, and the bonding strength is higher, but the degradation rate is greatly reduced, which is not conducive to biodegradation.

[0055] In Comparative Example 3, epoxy soybean oil is used to replace epoxy fatty acid. However, since the hot melt adhesive formula does not contain isocyanate, the epoxy soybean oil has little effect on improving the bonding performance of the hot melt adhesive and its water resistance is also poor.

[0056] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a degradable bio-based hot melt adhesive, characterized in that: The steps include: In a reactor, epoxy fatty acid, protein-based adhesive, L-glutamic acid, maleic anhydride and tetrabutylammonium iodide are dissolved and mixed in toluene under nitrogen protection, stirred and reacted at 80-120° C. for 2-3 hours, cooled to 60-70° C., silane coupling agent and bio-based silica gel are added, stirred and reacted for 0.5-1 hour, the solvent is rotary evaporated, and vacuum is evacuated until there are no bubbles to obtain a degradable bio-based hot melt adhesive.

2. The method for preparing a degradable bio-based hot melt adhesive according to claim 1, characterized in that: The usage ratio of the epoxy fatty acid, protein-based adhesive, L-glutamic acid, maleic anhydride, tetrabutylammonium iodide, toluene, silane coupling agent and bio-based silica gel is 10-20g: 15-25g: 1.2-1.5g: 3-4g: 1.5-1.8g: 100-150mL: 2-4g: 35-45g.

3. The method for preparing a degradable bio-based hot melt adhesive according to claim 2, characterized in that: The epoxy fatty acid is prepared by the following steps: Dissolve the esterified linoleic acid in dichloromethane in a reaction kettle, slowly add cyclohexanone peroxide into the reaction kettle under an ice bath, heat to 20-25° C., stir and react for 16-18 hours, wash with 1M sodium hydroxide solution, separate the organic layer after stratification, dry and vacuum evaporation to remove the solvent, and obtain epoxy fatty acid; The esterified linoleic acid is prepared by the following steps: In a reaction kettle, linoleic acid, ethanol and p-toluenesulfonic acid monohydrate are added to toluene, heated to 60-70° C. and refluxed for reaction for 4-5 hours, and the solvent is removed under reduced pressure to obtain esterified linoleic acid.

4. The method for preparing a degradable bio-based hot melt adhesive according to claim 3, characterized in that: The usage ratio of the esterified linoleic acid, dichloromethane and cyclohexanone peroxide is 8-12 g: 100-150 mL: 10-15 g.

5. The method for preparing a degradable bio-based hot melt adhesive according to claim 3, characterized in that: The usage ratio of the linoleic acid, ethanol, p-toluenesulfonic acid monohydrate and toluene is 20-40 g: 4-6 mL: 0.2-0.3 g: 200-250 mL.

6. The method for preparing a degradable bio-based hot melt adhesive according to claim 2, characterized in that: The protein-based adhesive is prepared by the following steps: In a reactor, the soy protein isolate is dissolved in deionized water, maleic anhydride is added, the temperature is raised to 50-60°C for reaction for 2-2.5 hours, and then hexamethylenediamine is added, the temperature is raised to 85-95°C for reaction for 2-2.5 hours, and after cooling, the water is removed by rotary evaporation for 1-1.5 hours to obtain a protein-based adhesive.

7. The method for preparing a degradable bio-based hot melt adhesive according to claim 6, characterized in that: The usage ratio of the soy protein isolate, deionized water, maleic anhydride and hexamethylenediamine is 25-30 g: 120-150 mL: 15-17 g: 30-35 g.

8. The method for preparing a degradable bio-based hot melt adhesive according to claim 2, characterized in that: The bio-based silica gel is prepared by the following steps: Dissolve polylactic acid in triethylene glycol divinyl ether in a reaction kettle, heat to 90-100° C. and stir to dissolve the polylactic acid, add nano-silica, stir and mix, then add polymethyl methacrylate and polyethylene glycol, stir at 65-75° C. for 1-2 hours, and vacuum dry to obtain bio-based silica gel.

9. The method for preparing a degradable bio-based hot melt adhesive according to claim 8, characterized in that: The usage ratio of the polylactic acid, triethylene glycol divinyl ether, nano silicon dioxide, polymethyl methacrylate and polyethylene glycol is 40-60g: 500-600g: 20-30g: 150-200g: 30-40g.

10. A biodegradable bio-based hot melt adhesive, characterized in that: Prepared by any preparation method described in claims 1-9.

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