Biodegradable hot melt adhesive with high shear strength as well as preparation method and application thereof

Abstract

The invention relates to a high-shear-strength biodegradable hot melt adhesive as well as a preparation method and application thereof. The hot melt adhesive is prepared by carrying out chemical reaction on a biodegradable high polymer material and epoxy resin through melt blending to form a covalent bonding product, during preparation, a coupling agent or a catalyst can be selectively added to promote the reaction. Wherein the mass ratio of the biodegradable high polymer material to the epoxy resin is (99.9: 0.1)-(80: 20), and the reaction is carried out at 80-200 DEG C for 5-30 minutes. The method is simple in process, green and environment-friendly. The obtained hot melt adhesive does not release volatile organic compounds and is biodegradable, the bonding strength can be remarkably improved only by adding a small amount of epoxy resin, and the maximum lap shear strength can reach 34.37 MPa. The product is suitable for structural or semi-structural bonding in the fields of packaging, electronic and electric appliances, wood manufacturing, building materials, automobiles, traffic and transportation, mechanical manufacturing, new energy, medical treatment and public health, aerospace and the like with high strength requirements.

Description

Technical Field

[0001] This invention relates to the field of adhesive technology, specifically to a hot melt adhesive, and more particularly to a high shear strength biodegradable hot melt adhesive, its preparation method, and its application. Background Technology

[0002] Adhesives are widely used in packaging, furniture, automotive, and electronics industries due to their ability to efficiently bond various materials and distribute stress evenly. However, traditional solvent-based adhesives release volatile organic compounds during production and use, facing increasingly stringent environmental regulations. Against this backdrop, solvent-free and easy-to-use hot melt adhesives have become an important environmentally friendly alternative, with their market size continuing to expand. Currently, commercially available hot melt adhesives are mainly based on petroleum-based polymers such as ethylene-vinyl acetate copolymers, polyolefins, polyamides, or polyurethanes. These materials are difficult to degrade in the natural environment and easily cause white pollution after disposal. Furthermore, these traditional hot melt adhesives mainly rely on physical entanglement and van der Waals forces for bonding, and their lap shear strength is typically below 4 MPa, making it difficult to meet the high reliability requirements of structural or semi-structural bonding in wood processing, composite material preparation, and other applications.

[0003] To balance performance and sustainability, the development of high-performance bio-based or biodegradable hot melt adhesives has become an important research direction. One common technical approach is to physically blend biodegradable polymers such as polylactic acid (PLA) and polycaprolactone (PVC) with tackifying resins and waxes. For example, existing PLA hot melt adhesives are prepared through multi-component melt blending. Although some properties are improved by synergistic effects of the components, they are essentially still physical mixtures and fail to form strong chemical bonds, resulting in an inherent upper limit to the adhesive strength, making them unsuitable for structural load-bearing applications. Another approach is to chemically modify biodegradable polymers, such as by introducing polar groups through chlorination or chlorosulfonation reactions to improve the material's adhesion. This type of modification can increase the lap shear strength to approximately 3 MPa while retaining biodegradability. However, due to the lack of a strong three-dimensional cross-linked network, the cohesive strength of the adhesive layer is still insufficient, and creep is prone to occur under sustained stress. Therefore, it is mostly suitable for non-structural bonding applications.

[0004] Recent cutting-edge research has achieved significant improvements in adhesive properties through ingenious molecular design, introducing special forces into biodegradable frameworks, or utilizing novel polymerization methods. In some systems, the lap shear strength of steel plates has reached 20.6 MPa. These works demonstrate the enormous potential of chemical structure design; however, their synthetic routes are often complex, involving expensive raw materials or sophisticated catalytic systems, resulting in high costs and a significant distance from large-scale industrial applications. In contrast, chain extension modification routes that introduce multifunctional chain extenders to react with the end groups of biodegradable polymers to form moderately branched or cross-linked structures are considered a more promising direction for industrial application. Studies have shown that adding isocyanate chain extenders to specific blend systems can effectively improve molecular weight and interfacial adhesion properties, increasing the lap shear strength to 10 to 25 MPa. This route achieves a better balance between performance, processability, and cost.

[0005] Epoxy resins are widely used in structural adhesives due to their excellent mechanical properties, high bond strength, and high reactivity; however, their traditional curing systems are not biodegradable. If epoxy resin segments could be covalently bonded to biodegradable polymers through chemical reactions, it would be possible to create new materials that combine high bond strength with biodegradability. However, existing technologies rarely report on achieving deep integration of these two components through simple processes to construct truly high-performance biodegradable hot melt adhesive systems suitable for structural bonding. Therefore, developing a novel hot melt adhesive that uses readily available raw materials, employs a simple process, and combines the reinforcing effect of epoxy resin with biodegradability through chemical bonding has become a pressing technical problem in this field. Summary of the Invention

[0006] Technical Problem Solved: This invention addresses the common problem that existing biodegradable hot melt adhesives generally have low bonding strength, making them unsuitable for structural or semi-structural bonding requirements. Traditional high-strength epoxy resin adhesives are also non-biodegradable and do not align with green environmental trends. Furthermore, some high-performance biodegradable adhesives have complex preparation processes and high costs. This invention provides a hot melt adhesive, its preparation method, and applications that achieve covalent bonding between biodegradable polymer materials and epoxy resin through a melt blending process. This invention significantly improves the lap shear strength of hot melt adhesives while maintaining the biodegradability of the materials, making it suitable for structural bonding in fields such as packaging, electronics, wood manufacturing, building materials, automotive and transportation, machinery manufacturing, new energy, medical and health, and aerospace. Simultaneously, the process is simple, the raw materials are readily available, and it possesses good potential for industrial production.

[0007] Technical solution: A high shear strength biodegradable hot melt adhesive is a polymer comprising biodegradable polymer segments, epoxy resin segments, and epoxy functional groups, wherein the biodegradable polymer segments and epoxy resin segments are connected by covalent bonds to form a linear, branched, or cross-linked polymer network structure.

[0008] Based on the total mass of the polymer network, the content of structural units of the epoxy resin segments is from 0.1 wt.% to 20 wt.%.

[0009] The polymer network also includes linker residues or catalysts; based on the total mass of the structural units of the biodegradable polymer segments and epoxy resin segments, the mass fraction of the linker residues or catalysts is 0.1% to 10%.

[0010] The aforementioned biodegradable polymer segments are derived from at least one of the following materials: polypropylene carbonate, chlorinated polypropylene carbonate, chlorosulfonated polypropylene carbonate, polylactic acid, polycaprolactone, polyhydroxyalkanoate, polyglycolic acid, polybutylene succinate, poly(butylene succinate-adipate-butylene glycol), poly(butylene terephthalate-adipate-butylene glycol), poly(lactic acid-butylene terephthalate-butylene glycol), polytrimethylene carbonate, poly(trimethylene carbonate-co-caprolactone), polyanhydride, plasticized or esterified starch, cellulose, chitin, chitosan, or copolymers formed from the above polymers.

[0011] The epoxy resin segments mentioned above are derived from at least one of the following epoxy resins: bisphenol A type epoxy resin, bisphenol F type epoxy resin, alicyclic epoxy resin, and hydrogenated bisphenol A type epoxy resin.

[0012] The aforementioned linker residues are derived from compounds having two or more functional groups, selected from at least one of polybasic acids, acid anhydrides, polyols, polyamines, polyisocyanates, or silane coupling agents; the catalyst is a compound capable of promoting the ring-opening addition reaction between a carboxyl or hydroxyl group and an epoxy group, selected from at least one of 1-dimethylaminopyridine, triphenylphosphine, 2-methylimidazole, 1-methylimidazole, 2-ethyl-4-methylimidazole, stannous octoate, dibutyltin dilaurate, zinc acetylacetonate, tetramethylammonium chloride, tetraethylammonium bromide, tetrabutylammonium bromide, benzyltriethylammonium chloride, ethyltriphenylphosphine bromide, and butyltriphenylphosphine bromide.

[0013] The aforementioned high shear strength biodegradable hot melt adhesive has an overlap shear strength of not less than 5 MPa at room temperature.

[0014] A method for preparing a high shear strength biodegradable hot melt adhesive includes the steps of: mixing a biodegradable polymer material, an epoxy resin, and optional binders and / or catalysts in a molten state, and reacting them at 80°C to 200°C for 5 to 30 minutes, thereby forming covalent bonds between the biodegradable polymer material and the epoxy resin, and between them and the optional binders.

[0015] The mass ratio of the above-mentioned biodegradable polymer materials to epoxy resin is 99.9:0.1 to 80:20.

[0016] The aforementioned high shear strength biodegradable hot melt adhesives are used for structural or semi-structural bonding in the fields of packaging, electronics, wood manufacturing, building materials, automotive and transportation, machinery manufacturing, new energy, medical and health, or aerospace.

[0017] Beneficial Effects: The high shear strength biodegradable hot melt adhesive provided by this invention has the following beneficial effects. First, through the covalent bond chemical bonding formed between the biodegradable polymer material and epoxy resin, a synergistic effect on material performance is achieved. This chemical bonding not only introduces the rigid structure of epoxy resin, significantly enhancing the cohesive strength and interfacial adhesion of the material, but also retains the biodegradable characteristics of the biochain segments. Experimental data show that adding only a small amount of epoxy resin can significantly improve the lap shear strength of the hot melt adhesive. For example, in Example 3, using only 1% epoxy resin, its strength reached 34.37 MPa, far exceeding the corresponding unmodified biodegradable material and significantly better than Comparative Example 6, which was only physically blended. This proves that this chemical modification strategy can effectively overcome the performance bottlenecks of simple physical blending or simple chemical modification.

[0018] Secondly, the preparation method adopted in this invention is simple and requires only one-step melt blending reaction. It can be completed in a short time at conventional processing temperature using mature commercial raw materials. No complicated post-processing or harsh conditions are required, which significantly reduces production costs and equipment requirements and has excellent potential for large-scale industrial production.

[0019] Furthermore, the hot melt adhesive described in this invention exhibits excellent environmental friendliness throughout its entire lifecycle. Its preparation process is solvent-free, eliminating the emission of volatile organic compounds at the source; the final product does not contain harmful substances such as formaldehyde, and all embodiments show considerable biodegradability in soil. For example, Example 6 showed a mass loss rate of 75.89% within six months, achieving a green and environmentally friendly entire chain from production and use to disposal.

[0020] Finally, this technical solution boasts high raw material versatility and performance adjustability. By selecting different types of biodegradable polymers and epoxy resins and adjusting their ratios, or selectively using binders and catalysts, the mechanical properties, toughness, bond strength, and degradation cycle of the final hot melt adhesive can be adjusted within a wide range, thereby meeting the personalized needs of different application scenarios, from rigid structure bonding to flexible encapsulation. In summary, this invention successfully integrates the two previously difficult-to-balance key characteristics of high strength and biodegradability, providing a practical and environmentally friendly new solution for the field of structural bonding. Attached Figure Description

[0021] Figure 1Infrared spectra of hot melt adhesive (PBAT-EP, Example 1) prepared from polybutylene adipate terephthalate (PBAT) and epoxy resin-modified PBAT; compared with PBAT, the product PBAT-EP of Example 1 showed a characteristic peak of epoxy groups at 834 cm⁻¹. -1 The characteristic peak of the benzene ring is at 1601 cm⁻¹. -1 .

[0022] Figure 2 This is a displacement-lap shear strength curve for Example 2.

[0023] Figure 3 The results of the lap shear strength test of the stainless steel plate in Example 2 are shown. In example a, white hot melt adhesive remained on both sides of the steel plate, indicating that the failure mode was cohesive failure of the hot melt adhesive. In example b, due to the high lap shear strength of the sample in this example, the steel plate bent during the test, and the red dashed line in the figure marks the bending deformation area. Detailed Implementation

[0024] The following embodiments are further illustrations of the present invention and are not intended to limit the invention.

[0025] Example 1 PBAT-EP hot melt adhesive was prepared by melt-blending 96 g of polybutylene adipate terephthalate (PBAT), 4 g of bisphenol A epoxy resin (E-44), and 0.5 g of triphenylphosphine at 170℃ for 5 min.

[0026] FTIR analysis of the reaction product was performed, and compared with the starting material spectrum, the product PBAT-EP showed a characteristic peak of epoxy groups at 834 cm⁻¹. -1 The characteristic peak of the benzene ring is at 1601 cm⁻¹. -1 This confirms the ring-opening reaction of epoxy groups and the formation of covalent bonds.

[0027] Example 2 PPC-EP hot melt adhesive was prepared by melting and blending 98 g of polypropylene carbonate (PPC), 2 g of bisphenol A epoxy resin (E-51), and 8 g of hexamethylene diisocyanate (HDI) at 180°C for 8 min.

[0028] Example 3 CPPC-EP hot melt adhesive was prepared by melting and blending 99 g of chlorinated polypropylene carbonate (CPPC), 1 g of bisphenol F epoxy resin (BFE-170), and 5 g of diphenylmethane diisocyanate (MDI) at 150°C for 10 min.

[0029] Example 4 90 g of chlorosulfonated polypropylene carbonate (CSPPC), 10 g of bisphenol A type epoxy resin (E-20), and 2 g of methyl naphthalene anhydride were melt-blended at 150°C for 30 min to prepare CSPPC-EP hot melt adhesive.

[0030] Example 5 PLA-EP hot melt adhesive was prepared by melting and blending 90 g of polylactic acid (PLA), 10 g of alicyclic epoxy resin, and 2 g of 2-methylimidazole at 180℃ for 25 min.

[0031] Example 6 PCL-EP hot melt adhesive was prepared by melt-blending 92 g of polycaprolactone (PCL), 8 g of hydrogenated bisphenol A type epoxy resin, and 0.5 g of toluene diisocyanate (TDI) at 120℃ for 10 min.

[0032] Example 7 80 g of plasticized starch, 20 g of bisphenol A epoxy resin, and 10 g of MDI were melt-blended at 80°C for 30 min to prepare starch-EP hot melt adhesive.

[0033] Example 8 85 g of polyhydroxyalkanoate (PHA), 15 g of bisphenol A epoxy resin (E51), 2 g of pyromellitic dianhydride (linker), and 0.4 g of 1-methylimidazole (catalyst) were melt-blended at 160°C for 20 minutes to obtain PHA-EP hot melt adhesive.

[0034] Example 9: CPPC-EP-2 hot melt adhesive was prepared by reacting 99.9g of CPPC, 0.1g of epoxy resin, and 0.05g of 2-ethyl-4-methylimidazole at 150℃ for 5 minutes.

[0035] Comparative Example 1 Solid pure bisphenol A type epoxy resin (E-20) was used as a control.

[0036] Comparative Example 2 PPC was used as a control.

[0037] Comparative Example 3 CPCC was used as a control.

[0038] Comparative Example 4 CSPPC was used as a control.

[0039] Comparative Example 5 Use PBAT as a control.

[0040] Comparative Example 6 PBAT / EP hot melt adhesive was prepared by physically melting and blending 96 g of PBAT and 4 g of bisphenol A epoxy resin (E-44) at 170℃ for 5 min.

[0041] Comparative Example 7 According to Polymer Bulletin, 2025, 82: 5121–5137, CPPC-PBS hot melt adhesive was prepared by melting and blending 80 g of CPPC, 20 g of PBS, and 1.25 g of MDI at 160 °C for 8 min.

[0042] Comparative Example 8 Chlorinated polypropylene carbonate (CPPC) 100 g, MDI 5 g, melt-blended at 150℃ for 10 min to prepare chain-extended CPPC hot melt adhesive.

[0043] The preparation and performance testing methods for the test samples are as follows: 1. Overlap shear strength test (according to ASTM D1002 or GB / T 7124) Substrate: Standard 304 stainless steel sheet, 100mm×25mm×1.6mm in size. Before use, sand the bonding surfaces and ultrasonically clean and dry with acetone.

[0044] Sample preparation: Melt the prepared hot melt adhesive at the appropriate temperature and uniformly coat it onto the bonding area (12.5mm × 25mm) of a substrate, controlling the adhesive layer thickness to be 0.1-0.2 mm. Quickly cover it with another substrate to form an overlap joint. Hold it at the hot melt adhesive reaction temperature under a pressure of 0.1-0.2 MPa for 5 minutes, then cool it to room temperature with the press to cure, forming a standard overlap shear sample.

[0045] Testing: Perform the test on a universal testing machine at a tensile rate of 50 mm / min. Record the maximum load and calculate the lap shear strength (LSS) based on the bond area. Test at least 5 specimens for each formulation and take the average value.

[0046] 2. Tensile property testing (according to ASTM D638 or G / BT 1040) Sample preparation: The hot melt adhesive after reaction is hot-pressed into sheets and then punched into standard dumbbell samples.

[0047] Testing: Perform the test on a universal testing machine at a tensile rate of 10 mm / min. Record the tensile strength and elongation at break. Test at least 5 specimens for each formulation and take the average value.

[0048] 3. Degradation performance test The samples were cut into 3cm × 3cm cubes and dried in a 60℃ constant temperature drying oven until constant weight. Then, different samples were buried in natural soil at a depth of 15 cm to conduct soil degradation experiments. Initial and post-degradation data were recorded, and the mass loss rate was calculated and analyzed.

[0049] Table 1 Mechanical properties of different hot melt adhesive systems

[0050] Table 2 Degradation rates of different hot melt adhesive systems

[0051] Therefore, this invention addresses the challenges of insufficient adhesive strength and difficulty in balancing high mechanical properties with controllable degradation in existing biodegradable hot melt adhesives by providing an innovative solution: through chemical modification with a small amount of epoxy resin and biodegradable polymers, a hot melt adhesive system exhibiting both excellent adhesive strength and good biodegradability is successfully constructed. As shown in Tables 1 and 2, this technical approach achieves significant technical results: while maintaining the system's processability, its lap shear strength (up to 34.37 MPa) far exceeds that of existing biodegradable hot melt adhesives and commercially available non-degradable EVA hot melt adhesives, and is superior to existing chemically chain-extended modification systems (such as CN202410651414.4), while simultaneously ensuring effective degradation of the material in the natural environment (with a degradation rate of up to 78.56% in 6 months). This invention achieves a balance between strength and degradability at the molecular level through the covalent bonding of rigid segments of epoxy resin and degradable polymer chains, providing a practical new approach for developing high-performance, environmentally friendly hot melt adhesives applicable to semi-structural and even structural bonding applications.

Claims

1. A high shear strength biodegradable hot melt adhesive, characterized in that, It is a polymer containing biodegradable polymer segments, epoxy resin segments, and epoxy functional groups, wherein the biodegradable polymer segments and epoxy resin segments are connected by covalent bonds to form a linear, branched, or cross-linked polymer network structure.

2. The high shear strength biodegradable hot melt adhesive according to claim 1, characterized in that, Based on the total mass of the polymer network, the content of structural units of the epoxy resin segments is from 0.1 wt.% to 20 wt.%.

3. The high shear strength biodegradable hot melt adhesive according to claim 1, characterized in that, The polymer network also includes linker residues or catalysts; based on the total mass of the structural units of the biodegradable polymer segments and epoxy resin segments, the mass fraction of the linker residues or catalysts is 0.1% to 10%.

4. The high shear strength biodegradable hot melt adhesive according to claim 1, characterized in that, The biodegradable polymer segments are derived from at least one of the following materials: polypropylene carbonate, chlorinated polypropylene carbonate, chlorosulfonated polypropylene carbonate, polylactic acid, polycaprolactone, polyhydroxyalkanoate, polyglycolic acid, polybutylene succinate, poly(butylene succinate-adipate-butylene glycol), poly(butylene terephthalate-adipate-butylene glycol), poly(lactic acid-butylene terephthalate-butylene glycol), polytrimethylene carbonate, poly(trimethylene carbonate-co-caprolactone), polyanhydride, plasticized or esterified starch, cellulose, chitin, chitosan, or copolymers formed from the above polymers.

5. The high shear strength biodegradable hot melt adhesive according to claim 1, characterized in that, The epoxy resin segments are derived from at least one of the following epoxy resins: bisphenol A type epoxy resin, bisphenol F type epoxy resin, alicyclic epoxy resin, and hydrogenated bisphenol A type epoxy resin.

6. The high shear strength biodegradable hot melt adhesive according to claim 3, characterized in that, The linker residues are derived from compounds having two or more functional groups, selected from at least one of polybasic acids, acid anhydrides, polyols, polyamines, polyisocyanates, or silane coupling agents; the catalyst is a compound capable of promoting the ring-opening addition reaction between a carboxyl or hydroxyl group and an epoxy group, selected from at least one of 1-dimethylaminopyridine, triphenylphosphine, 2-methylimidazole, 1-methylimidazole, 2-ethyl-4-methylimidazole, stannous octoate, dibutyltin dilaurate, zinc acetylacetonate, tetramethylammonium chloride, tetraethylammonium bromide, tetrabutylammonium bromide, benzyltriethylammonium chloride, ethyltriphenylphosphine bromide, and butyltriphenylphosphine bromide.

7. The high shear strength biodegradable hot melt adhesive according to any one of claims 1 to 6, characterized in that, Its lap shear strength at room temperature is not less than 5 MPa.

8. A method for preparing a high shear strength biodegradable hot melt adhesive as described in any one of claims 1 to 6, characterized in that, include: The biodegradable polymer, epoxy resin, and optional binder and / or catalyst are mixed in a molten state and reacted at 80°C to 200°C for 5 to 30 minutes to form covalent bonds between the biodegradable polymer and the epoxy resin, and between them and the optional binder.

9. The preparation method according to claim 8, characterized in that, The mass ratio of the biodegradable polymer material to the epoxy resin is from 99.9:0.1 to 80:

20.

10. The use of the high shear strength biodegradable hot melt adhesive according to any one of claims 1 to 6 for structural or semi-structural bonding in the fields of packaging, electronics, wood manufacturing, building materials, automobiles and transportation, machinery manufacturing, new energy, medical and health care, or aerospace.

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