Polyester type biodegradable adhesive and preparation method thereof

Abstract

The invention discloses a polyester type biodegradable adhesive and a preparation method thereof. The polyester type biodegradable adhesive comprises the following raw materials in molar percentage: 1: 1.1 of bio-based dibasic acid and dihydric alcohol; the weight of the trimethylolpropane accounts for 0.5%-5.0% of the total weight of the bio-based binary acid and the dihydric alcohol, and the weight of the dimethylolpropionic acid accounts for 1.0%-7.0% of the total weight of the bio-based binary acid and the dihydric alcohol.

Description

Technical Field

[0001] The invention relates to the field of biodegradability, in particular to a polyester biodegradable adhesive and a preparation method thereof. Background Art

[0002] Adhesives are elastic materials that can connect a variety of identical or different materials together through surface bonding, using adhesion and cohesion. They play an important role in the fields of wood processing, construction, aerospace, automobiles, logistics and express delivery, electronics and electrical appliances.

[0003] Most commercial adhesives are derived from petrochemical raw materials, such as epoxy resins, polyurethanes and acrylic resins. These petroleum-based adhesives are widely used due to their excellent mechanical strength, good water resistance, variety, large market share and high economic benefits. They also face severe challenges: due to the stable CC / CO bond, more than 80% of discarded adhesives can remain in the ecosystem for more than 50 years; the residual isocyanate in polyurethane adhesives will release carcinogenic amines during the degradation process; the production of epoxy adhesives will emit carbon dioxide, causing environmental pressure.

[0004] The degradable adhesives currently studied are divided into water-based adhesives and solvent-based adhesives according to the different dispersion media. Water-based biodegradable adhesives use water as the dispersion medium and are a heterogeneous system. For example, some adhesives modified from natural polymers such as starch and cellulose, as well as synthetic water-based polyurethanes, water-based epoxy resins and other biodegradable adhesives. Solvent-based biodegradable adhesives use organic solvents as dispersion media to form a homogeneous system. Common organic solvents include benzene, toluene, dichloromethane, etc. However, solvent-based adhesives will volatilize organic solvents to produce VOCs during use, polluting the atmosphere, and are toxic, flammable and explosive, with limited water and heat resistance. In addition, due to the need for continuous replenishment of volatilization, the cost increases. These disadvantages greatly limit its wide application as a biodegradable adhesive. Water-based adhesives generally have the advantages of environmental protection, low cost, non-flammability, safe production and use, but for non-polar or weakly polar materials, there are still problems such as low crosslinking density, hydrophilic-water resistance paradox and incomplete biodegradation. The research on the preparation method of water-based biodegradable adhesive based on TMP-DMPA has great application value and market value, as it can achieve water-based processability without sacrificing performance. Summary of the invention

[0005] In view of the shortcomings of the prior art, the adhesive of the present invention uses bio-based dibasic acid (succinic acid, adipic acid) and diol (1,3-propylene glycol, 1,4-butanediol) as the polycondensation main chain, and constructs a three-dimensional cross-linked network by introducing trimethylolpropane (TMP), which significantly improves the cohesive strength and heat resistance of the adhesive layer. At the same time, dimethylolpropionic acid (DMPA) is used as a water-based functional monomer, and its carboxylic acid group is used to achieve self-emulsification dispersion, avoiding the interface weakening problem of traditional surfactants; the trihydroxy branched structure (neopentyl skeleton) of TMP gives the adhesive excellent anti-crystallization and flexibility, and the ionization characteristics of DMPA not only ensure the stability of the water-based system, but also accelerate the degradation process by catalyzing the hydrolysis of ester bonds. The adhesive has both the mechanical properties of petroleum-based products and the environmental protection of bio-based materials, with a VOC emission of <50 g / L, and can be widely used in food packaging, medical materials, electronic devices and other fields. The present invention solves the long-term contradiction between environmental toxicity, degradability and mechanical properties of traditional adhesives, and has the feasibility of industrial production and cost competitiveness.

[0006] The present invention provides a polyester-type biodegradable adhesive. The raw materials of the water-based biodegradable adhesive include, by molar percentage, 1:1.1 bio-based dibasic acid and diol; and 0.5% to 5.0% of trimethylolpropane and 1.0% to 7.0% of dimethylolpropionic acid, based on the total weight of the bio-based monomer raw materials, when preparing the water-based biodegradable adhesive.

[0007] As a further solution of the present invention, trimethylolpropane is a trifunctional polyol with three hydroxyl groups. The three hydroxyl groups (-OH) participate in polycondensation to form a three-dimensional network structure. The branched aliphatic chain can improve flexibility and thermal stability, prevent crystallization, and has a high crosslinking density and mechanical strength. Its structural formula is as follows: Specifically, cross-linked trimethylolpropane (TMP) is a polyol compound containing three hydroxymethyl groups, and its molecular formula is C 6 H 14 O 3 The structural center is a propane skeleton connected to three hydroxymethyl groups, which gives it high reactivity and symmetry. Its strong polarity and hydroxyl hydrophilic groups make it easily soluble in water and polar solvents, suitable for water-based system applications. When used as a cross-linking agent, the three hydroxyl groups can react with isocyanate, carboxylic acid and other groups in the resin to form a three-dimensional network structure, significantly improving the cohesion and interfacial bonding strength of the material, and giving adhesives and coatings excellent heat resistance, mechanical stability and chemical corrosion resistance. Its advantage is that it balances flexibility and hardness by regulating the cross-linking density. It is widely used in polyurethane, epoxy resin and other fields, and has both environmental friendliness and high performance.

[0008] As a further embodiment of the present invention, the biodegradable adhesive containing TMP is prepared by the following method: (1) Prepolymer synthesis: A certain proportion of SA, AA, PDO and BDO were added into a 250 mL reactor. The catalysts were antimony ethylene glycol and tetrabutyl titanate, and the molar ratio of acid to alcohol was 1:1.1.

[0009] (2) Set the heating temperature to 165 °C, react for 30 min, then raise the temperature to 195 °C for 30 min, and continue to raise the temperature to 215 °C. Control the esterification reaction for 90 min, and no more water will evaporate during the reaction. During the above process, nitrogen was continuously introduced to keep the reaction system in a stable nitrogen atmosphere. The amount of catalyst antimony glycol and tetrabutyl titanate was 0.1wt% of the total mass of acid and alcohol, and they were mixed evenly. In a nitrogen environment, the temperature was controlled at 165 °C~215 °C and the reaction was carried out for 2.5 h until no more water evaporated.

[0010] (3) Cross-linking and chain extension: Add trimethylolpropane with the corresponding total system mass fraction (0.5wt%, 0.8wt%, 1wt%, 3wt%, 5wt%), add an appropriate amount of tetrabutyl titanate catalyst, and continue the reaction for 60 min to obtain a polyester-type biodegradable adhesive.

[0011] As a further solution of the present invention, the dimethylol propionic acid is a diol containing a carboxylic acid group, and the two hydroxyl groups allow the chain to be extended; the carboxylic acid (-COOH) introduces an ionic group, which can catalyze the hydrolysis of the ester bond, accelerate biodegradation, has hydrophilicity, is conducive to water dispersion, and can serve as a reaction site for chain extension. Its structural formula is as follows: Specifically, cross-linked dimethylol propionic acid (DMPA) is an organic compound containing two hydroxymethyl groups and one carboxylic acid group, with a molecular formula of C 5 H 10 O 4 Its structure is based on propionic acid as the core, with hydroxymethyl groups on both sides enhancing the reactivity, and carboxylic acid groups imparting hydrophilicity and ionic properties. Its strong polarity and carboxylic acid dissociation ability make it easily soluble in water and polar solvents, especially in aqueous systems, where it can improve the dispersion stability of the resin through self-emulsification. As a functional monomer, the two hydroxymethyl groups can react with isocyanate, epoxy groups, etc. to form a dense cross-linked network, while the carboxylic acid groups enhance the interfacial adhesion through hydrogen bonds or ionic effects, giving the material excellent water resistance, mechanical strength and thermal stability. Its advantages are water-based environmental protection and low toxicity. At the same time, the pH and compatibility of the system are adjusted by the carboxylic acid group. It is widely used in the fields of waterborne polyurethanes, coatings and adhesives, and has both efficient bonding and green process characteristics.

[0012] As a further solution of the present invention, a method for preparing a water-based biodegradable adhesive based on TMP-DMPA is prepared by the following method: (1) Prepolymer synthesis: A certain proportion of SA, AA, PDO and BDO were added into a 250 mL reactor. The catalysts were antimony ethylene glycol and tetrabutyl titanate, and the molar ratio of acid to alcohol was 1:1.1.

[0013] (2) Set the heating temperature to 165 °C, react for 30 min, then raise the temperature to 195 °C for 30 min, and continue to raise the temperature to 215 °C. Control the esterification reaction for 90 min, and no more water evaporates during the reaction. During the above process, nitrogen is continuously introduced to keep the reaction system in a stable nitrogen atmosphere.

[0014] (3) Cross-linking and chain extension: Add trimethylolpropane with the corresponding total system mass fraction (0.5wt%, 0.8wt%, 1wt%, 3wt%, 5wt%), add an appropriate amount of tetrabutyl titanate catalyst, continue the reaction for 60 min, and finally obtain the product copolyester.

[0015] (4) Aqueous chain extension: The obtained copolyester was heated to 235 °C, and dimethylolpropionic acid was added with the corresponding total system mass fraction (1wt%, 3wt%, 5wt%, 7wt%), and an appropriate amount of tetrabutyl titanate catalyst was added dropwise, and the reaction was continued for 60 min.

[0016] (5) Vacuum polycondensation: vacuum degree <100Pa, vacuum polycondensation for 60 min, the reaction is completed, and the final product, a water-based biodegradable adhesive, is obtained. In addition, the TMP-DMPA-based water-based biodegradable adhesive is coated on a substrate and cured at 50°C, and degraded under aerobic conditions of composting for 90 days. The water-based biodegradable adhesive based on TMP-DMPA of the present invention has excellent water-based processability and excellent biodegradability, and also solves the problems of poor environmental protection, high cost, low degradability, and complex preparation process of existing common adhesives.

[0017] As a further embodiment of the present invention, the molar ratio of the raw material dibasic acid to diol is 1:1.1, the amount of catalyst ethylene glycol antimony and tetrabutyl titanate is 0.1wt% of the total weight of acid and alcohol, and the amount of catalyst tetrabutyl titanate used in TMP cross-linking chain extension and DMPA aqueous chain extension reaction is 0.2g.

[0018] As a further embodiment of the present invention, a method for preparing a polyester water-based biodegradable adhesive film comprises weighing the water-based biodegradable adhesive, coating it on a substrate, and curing it at 50° C. to form a cross-linked network.

[0019] In the present invention, the 180° peel strength of the TMP-DMPA water-based biodegradable adhesive is 40.67 N / mm, the single-twist shear strength is 62.55 Kpa, the strength retention rate after immersion in water can reach 82.5%, and the biodegradability rate of composting for 90 days is 90.1% (relative to cellulose).

[0020] The present invention has the following beneficial effects: the adhesive of the present invention uses bio-based dibasic acid (succinic acid, adipic acid) and diol (1,3-propylene glycol, 1,4-butanediol) as the polycondensation main chain, and constructs a three-dimensional cross-linked network by introducing trimethylolpropane (TMP), which significantly improves the cohesive strength and heat resistance of the adhesive layer. At the same time, dimethylolpropionic acid (DMPA) is used as a water-based functional monomer, and its carboxylic acid group is used to achieve self-emulsification dispersion, avoiding the interface weakening problem of traditional surfactants; the trihydroxy branched structure (neopentyl skeleton) of TMP gives the adhesive excellent anti-crystallization and flexibility, and the ionization characteristics of DMPA not only ensure the stability of the water-based system, but also accelerate the degradation process by catalyzing the hydrolysis of ester bonds. The adhesive has both the mechanical properties of petroleum-based products and the environmental protection of bio-based materials, with a VOC emission of <50 g / L, and can be widely used in food packaging, medical materials, electronic devices and other fields. The present invention solves the long-term contradiction between environmental toxicity, degradability and mechanical properties of traditional adhesives, and has the feasibility of industrial production and cost competitiveness.

[0021] In order to more clearly illustrate the structural features and effects of the present invention, the present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic diagram of the reaction principle of the polyester type water-based biodegradable adhesive of the present invention. DETAILED DESCRIPTION

[0023] The present invention will be further explained below in conjunction with the accompanying drawings and related knowledge, and described clearly and completely. Obviously, the described application is only a part of the embodiments of the present invention, rather than all the embodiments.

[0024] In the following embodiments, the testing methods of technical parameters are as follows: The 180° peel strength under normal conditions is measured according to the Test Method for Peel Strength of Adhesive Tapes (GB / T 2792-2014).

[0025] The single joint shear strength under normal conditions is measured according to GB / T 33334-2016 "Test method for tensile shear strength of adhesive single joints" The number average molecular weight was determined using a 410 gel permeation chromatograph from Waters, USA, with tetrahydrofuran as the mobile phase, a flow rate of 1 mL / min, and polystyrene as the standard sample.

[0026] The 90-day biodegradation rate is determined according to "Determination of the ultimate aerobic biodegradability of materials under controlled composting conditions - Method for measuring the released carbon dioxide - Part 1: General method" (GB / T 19277.1-2011).

[0027] The raw materials used in the present invention are all commercially available and are environmentally friendly raw materials with green development prospects; trimethylolpropane (AR 98%), density is 1.116 g / ml, melting point is 56 ℃-60 ℃, boiling point is 295.7 ℃. Dimethylolpropionic acid (AR 98%), density is 1.3 g / cm 3 , melting point is 178 ℃-187 ℃, boiling point is 336.7 ℃.

[0028] Example 1 Preparation of TMP-based polyester biodegradable adhesive, the specific operation is as follows: Step 1: Synthesis of prepolymer.

[0029] In a 250 mL three-necked flask, add 22.8 g PDO, 27 g BDO, 39 g SA, 48.2 g AA and 1.37 g catalyst (ethylene glycol antimony + tetrabutyl titanate); The heating temperature was set at 165 °C. After reacting for 30 min, the temperature was raised to 195 °C for 30 min, and then the temperature was raised to 215 °C. The esterification reaction was controlled for 90 min, and no water was evaporated during the reaction. Nitrogen was continuously introduced during the above process to keep the reaction system in a stable nitrogen atmosphere. Step 2: Cross-linking structure chain extension reaction.

[0030] Keeping the temperature constant, add 0.5% of the total system mass of trimethylolpropane (0.685 g) and 0.2 g of tetrabutyl titanate catalyst; The reaction was carried out at 215 °C for 60 min. After the reaction was completed, a vacuum pump was connected to evacuate for 60 min, and then the reaction was stopped to obtain the product polyester biodegradable adhesive. The performance indicators of the TMP-based biodegradable adhesive are shown in Table 1.

[0031] Example 2 Preparation of TMP-based polyester biodegradable adhesive, the specific operation is as follows: Step 1: Synthesis of prepolymer.

[0032] In a 250 mL three-necked flask, add 22.8 g PDO, 27 g BDO, 39 g SA, 48.2 g AA and 1.37 g catalyst (ethylene glycol antimony + tetrabutyl titanate); The heating temperature was set at 165 °C. After 30 min of reaction, the temperature was raised to 195 °C for 30 min, and then the temperature was raised to 215 °C. The esterification reaction was controlled for 90 min, and no water was evaporated during the reaction. Nitrogen was continuously introduced during the above process to keep the reaction system in a stable nitrogen atmosphere. Step 2: Cross-linking structure chain extension reaction.

[0033] Keeping the temperature constant, add 0.8% of the total system mass of trimethylolpropane (1.096 g) and 0.2 g of tetrabutyl titanate catalyst; The reaction was carried out at 215°C for 60 min. After the reaction was completed, a vacuum pump was connected to evacuate for 60 min, and then the reaction was stopped to obtain a polyester biodegradable adhesive product.

[0034] The performance indicators of TMP-based biodegradable adhesive are shown in Table 1.

[0035] Example 3 Preparation of TMP-based polyester biodegradable adhesive, the specific operation is as follows: Step 1: Synthesis of prepolymer.

[0036] In a 250 mL three-necked flask, add 22.8 g PDO, 27 g BDO, 39 g SA, 48.2 g AA and 1.37 g catalyst (ethylene glycol antimony + tetrabutyl titanate); The heating temperature was set at 165 °C. After 30 min of reaction, the temperature was raised to 195 °C for 30 min, and then the temperature was raised to 215 °C. The esterification reaction was controlled for 90 min, and no water was evaporated during the reaction. Nitrogen was continuously introduced during the above process to keep the reaction system in a stable nitrogen atmosphere. Step 2: Cross-linking structure chain extension reaction.

[0037] Keeping the temperature constant, add 1.0% of the total system mass of trimethylolpropane (1.37 g) and 0.2 g of tetrabutyl titanate as catalyst; The reaction was carried out at 215°C for 60 min. After the reaction was completed, a vacuum pump was connected to evacuate for 60 min, and then the reaction was stopped to obtain a polyester biodegradable adhesive product.

[0038] The performance indicators of TMP-based biodegradable adhesive are shown in Table 1.

[0039] Example 4 Preparation of TMP-based polyester biodegradable adhesive, the specific operation is as follows: Step 1: Synthesis of prepolymer.

[0040] In a 250 mL three-necked flask, add 22.8 g PDO, 27 g BDO, 39 g SA, 48.2 g AA and 1.37 g catalyst (ethylene glycol antimony + tetrabutyl titanate); The heating temperature was set at 165 °C. After 30 min of reaction, the temperature was raised to 195 °C for 30 min, and then the temperature was raised to 215 °C. The esterification reaction was controlled for 90 min, and no water was evaporated during the reaction. Nitrogen was continuously introduced during the above process to keep the reaction system in a stable nitrogen atmosphere. Step 2: Cross-linking structure chain extension reaction.

[0041] Keeping the temperature constant, add 3.0% of the total system mass of trimethylolpropane (4.11 g) and 0.2 g of tetrabutyl titanate catalyst; The reaction was carried out at 215°C for 60 min. After the reaction was completed, a vacuum pump was connected to evacuate for 60 min, and then the reaction was stopped to obtain a polyester biodegradable adhesive product.

[0042] The performance indicators of TMP-based biodegradable adhesive are shown in Table 1.

[0043] Example 5 Preparation of TMP-based polyester biodegradable adhesive, the specific operation is as follows: Step 1: Synthesis of prepolymer.

[0044] In a 250 mL three-necked flask, add 22.8 g PDO, 27 g BDO, 39 g SA, 48.2 g AA and 1.37 g catalyst (ethylene glycol antimony + tetrabutyl titanate); The heating temperature was set at 165 °C. After 30 min of reaction, the temperature was raised to 195 °C for 30 min, and then the temperature was raised to 215 °C. The esterification reaction was controlled for 90 min, and no water was evaporated during the reaction. Nitrogen was continuously introduced during the above process to keep the reaction system in a stable nitrogen atmosphere. Step 2: Cross-linking structure chain extension reaction.

[0045] Keeping the temperature constant, add 5.0% of the total system mass of trimethylolpropane (6.85 g) and 0.2 g of tetrabutyl titanate as catalyst; The reaction was carried out at 215°C for 60 min. After the reaction was completed, a vacuum pump was connected to evacuate for 60 min, and then the reaction was stopped to obtain a polyester biodegradable adhesive product.

[0046] The performance indicators of TMP-based biodegradable adhesive are shown in Table 1.

[0047] Example 6 Preparation of TMP-DMPA-based water-based biodegradable adhesive, the specific operation is as follows: Step 1: Synthesis of prepolymer.

[0048] In a 250 mL three-necked flask, add 22.8 g PDO, 27 g BDO, 39 g SA, 48.2 g AA and 1.37 g catalyst (ethylene glycol antimony + tetrabutyl titanate); The heating temperature was set at 165 °C. After 30 min of reaction, the temperature was raised to 195 °C for 30 min, and then the temperature was raised to 215 °C. The esterification reaction was controlled for 90 min, and no water was evaporated during the reaction. Nitrogen was continuously introduced during the above process to keep the reaction system in a stable nitrogen atmosphere. Step 2: Cross-linking structure chain extension reaction.

[0049] Keeping the temperature constant, add 3.0% of the total system mass of trimethylolpropane (4.11 g) and 0.2 g of tetrabutyl titanate catalyst; The reaction was carried out at 215°C for 60 min. After the reaction was completed, a vacuum pump was connected to evacuate for 60 min to obtain the product copolyester.

[0050] Step 3: Water-based chain extension reaction After the polycondensation was completed, the obtained copolyester was heated to 235 °C, and 1.0% of the total system mass of dimethylolpropionic acid (1.37 g) and 0.2 g of tetrabutyl titanate as a catalyst were added; The reaction was carried out at 235 °C for 60 min. After the reaction was completed, a vacuum pump was connected and vacuum was drawn for 60 min to obtain the final product, a water-based biodegradable adhesive.

[0051] The performance indicators of TMP-DMPA based water-based biodegradable adhesive are shown in Table 1.

[0052] Example 7 Preparation of TMP-DMPA-based water-based biodegradable adhesive, the specific operation is as follows: Step 1: Synthesis of prepolymer.

[0053] In a 250 mL three-necked flask, add 22.8 g PDO, 27 g BDO, 39 g SA, 48.2 g AA and 1.37 g catalyst (ethylene glycol antimony + tetrabutyl titanate); The heating temperature was set at 165 °C. After 30 min of reaction, the temperature was raised to 195 °C for 30 min, and then the temperature was raised to 215 °C. The esterification reaction was controlled for 90 min, and no water was evaporated during the reaction. Nitrogen was continuously introduced during the above process to keep the reaction system in a stable nitrogen atmosphere. Step 2: Cross-linking structure chain extension reaction.

[0054] Keeping the temperature constant, add 3.0% of the total system mass of trimethylolpropane (4.11 g) and 0.2 g of tetrabutyl titanate catalyst; The reaction was carried out at 215°C for 60 min. After the reaction was completed, a vacuum pump was connected to evacuate for 60 min to obtain the product copolyester.

[0055] Step 3: Water-based chain extension reaction After the polycondensation was completed, the obtained copolyester was heated to 235 °C, and 3.0% of the total system mass of dimethylolpropionic acid (4.11 g) and 0.2 g of tetrabutyl titanate as a catalyst were added; The reaction was carried out at 235 °C for 60 min. After the reaction was completed, a vacuum pump was connected and vacuum was drawn for 60 min to obtain the final product, a water-based biodegradable adhesive.

[0056] The performance indicators of TMP-DMPA based water-based biodegradable adhesive are shown in Table 1.

[0057] Example 8 Preparation of DMPA-based water-based biodegradable adhesive, the specific operation is as follows: Step 1: Synthesis of prepolymer.

[0058] In a 250 mL three-necked flask, add 22.8 g PDO, 27 g BDO, 39 g SA, 48.2 g AA and 1.37 g catalyst (ethylene glycol antimony + tetrabutyl titanate); The heating temperature was set at 165 °C. After 30 min of reaction, the temperature was raised to 195 °C for 30 min, and then the temperature was raised to 215 °C. The esterification reaction was controlled for 90 min, and no water was evaporated during the reaction. Nitrogen was continuously introduced during the above process to keep the reaction system in a stable nitrogen atmosphere. Step 2: Cross-linking structure chain extension reaction.

[0059] Keeping the temperature constant, add 3.0% of the total system mass of trimethylolpropane (4.11 g) and 0.2 g of tetrabutyl titanate catalyst; The reaction was carried out at 215°C for 60 min. After the reaction was completed, a vacuum pump was connected to evacuate for 60 min to obtain the product copolyester.

[0060] Step 3: Water-based chain extension reaction After the polycondensation was completed, the obtained copolyester was heated to 235 °C, and 5.0% of the total system mass of dimethylolpropionic acid (6.85 g) and 0.2 g of tetrabutyl titanate as a catalyst were added; The reaction was carried out at 235 °C for 60 min. After the reaction was completed, a vacuum pump was connected and vacuum was drawn for 60 min to obtain the final product, a water-based biodegradable adhesive.

[0061] The performance indicators of TMP-DMPA based water-based biodegradable adhesive are shown in Table 1.

[0062] Example 9 Preparation of TMP-DMPA-based water-based biodegradable adhesive, the specific operation is as follows: Step 1: Synthesis of prepolymer.

[0063] In a 250 mL three-necked flask, add 22.8 g PDO, 27 g BDO, 39 g SA, 48.2 g AA and 1.37 g catalyst (ethylene glycol antimony + tetrabutyl titanate); The heating temperature was set at 165 °C. After the reaction lasted for 30 min, the temperature was raised to 195 °C for 30 min, and then the temperature was raised to 215 °C. The esterification reaction was controlled for 90 min, and no water was evaporated during the reaction. Nitrogen was continuously introduced during the above process to keep the reaction system in a stable nitrogen atmosphere.

[0064] Step 2: Cross-linking structure chain extension reaction.

[0065] Keeping the temperature constant, add 3.0% of the total system mass of trimethylolpropane (4.11 g) and 0.2 g of tetrabutyl titanate catalyst; The reaction was carried out at 215 °C for 60 min. After the reaction was completed, a vacuum pump was connected to evacuate for 60 min to obtain the product copolyester. Step 3: Water-based chain extension reaction After the polycondensation was completed, the obtained copolyester was heated to 235 °C, and 7.0% of the total system mass of dimethylolpropionic acid (9.59 g) and 0.2 g of tetrabutyl titanate as a catalyst were added; The reaction was carried out at 235 °C for 60 min. After the reaction was completed, a vacuum pump was connected and vacuum was drawn for 60 min to obtain the final product, a water-based biodegradable adhesive.

[0066] The performance indicators of TMP-DMPA based water-based biodegradable adhesive are shown in Table 1.

[0067] Table 1 Main performance indicators of water-based biodegradable adhesives based on TMP-DMPA Number average molecular weight 180° peel strength N / mm Single shear strength MPa Strength retention after immersion in water% 90-day biodegradation rate% Example 1 15023 3.19 4.12 / 92.0 Example 2 17432 9.93 9.33 / 91.8 Example 3 19123 16.20 19.55 / 91.5 Example 4 23462 29.34 31.01 / 91.1 Example 5 21023 25.87 28.46 / 91.2 Example 6 24565 31.46 36.72 81.6 90.6 Example 7 25763 34.23 45.89 81.9 90.4 Example 8 27158 37.45 53.37 82.3 90.3 Example 9 28004 40.67 62.55 82.5 90.1 As can be seen from the results of the examples, the water-based biodegradable adhesive based on TMP-DMPA of the present invention is prepared by esterification reaction at high temperature using bio-based dibasic acid and diol as raw materials, and then by introducing cross-linked structure trimethylolpropane and water-based structure dimethylolpropionic acid to carry out chain extension reaction. The water-based biodegradable adhesive of the present invention has excellent bonding performance and biodegradable performance, and solves the problems of poor environmental protection, high cost, easy combustion, and complex preparation process of current common adhesives. Among them, in particular, the strength of the composite system (36.72-62.55MPa) is up to 200% higher than that of the single TMP system (4.12-31.01MPa), solving the core problem of insufficient strength of bio-based adhesives.

[0068] The technical principle of the present invention is described above in combination with the specific embodiments, which are only preferred implementations of the present invention. The protection scope of the present invention is not limited to the above embodiments, and all technical solutions under the idea of ​​the present invention belong to the protection scope of the present invention. Those skilled in the art can think of other specific implementations of the present invention without creative work, and these methods will fall within the protection scope of the present invention.

Claims

1. A polyester biodegradable adhesive, characterized in that: The raw materials include, by mole percentage, 1:1.1 bio-based dibasic acid and diol; and 0.5% to 5.0% of trimethylolpropane and 1.0% to 7.0% of dimethylolpropionic acid, based on the total weight of the bio-based dibasic acid and diol.

2. A polyester biodegradable adhesive as claimed in claim 1, characterized in that: The trimethylolpropane is a trifunctional polyol having three hydroxyl groups, and the three hydroxyl groups (-OH) participate in polycondensation to form a three-dimensional network structure; its structural formula is as follows: 。 3. A polyester biodegradable adhesive as claimed in claim 2, characterized in that: The dimethylol propionic acid is a diol containing a carboxylic acid group, and two hydroxyl groups extend the chain; the carboxylic acid (-COOH) introduces an ionic group, and its structural formula is as follows: 。 4. A polyester biodegradable adhesive as claimed in claim 3, characterized in that: The invention also comprises a catalyst, wherein the catalyst is antimony ethylene glycol and tetrabutyl titanate; the bio-based dibasic acid is SA and AA; and the diol is PDO and BDO.

5. A method for preparing the polyester water-based biodegradable adhesive as claimed in claim 1, characterized in that: The following steps are involved: Prepolymer synthesis: bio-based dibasic acid and diol were added into a 250 mL reactor. The catalysts were ethylene glycol antimony and tetrabutyl titanate. The molar ratio of bio-based dibasic acid to diol was 1:1.

1. Cross-linking and chain extension: add trimethylolpropane or dimethylolpropionic acid in the corresponding total system mass fraction, dropwise add an appropriate amount of tetrabutyl titanate catalyst, and continue the reaction for 60 min; vacuumize to obtain the product polyester-type biodegradable adhesive.

6. The method for preparing a polyester biodegradable adhesive according to claim 5, characterized in that: The method comprises the following steps: prepolymer synthesis: adding bio-based dibasic acid and diol into a 250 mL reactor, wherein the catalysts are ethylene glycol antimony and tetrabutyl titanate, and the molar ratio of the bio-based dibasic acid to the diol is 1:1.1; setting the heating temperature to 165°C, reacting for 30 min, raising the temperature to 195°C for 30 min, and continuing to raise the temperature to 215°C, controlling the esterification reaction for 90 min, and no water is evaporated during the reaction, and continuously introducing nitrogen during the above process to keep the reaction system in a stable nitrogen atmosphere; Cross-linking and chain extension: add 0.5wt%-5wt% of trimethylolpropane in the corresponding total system mass fraction, dropwise add an appropriate amount of tetrabutyl titanate catalyst, continue the reaction for 60 min, and finally obtain the product copolyester; Water-based chain extension: the obtained copolyester is heated to 235 °C, 1wt%-7wt% of dihydroxymethylpropionic acid is added, an appropriate amount of tetrabutyl titanate catalyst is added dropwise, and the reaction is continued for 60 min; vacuum polycondensation: the vacuum degree is <100Pa, and the vacuum polycondensation is carried out for 60 min. The reaction is terminated to obtain the final product, a water-based biodegradable adhesive.

7. The method for preparing a polyester biodegradable adhesive according to claim 6, characterized in that: The trimethylolpropane is added into the corresponding total system at any one of 0.5wt%, 0.8wt%, 1wt%, 3wt%, and 5wt% mass fraction.

8. The method for preparing a polyester biodegradable adhesive according to claim 7, characterized in that: The dimethylolpropionic acid is added into the corresponding total system at any one of 1wt%, 3wt%, 5wt% and 7wt%.

9. The method for preparing a polyester biodegradable adhesive according to claim 8, characterized in that: The amount of the catalyst tetrabutyl titanate used in the trimethylolpropane cross-linking chain extension and dimethylolpropionic acid aqueous chain extension reaction is 0.2 g.

10. A method for preparing an adhesive film using the polyester water-based biodegradable adhesive according to claim 9, characterized in that: The polyester water-based biodegradable adhesive was weighed and coated on the substrate and cured at 50°C to form a cross-linked network.

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