Low-temperature-resistant degradable copolyester adhesive and preparation method thereof

Abstract

The invention relates to the technical field of degradable adhesives, and discloses a low-temperature-resistant degradable copolyester adhesive and a preparation method thereof.The method comprises the following steps that 1, adipic acid, aliphatic dihydric alcohol, a rigid crystallization inhibition unit and a catalyst are mixed and then subjected to an esterification reaction; the aliphatic dihydric alcohol is 1, 3-propylene glycol and / or diethylene glycol; the rigid crystallization inhibition unit is 2, 5-furandicarboxylic acid and / or 1, 4-cyclohexanedicarboxylic acid; (2) when the discharge amount of the byproduct water reaches 80-90% of a theoretical value, reducing the absolute pressure to be less than or equal to 100 Pa, and sequentially carrying out pre-polycondensation reaction and final polycondensation reaction; and (3) terminating the reaction to obtain the copolyester adhesive. On the basis of an aliphatic polyester skeleton, a rigid crystallization inhibition unit is introduced for molecular regulation, so that the degradation rate of the copolyester adhesive is controllable while the normal-temperature crystallization tendency is reduced, Tg is regulated and the peel strength is improved.

Description

Technical Field

[0001] This invention relates to the technical field of biodegradable adhesives, and in particular to a low-temperature resistant biodegradable copolyester adhesive and its preparation method. Background Technology

[0002] Adhesives are functional materials that can bond the surfaces of similar or dissimilar solid materials together, and are widely used in construction, automotive, electronics, packaging, and medical fields. Existing adhesive systems mainly rely on petroleum-based raw materials, which are difficult to degrade in the natural environment and can easily cause long-term cumulative impacts on water bodies, soil, and the food chain. Furthermore, during use and aging, they may release migratory components, posing health and ecological risks. Therefore, developing green, biodegradable, and stable adhesives has become an important direction in the field of adhesive materials.

[0003] Currently, biodegradable adhesives are mainly divided into natural bio-based adhesives and synthetic biodegradable adhesives. Natural systems, derived from starch, proteins, polysaccharides, etc., are limited in application due to insufficient mechanical properties and durability. Synthetic biodegradable adhesives are mostly based on polyesters such as polylactic acid (PLA), polyhydroxyalkanoates (PHA), polycaprolactone (PCL), and polybutylene succinate (PBS). For example, invention patent CN113908327B discloses a biodegradable polyester bioadhesive using a multi-component block polyester combination, its preparation method, and its application. It is obtained by mixing two block polyesters A and B with different molecular weights, wherein component A or component B is a block polyester composed of ε-caprolactone and DL-lactide. Although possessing a certain degree of degradability, the following prominent problems still exist: 1) High cost and process complexity: The sources of monomers such as PLA and PHA are limited, and their prices are about 30-50% higher than those of traditional petroleum-based systems. In addition, some systems require additional modification, blending or UV curing processes, which are complex to prepare and not conducive to large-scale application. 2) Glass transition temperature ( T g - The structural contradiction of crystallinity: T in PLA g Typically, it exists at around 55~65℃, exhibiting a glassy state at room temperature, but exhibits insufficient wetting and initial tack at low temperatures; in contrast, PCL ( T g ≈-60 ℃) and PBS ( T g (≈-30~-40 ℃) Although the chain segment has good flexibility, it is a semi-crystalline polyester, which is prone to secondary crystallization during its service life, leading to interface wetting degradation and a decrease in peel strength; 3) Insufficient mechanical and adhesive properties: Many biodegradable polyester-based adhesives have a high tendency to crystallize at room temperature, poor interfacial wettability, and insufficient peel strength, making it difficult to meet the actual requirements of packaging heat sealing and assembly scenarios; 4) Degradation behavior is difficult to control precisely: The degradation rate of polyester is highly dependent on crystallinity, hydrophilicity / hydrophobicity and service environment (temperature, humidity, pH, enzymes). Without the synergistic regulation of structure and process, the degradation rate often fluctuates and the reliability is insufficient.

[0004] In summary, existing biodegradable adhesives have significant shortcomings in terms of low-cost preparation, low-temperature adaptability, peel strength, and controllable degradation. Summary of the Invention

[0005] To address the technical problems of existing biodegradable adhesives, such as insufficient low-temperature adaptability, adhesion failure due to crystallization at room temperature, low peel strength, and unstable degradation behavior, this invention provides a low-temperature resistant biodegradable copolyester adhesive and its preparation method. An aliphatic polyester backbone is constructed using adipic acid (AA) and 1,3-propanediol (PDO) and / or diethylene glycol (DEG). Based on this, a small amount of rigid crystallization-inhibiting units (2,5-furandicarboxylic acid and / or 1,4-cyclohexanedicarboxylic acid) are introduced for molecular regulation, reducing the tendency for crystallization at room temperature and regulating… T g While improving peel strength, the degradation rate is controlled. The resulting adhesive combines low cost and low degradation rate. T g With its comprehensive properties of non-crystallization at room temperature, high peel strength, and adjustable degradation rate, it is suitable for applications such as heat sealing in cold chain packaging, low-temperature assembly, and label adhesives, and has broad market prospects and promotional value.

[0006] The objective of this invention is achieved through the following technical solution: In a first aspect, the present invention provides a method for preparing a low-temperature resistant biodegradable copolyester adhesive, comprising the following steps: (1) Adipic acid, aliphatic diol, rigid crystallization inhibition unit and catalyst are mixed and then subjected to esterification reaction; the aliphatic diol is 1,3-propanediol and / or diethylene glycol; the rigid crystallization inhibition unit is 2,5-furandicarboxylic acid and / or 1,4-cyclohexanedicarboxylic acid; (2) When the amount of by-product water discharged reaches 80-90% of the theoretical value, the absolute pressure is reduced to ≤100 Pa, and the pre-condensation reaction and final condensation reaction are carried out in sequence; (3) The reaction was terminated to obtain copolyester adhesive.

[0007] This invention selects aliphatic dicarboxylic acid (adipic acid (AA)) and aliphatic diols (1,3-propanediol (PDO) and / or diethylene glycol (DEG)) as the basic aliphatic polyester backbone. Adipic acid has moderate molecular chain flexibility, providing a good flexible foundation for the polyester. Furthermore, compared to ethylene glycol (EG) and 1,4-butanediol (BDO), 1,3-propanediol (PDO) has a chain segment length and configurational flexibility between EG and BDO, exhibiting greater rotational freedom and moderate interchain spacing, thereby reducing... T g This reduces the tendency for orderly stacking, avoiding the crystallization problem of the EG system while overcoming the high crystal density and excessive flexibility of the BDO system. Therefore, selecting PDO as the diol monomer achieves the best balance between chain flexibility and controllable crystallization, allowing the polyester to maintain an amorphous state and excellent adhesion properties at room temperature. DEG, on the other hand, enhances polarity and wettability by introducing ether bonds, thereby ensuring low... T g It effectively inhibits crystallization at the same time, and compared with other dicarboxylic acid systems, it can take into account flexibility, controllable crystallization and adhesion properties.

[0008] Building upon this, 2,5-furandicarboxylic acid (FDCA) and / or 1,4-cyclohexanedicarboxylic acid (CHDA) are introduced as rigid crystallization-inhibiting units. By rationally controlling the type and proportion of these rigid units, they synergistically work with the aliphatic polyester backbone to further reduce the orderly stacking and crystallization tendency of polyester segments, while maintaining low... T g While maintaining good interfacial wettability, it significantly improves peel strength and achieves tunable degradation rate. Among them, FDCA tends to enhance peel strength through π-π stacking, while CHDA provides volumetric steric hindrance through non-coplanar ring structure, inhibiting crystallization and improving flexibility. The two can be used alone or in synergistic combination.

[0009] Preferably, the chemical structural formula of the biodegradable copolyester adhesive is (1) or (2): (1) ; (2) ; Where R is R1 and / or R2, .

[0010] Preferably, the molar amount of the rigid crystallization inhibition unit is 3-18% of the total molar amount of adipic acid and the rigid crystallization inhibition unit; more preferably, the molar amount of the rigid crystallization inhibition unit is 5-18% of the total molar amount of adipic acid and the rigid crystallization inhibition unit.

[0011] If the proportion of rigid crystallization inhibition units is too large, the proportion of rigid polyester chain segments is too high, the free volume decreases, and the chain segment movement is restricted, leading to... T g Increased rigidity and decreased flexibility; furthermore, the hydrophobicity of the rigid ring structure inhibits hydrolysis and penetration, resulting in a slower and more uneven degradation rate. Therefore, this invention controls the proportion of rigid units within the range of 3-18 mol% to balance crystallization inhibition, flexibility, bonding strength, and degradation controllability.

[0012] Preferably, the molar ratio of the aliphatic diol to the total molar ratio of adipic acid and the rigid crystallization inhibition unit is 1.05~1.30:1, that is, the molar ratio of the diol to the dicarboxylic acid is 1.05~1.30:1.

[0013] Preferably, the catalyst is one or more of tetrabutyl titanate, tetraisopropyl titanate, tetraethyl titanate, antimony trioxide, antimony glycolate, antimony acetate, stannous octoate, stannous chloride, and stannous oxide.

[0014] Preferably, the amount of the catalyst is 0.01 to 0.5% of the total mass of adipic acid, aliphatic diol and rigid crystallization inhibition unit.

[0015] Preferably, the esterification reaction is carried out at 160-200 °C for 0.5-6 h under an inert atmosphere; the inert atmosphere is a nitrogen atmosphere or an argon atmosphere.

[0016] As a preferred option, when the amount of by-product water discharged reaches 80-90% of the theoretical value, the pressure is gradually reduced, first rapidly from atmospheric pressure to several hundred Pa (200-500 Pa), and then slowly reduced to ≤100 Pa.

[0017] During the esterification reaction, the carboxyl and hydroxyl groups undergo condensation and the byproduct water is continuously discharged, providing a fully converted prepolymer for subsequent polycondensation. Furthermore, vacuum was not immediately applied at the beginning of the reaction; instead, depressurization was initiated when the byproduct water discharge reached 80-90% of the theoretical value. This prevented premature entry into a vacuum state, which could lead to insufficient FDCA / CHDA conversion or increased side reactions, thus ensuring the effective introduction of rigid units. A step-by-step depressurization strategy was employed during the vacuuming process to ensure a smooth transition of the system to a high vacuum state.

[0018] Preferably, the pre-condensation reaction is carried out at 190~230 °C for 0.1~2 h.

[0019] Preferably, the final polycondensation reaction is carried out at 200~250 °C for 0.5~4 h.

[0020] After the vacuum conditions stabilize, the pre-condensation and final condensation reactions are carried out by staged heating to achieve the construction of the target molecular weight. This process sequence of "staged decompression followed by staged heating" can reduce the risk of chain breakage and thermal degradation.

[0021] Preferably, the endpoint of the polycondensation reaction is determined by melt viscosity and / or reaction torque.

[0022] Unlike traditional methods that rely on time or by-product water volume to determine the reaction endpoint, this invention monitors melt viscosity and / or reaction torque in real time during the polycondensation reaction. When the viscosity and torque signals stabilize within a preset window, the reaction is terminated. This closed-loop control method ensures a high degree of consistency in polymer molecular weight and its distribution.

[0023] Preferably, the intrinsic viscosity of the copolyester adhesive is 0.45~0.80 dL / g.

[0024] Secondly, the present invention provides a low-temperature resistant biodegradable copolyester adhesive prepared by the above-mentioned preparation method.

[0025] Compared with the prior art, the present invention has the following beneficial effects: (1) Green and low-cost raw materials: The aliphatic dicarboxylic acid, aliphatic diol, and rigid crystallization inhibition unit selected in this invention can all be derived from biomass, and are inexpensive and have a stable supply. Compared with traditional adhesives that rely on petroleum-based multi-components, this invention significantly reduces dependence on non-renewable resources and carbon emissions, and has outstanding economic and environmental benefits.

[0026] (2) Precise control of molecular structure: By introducing appropriate amounts of rigid crystallization inhibition units (FDCA and / or CHDA) into the aliphatic polyester backbone, the crystallization behavior, glass transition temperature, and molecular chain flexibility can be adjusted, allowing for the control of crystallization behavior, glass transition temperature, and molecular chain flexibility at low temperatures. T g Achieving a balance between strength and low temperature wettability overcomes the common technical problem of "contradiction between low temperature wettability and mechanical properties" in existing biodegradable adhesives.

[0027] (3) Optimized and innovative process path: The preparation strategy of "staged dehydration - delayed vacuuming - graded heating - viscosity / torque closed-loop control" proposed in this invention is different from the traditional endpoint determination mode that relies on fixed time or by-product water volume. This process innovation not only avoids the problem of insufficient conversion of FDCA / CHDA due to premature vacuuming, but also effectively reduces the risk of chain breakage and thermal degradation through graded heating, and achieves the consistency of polymer molecular weight distribution by relying on dual monitoring of viscosity and torque, so that the performance of the obtained product is stable and predictable.

[0028] (4) Significant comprehensive performance advantages: Compared with existing petroleum-based or bio-based biodegradable adhesives, the copolyester adhesive in this invention has a low glass transition temperature (ensuring low-temperature wettability), high peel strength (ensuring bonding reliability), and controllable degradation rate (ensuring environmental friendliness). This combination of performances makes it exhibit significant technical advantages and broad market prospects in application scenarios such as low-temperature assembly and packaging heat sealing, where both biodegradability and low-temperature resistance are required. Detailed Implementation

[0029] The technical solution of the present invention will be illustrated below with specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0030] The preparation method of the low-temperature resistant biodegradable copolyester adhesive of the present invention includes the following steps: (1) Add adipic acid, aliphatic diol, rigid crystallization inhibition unit and catalyst to the reaction vessel and mix. The rigid crystallization inhibition unit is 2,5-furandicarboxylic acid and / or 1,4-cyclohexanedicarboxylic acid, and its molar amount is 3~18% of the total molar amount of adipic acid and rigid crystallization inhibition unit. The aliphatic diol is 1,3-propanediol (PDO) and / or diethylene glycol (DEG). The molar amount of aliphatic diol to the total molar amount of adipic acid and rigid crystallization inhibition unit is 1.05~1.30:1. The amount of catalyst is 0.01~0.5% of the total mass of adipic acid, aliphatic diol and rigid crystallization inhibition unit. Nitrogen gas is used to replace the reaction vessel three times at 60 °C. The temperature is raised to 160~200 °C under nitrogen atmosphere to carry out the esterification reaction for 0.5~6 h. By-product water is discharged during the reaction.

[0031] (2) When the amount of by-product water discharged reaches 80-90% of the theoretical value, the pressure is reduced stepwise. First, the pressure is rapidly reduced from atmospheric pressure to an absolute pressure of several hundred Pa (200-500 Pa), and then slowly reduced to an absolute pressure ≤100 Pa. After the vacuum conditions are stable, the pre-condensation and final condensation reactions are carried out by staged heating. First, the temperature is raised to 190-230 ℃ for pre-condensation reaction, and the reaction is carried out for 0.1-2 h, with the torque monitored in real time. Then, the temperature is raised to 200-250 ℃ for final condensation reaction, and the reaction is carried out for 0.5-4 h, with the viscosity and torque monitored in real time. (3) When the viscosity and torque signals stabilize and enter the preset window, the reaction is terminated to obtain a copolyester adhesive with an intrinsic viscosity of 0.45~0.80 dL / g.

[0032] In a specific embodiment of the present invention, the catalyst is one or more of tetrabutyl titanate, tetraisopropyl titanate, tetraethyl titanate, antimony trioxide, antimony glycolate, antimony acetate, stannous octoate, stannous chloride, and stannous oxide.

[0033] Example 1 (DEG system, FDCA 3 mol%) (1) 509.38 g (4.80 mol) of diethylene glycol, 567.02 g (3.88 mol) of adipic acid, 18.73 g (0.12 mol) of 2,5-furandicarboxylic acid and 0.329 g (0.03 wt%) of antimony glycol were added to the reactor and purged with nitrogen three times at 60 °C. The temperature was raised to 190 °C under a nitrogen atmosphere to carry out the esterification reaction for 2 h, and by-product water was discharged during the reaction.

[0034] (2) When the amount of by-product water discharged reaches 85% of the theoretical value, start vacuuming and adopt staged decompression. First, reduce the pressure from atmospheric pressure to 300 Pa within 15 min, and then slowly reduce it to ≤100 Pa within 20 min, so that the system can smoothly enter the high vacuum.

[0035] After vacuum stabilization, a staged heating process was implemented. First, the temperature was raised to 210 °C for a pre-condensation reaction, which was carried out for 1 h, with the torque monitored in real time (45±5 N•m). Then, the temperature was raised to 240 °C for a final condensation reaction, with the viscosity and torque monitored in real time.

[0036] (3) When the viscosity reaches 1.5 Pa•s or above (250℃, 100 s) -1 The reaction was terminated when the torque stabilized at 85±5 N•m. The mixture was then cooled and pelletized to obtain poly(diethylene glycol-adipic acid / FDCA) ester.

[0037] Example 2 (DEG system, FDCA 10 mol%) This embodiment uses the same preparation process as Example 1, except that the raw materials include 509.38 g (4.80 mol) of diethylene glycol, 526.10 g (3.60 mol) of adipic acid, 62.44 g (0.40 mol) of 2,5-furandicarboxylic acid, and 0.329 g (0.03 wt%) of antimony glycolide, and finally poly(diethylene glycol-adipic acid / FDCA) ester is obtained.

[0038] Example 3 (DEG system, FDCA 18 mol%) This embodiment uses the same preparation process as Example 1, except that the raw materials include 509.38 g (4.80 mol) of diethylene glycol, 479.34 g (3.28 mol) of adipic acid, 112.38 g (0.72 mol) of 2,5-furandicarboxylic acid, and 0.330 g (0.03 wt%) of antimony glycolide, and finally poly(diethylene glycol-adipic acid / FDCA) ester is obtained.

[0039] Example 4 (DEG system, CHDA 3 mol%) This embodiment uses the same preparation process as Example 1, the only difference being that the raw materials include 509.38 g (4.80 mol) of diethylene glycol, 567.02 g (3.88 mol) of adipic acid, 20.66 g (0.12 mol) of 1,4-cyclohexanedicarboxylic acid and 0.329 g (0.03 wt%) of antimony glycolide, and finally poly(diethylene glycol-adipic acid / CHDA) ester is obtained.

[0040] Example 5 (DEG system, CHDA 10 mol%) This embodiment uses the same preparation process as Example 1, except that the raw materials include 509.38 g (4.80 mol) of diethylene glycol, 526.10 g (3.60 mol) of adipic acid, 68.87 g (0.40 mol) of 1,4-cyclohexanedicarboxylic acid, and 0.331 g (0.03 wt%) of antimony glycolide, and finally poly(diethylene glycol-adipic acid / CHDA) ester is obtained.

[0041] Example 6 (DEG system, CHDA 18 mol%) This embodiment uses the same preparation process as Example 1, except that the raw materials include 509.38 g (4.80 mol) of diethylene glycol, 479.34 g (3.28 mol) of adipic acid, 123.97 g (0.72 mol) of 1,4-cyclohexanedicarboxylic acid, and 0.334 g (0.03 wt%) of antimony glycolide, and finally poly(diethylene glycol-adipic acid / CHDA) ester is obtained.

[0042] Example 7 (PDO system, FDCA 3 mol%) This embodiment uses the same preparation process as Example 1, except that the raw materials include 366.50 g (4.80 mol) of 1,3-propanediol, 567.02 g (3.88 mol) of adipic acid, 18.73 g (0.12 mol) of 2,5-furandicarboxylic acid, and 0.285 g (0.03 wt%) of antimony glycolide, and finally poly(1,3-propanediol-adipic acid / FDCA) ester is obtained.

[0043] Example 8 (PDO system, FDCA 5 mol%) This embodiment uses the same preparation process as Example 1, except that the raw materials include 366.50 g (4.80 mol) of 1,3-propanediol, 555.33 g (3.80 mol) of adipic acid, 31.22 g (0.20 mol) of 2,5-furandicarboxylic acid, and 0.286 g (0.03 wt%) of antimony glycolide, and finally poly(1,3-propanediol-adipic acid / FDCA) ester is obtained.

[0044] Example 9 (PDO system, FDCA 10 mol%) This embodiment uses the same preparation process as Example 1, except that the raw materials include 366.50 g (4.80 mol) of 1,3-propanediol, 526.10 g (3.60 mol) of adipic acid, 62.44 g (0.40 mol) of 2,5-furandicarboxylic acid, and 0.286 g (0.03 wt%) of antimony glycolide, and finally poly(1,3-propanediol-adipic acid / FDCA) ester is obtained.

[0045] Example 10 (PDO system, FDCA 18 mol%) This embodiment uses the same preparation process as Example 1, except that the raw materials include 366.50 g (4.80 mol) of 1,3-propanediol, 479.34 g (3.28 mol) of adipic acid, 112.38 g (0.72 mol) of 2,5-furandicarboxylic acid, and 0.287 g (0.03 wt%) of antimony glycolide, and finally poly(1,3-propanediol-adipic acid / FDCA) ester is obtained.

[0046] Example 11 (DEG system, 5 mol% each of FDCA and CHDA) This embodiment uses the same preparation process as Example 1, the only difference being that the raw materials include 509.38 g (4.80 mol) of diethylene glycol, 526.10 g (3.60 mol) of adipic acid, 31.22 g (0.20 mol) of 2,5-furandicarboxylic acid, 34.44 g (0.20 mol) of 1,4-cyclohexanedicarboxylic acid, and 0.330 g (0.03 wt%) of antimony glycolide, finally yielding poly(1,3-propanediol-adipic acid / FDCA / CHDA) ester.

[0047] Example 12 (PDO+DEG mixed system, FDCA 10 mol%) This embodiment uses the same preparation process as Example 1, except that the raw materials include 183.25 g (2.40 mol) of 1,3-propanediol, 254.69 g (2.40 mol) of diethylene glycol, 526.10 g (3.60 mol) of adipic acid, 62.44 g (0.40 mol) of 2,5-furandicarboxylic acid, and 0.308 g (0.03 wt%) of antimony glycolide, and finally poly(1,3-propanediol / diethylene glycol-adipic acid / FDCA) ester is obtained.

[0048] Comparative Example 1 (DEG system, without rigid crystallization inhibition unit) This comparative example uses the same preparation process as Example 1, except that the raw materials include 509.38 g (4.80 mol) of diethylene glycol, 584.56 g (4.00 mol) of adipic acid, and 0.328 g (0.03 wt%) of antimony glycol, and finally poly(diethylene glycol-adipic acid) ester is obtained.

[0049] Comparative Example 2 (DEG system, TPA 10 mol%) This comparative example uses the same preparation process as Example 1, except that the raw materials include 509.38 g (4.80 mol) of diethylene glycol, 526.10 g (3.60 mol) of adipic acid, 66.45 g (0.40 mol) of terephthalic acid, and 0.331 g (0.03 wt%) of antimony glycol, and finally poly(diethylene glycol-adipic acid / TPA) ester is obtained.

[0050] Comparative Example 3 (PDO system, without rigid crystallization inhibition unit) This comparative example uses the same preparation process as Example 1, except that the raw materials include 366.50 g (4.80 mol) of 1,3-propanediol, 584.56 g (4.00 mol) of adipic acid, and 0.285 g (0.03 wt%) of antimony glycolide, and finally poly(1,3-propanediol-adipic acid) ester is obtained.

[0051] Comparative Example 4 (PDO system, TPA 10 mol%) This comparative example uses the same preparation process as Example 1, except that the raw materials include 366.50 g (4.80 mol) of 1,3-propanediol, 526.10 g (3.60 mol) of adipic acid, 66.45 g (0.40 mol) of terephthalic acid, and 0.287 g (0.03 wt%) of antimony glycolide, and finally poly(1,3-propanediol-adipic acid / TPA) ester is obtained.

[0052] Comparative Example 5 (DEG system, FDCA 25 mol%) This comparative example uses the same preparation process as Example 1, except that the raw materials include 509.38 g (4.80 mol) of diethylene glycol, 438.42 g (3.00 mol) of adipic acid, 156.09 g (1.00 mol) of 2,5-furandicarboxylic acid, and 0.331 g (0.03 wt%) of antimony glycolide, and finally poly(diethylene glycol-adipic acid / FDCA) ester is obtained.

[0053] Comparative Example 6 (1,4-Butanediol system, FDCA 18 mol%) This comparative example uses the same preparation process as Example 1, except that the raw materials include 432.58 g (4.80 mol) of 1,4-butanediol, 479.34 g (3.28 mol) of adipic acid, 112.38 g (0.72 mol) of 2,5-furandicarboxylic acid, and 0.307 g (0.03 wt%) of antimony glycolide, and finally poly(1,4-butanediol-adipic acid / FDCA) ester is obtained.

[0054] Structural and performance testing: 1. Chemical Structure Testing: A 600 MHz nuclear magnetic resonance (NMR) spectrometer was used, with deuterated chloroform as the solvent and tetramethylsilane as the internal standard. The testing temperature was 25 ℃. Based on the 1H NMR spectrum results, the content of rigid units in the copolyester was calculated according to the area ratio of the characteristic peaks of rigid units and short-chain diols.

[0055] 2. Thermal Performance Testing: Using a DSC 214 Polyma differential scanning calorimeter under a nitrogen atmosphere, the copolyester was heated from room temperature to 200 °C at a heating rate of 10 °C / min and held for 2 min to eliminate thermal history. Then, it was cooled to -70 °C at a cooling rate of 10 °C / min to obtain the crystallization temperature. After holding at -70 °C for 2 min, it was heated to 200 °C at a heating rate of 10 °C / min to obtain the melting point of the copolyester. Simultaneously, after eliminating thermal history, it was rapidly cooled to -70 °C and held for 2 min, then heated to 200 °C at a heating rate of 10 °C / min to obtain the glass transition temperature of the copolyester.

[0056] 3. 180º Peel Strength Test: A UTM2503 electronic universal testing machine was used with a peel rate of 300 mm / min. The lower clamp was fixed while the upper clamp moved upwards. The automatic recording instrument recorded the value every 0.02 s, and the average value was calculated after the tensile force stabilized. The test sample was evenly coated onto a biaxially oriented polypropylene film (24 mm wide) using a coater, with an adhesive layer thickness of approximately 5 µm. The coated sample was then adhered to a stainless steel plate (200 mm long, 32 mm wide, and 1.4 mm thick) that had been cleaned three times with acetone. A 2 kg roller was used to roll the sample back and forth twice. Each sample was tested in parallel three times, and the average value was taken.

[0057] 4. Degradation Performance Test: A certain amount of sample was placed in a test tube containing lipase (from porcine pancreas) in a phosphate buffer solution (pH = 7.4), and placed in a shaking water bath at 37 ℃ for degradation performance testing. The degradation solution was changed every 7 days. After 28 days of degradation, the sample was removed, dried, and weighed. The degradation rate was calculated based on the mass change of the sample before and after degradation.

[0058] Table 1. Specific molar contents of rigid crystallization inhibition units in Examples 1-12 and Comparative Examples 1-6 Table 2 Performance data of the copolyesters prepared in Examples 1-12 and Comparative Examples 1-6 As shown in Table 1, the intrinsic viscosity of the samples prepared in each embodiment and comparative example of this invention remained around 0.8 dL / g, indicating that the improved polycondensation process can stably obtain high molecular weight products under different formulations, thus ensuring that the performance differences mainly stem from molecular structure design. Table 2 shows the crystallization temperature, melting point, glass transition temperature, 180º peel strength, and degradation test results of the copolyesters prepared in Examples 1-12 and Comparative Examples 1-6. Although the peel strength test was conducted at room temperature, the copolyester adhesive of this invention... T g The material remains in a rubbery state at low temperatures, with sufficient mobility and wetting ability in its chain segments, thus ensuring good adhesion performance even at temperatures below room temperature.

[0059] Table 2 shows that the type of diol plays a crucial role in the crystallinity and low-temperature adhesion properties of polyesters. Examples 1-6, 11, and Comparative Examples 1-2 all used diethylene glycol as the diol; none of these systems showed a crystalline peak in DSC testing, exhibiting an amorphous state. The copolymers in Examples 1-6, 11... T gLocated in the -60 to -50 °C range, it maintains flexibility and wettability at room temperature, with a peel strength of 5.7 to 6.6 N / 25 mm. In degradation experiments, the degradation rate after 28 days was 22% to 32%, demonstrating good low-temperature adhesion and degradability. In contrast, Comparative Example 3, a system using 1,3-propanediol as the diol and without the addition of rigid crystallization inhibition units, exhibited crystallization behavior and showed no adhesion at room temperature. Example 7 (PDO system, FDCA 3 mol%) failed to effectively disrupt chain segment regularity due to the low content of added rigid units, and its peel performance was consistent with Comparative Example 3, indicating that a low amount of rigid units is insufficient to inhibit crystallization. Further increasing the content of rigid units resulted in the disappearance of crystallization signals in Examples 8-10, with the samples remaining amorphous. Although Example 10 had a higher amount of rigid units added compared to Example 9, the peel strength decreased from 5.2 N / 25 mm to 4.8 N / 25 mm. This indicates that in the PDO system, low-dosage rigid units are insufficient to suppress crystallization, while medium-dosage units show significant improvement. Further increasing the dosage leads to an increase in the glass transition temperature of the copolyester and a decrease in chain segment mobility, resulting in decreased adhesion properties due to excessive rigid unit content. Furthermore, in Comparative Example 6, a system using 1,4-butanediol as the diol, even with the addition of 18 mol% FDCA as a rigid unit, crystallization could not be completely suppressed, and it exhibited no adhesion at room temperature.

[0060] As shown in Examples 1-3 and 4-6, different rigid crystallization inhibition units exhibit differences in structure and performance regulation. FDCA, with its planar heteroaromatic rings and strong polarity, can enhance interchain forces and interfacial bearing capacity even at low dosages through π-π interactions and rigid constraints. CHDA, with its non-coplanar ring structure and significant steric hindrance, can more effectively disrupt chain segment regularity and inhibit crystallization. Therefore, at the same content of rigid crystallization inhibition units, polyesters using CHDA as the rigid crystallization inhibition unit exhibit lower glass transition temperatures, higher peel strengths, and higher degradation rates compared to polyesters using FDCA or PTA as rigid crystallization inhibition units. Comparative Example 2 and Examples 2 and 5 all added approximately 10 mol% of rigid units to the DEG system, while Comparative Example 4 and Example 9 all added approximately 10 mol% of rigid units to the PDO system. However, Comparative Examples 2 and 4 used terephthalic acid (TPA) as the rigid unit. Because terephthalic acid is highly symmetrical, its ability to inhibit crystallization is weaker than that of FDCA and CHDA. Therefore, its addition to the DEG / PDO system of this invention will significantly increase T. gThis weakens the peel strength and degradation rate, therefore it is only used as a comparative example and not a preferred embodiment of the present invention. Furthermore, Example 11, which uses FDCA and CHDA synergistically in the DEG system of the present invention, also achieves a good effect in inhibiting crystallization. Their mechanisms of action are complementary, allowing the material to possess both high interfacial bearing capacity and maintain flexibility and amorphous characteristics, achieving a peel strength of up to 6.6 N / 25 mm. However, Comparative Example 5, due to the addition of excessive rigid units, has reduced free volume and restricted chain segment movement, resulting in T... g Increased rigidity and decreased flexibility; furthermore, the hydrophobicity of excessive rigid ring structures inhibits hydrolysis and penetration, resulting in a slower and more uneven degradation rate. Example 12 uses a DEG+PDO compound system. Due to the presence of ether bonds and flexibility in the DEG matrix, it has a lower glass transition temperature and a higher degradation rate than Example 9. The performance of the copolyester in Example 12 is between that of Example 2 and Example 9.

[0061] In summary, the data results indicate that by rationally selecting diols and rigid units and optimizing their dosage, it is possible to achieve low... T g This approach achieves a balance between strong adhesion and biodegradability, thus providing an effective material design solution for green adhesives in low-temperature environments.

[0062] The above are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made using the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for preparing a low-temperature resistant, biodegradable copolyester adhesive, characterized in that, Includes the following steps: (1) Adipic acid, aliphatic diol, rigid crystallization inhibition unit and catalyst are mixed and then subjected to esterification reaction; the aliphatic diol is 1,3-propanediol and / or diethylene glycol; the rigid crystallization inhibition unit is 2,5-furandicarboxylic acid and / or 1,4-cyclohexanedicarboxylic acid; (2) When the amount of by-product water discharged reaches 80-90% of the theoretical value, the absolute pressure is reduced to ≤100 Pa, and the pre-condensation reaction and final condensation reaction are carried out in sequence; (3) The reaction was terminated to obtain copolyester adhesive.

2. The method for preparing the low-temperature resistant biodegradable copolyester adhesive according to claim 1, characterized in that, The molar amount of the rigid crystallization inhibition unit is 3-18% of the total molar amount of adipic acid and the rigid crystallization inhibition unit.

3. The method for preparing the low-temperature resistant biodegradable copolyester adhesive according to claim 1, characterized in that, The molar ratio of the aliphatic diol to the total molar ratio of adipic acid and rigid crystallization inhibition unit is 1.05~1.30:

1.

4. The method for preparing the low-temperature resistant biodegradable copolyester adhesive according to claim 1, 2, or 3, characterized in that, The esterification reaction is carried out under an inert atmosphere at 160-200 °C for 0.5-6 h.

5. The method for preparing the low-temperature resistant biodegradable copolyester adhesive according to claim 1, characterized in that, The pre-condensation reaction is carried out at 190~230 °C for 0.1~2 h.

6. The method for preparing the low-temperature resistant biodegradable copolyester adhesive according to claim 1 or 5, characterized in that, The final polycondensation reaction is carried out at 200~250 °C for 0.5~4 h.

7. The method for preparing the low-temperature resistant biodegradable copolyester adhesive according to claim 1, characterized in that, The catalyst is one or more of the following: tetrabutyl titanate, tetraisopropyl titanate, tetraethyl titanate, antimony trioxide, antimony glycolate, antimony acetate, stannous octoate, stannous chloride, and stannous oxide.

8. The method for preparing the low-temperature resistant biodegradable copolyester adhesive according to claim 1 or 7, characterized in that, The amount of catalyst used is 0.01 to 0.5% of the total mass of adipic acid, aliphatic diol, and rigid crystallization inhibition unit.

9. The method for preparing the low-temperature resistant biodegradable copolyester adhesive according to claim 1, characterized in that, The intrinsic viscosity of the copolyester adhesive is 0.45~0.80 dL / g.

10. A low-temperature resistant biodegradable copolyester adhesive prepared by the preparation method according to any one of claims 1-9.

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