A biobased degradable polyurethane pressure sensitive adhesive and a method of making the same

Abstract

The application discloses a kind of biobased degradable polyurethane pressure sensitive adhesive and its preparation method, the preparation method of the biobased degradable polyurethane pressure sensitive adhesive includes the following steps: S1, measured biobased polycaprolactone dihydric alcohol, trimethylolpropane monoallyl ether, diisocyanate, catalyst 1, solvent are put into reaction device, under the condition of stirring at 80~85 ℃, isocyanate group content in system is measured during reaction process, when its content is less than 0.5%, isocyanate group is capped by adding capping agent until isocyanate group is completely reacted, remove solvent, obtain polyurethane intermediate;S2, measured polyurethane intermediate and glycine ester are reacted under the action of catalyst 2 at 70±5 ℃ to obtain polyurethane pressure sensitive adhesive by Michael addition reaction.The biobased degradable polyester type pressure sensitive adhesive disclosed in the application can simultaneously consider excellent initial adhesion, holding adhesion and high degradation rate.

Description

Technical Field

[0001] This invention relates to the field of biodegradable materials technology, specifically to a bio-based biodegradable polyurethane pressure-sensitive adhesive and its preparation method. Background Technology

[0002] Pressure-sensitive adhesives (PSAs), as viscoelastic adhesives, can adhere items to various surfaces with the application of pressure. Furthermore, if the bonded surfaces are damaged, the adhesive does not contaminate them. Due to their low cost and ease of use, they are widely used in electronics, packaging, medical, and automotive industries. Currently, commercially available PAs include acrylic, epoxy, silicone, and polyurethane types. Among them, polyurethane (PU) PAs are widely used in industrial production and daily life due to their excellent adhesion, flexibility, chemical resistance, and designability. However, traditional polyurethanes use petroleum-based polyols (such as polyethers and polyester polyols) and polyisocyanates (such as MDI and TDI) as raw materials. Their production is highly dependent on non-renewable fossil resources. Petroleum-based raw materials are non-renewable resources with limited reserves, and their extraction and utilization are accompanied by high carbon emissions. This dependence on fossil resources has become a major issue for the sustainable development of the industry. In addition, the synthesis process may release volatile organic compounds (VOCs), which have negative impacts on the environment and human health. In addition, the molecular structure of petroleum-based polyurethane pressure-sensitive adhesive is stable and difficult to degrade in the natural environment, making its waste difficult to dispose of.

[0003] As bio-based materials have become a research hotspot due to their renewability, low carbon emissions, and environmental friendliness, biodegradable bio-based polyurethane pressure-sensitive adhesives represent a crucial direction for the green transformation of pressure-sensitive adhesives. Some raw materials for bio-based polyurethane pressure-sensitive adhesives can be obtained from plants, crops, agricultural waste, or microbial fermentation products, effectively replacing petroleum-based raw materials, breaking the dependence on non-renewable resources, reducing the carbon footprint of the production process, and aligning with the development direction of low-carbon industries. Furthermore, bio-based polyurethane possesses excellent biodegradability, naturally decomposing in soil, freshwater, or compost environments, completely solving the environmental pollution problems associated with traditional pressure-sensitive adhesives. Bio-based biodegradable pressure-sensitive adhesives effectively overcome the resource and environmental dilemmas of traditional petroleum-based pressure-sensitive adhesives by combining resource renewability and environmental degradability, expanding the application boundaries of pressure-sensitive adhesives in high-end environmental protection fields. However, currently available polyurethane pressure-sensitive adhesives struggle to simultaneously achieve high degradability and excellent pressure-sensitive and tack properties, hindering their application and development. Summary of the Invention

[0004] Based on this, the present invention aims to overcome at least one defect of the prior art and provide a bio-based biodegradable polyester pressure-sensitive adhesive that can simultaneously achieve excellent initial tack, holding power and high degradation rate.

[0005] The technical solution is as follows: A method for preparing a bio-based biodegradable polyurethane pressure-sensitive adhesive includes the following steps: S1. The measured amounts of bio-based polycaprolactone diol, trimethylolpropane monoallyl ether, diisocyanate, catalyst 1, and solvent are added to the reaction apparatus and reacted under stirring at 80~85℃. During the reaction, the content of isocyanate groups in the system is measured. When the content is lower than 0.5%, a capping agent is added to cap the isocyanate groups until the isocyanate groups react completely. The solvent is then removed to obtain a polyurethane intermediate. S2. The measured polyurethane intermediate and glycine ester were subjected to a Michael addition reaction at 70±5℃ under the action of catalyst 2 to obtain polyurethane pressure-sensitive adhesive. The bio-based polycaprolactone diol has a number-average molecular weight of 1000-3000, and the molar ratio of the bio-based polycaprolactone diol, trimethylolpropane monoallyl ether, and diisocyanate is (0.525-0.66):(0.42-0.55):1, wherein the molar ratio of the bio-based polycaprolactone diol to trimethylolpropane monoallyl ether is (1.5-1):1. The amount of catalyst 1 added is 0.1-1 wt% of the total mass of the bio-based polycaprolactone diol, trimethylolpropane monoallyl ether, and diisocyanate, and the amount of solvent added is 100-200 wt% of the total mass of the bio-based polycaprolactone diol, trimethylolpropane monoallyl ether, and diisocyanate. wt%; the molar ratio of the polyurethane intermediate to the glycine ester is 1:(0.95~0.98), and the amount of catalyst 2 is 10~20% of the molar amount of glycine ester.

[0006] The polyurethane pressure-sensitive adhesive of this application is mainly prepared from bio-based polycaprolactone diol, trimethylolpropane monoallyl ether, and diisocyanate obtained from corn as raw materials to obtain polyurethane intermediates, which are then reacted with glycine esters via Michael addition reaction to obtain the polyurethane pressure-sensitive adhesive. The bio-based polycaprolactone diol is used as a raw material to replace the diols from petrochemical products, which reduces dependence on petrochemical products, meets the requirements of sustainable development, has a high degree of environmental friendliness, and possesses excellent degradation ability, giving the pressure-sensitive adhesive excellent biodegradability. Simultaneously, the bio-based polycaprolactone diol, as a soft segment material, imparts good flexibility, adhesive toughness, and substrate wetting ability to the pressure-sensitive adhesive; the diisocyanate, as a hard segment material, imparts good adhesive strength and cohesive strength to the pressure-sensitive adhesive; and the trimethylolpropane monoallyl ether, as a small molecule chain extender, introduces side-branched double bonds into the linear polyurethane through chain extension modification, providing active sites for subsequent reactions and realizing the transformation of the molecular structure from linear to a controllable branched morphology. The carbon-carbon double bonds on the molecular side chain can undergo a Michael addition reaction with the biomass-based derivative—glycine ester, introducing ester functional groups into the side chain structure, thus enabling polyurethane materials to possess both excellent pressure-sensitive properties and substrate interface adhesion performance.

[0007] Specifically, polycaprolactone diol imparts excellent biodegradability to polyurethane pressure-sensitive adhesives primarily due to the following reasons: the biodegradability of polycaprolactone diol relies on the action of specific enzymes such as esterases and lipases secreted by microorganisms. These enzymes can precisely identify and attack the ester bonds on the main chain of the molecule, catalyzing their cleavage into small molecular fragments (such as caprolactone monomers and short-chain fatty acids). These small molecular fragments can be absorbed and metabolized by microorganisms, ultimately converting into CO2 and H2O, completing the entire biodegradation process. Furthermore, the main chain of polycaprolactone diol is a linear aliphatic carbon chain and does not contain aromatic compounds. Rigid groups such as rings have good molecular chain flexibility, relatively low packing density, and a relatively loose structure. This structure allows water, microorganisms, or enzymes to penetrate into the material more easily, fully contact and act on the ester bond sites, accelerating the degradation process. The main chain of polycaprolactone diol is composed of repeating aliphatic ester bonds -COO-. Ester bonds are polar functional groups with weak chemical stability and are very prone to hydrolysis. In acidic or alkaline environments or under humid conditions, ester bonds will break to generate carboxylic acids and alcohols, causing the long polymer chain to gradually degrade into low molecular weight oligomers, and finally decompose into small molecule compounds.

[0008] Introducing biomass-based glycine esters into the side chains endows polyurethane pressure-sensitive adhesives with excellent initial tack properties. This is primarily because the primary amino group (-NH2) in the glycine ester molecule is a strong nucleophile, capable of undergoing a Michael addition reaction with the unsaturated double bonds of the polyurethane side chains. The glycine ester molecule contains an ester group (-COO-), and the secondary amino group (-NH-) generated after the reaction is also a strongly polar group. These polar groups form hydrogen bonds and dipole-dipole interactions with polar groups on the surface of the adherends (such as hydroxyl groups in wood, hydroxyl groups in metal oxides, and carboxyl groups in plastics), significantly enhancing interfacial adsorption and allowing the adhesive to firmly "anchor" itself to the adherend surface upon contact. The polar groups also increase the surface tension of the adhesive, optimizing its wetting and spreading ability, further strengthening the initial adhesion effect. The ester bonds in the side chains are easily hydrolyzed and enzymatically degraded, serving as the main initiation sites for the secondary degradation of the materials in this system. Under composting conditions, high temperatures promote the nucleophilic attack of water molecules on the carbonyl carbon of esters, causing chemical hydrolysis of the ester bond. Microbial esterases and lipases specifically catalyze this reaction, making enzymatic hydrolysis the primary degradation pathway with a higher kinetic rate. The steric hindrance of ester bonds distributed on the side chains is weak, making them more easily acted upon and preferentially broken, thus causing the side groups to detach from the main chain. This system belongs to a nonlinear polyurethane with controllable branching. Compared to a purely linear structure, the molecular chain stacking is more loose, the matrix free volume is larger, and the permeation resistance of water, microorganisms, and hydrolytic enzymes is significantly reduced. Simultaneously, the branched structure further increases the intermolecular gaps, accelerating the diffusion of degradation media into the material interior, thus macroscopically accelerating the overall degradation process.

[0009] Furthermore, the glycine ester is one or more of glycine ethyl ester, glycine butyl ester, glycine hexyl ester, or glycine octyl ester.

[0010] Furthermore, the glycine ester is prepared by esterification of glycine and C2-C8 short-chain alcohol.

[0011] Furthermore, the catalyst 1 is stannous octoate, and the catalyst 2 can be a weakly basic small molecule such as triethylamine, N,N-diisopropylethylamine (DIPEA), 1,8-diazabicyclo[5.4.0]undec-7-ene, or pyridine.

[0012] Furthermore, the diisocyanate is hexamethylene diisocyanate or isophorone diisocyanate.

[0013] Furthermore, the capping agent is sec-butanol.

[0014] Furthermore, the amount of the capping agent is 1 to 5% of the amount of diisocyanate.

[0015] Furthermore, the bio-based polycaprolactone diol underwent the following pretreatment before the reaction: constant temperature dehydration for 2 h under vacuum of 0.01~0.05 kPa and temperature of 105~120 ℃, so that the moisture content of the material was reduced to below 50 ppm.

[0016] This application also discloses a bio-based biodegradable polyurethane pressure-sensitive adhesive prepared by the aforementioned preparation method.

[0017] Furthermore, the degradation rate of the bio-based biodegradable polyurethane pressure-sensitive adhesive is not less than 90%.

[0018] The beneficial effects of this invention are as follows: The polyurethane pressure-sensitive adhesive prepared by this invention possesses multiple advantages. This product uses corn-based bio-based polycaprolactone diol as the core raw material, replacing petrochemical raw materials with bio-based raw materials, reducing petrochemical resource consumption, and making the raw material system green and sustainable. By introducing side-linked double bonds through trimethylolpropane monoallyl ether chain extension, the linear structure of polyurethane is transformed into a branched structure with controllable branching, retaining the active sites required for subsequent modification while effectively improving the adhesive's cohesive strength, tear resistance, and bonding durability. In terms of performance, the synergistic effect of soft and hard segments endows the material with excellent flexibility, bonding strength, and substrate wetting ability; after Michael addition with glycine ethyl ester, the molecular polarity is significantly enhanced, and the initial tack, interfacial adhesion performance, and pressure-sensitive properties are greatly improved through hydrogen bonding and dipole interactions. Furthermore, both the main and side chains of the material contain easily hydrolyzed and enzymatically decomposed ester bonds, combined with the loosely structured and controllable branched structure of the molecular chain, allowing for efficient biodegradation in a composting environment, ultimately decomposing into carbon dioxide and water, thus achieving both excellent application performance and environmental friendliness. Attached Figure Description

[0019] Figure 1 The image shows the infrared spectrum of the polyurethane pressure-sensitive adhesive PUA1 from Example 1.

[0020] Figure 1 In the middle of 3000cm -1 ~3600cm -1 There is a broad and strong absorption band at 2850~2930 cm⁻¹, attributed to the stretching vibrations of the NH and -OH bonds in the urethane bond; -1 The methylene band of the polyurethane molecule is located at 1720 cm⁻¹, comprising polycaprolactone, glycine ester, trimethylolpropane monoallyl ether, and diisocyanate; -1 A sharp peak is observed, attributed to the stretching vibration of the carbonyl C=O group; at 1150 cm⁻¹ -1 The characteristic peaks at the specified locations are attributed to the -COC bonds on polycaprolactone. Overall, this indicates the successful synthesis of the polyurethane pressure-sensitive adhesive in Example 1. Detailed Implementation

[0021] To enable those skilled in the art to better understand this solution, the following detailed description is provided in conjunction with specific embodiments. Unless otherwise specified, the process methods used in the embodiments are conventional methods; and unless otherwise specified, the materials used are commercially available.

[0022] The bio-based polycaprolactone diol used in this application is from Hunan Juren Chemical New Material Technology Co., Ltd., glycine ethyl ester is from coconut oil-based glycine ethyl ester of Changsha Puji Biotechnology Co., Ltd., glycine butyl ester is from Shanghai Haohong Biomedical Technology Co., Ltd., glycine hexyl ester is from Shanghai Bide Pharmaceutical Technology Co., Ltd., and glycine octyl ester is from Shanghai Jizhi Biochemical Technology Co., Ltd.

[0023] The bio-based polycaprolactone diol used in this application underwent the following pretreatment before being used to synthesize polyurethane pressure-sensitive adhesive: it was dehydrated at a constant temperature of 0.01~0.05 kPa and 105~120 ℃ for 2 h to reduce the moisture content of the material to below 50 ppm.

[0024] Example 1 A bio-based biodegradable polyurethane pressure-sensitive adhesive, the preparation process of which is as follows: (1) The calculated proportions of bio-based polycaprolactone diol (number average molecular weight of 2000), trimethylolpropane monoallyl ether, hexamethylene diisocyanate, stannous octoate catalyst, and ethyl acetate solvent were added to a reactor equipped with a stirrer, thermometer, condenser, and reflux tube. The stirring was turned on (speed set to 200 rpm), and the reaction was carried out at 80~85℃ to synthesize a polyurethane intermediate. The molar ratio of bio-based polycaprolactone diol, trimethylolpropane monoallyl ether, and hexamethylene diisocyanate was 0.63:0.42:1. The amount of stannous octoate catalyst added was 0.2 wt% of the total mass of bio-based polycaprolactone diol, trimethylolpropane monoallyl ether, and hexamethylene diisocyanate. The amount of ethyl acetate solvent added was 100 wt% of the total mass of bio-based polycaprolactone diol, trimethylolpropane monoallyl ether, and hexamethylene diisocyanate. The isocyanate group content in the system is monitored using the n-butyldiamine method. When the required concentration is reached (isocyanate content < 0.5%), the end-capping agent sec-butanol is added (the amount added is 1 mol% of the initial hexamethylene diisocyanate substance) until the isocyanate groups react completely. The unreacted end-capping agent and solvent ethyl acetate are removed by vacuum pumping under reduced pressure, and the polyurethane intermediate is obtained by discharge.

[0025] (2) Michael addition reaction The polyurethane intermediate prepared in step (1) was placed in a reactor at 70±5℃, and glycine ethyl ester (the molar ratio of polyurethane intermediate to glycine ethyl ester was 1:0.95) and triethylamine (the amount added was 15% of the molar amount of glycine ethyl ester) were added. The reaction was carried out in a nitrogen atmosphere until the endpoint was reached to obtain polyurethane pressure-sensitive adhesive PUA-1.

[0026] The synthesis route of polyurethane pressure-sensitive adhesive PUA-1 is as follows:

[0027] Example 2 A bio-based biodegradable polyurethane pressure-sensitive adhesive, the preparation process of which is as follows: (1) The calculated proportions of bio-based polycaprolactone diol (number average molecular weight of 2000), trimethylolpropane monoallyl ether, hexamethylene diisocyanate, stannous octoate catalyst, and ethyl acetate solvent were added to a reactor equipped with a stirrer, thermometer, condenser, and reflux tube. The stirring was turned on (speed set to 200 rpm), and the reaction was carried out at 80~85℃ to synthesize a polyurethane intermediate. The molar ratio of bio-based polycaprolactone diol, trimethylolpropane monoallyl ether, and hexamethylene diisocyanate was 0.55:0.55:1. The amount of stannous octoate catalyst added was 1 wt% of the total mass of bio-based polycaprolactone diol, trimethylolpropane monoallyl ether, and hexamethylene diisocyanate. The amount of ethyl acetate solvent added was 140 wt% of the total mass of bio-based polycaprolactone diol, trimethylolpropane monoallyl ether, and hexamethylene diisocyanate. The isocyanate group content in the system is monitored using the n-butyldiamine method. When the required concentration is reached (isocyanate content < 0.5%), the end-capping agent sec-butanol is added (the amount added is 5 mol% of the initial hexamethylene diisocyanate substance) until the isocyanate groups react completely. The unreacted end-capping agent and solvent ethyl acetate are removed by vacuum pumping under reduced pressure, and the polyurethane intermediate is obtained by discharge.

[0028] (2) Michael addition reaction The polyurethane intermediate prepared in step (1) was placed in a reactor at 70±5℃, and glycine butyl ester (the molar ratio of polyurethane intermediate to glycine butyl ester was 1:0.97) and 1,8-diazabicyclo[5.4.0]undec-7-ene (the amount added was 15% of the molar amount of glycine butyl ester) were added. The reaction was carried out in a nitrogen atmosphere until the endpoint was reached to obtain polyurethane pressure-sensitive adhesive PUA-2.

[0029] Example 3 A bio-based biodegradable polyurethane pressure-sensitive adhesive, the preparation process of which is as follows: (1) The calculated proportions of bio-based polycaprolactone diol (number average molecular weight of 3000), trimethylolpropane monoallyl ether, isophorone diisocyanate, catalyst stannous octoate and solvent ethyl acetate were added to a reactor equipped with a stirrer, thermometer, condenser and reflux tube. The stirring was turned on (speed set to 200 rpm), and the reaction was carried out at 80~85℃ to synthesize polyurethane intermediate. The molar ratio of bio-based polycaprolactone diol, trimethylolpropane monoallyl ether and isophorone diisocyanate was 0.525:0.525:1. The amount of catalyst stannous octoate added was 0.1 wt% of the total mass of bio-based polycaprolactone diol, trimethylolpropane monoallyl ether and isophorone diisocyanate. The amount of solvent ethyl acetate added was 200 wt% of the total mass of bio-based polycaprolactone diol, trimethylolpropane monoallyl ether and isophorone diisocyanate. The isocyanate group content in the system is monitored using the n-butyldiamine method. When the required concentration is reached (isocyanate content < 0.5%), the end-capping agent sec-butanol is added (the amount added is 2 mol% of the initial amount of isophorone diisocyanate) until the isocyanate groups react completely. The unreacted end-capping agent and solvent ethyl acetate are removed by vacuum pumping under reduced pressure, and the polyurethane intermediate is obtained by discharge.

[0030] (2) Michael addition reaction The polyurethane intermediate prepared in step (1) was placed in a reactor at 70±5℃, and glycine hexyl ester (the molar ratio of polyurethane intermediate to glycine hexyl ester was 1:0.96) and N,N-diisopropylethylamine (the amount added was 10% of the molar amount of glycine hexyl ester) were added. The reaction was carried out in a nitrogen atmosphere until the endpoint was reached to obtain polyurethane pressure-sensitive adhesive PUA-3.

[0031] Example 4 A bio-based biodegradable polyurethane pressure-sensitive adhesive, the preparation process of which is as follows: (1) The calculated proportions of bio-based polycaprolactone diol (number average molecular weight of 1000), trimethylolpropane monoallyl ether, isophorone diisocyanate, catalyst stannous octoate and solvent ethyl acetate were added to a reactor equipped with a stirrer, thermometer, condenser and reflux tube. The stirring was turned on (speed set to 200 rpm), and the reaction was carried out at 80~85℃ to synthesize polyurethane intermediate. The molar ratio of bio-based polycaprolactone diol, trimethylolpropane monoallyl ether and isophorone diisocyanate was 0.66:0.44:1. The amount of catalyst stannous octoate added was 0.6 wt% of the total mass of bio-based polycaprolactone diol, trimethylolpropane monoallyl ether and isophorone diisocyanate. The amount of solvent ethyl acetate added was 180 wt% of the total mass of bio-based polycaprolactone diol, trimethylolpropane monoallyl ether and isophorone diisocyanate. The isocyanate group content in the system is monitored using the n-butyldiamine method. When the required concentration is reached (isocyanate content < 0.5%), the end-capping agent sec-butanol is added (the amount added is 3 mol% of the initial amount of isophorone diisocyanate) until the isocyanate groups react completely. The unreacted end-capping agent and solvent ethyl acetate are removed by vacuum pumping under reduced pressure, and the polyurethane intermediate is obtained by discharge.

[0032] (2) Michael addition reaction The polyurethane intermediate prepared in step (1) was placed in a reactor at 70±5℃, and glycine octyl ester (the molar ratio of polyurethane intermediate to glycine octyl ester was 1:0.98) and pyridine (the amount added was 20% of the molar amount of glycine octyl ester) were added. The reaction was carried out in a nitrogen atmosphere until the endpoint was reached to obtain polyurethane pressure-sensitive adhesive PUA-4.

[0033] Comparative Example 1 A polyurethane pressure-sensitive adhesive is prepared in the same way as step (1) of Example 1, except that step (2) is not performed in this comparative example 1.

[0034] Comparative Example 2 A bio-based biodegradable polyurethane pressure-sensitive adhesive, the preparation process of which is as follows: (1) The calculated proportions of bio-based polycaprolactone diol, trimethylolpropane monoallyl ether, hexamethylene diisocyanate, stannous octoate catalyst, and ethyl acetate solvent were added to a reactor equipped with a stirrer, thermometer, condenser, and reflux tube. The stirring was turned on (speed set to 200 rpm), and the reaction was carried out at 80~85℃ to synthesize a polyurethane intermediate. The molar ratio of bio-based polycaprolactone diol, trimethylolpropane monoallyl ether, and hexamethylene diisocyanate was 0.525:0.525:1. The amount of stannous octoate catalyst added was 0.2 wt% of the total mass of bio-based polycaprolactone diol, trimethylolpropane monoallyl ether, and hexamethylene diisocyanate. The amount of ethyl acetate solvent added was 100 wt% of the total mass of bio-based polycaprolactone diol, trimethylolpropane monoallyl ether, and hexamethylene diisocyanate. The isocyanate group content in the system is monitored using the n-butyldiamine method. When the required concentration is reached (isocyanate content < 0.5%), the end-capping agent sec-butanol is added (the amount added is 4 mol% of the initial hexamethylene diisocyanate substance) until the isocyanate groups react completely. The unreacted end-capping agent and solvent ethyl acetate are removed by vacuum pumping under reduced pressure, and the polyurethane intermediate is obtained by discharge.

[0035] (2) The polyurethane intermediate prepared in step (1) is put into a reaction vessel at 70°C, and alanine methyl ester and triethylamine are added in the same amount as glycine ethyl ester in Example 1. The reaction is carried out in a nitrogen atmosphere until the endpoint is reached to obtain polyurethane pressure-sensitive adhesive.

[0036] Comparative Example 3 A polyurethane pressure-sensitive adhesive is prepared in a manner largely the same as in Example 1, except that in Comparative Example 3, an equal amount of 1-allylglycerol ether is used instead of trimethylolpropane monoallyl ether in Example 1.

[0037] Comparative Example 4 A polyurethane pressure-sensitive adhesive is prepared in a manner largely the same as in Example 1, except that the molar ratio of bio-based polycaprolactone diol (number average molecular weight of 2000), trimethylolpropane monoallyl ether, and hexamethylene diisocyanate in Comparative Example 4 is 0.7:0.35:1.

[0038] Comparative Example 5 A polyurethane pressure-sensitive adhesive is prepared in a manner largely the same as in Example 1, except that in Comparative Example 5, an equal amount of bio-based polybutylene terephthalate-adipate is used instead of the bio-based polycaprolactone diol in Example 1.

[0039] Performance testing Peel strength, initial tack, holding power, and biodegradability tests were performed on the pressure-sensitive adhesives described in Examples 1 to 6 and Comparative Examples 1 to 5. The test results are shown in the table below. Specifically, the peel strength test was conducted according to GB / T 2792~2014, using Method 1 with a 180° peel angle; the initial tack test was conducted according to GB / T 4852~2002, using the inclined plane rolling ball method; the holding power test was conducted according to GB / T 4851~2014, using Method A; and the biodegradability test involved placing the pressure-sensitive adhesive sample in a 1 mol / L mixed solution of p-toluenesulfonic acid and tetrahydrofuran (THF) at 60°C, and recording the mass change of the pressure-sensitive adhesive. The tensile testing machine for testing the peel strength of adhesives was purchased from Dongguan Kejian Testing Instruments Co., Ltd. (KJ-1065); the initial tack tester for testing the initial tack properties of adhesives was purchased from Jinan Sanquan Zhongshi Experimental Instruments Co., Ltd. (CNY-1); and the holding power tester for testing the holding power properties of adhesives was purchased from Jinan Sanquan Zhongshi Experimental Instruments Co., Ltd. (CNY-2).

[0040] The test results are shown in the table below.

[0041]

[0042] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the technical solution of the present invention, and are not intended to limit the specific implementation of the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the claims of the present invention should be included within the protection scope of the claims of the present invention.

Claims

1. A method for preparing a bio-based biodegradable polyurethane pressure-sensitive adhesive, characterized in that, Includes the following steps: S1. The measured amounts of bio-based polycaprolactone diol, trimethylolpropane monoallyl ether, diisocyanate, catalyst 1, and solvent are added to the reaction apparatus and reacted under stirring at 80~85℃. During the reaction, the content of isocyanate groups in the system is measured. When the content is lower than 0.5%, a capping agent is added to cap the isocyanate groups until the isocyanate groups react completely. The solvent is then removed to obtain a polyurethane intermediate. S2. The measured polyurethane intermediate and glycine ester were subjected to a Michael addition reaction at 70±5℃ under the action of catalyst 2 to obtain a 100% solid content polyurethane pressure-sensitive adhesive. The bio-based polycaprolactone diol has a number-average molecular weight of 1000-3000; the molar ratio of the bio-based polycaprolactone diol, trimethylolpropane monoallyl ether, and diisocyanate is (0.525-0.66):(0.42-0.55):1; the amount of catalyst 1 added is 0.1-1 wt% of the total mass of the bio-based polycaprolactone diol, trimethylolpropane monoallyl ether, and diisocyanate; the amount of solvent added is 100-200 wt% of the total mass of the bio-based polycaprolactone diol, trimethylolpropane monoallyl ether, and diisocyanate; the molar ratio of the polyurethane intermediate to the glycine ester is 1:(0.95-0.98); and the amount of catalyst 2 is 10-20% of the molar amount of glycine ester.

2. The preparation method according to claim 1, characterized in that, The glycine ester is one or more of glycine ethyl ester, glycine butyl ester, glycine hexyl ester, or glycine octyl ester.

3. The preparation method according to claim 2, characterized in that, The glycine ester is prepared by esterification of glycine and C2-C8 short-chain alcohol.

4. The preparation method according to claim 1, characterized in that, The catalyst 1 is stannous octoate, and the catalyst 2 is one or more of triethylamine, N,N-diisopropylethylamine, 1,8-diazabicyclo[5.4.0]undec-7-ene or pyridine.

5. The preparation method according to claim 1, characterized in that, The diisocyanate is hexamethylene diisocyanate or isophorone diisocyanate.

6. The preparation method according to claim 1, characterized in that, The capping agent is sec-butanol.

7. The preparation method according to claim 6, characterized in that, The amount of the capping agent is 1 to 5% of the amount of diisocyanate.

8. The preparation method according to claim 1, characterized in that, The bio-based polycaprolactone diol underwent the following pretreatment before the reaction: constant temperature dehydration for 2 h under vacuum of 0.01~0.05 kPa and temperature of 105~120 ℃, so that the moisture content of the material was reduced to below 50 ppm.

9. A bio-based biodegradable polyurethane pressure-sensitive adhesive prepared by the preparation method according to any one of claims 1 to 8.

10. The bio-based biodegradable polyurethane pressure-sensitive adhesive according to claim 9, characterized in that, The degradation rate of the bio-based biodegradable polyurethane pressure-sensitive adhesive is not less than 90%.

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