A fully bio-based tough polyester hot melt adhesive and its preparation method

Abstract

A fully bio-based tough polyester hot melt adhesive and a preparation method thereof, comprising a hard segment of butylene 2,5-furandicarboxylate and a soft segment of hydrogenated butylene dimer acid ester. The hot melt adhesive exhibits outstanding bonding properties on stainless steel substrates and has a wide range of bonding applicability to glass, plastic, wood, and the like. The polyester hot melt adhesive has excellent high- and low-temperature resistance, maintaining a bonding strength of 10.6 MPa even at -70°C. The polyester hot melt adhesive also exhibits excellent solvent resistance, maintaining a bonding strength retention rate exceeding 80% after immersion in various polar solvents for 24 hours. The copolyester can undergo chemical recycling degradation and regeneration, with a chemical recovery rate exceeding 99% as determined by gas chromatography, and the hot melt adhesive obtained by repolymerizing the degraded raw materials exhibits no degradation in performance.

Description

Technical Field

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

[0002] Adhesives are used in all aspects of our daily lives to join materials temporarily or permanently. Synthetic polymers are widely used as adhesives due to their ability to provide good contact between surfaces and dissipate energy under stress. Common adhesives are divided into two categories: strong adhesives or tough adhesives. Strong adhesives used for structural applications, including epoxies, polyurethanes, or acrylics, generally have strong adhesion, but due to brittleness, they have low debonding work and poor bond toughness, often leading to undesirable cohesive failure ( Figure 1 In contrast, tough adhesives, such as tape adhesives, do not have strong adhesion but can distribute mechanical stress through the soft matrix, preventing sudden bond failure ( Figure 1 The curve in Figure 2). Tough adhesives are made of low modulus materials, which limits their use in structural applications. Ideal tough adhesives that possess both strong adhesion and tough adhesion are extremely rare because the combination of these adhesive properties is difficult to achieve due to their conflicting nature. Tough adhesives are characterized by both high adhesion and high debonding work ( Figure 1 This will improve the safety and service life of the structure while minimizing adhesive failure. Therefore, the successful development of strong adhesives will affect many applications in the electronics, construction and automotive industries.

[0003] Modern hot melt adhesives have increasingly higher performance requirements and are becoming more and more versatile. At the same time, ideal hot melt adhesive materials should be prepared through a convenient, low-energy route, preferably with bio-based raw materials. Replacing traditional petroleum-based hot melt adhesives with all-biobased materials can accelerate the reduction of carbon emissions, help guide green technology innovation, and enhance the global competitiveness of industry and the economy. The demand for multiple properties for hot melt adhesive materials, including high strength, high debonding work (high toughness), high and low temperature resistance, and physical or chemical recyclability, has led to increased structural complexity and synthesis difficulty, which also increases costs. Therefore, how to prepare hot melt adhesive materials with complex and comprehensive properties from bio-based raw materials through an extremely simplified route is a major challenge. Therefore, the invention of preparing all-biobased, recyclable, degradable, and tough polyester hot melt adhesives has certain scientific and application significance. Summary of the Invention

[0004] Technical Problem Solved: This invention provides a fully bio-based, strong, and tough polyester hot melt adhesive and its preparation method. By directly esterifying and polycondensing bio-based 2,5-furandicarboxylic acid, bio-based hydrogenated dimer acid, and bio-based 1,4-butanediol, a fully bio-based thermoplastic polyester is prepared. The resulting thermoplastic polyester hot melt adhesive exhibits high strength and toughness, excellent solvent resistance, and high and low temperature resistance, and is chemically and physically recyclable, offering broad application prospects.

[0005] Technical solution: A fully bio-based tough polyester hot melt adhesive, the hot melt adhesive is a copolymer formed by copolymerizing a hard segment of butylene 2,5-furandicarboxylate and a soft segment of hydrogenated dimerized butylene glycol ester; the structure of the hard segment of butylene 2,5-furandicarboxylate is shown in formula (I):

[0006] (I)

[0007] The structure of the hydrogenated dimerized butylene glycol ester soft segment is shown in formula (II):

[0008] (II)

[0009] The structure of the tough polyester hot melt adhesive is shown in formula (III):

[0010] (III)

[0011] q is 6, 7 or 8; m and n are the polymerization degrees of their respective blocks, and the molecular weight is 20,000 to 30,000.

[0012] The above-mentioned hydrogenated dimerized butylene glycol soft segment accounts for 1 wt.% to 50 wt.% of the copolymer.

[0013] The ratio of the polymerization degree m of the soft segment of the hydrogenated dimerized butylene glycol ester to the polymerization degree n of the hard segment of the butylene 2,5-furandicarboxylate is 0.17-0.45.

[0014] The preparation method of the above-mentioned all-biobased tough polyester hot melt adhesive comprises the following steps: (1) in the presence of nitrogen and catalyst A, 2,5-furandicarboxylic acid, hydrogenated dimer acid and 1,4-butanediol are mixed for esterification reaction to obtain dihydroxybutyl furandicarboxylate and dihydroxybutyl dimer acid, wherein the catalyst A is tetrabutyl titanate or tetraisopropyl titanate, and the amount of catalyst A accounts for 0.2‰-0.8‰ of the total mass of the reactants, the reaction temperature is 150-200°C, and the molar ratio of the 2,5-furandicarboxylic acid and the hydrogenated dimer acid is 0.2‰-0.8‰. The ratio is (0.17-0.45):1, and the molar ratio of diol to diacid contained in the above compound group is (2.0-4.0):1.0; (2) catalyst B is continuously added to the mixture of dihydroxybutyl furandicarboxylate and dihydroxybutyl dimer acid obtained in step (1) to carry out a second step polycondensation reaction, the polycondensation temperature is 180-220°C, and a strong and tough polyester hot melt adhesive is obtained, the catalyst B is antimony trioxide, lithium acetylacetonate, zinc acetate or germanium oxide, and the amount of catalyst B accounts for 0.2‰-0.8‰ of the total mass of the reactants.

[0015] In step (1), the reaction temperature is first raised to 175°C, kept at this temperature for 2-4 hours, and then further raised to 180-200°C.

[0016] The reaction temperature in step (1) is 175° C. and the temperature is maintained for 3.5 hours. The molar ratio of 2,5-furandicarboxylic acid to hydrogenated dimer acid is 0.2:1. The molar ratio of diol to diacid is 3.5:1.

[0017] Beneficial Effects: The advantages of the bio-based environmentally friendly materials involved in the present invention are that, compared with traditional materials, bio-based materials not only have the advantages of being green and environmentally friendly, energy-saving and emission-reducing, and having renewable raw materials, but also have good biodegradability, which meets the requirements of a "low-carbon economy." It is precisely because of the excellent environmental protection properties of bio-based materials that they have a wide range of application value. In the future, they are expected to become new materials that replace traditional petroleum-based materials, solving the drawbacks of the non-degradability of most petroleum-based materials, and thus achieving multiple goals such as green production, environmental friendliness, and resource conservation. Bio-based environmentally friendly materials will also become a major direction of future development.

[0018] The present invention uses environmentally friendly and renewable biomass resources 2,5-furandicarboxylic acid, bio-based hydrogenated dimer acid and bio-based 1,4-butanediol as raw materials, and adopts a two-step esterification-polycondensation process to obtain a fully bio-based, recyclable, degradable and tough polyester hot melt adhesive based on furan rings. (I) The hot melt adhesive exhibits outstanding bonding performance on stainless steel substrates and has wide bonding applicability to glass, plastic, wood, etc.; (II) The polyester hot melt adhesive has excellent high-temperature and low-temperature resistance and can still maintain a bonding strength of 10.6 MPa even at minus 70°C; (III) The polyester hot melt adhesive has excellent solvent resistance and its bonding strength retention rate is higher than 80% after being immersed in various polar solvents for 24 hours; (IV) The copolyester can be chemically recycled and regenerated, and its chemical recovery rate is greater than 99% as determined by gas chromatography, and the performance of the hot melt adhesive obtained by repolymerizing the degraded raw materials does not decrease. The hot melt adhesive and the preparation method thereof of the present invention have the advantages of green raw material source, simple preparation method, excellent comprehensive properties such as adhesion, solvent resistance, high and low temperature resistance, low energy consumption and carbon dioxide emissions, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The present invention relates to a conceptual diagram of preparing a strong and tough polyester hot melt adhesive with a phase separation structure based on biomimetic principles.

[0020] Figure 2 Fully bio-based polyester containing furan rings mimics the microphase separation structure of spider silk.

[0021] Figure 3 The unstable crystals formed by the asymmetric furan ring structure are destroyed after stretching and the formation mechanism of fibrous crystals.

[0022] Figure 4 Shear test of furan ring-containing bio-based polyester hot melt adhesive. Stainless steel bonding specimen (25×12.5 mm 2 ) can bear a mass of more than 330 kg, and the cross-section of the adhesive layer is the simultaneous destruction of cohesion and adhesion, showing a good balance between cohesion and interfacial adhesion.

[0023] Figure 5 Shear strength and toughness data of furan ring-containing bio-based polyester hot melt adhesive (strength: 12.1MPa, toughness 13225 Nm -1 ).

[0024] Figure 6 Crystallization rate and morphology of a furan ring-containing, fully bio-based polyester hot melt adhesive. The crystallization rate of the fully bio-based polyester hot melt adhesive containing hydrogenated dimer acid (green curve) is significantly higher than that of the polyester without hydrogenated dimer acid (yellow curve), which helps the hot melt adhesive achieve better initial tack and achieve rapid positioning and bonding. Furthermore, the crystallization morphology is fine-grained spherulites, which helps improve the cohesive strength of the hot melt adhesive.

[0025] Figure 7 Cyclic bond strength curve of a furan ring-containing, fully bio-based polyester hot melt adhesive. After six cycles of repeated use (bonding-destruction-bonding), the adhesive retained over 90% of its strength, demonstrating excellent reusability.

[0026] Figure 8 Schematic diagram of the preparation, processing and chemical recycling degradation of fully bio-based polyester hot melt adhesive containing furan rings.

[0027] Figure 9 Gas chromatogram of a fully bio-based polyester hot melt adhesive containing furan rings after degradation (left), and a gas chromatogram of a dimethyl 2,5-furandicarboxylate external standard sample (right). Gas chromatography showed that the molar recovery of the hot melt adhesive after chemical degradation with methanol, calculated using the external standard method, exceeded 99%, indicating virtually no loss.

[0028] Figure 10 A physical image of the original raw material obtained by separating and purifying the fully bio-based polyester hot melt adhesive prepared in the present invention after chemical degradation by methanol.

[0029] Figure 11 The solvent resistance of the bio-based polyester hot melt adhesive was compared with that of various commercial hot melt adhesives in different solvents. The solvents ranged from the less polar n-hexane to the more polar water. After 24 hours of immersion, the hot melt adhesive prepared by the present invention exhibited significantly higher bond strength than the commercial hot melt adhesives in all solvent systems. Furthermore, the polyester hot melt adhesive prepared by the present invention exhibited good bond strength retention in solvents of various polarities, demonstrating excellent solvent resistance.

[0030] Figure 12 A comparison of the strength retention of a fully bio-based polyester hot melt adhesive and various commercial hot melt adhesives after immersion in N,N-dimethylformamide (DMF) for 24 hours. After immersion in DMF for 24 hours, the polyester hot melt adhesive prepared by this invention exhibits the best strength retention and superior solvent resistance to various commercial hot melt adhesives.

[0031] Figure 13 The low-temperature resistance of the all-biobased polyester hot melt adhesive (left) is compared with the high-temperature resistance of commercial hot melt adhesives (right). The all-biobased polyester hot melt adhesive prepared by this invention exhibits a bond strength of 12.1 MPa on a stainless steel substrate at room temperature and a bond strength of 10.6 MPa at -70°C (left), demonstrating excellent low-temperature resistance. Compared to other commercial hot melt adhesives, the polyester hot melt adhesive prepared by this invention also exhibits excellent bond strength at high temperatures, even exceeding that of two-component thermosetting hot melt adhesives, and also demonstrates excellent high-temperature resistance.

[0032] Figure 14 Comparison of the bonding strength of a fully bio-based polyester hot melt adhesive and other commercial hot melt adhesives on various substrates. The fully bio-based polyester hot melt adhesive prepared in this invention exhibits the best bonding strength compared to commercial hot melt adhesives on all studied substrates, demonstrating its broad applicability.

[0033] Figure 15 The fully bio-based polyester hot melt adhesive prepared by the present invention can be used as a product to prepare corresponding hot melt adhesive films and hot melt adhesive sticks. DETAILED DESCRIPTION

[0034] The technical scheme of the present invention is further described below in conjunction with examples, but the purpose of these examples is not to limit the scope of protection of the present invention. In these examples, unless otherwise stated, all percentages are by weight.

[0035] Bio-based 2,5-furandicarboxylic acid comes from Hubei Jiufenglong Chemical Co., Ltd. and Mianyang Dagaote New Materials Co., Ltd., bio-based 1,4-butanediol comes from Yuanli Chemical Group Co., Ltd. and Shandong Longmai Group, and bio-based hydrogenated dimer acid comes from Anqing Hongtai New Materials Co., Ltd. and Croda Chemicals (Shanghai) Co., Ltd. Example 1

[0036] A fully bio-based, recyclable, degradable, strong and tough polyester hot melt adhesive containing a furan ring and its preparation method:

[0037] In a flask equipped with a constant temperature overhead stirrer, a distillation tower, a temperature measuring device and a nitrogen gas flow device, 0.27 mol (41.82 g) of bio-based 2,5-furandicarboxylic acid, 1.34 mol (120.64 g) of bio-based 1,4-butanediol, 0.066 mol (37.53 g) of bio-based hydrogenated dimer acid and 0.12 g of tetraisopropyl titanate were added. The esterification reaction was completed at 160 ° C for 1 hour, 175 ° C for 2 hours and 180 ° C for 1 hour under a nitrogen atmosphere.

[0038] Add 0.1 g of zinc acetate, stir and gradually heat to 200°C, reduce the system pressure to 40±5 Pa within 60 minutes, then increase the temperature to 210°C and vacuum polycondense for 6 hours. Stop the reaction when the torque of the stirring shaft no longer increases.

[0039] The prepared all-biobased polyester hot melt adhesive was used to prepare the corresponding hot melt adhesive film using a molding device ( Figure 15 The corresponding hot melt adhesive film) is directly used for bonding various substrates. The bonding process is as follows:

[0040] The prepared all-biobased polyester hot melt adhesive film was laminated between two metal plates and fixed with a dovetail clip. It was placed in an oven at 180°C for 10 minutes and allowed to cool naturally to room temperature before the bonding shear strength was measured. Figure 4 In an outdoor tensile test of a stainless steel plate bonded with the polyester hot melt adhesive prepared in this embodiment, a bonding area of ​​25 mm × 12.5 mm can withstand a mass of more than 330 kg without being damaged; Figure 5 The lap shear curve of the hot melt adhesive bonded to the stainless steel plate prepared in this example shows that the bonding strength reaches 12.1 MPa. Small angle X-ray scattering and atomic force scanning (AFS) were performed on the tensile process. Figure 2 ), analysis found that the hot melt adhesive prepared by the present invention has an obvious microphase separation structure, and during the stretching process, the unstable crystals formed by the asymmetric structure of the furan ring will undergo orientation and slip, thereby improving the toughness of the material. Example 2

[0041] A fully bio-based, recyclable, degradable, strong and tough polyester hot melt adhesive containing a furan ring and its preparation method:

[0042] In a flask equipped with a constant temperature overhead stirrer, a distillation tower, a temperature measuring device and a nitrogen flow device, 0.27 mol (41.82 g) of bio-based 2,5-furandicarboxylic acid, 1.01 mol (90.83 g) of bio-based 1,4-butanediol, 0.066 mol (37.53 g) of bio-based hydrogenated dimer acid and 0.12 g of tetrabutyl titanate were added. The esterification reaction was completed at 160 ° C for 1 hour, 175 ° C for 2 hours and 185 ° C for 3 hours under a nitrogen atmosphere.

[0043] Add 0.1 g of antimony trioxide, stir and gradually heat to 200°C, reduce the system pressure to 40±5 Pa within 60 minutes, then maintain the temperature at 200°C and perform vacuum polycondensation for 8 hours. Stop the reaction when the torque of the stirring shaft no longer increases.

[0044] The prepared all-biobased polyester hot melt adhesive was used to prepare the corresponding hot melt adhesive sticks ( Figure 15 The corresponding hot melt glue stick is fixed on the hot melt glue gun and directly used for bonding various substrates. The bonding process is as follows:

[0045] Heat a hot melt glue gun equipped with a fully bio-based polyester hot melt glue stick to an appropriate temperature, and slowly extrude the molten polyester hot melt glue onto the surface of the eucalyptus substrate or glass substrate. Then, attach the corresponding blank eucalyptus board or glass plate to the glued substrate, fix it with a dovetail clip, and naturally cool it to room temperature. Then, soak it in solvents of different polarities for 24 hours, and measure the bonding shear strength. Figure 11 and Figure 12The results of the solvent resistance of the polyester hot melt adhesive prepared in this example are shown in the figure. As can be seen from the figure, the hot melt adhesive prepared in the present invention has very excellent solvent resistance in various solvents of different polarities. The reason is that the polyester hot melt adhesive has a microscopic morphology of crystallization-induced microphase separation. Figure 6 The crystalline phase (spherulites) is clearly visible, and the furan rings in the polymer chain interact strongly, making them difficult for solvents to break down. Compared to commercial hot melt adhesives, the polyester hot melt adhesive prepared in this invention exhibits the highest bonding strength and the best solvent resistance. Example 3

[0046] A fully bio-based, recyclable, degradable, strong and tough polyester hot melt adhesive containing a furan ring and its preparation method:

[0047] In a flask equipped with a constant temperature overhead stirrer, a distillation tower, a temperature measuring device and a nitrogen flow device, 0.27 mol (41.82 g) of bio-based 2,5-furandicarboxylic acid, 0.81 mol (72.58 g) of bio-based 1,4-butanediol, 0.066 mol (37.53 g) of bio-based hydrogenated dimer acid and 0.13 g of germanium oxide were added. The esterification reaction was completed at 160 ° C for 1 hour and at 175 ° C for 3.5 hours under a nitrogen atmosphere.

[0048] Add 0.13 g of lithium acetylacetonate, stir and gradually heat to 200°C, reduce the system pressure to 40±5 Pa within 60 minutes, then maintain the temperature at 210°C and vacuum polycondense for 6 hours. Stop the reaction when the torque of the stirring shaft no longer increases.

[0049] The prepared all-biobased polyester hot melt adhesive is used to prepare the corresponding hot melt adhesive stick using injection molding extrusion equipment. The hot melt adhesive stick is fixed on a hot melt adhesive gun and directly used for bonding various substrates. The bonding process is as follows:

[0050] Filled with all-bio-based polyester hot melt glue stick ( Figure 15 Heat the hot melt glue gun (corresponding hot melt glue stick) to the appropriate temperature, slowly squeeze out the molten polyester hot melt glue on the surface of the stainless steel plate substrate, then stick the corresponding blank stainless steel plate on the adhesive substrate, fix it with a dovetail clip and let it cool naturally to room temperature, then carry out cyclic bonding ( Figure 7 ) and chemical degradation ( Figure 8 and Figure 9 ). Figure 7It can be seen that after 6 cycles of bonding-debonding-bonding, the bonding strength can still be maintained above 92%, showing very good cyclic bonding performance; the polyester hot melt adhesive is placed in methanol for chemical degradation, and the degradation liquid is transferred to N,N-dimethylformamide for full dissolution and gas chromatography determination. Combined with the external standard method of standard substances, it is found that the recovery rate of the raw material 2,5-furandicarboxylic acid exceeds 99%, which can almost be considered as quantitative recovery, and the material has achieved a chemical cycle close to 100%.

Claims

1. A fully bio-based tough polyester hot melt adhesive, characterized in that: The hot melt adhesive is a copolymer formed by copolymerizing a hard segment of butylene 2,5-furandicarboxylate and a soft segment of hydrogenated dimerized butylene glycol ester; the structure of the hard segment of butylene 2,5-furandicarboxylate is shown in formula (I): （Ⅰ） The structure of the hydrogenated dimerized butylene glycol ester soft segment is shown in formula (II): （Ⅱ） The structure of the tough polyester hot melt adhesive is shown in formula (III): （Ⅲ） q is 6, 7 or 8; m and n are the polymerization degrees of their respective blocks, the molecular weight is 20,000 to 30,000, the chemical recovery rate after methanol degradation is greater than 99%, and the copolymer has a microphase separation structure.

2. The all-biobased tough polyester hot melt adhesive according to claim 1, characterized in that: The hydrogenated dimerized butylene glycol soft segment accounts for 1 wt.% to 50 wt.% of the copolymer.

3. The all-biobased tough polyester hot melt adhesive according to claim 1, characterized in that: The ratio of the polymerization degree m of the soft segment of the hydrogenated dimerized butylene glycol ester to the polymerization degree n of the hard segment of the 2,5-furandicarboxylic acid butylene glycol ester is 0.17-0.

45.

4. The method for preparing the all-biobased tough polyester hot melt adhesive according to any one of claims 1 to 3, characterized in that: The steps are as follows: (1) in the presence of nitrogen and catalyst A, 2,5-furandicarboxylic acid, hydrogenated dimer acid and 1,4-butanediol are mixed for esterification reaction to obtain dihydroxybutyl furandicarboxylate and dihydroxybutyl dimer acid, wherein the catalyst A is tetrabutyl titanate or tetraisopropyl titanate, the amount of the catalyst A accounts for 0.2‰-0.8‰ of the total mass of the reactants, the reaction temperature is 150-200°C, and the molar ratio of the hydrogenated dimer acid to 2,5-furandicarboxylic acid is (0.17-0. 45):1, the molar ratio of diol to diacid contained in the above compound group is (2.0-4.0):1.0; (2) catalyst B is continuously added to the mixture of dihydroxybutyl furandicarboxylate and dihydroxybutyl dimer acid obtained in step (1) to carry out a second step polycondensation reaction, the polycondensation temperature is 180-220°C, and a strong and tough polyester hot melt adhesive is obtained, the catalyst B is antimony trioxide, lithium acetylacetonate, zinc acetate or germanium oxide, and the amount of catalyst B accounts for 0.2‰-0.8‰ of the total mass of the reactants.

5. The method for preparing the all-biobased tough polyester hot melt adhesive according to claim 4, characterized in that: In step (1), the reaction temperature is first raised to 175°C, kept at this temperature for 2-4 hours, and then further raised to 180-200°C.

6. The method for preparing the all-biobased tough polyester hot melt adhesive according to claim 4, characterized in that: The reaction temperature of step (1) is 175° C. and the temperature is kept for 3.5 hours; the molar ratio of the hydrogenated dimer acid to 2,5-furandicarboxylic acid is 0.2:1; and the molar ratio of the diol to the diacid is 3.5:1.

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