Hydrolysis-resistant thermoplastic polyester elastomer and method for preparing the same

Abstract

The application discloses a hydrolysis-resistant thermoplastic polyester elastomer and a preparation method thereof. The thermoplastic polyester elastomer is copolymerized from hard segments and soft segments. The hard segments are derived from regenerated terephthalic acid (r-PTA) meeting the conditions of 4-CBA content less than or equal to 10 ppm and p-toluic acid (p- TA) content less than or equal to 30 ppm. The initial terminal carboxyl content of the polyester elastomer is 4 to 20 mol / t. The content of the hydrolysis-resistant stabilizer used in the preparation process of the thermoplastic polyester elastomer is 0 to 0.1 wt%. By limiting the 4-CBA and p- TA contents of the regenerated terephthalic acid (r-PTA), the chain-oxidation reaction of the polyether soft segment initiated by 4-CBA is blocked from the source. By limiting the initial terminal carboxyl content, the hydrolysis autocatalytic cycle is effectively avoided, the bulk oxidation resistance and hydrolysis resistance of the TPEE are improved, the dependence on high-priced hydrolysis-resistant agents or special antioxidants is eliminated, and the production cost is reduced.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, and in particular to a hydrolysis-resistant thermoplastic polyester elastomer and its preparation method. Background Technology

[0002] Thermoplastic polyester elastomers (TPEEs) are block copolymers containing hard polyester segments (such as polybutylene terephthalate, PBT) and soft polyether segments (such as polytetrahydrofuran ether glycol, PTMEG). Due to their combination of rubber elasticity and engineering plastic strength, they are widely used in high-end applications such as automotive constant velocity joint (CVJ) sheaths, airbag covers, and new energy cables.

[0003] In the aforementioned operating environments, thermoplastic polyester elastomers (TPEEs) often require high hydrolysis resistance and oxidation resistance. However, TPEE molecular chains contain a large number of ester bonds, making them highly susceptible to hydrolysis in humid and hot environments (such as high humidity environments above 80°C). The terminal carboxyl groups (AV) generated by hydrolysis are acidic, further catalyzing the hydrolysis of remaining ester bonds, forming a vicious cycle of "self-catalysis." To improve hydrolysis resistance, existing technologies typically add expensive polycarbodiimide hydrolysis stabilizers, but this leads to increased costs and product yellowing. Existing technologies often use hindered phenolic antioxidants (such as Irganox 1010) to inhibit oxidation; however, these antioxidants contain ester bonds in their molecular structure. In the harsh hydrolytic environment faced by TPEEs, the antioxidants themselves will hydrolyze and become ineffective, even producing small molecule acidic substances that accelerate matrix degradation.

[0004] Therefore, developing a thermoplastic polyester elastomer (TPEE) product that can have high hydrolysis resistance and oxidation resistance without adding or with little addition of hydrolysis-resistant agents is a problem that the industry urgently needs to solve. Summary of the Invention

[0005] In response to the aforementioned shortcomings in existing production processes, the applicant provides a hydrolysis-resistant thermoplastic polyester elastomer and its preparation method, which can significantly improve the hydrolysis resistance and aging resistance of the product without adding or with minimal addition of hydrolysis-resistant agents, or by using only ordinary ester-containing antioxidants.

[0006] The technical solution adopted in this invention and its beneficial effects compared with the prior art are as follows:

[0007] This application provides a hydrolysis-resistant thermoplastic polyester elastomer (TPEE) composed of hard and soft segments copolymerized together. The hard segments are derived from recycled terephthalic acid (r-PTA) with a 4-CBA content of less than or equal to 10 ppm and a p-methylbenzoic acid (p-TA) content of less than or equal to 30 ppm. The initial terminal carboxyl group content of the polyester elastomer is 4 to 20 mol / t, and the content of the hydrolysis-resistant stabilizer used in the preparation process is 0 to 0.1 wt%. By limiting the 4-CBA (≤10 ppm) and p-TA (≤30 ppm) content of the recycled terephthalic acid (r-PTA), the chain oxidation reaction of the polyether soft segments initiated by 4-CBA is blocked at the source. At the same time, limiting the initial terminal carboxyl group content effectively avoids the hydrolysis autocatalytic cycle, improves the bulk oxidation resistance and hydrolysis resistance of TPEE, eliminates the need for expensive hydrolysis-resistant agents or special antioxidants, and reduces production costs.

[0008] Current technology generally believes that 4-CBA (p-carboxybenzaldehyde) only needs to be controlled below 25 ppm to avoid affecting the product's color. This overlooks the unique structural characteristics of TPEE, which contains a large amount of polyether soft segments (-COC-). Unlike the stable methylene groups in PBT hard segments, the hydrogen atoms (α-H) on the α-carbons connected to the ether oxygen atoms in TPEE soft segments have lower bond energies. Furthermore, the aldehyde groups in 4-CBA readily generate free radicals under thermo-oxidative conditions. These free radicals preferentially plunder the α-H in the soft segments and trigger a chain reaction of oxidation. Therefore, 4-CBA in the TPEE system not only causes coloring but also leads to the targeted degradation of the soft segments. This invention recognizes the specific harm 4-CBA causes to polyether soft segments (coloring and oxidation), breaking the traditional understanding that simply applying PBT raw material standards to TPEE is sufficient. By specifically controlling the 4-CBA content in TPEE raw materials, the chain reaction of preferential oxidation and degradation of soft segments is blocked at the source, solving the long-standing problem of insufficient thermo-oxidative stability in TPEE and significantly improving the product's mechanical properties, durability, and reliability.

[0009] This invention controls 4-CBA to below 10 ppm, effectively reducing the free radical source that triggers the α-H hydrogen abstraction reaction in the soft segments of polyethers, protecting the soft segments, and significantly improving the bulk antioxidant and hydrolysis resistance of TPEE. Simultaneously, it reduces the tendency of the matrix to undergo autocatalytic degradation, allowing the use of conventional ester-containing antioxidants to meet basic requirements, or eliminating or minimizing the addition of hydrolysis-resistant agents, thus reducing dependence on special additives. Limiting the hydrolysis-resistant stabilizer content to 0-0.1 wt% avoids the increased costs and yellowing problems caused by excessive addition of polycarbodiimide stabilizers in existing technologies.

[0010] After the thermoplastic polyester elastomer is treated in a boiling water environment at 100℃ for 168 hours, the end carboxyl group increment ΔAV ≤ 15 mol / t and the color difference change Δb* ≤ 5.0. The final aging performance indicators (ΔAV ≤ 15 mol / t, Δb* ≤ 5.0) ensure that the product has both high hydrolysis resistance and yellowing resistance in humid and hot environments.

[0011] The regenerated terephthalic acid (r-PTA) has specific stable carbon isotope characteristics, its δ 13 The C value ranges from -24‰ to -27‰. This is determined by δ... 13 The C value (-24‰ to -27‰) clearly defines the carbon isotope characteristics of r-PTA, which can quickly distinguish between recycled materials and petrochemical materials (v-PTA: -28‰ to -30‰), enabling raw material traceability and quality control.

[0012] The polyester elastomer contains an antioxidant, which comprises a hindered phenolic compound whose molecular structure does not contain ester bonds, and the relative molecular mass of the antioxidant is greater than 700 g / mol. The inclusion of a hindered phenolic antioxidant without ester bonds and with a relative molecular mass >700 g / mol solves the problem of existing ester-bonded antioxidants (such as Irganox 1010) being prone to hydrolysis and failure under humid and hot environments, and generating acidic substances that accelerate matrix degradation. The antioxidant itself has a stable structure and can exert a long-lasting antioxidant effect, further improving the aging resistance and durability of TPEE.

[0013] The antioxidant is 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene. The preferred antioxidant is Irganox 1330, whose specific chemical structure (no ester bonds, high molecular weight) exhibits optimal compatibility with the TPEE system. Example data shows that using this antioxidant results in a ΔAV of only 8.0 mol / t and a Δb* of only 2.3. Compared to other antioxidants, it achieves superior synergistic effects in hydrolysis resistance and anti-yellowing, meeting the stringent long-term performance requirements of high-end applications.

[0014] The soft segment is derived from polyether polyol units, which are selected from at least one of polytetrahydrofuran ether diol (PTMEG), polyethylene glycol (PEG), polypropylene glycol (PPG), or copolymers thereof, and the number-average molecular weight (Mn) of the polyether polyol is 600 to 3000 g / mol. Limiting the type of polyether polyol (PTMEG / PEG / PPG, etc.) and its number-average molecular weight (600-3000 g / mol) ensures good compatibility between the soft segment and the hard segment (PBT), retaining the core characteristics of TPEE—combining rubber elasticity and engineering plastic strength—while also allowing for molecular weight adjustment to adapt to the mechanical requirements of different application scenarios (such as soft sheaths and structural components).

[0015] The polyester elastomer has a Shore D hardness of 20D to 75D, and its hard segment to soft segment mass ratio is 20:80 to 80:20. The Shore D hardness (20D-75D) and the hard segment to soft segment mass ratio (20:80-80:20) allow for flexible adjustment of the product's elasticity and rigidity balance, covering the application needs of different high-end fields such as automotive CVJ covers (low hardness, high elasticity) and airbag covers (medium-high hardness, high strength), thereby enhancing the product's applicability and market competitiveness.

[0016] The 4-CBA content of the recycled terephthalic acid (r-PTA) is preferably less than or equal to 5 ppm, and the p-methylbenzoic acid (p-TA) content is preferably less than or equal to 20 ppm. After the polyester elastomer is treated in a boiling water environment at 100°C for 168 hours, its terminal carboxyl group increment ΔAV ≤ 12 mol / t and color difference change value Δb* ≤ 4.0. By optimizing the 4-CBA (≤ 5 ppm), p-TA (≤ 20 ppm), and more stringent aging performance indicators (ΔAV ≤ 12 mol / t, Δb* ≤ 4.0) of r-PTA, the upper limit of product performance is further improved, making it suitable for high-end applications with extremely high requirements for hydrolysis resistance and yellowing resistance (such as new energy cables and components in long-term humid and hot environments). At the same time, the raw material standards are refined to help with precise quality control in the production process and ensure batch stability of products.

[0017] The polyester elastomer is molded into automotive constant velocity joint sleeves, foam materials, functional films, or monofilaments and fibers.

[0018] This application provides a method for preparing the hydrolysis-resistant thermoplastic polyester elastomer, characterized by comprising the following steps:

[0019] (1) Hard segment esterification: Regenerated terephthalic acid (r-PTA) is mixed with 1,4-butanediol (BDO) and the first part of the catalyst, and the esterification reaction is carried out under an inert atmosphere until the reaction system is clear and transparent;

[0020] (2) Soft segment introduction and antioxidant addition: Polyether polyol and antioxidant are added to the product of step (1), and the remaining catalyst is added to carry out transesterification reaction;

[0021] (3) Polycondensation: Pre-polymerization and final polymerization reactions are carried out under vacuum conditions until the predetermined torque value is reached. Detailed Implementation

[0022] This invention provides a hydrolysis-resistant thermoplastic polyester elastomer, copolymerized from hard and soft segments. The hard segments are formed by the condensation polymerization of recycled terephthalic acid (r-PTA) and 1,4-butanediol (BDO), while the soft segments are derived from polyether polyol units selected from at least one of polytetrahydrofuran ether glycol (PTMEG), polyethylene glycol (PEG), polypropylene glycol (PPG), or copolymers thereof, wherein the number-average molecular weight (Mn) of the polyether polyol is 600 to 3000 g / mol. The polyester elastomer has a Shore hardness (Shore D) of 20D to 75D, and the mass ratio of hard segments to soft segments is 20:80 to 80:20.

[0023] The recycled terephthalic acid (r-PTA) contains ≤10 ppm of p-carboxybenzaldehyde (4-CBA) and ≤30 ppm of p-methylbenzoic acid (p-TA); the initial carboxyl group content (AVinitial) of the thermoplastic polyester elastic is 4 to 20 mol / t. Recycled terephthalic acid (r-PTA) exhibits a specific stable carbon isotope abundance (δ¹⁰). 13 C) Characteristics, δ 13 The C value typically ranges from -24‰ to -27‰ (relative to the VPDB standard). This characteristic is used to distinguish terephthalic acid (v-PTA) derived from petroleum cracking (typically -28‰ to -30‰). Those skilled in the art will know that this value may vary reasonably depending on the source of the raw materials.

[0024] The hydrolysis-resistant thermoplastic polyester elastomer of the present invention, when treated in a boiling water environment at 100°C for 168 hours (7 days) with a hydrolysis-resistant stabilizer (such as carbodiimide) content of 0 to 0.1 wt%, exhibits an end carboxyl group increment ΔAV = AV(168h) - AV(initial) ≦ 15 mol / t and a color difference change value Δb* ≦ 5.0.

[0025] The regenerated terephthalic acid (r-PTA) of this invention, combined with conventional antioxidants, can meet basic hydrolysis resistance requirements. The antioxidants comprise hindered phenolic compounds whose molecular structures are ester-bond-free, and whose relative molecular mass is greater than 700 g / mol. For superior performance, 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene is preferred.

[0026] The r-PTA described in this invention is a recycled terephthalic acid obtained from waste polyester clothing as a base material through an enzyme-catalyzed depolymerization and crystallization purification process or a photocatalytic degradation and multi-stage refining process. The v-PTA is terephthalic acid synthesized from fossil resources such as petroleum and natural gas through a p-xylene (PX) liquid-phase oxidation process.

[0027] The specifications of the main raw materials used in the embodiments and comparative examples of the present invention are shown in Table 1:

[0028] Table 1:

[0029] code name type p-TA content (ppm) 4-CBA content (ppm) <![CDATA[δ 13 C value]]> r-PTA-1 This invention / enzymatic hydrolysis method 12 2.5 -26.2‰ r-PTA-2 This invention / photolysis method 25 8.0 -26.4‰ v-PTA Comparative / Petrochemical Grade 150 25 -28.5‰

[0030] Other raw materials used in this invention are as follows: 1,4-Butanediol (BDO) with a purity ≥99.7% and moisture content ≤0.03%. Polytetrahydrofuran ether glycol (PTMEG) with a number-average molecular weight of Mn = 2000 ± 25 g / mol. Antioxidant A (without ester bonds) is chemically named 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene, brand name: Irganox 1330. Antioxidant B (containing ester bonds) is chemically named pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate], brand name: Irganox 1010. The hydrolysis-resistant stabilizer is polymerized carbodiimide, brand name: Stabaxol P. The catalyst is tetrabutyl titanate (TBT).

[0031] The specific testing methods are as follows (all quantitative analyses were performed in at least three parallel experiments, and the average value was taken):

[0032] 1. Test method for terminal carboxyl group content (AV) and its increment (ΔAV): Refer to the textile industry standard FZ / T50012-2006 for specific details. The solvent system is o-cresol and chloroform (volume ratio 7:3), the indicator is bromocresol green solution, and the titrant is 0.05 mol / L potassium hydroxide-ethanol standard titrant solution. Calculation results: AV(mol / t) = [(V-V0)×c×1000] / m, ΔAV = AV(168h) - AV(initial).

[0033] 2. Boiling water hydrolysis resistance test (100℃ / 168h): TPEE resin was dried in a vacuum oven at 100℃ for 4 hours and then molded into standard tensile specimens using an injection molding machine. The specimens were placed in a flask equipped with a reflux condenser for aging, and kept in boiling water at 100±1℃ for 168 hours. After drying, they were tested.

[0034] 3. Color difference test (Δb*): The instrument selected is the HunterLab spectrophotometer, Δb*=b*(168h)-b*(initial).

[0035] 4. Content determination (4-CBA and p-TA): The specific procedure shall be performed in accordance with the national standard GB / T30921.1-2014, using high performance liquid chromatography (HPLC) with a C18 reversed-phase column; the ultraviolet detection wavelength is 254 nm; the sample is dissolved in ammonia water, and the detection limit is LOD≦0.5ppm.

[0036] 5. Stable carbon isotope ratio (δ) 13 C) Determination: Elemental analysis-isotope ratio mass spectrometry (EA-IRMS) was used. The sample was instantaneously combusted at high temperature to convert into CO2 gas, and the 13C / 12C ratio was determined by mass spectrometry. The instrumentation consisted of an elemental analyzer (e.g., Flash2000) coupled with an isotope ratio mass spectrometer (e.g., ThermoDeltaVPlus). Test conditions: Combustion temperature was 1020℃ (ensuring complete oxidation of the sample). High-purity helium was used as the carrier gas. The test results are expressed as parts per thousand (δ‰) relative to the Vienna Pee Dee Belemnite (VPDB) standard, and the test accuracy (SD) should be ≤0.15‰. Calculation formula: δ 13 C(‰) = [(Rsample / Rstandard)-1]×1000, where: Rsample: abundance ratio of 13C / 12C in the sample; Rstandard: standard ratio of VPDB (0.0112372).

[0037] This invention employs a step-by-step feeding process to ensure complete esterification of the hard segments and to maximize the protection of the soft segments from degradation. The specific steps are as follows:

[0038] Step 1: Hard segment esterification reaction (PBT oligomer synthesis)

[0039] 1. Feeding: Check the cleanliness of the 30L polymerization reactor and ensure that the jacket oil temperature heating system, condensation system, and vacuum system are functioning properly. At room temperature, open the feeding port and sequentially add accurately weighed BDO (3.682kg), r-PTA (3.773kg) or v-PTA (3.773kg), and the first part of the catalyst TBT (9.0g).

[0040] 2. Nitrogen purging: Close the feed inlet and start the agitator (40 rpm). Purge the reactor with nitrogen three times (purge to 0.2 MPa and then release the pressure), and finally maintain a slight positive pressure nitrogen protection.

[0041] 3. Esterification reaction: Set the oil bath temperature to 245℃ and control the material temperature inside the vessel at 225-235℃. At this time, water begins to exit from the top of the distillation column. Control the column top temperature at 100-105℃ to separate the generated byproduct water and reflux it to BDO.

[0042] 4. Esterification reaction complete: Closely observe the output water volume and the appearance of the system. When the theoretical output water volume (approximately 818g of water) reaches more than 95%, and the reaction system in the sight glass changes from a white, turbid state to a clear, transparent state, it indicates that the hard segment esterification is basically complete. This process takes approximately 120-150 minutes.

[0043] Step 2: Soft segment introduction and transesterification

[0044] 1. Cooling and feeding: Keep the kettle temperature at 230℃ with fine adjustment. Under continuous nitrogen gas flow protection, quickly feed PTMEG (5.000kg), antioxidant A (ester-free) Irganox 1330 (20.0g) or antioxidant B (ester-containing) Irganox 1010 (20.0g) and the second catalyst TBT (7.0g) through the feed port.

[0045] 2. Ester exchange equilibrium: Increase the stirring speed to 60 rpm and continue stirring the reaction for 20-30 minutes under a normal pressure nitrogen atmosphere. At this time, the PTMEG hydroxyl groups undergo ester exchange with the PBT hard segment end groups, pre-blocking the soft and hard segments and ensuring that the catalyst and antioxidant are mixed evenly.

[0046] Step 3: Pre-condensation (low vacuum stage)

[0047] 1. Linear vacuuming: Within 30-40 minutes, the pressure inside the vessel is linearly reduced from atmospheric pressure to 5000 Pa (50 mbar).

[0048] 2. Heating: Simultaneously, gradually increase the material temperature to 240℃. This stage mainly removes excess BDO and small molecules generated from transesterification. Care must be taken to prevent bumping, which could cause material to rush into the condenser.

[0049] Step 4: Final polycondensation (high vacuum stage)

[0050] 1. High vacuum: Continue to reduce the pressure until the absolute pressure inside the vessel reaches below 50 Pa (0.5 mbar) within 15 minutes.

[0051] 2. Final polymerization temperature control: Control the material temperature at 240-250℃.

[0052] 3. Torque Monitoring: Closely monitor the stirring power (or current / torque value). As the molecular weight increases, the melt viscosity rises rapidly. The TBT catalyst added in step 2 accelerates the polycondensation rate.

[0053] 4. Reaction endpoint: When the stirring torque reaches the preset target value (corresponding to an intrinsic viscosity IV of approximately 1.8-2.0 dL / g), immediately stop heating and stirring.

[0054] Step 5: Discharge and Post-processing

[0055] 1. Break the vacuum: Quickly fill with high-purity nitrogen to atmospheric pressure, and continue to pressurize to a slightly positive pressure.

[0056] 2. Casting strip pelletizing: Open the bottom discharge valve of the kettle and use nitrogen pressure to force the melt into the cooling water tank (the water temperature is controlled at 10-20℃). After cooling into strips, the melt is cut into pellets by a pelletizer.

[0057] 3. Drying: Collect the particles, place them in a vacuum oven, and dry them at 100-110℃ for 4-6 hours. Seal the package and wait for testing.

[0058] To verify the effects of different combinations of raw materials and antioxidants, the experimental formulations and reaction parameters of specific embodiments and comparative examples are shown in Table 2.

[0059] Table 2:

[0060] project Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 PTA r-PTA-1 r-PTA-1 r-PTA-2 r-PTA-1 v-PTA v-PTA v-PTA r-PTA-1 4-CBA / p-TA 2.5 / 12 2.5 / 12 8.0 / 25 2.5 / 12 25 / 150 25 / 150 25 / 150 2.5 / 12 Antioxidant types B (containing esters) A (Ester-free) A (Ester-free) B (containing esters) B (containing esters) A (Ester-free) B (containing esters) B (containing esters) Hydrolysis resistant agent 0 0 0 0.1% 0 0 0.8% 0.5% Polycondensation time (min) 95 90 105 96 130 120 130 105 Initial AV (mol / t) 12.2 9.5 15.5 11.5 27.6 20.5 12.2 6.1 initial b (background color)* 5.5 5.0 5.7 5.6 4.2 4.0 4.5 6.3

[0061] Example 1: Using r-PTA-1 from Table 1 as the raw material, antioxidant B (containing ester bonds) was selected as the antioxidant. No hydrolysis-resistant agent was used. The polycondensation time was 95 minutes. The resulting thermoplastic polyester elastomer particles had an initial AV of 12.2 mol / t and an initial b (base color)* of 5.5. The specific preparation process is as follows:

[0062] Step 1: Hard segment esterification reaction (PBT oligomer synthesis)

[0063] 1. Feeding: Check the cleanliness of the 30L polymerization reactor and ensure that the jacket oil temperature heating system, condensation system, and vacuum system are functioning properly. At room temperature, open the feeding port and sequentially add accurately weighed BDO (3.682kg), r-PTA (3.773kg), and the first part of the catalyst TBT (9.0g).

[0064] 2. Nitrogen purging: Close the feed inlet and start the agitator (40 rpm). Purge the reactor with nitrogen three times (purge to 0.2 MPa and then release the pressure), and finally maintain a slight positive pressure nitrogen protection.

[0065] 3. Esterification reaction: Set the oil bath temperature to 245℃ and control the material temperature inside the vessel at 230℃. At this point, water begins to exit from the top of the distillation column, and the column top temperature is controlled at 100℃.

[0066] 4. Esterification reaction complete: Closely observe the output water and the appearance of the system. When the theoretical output water (approximately 818g of water) reaches more than 95%, and the reaction system in the sight glass changes from a white, turbid state to a clear, transparent state, it indicates that the hard segment esterification is basically complete. This process takes approximately 130 minutes.

[0067] Step 2: Soft segment introduction and transesterification

[0068] 1. Cooling and feeding: Keep the kettle temperature at 230℃ with fine adjustment. Under continuous nitrogen gas flow protection, quickly feed PTMEG (5.000kg), antioxidant B (containing ester bond) (20.0g) and the second part catalyst TBT (7.0g) through the feed port.

[0069] 2. Ester exchange equilibrium: Increase the stirring speed to 60 rpm and continue stirring for 25 minutes under a normal pressure nitrogen atmosphere. At this time, the PTMEG hydroxyl group undergoes ester exchange with the PBT hard segment end group, pre-blocking the soft and hard segments and ensuring that the catalyst and antioxidant are mixed evenly.

[0070] Step 3: Pre-condensation (low vacuum stage)

[0071] 1. Linear vacuuming: Within 35 minutes, the pressure inside the vessel is linearly reduced from atmospheric pressure to 5000 Pa (50 mbar).

[0072] 2. Heating: Gradually increase the material temperature to 240℃.

[0073] Step 4: Final polycondensation (high vacuum stage)

[0074] 1. High vacuum: Continue to reduce the pressure until the absolute pressure inside the vessel reaches below 50 Pa (0.5 mbar) within 15 minutes.

[0075] 2. Final polymerization temperature control: Control the material temperature at 245℃.

[0076] 3. Torque Monitoring: Closely monitor the stirring power (or current / torque value). As the molecular weight increases, the melt viscosity rises rapidly. The TBT catalyst added in step 2 accelerates the polycondensation rate.

[0077] 4. Reaction endpoint: When the stirring torque reaches the preset target value (corresponding to an intrinsic viscosity IV of approximately 1.8-2.0 dL / g), immediately stop heating and stirring.

[0078] Step 5: Discharge and Post-processing

[0079] 1. Break the vacuum: Quickly fill with high-purity nitrogen to atmospheric pressure, and continue to pressurize to a slightly positive pressure.

[0080] 2. Casting strip pelletizing: Open the bottom discharge valve of the kettle and use nitrogen pressure to force the melt into the cooling water tank (the water temperature is controlled at 15℃). After cooling into strips, the melt is cut into pellets by a pelletizer.

[0081] 3. Drying: Collect the particles, place them in a vacuum oven, dry them at 105℃ for 4-6 hours, and seal them in packaging for testing.

[0082] Example 2: Using r-PTA-1 from Table 1 as the raw material, antioxidant A (without ester bonds) was selected as the antioxidant, and no hydrolysis-resistant agent was used. The polycondensation time was 90 minutes. The obtained thermoplastic polyester elastomer particles had an initial AV of 9.5 mol / t and an initial b (base color)* of 5.0. The specific preparation process was the same as in Example 1.

[0083] Example 3: Using r-PTA-2 from Table 1 as the raw material, antioxidant A (without ester bonds) was selected as the antioxidant, and no hydrolysis-resistant agent was used. The polycondensation time was 105 minutes. The obtained thermoplastic polyester elastomer particles had an initial AV of 15.5 mol / t and an initial b (base color)* of 5.7. The specific preparation process was the same as in Example 1.

[0084] Example 4: Using r-PTA-1 from Table 1 as the raw material, antioxidant B (containing ester bonds) was selected as the antioxidant, and the polycondensation time was 96 minutes. The obtained thermoplastic polyester elastomer particles had an initial AV of 11.5 mol / t and an initial b (base color)* of 5.6. After polycondensation was completed, 0.1% of a polycarbodiimide hydrolytic stabilizer was added, and the mixture was stirred. The specific preparation process was the same as in Example 1.

[0085] Comparative Example 1:

[0086] Using v-PTA from Table 1 as the raw material, antioxidant B (containing ester bonds) was selected as the antioxidant, and no hydrolysis-resistant agent was used. The polycondensation time was 130 minutes. The obtained thermoplastic polyester elastomer particles had an initial AV of 27.6 mol / t and an initial b (base color)* of 4.2. The specific preparation process was the same as in Example 1.

[0087] Comparative Example 2:

[0088] Using v-PTA from Table 1 as the raw material, antioxidant A (without ester bonds) was selected as the antioxidant, and no hydrolysis-resistant agent was used. The polycondensation time was 120 minutes. The obtained thermoplastic polyester elastomer particles had an initial AV of 20.5 mol / t and an initial b (base color)* of 4.0. The specific preparation process was the same as in Example 1.

[0089] Comparative Example 3:

[0090] Using v-PTA from Table 1 as the raw material, antioxidant B (containing ester bonds) was selected as the antioxidant, and the polycondensation time was 130 minutes. After polycondensation, 0.8% of a polycarbodiimide hydrolytic stabilizer was added, and the mixture was stirred. The resulting thermoplastic polyester elastomer particles had an initial AV of 12.2 mol / t and an initial b (base color)* of 4.4. The specific preparation process was the same as in Example 1.

[0091] Comparative Example 4:

[0092] Using r-PTA-1 from Table 1 as the raw material, antioxidant B (containing ester bonds) was selected as the antioxidant, and the polycondensation time was 105 minutes. After polycondensation, 0.5% of a polycarbodiimide hydrolytic stabilizer was added and stirred. The resulting thermoplastic polyester elastomer particles had an initial AV of 6.1 mol / t and an initial b (base color)* of 6.3. The specific preparation process was the same as in Example 1.

[0093] The final thermoplastic polyester elastomer particles were tested using the above method, and the physical properties are shown in Table 3.

[0094] Table 3:

[0095] Test Project Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 AV (mol / t) after 168h 26.0 17.5 28.0 24.5 56.6 47.2 18.5 13.2 ΔAV (increment, mol / t) 13.8 8.0 12.5 13 29.0 26.7 6.3 7.1 168h later b* 9.1 7.3 9.3 9.8 12.0 10.5 14.0 12.9 * 3.6 2.3 3.6 4.2 7.8 6.5 9.5 6.6 Judgment Result qualified excellence qualified qualified degradation degradation Yellowing / Failure Yellowing / Failure

[0096] Comparing the example group with the comparative example group, it can be seen that the initial background color of the example group (5.0-6.0) is slightly darker than that of the petrochemical comparative example (4.0-4.5). This is because the r-PTA used in the example group is recycled material, and the recycled material has a darker initial background color due to trace element residues. After aging tests, it can be seen that the examples of the present invention have excellent color retention. After 168 hours of damp heat aging, the comparative example 1 (petrochemical material) reached 7.8, showing a clear yellowing trend. This is due to the oxidation of the polyether soft segment induced by the high content of 4-CBA. Although the example 2 was slightly yellow at the beginning (5.0), the aging process was extremely stable, and the Δb* was only 2.3, less than one-third of that of the comparative example 1. Furthermore, the initial AV (9.5-15.5 mol / t) of the example groups were all within the range of 4-20 mol / t, and the ΔAV after aging was ≤15 mol / t; while the initial AV of Comparative Example 1 was 27.6 mol / t (exceeding the standard), and the ΔAV after aging was 29.0 mol / t, indicating severe degradation. This demonstrates that controlling the initial terminal carboxyl content to 4-20 mol / t is also an important auxiliary condition for ensuring hydrolysis resistance. This invention ensures the appearance stability of the material during long-term use by controlling the 4-CBA content of the raw material r-PTA to below 10 ppm and controlling the initial terminal carboxyl content to 4 to 20 mol / t. The polycondensation time of the example groups was only 95-105 minutes, compared to 120-130 minutes of the comparative examples, significantly shortening the reaction time, improving reaction efficiency, shortening the production cycle, and reducing energy consumption.

[0097] Comparing Example 1 and Example 2, Example 2, using the ester-free antioxidant Irganox 1330, showed a ΔAV of only 8.0 mol / t and a Δb* of only 2.3. Compared to Example 1, which used an ester-free antioxidant, this resulted in a product with superior hydrolysis resistance and aging resistance. This indicates that the ester-free, high-molecular-weight antioxidant (Irganox 1330) is more suitable for this system than the ester-containing antioxidant (Irganox 1010), exhibiting better stability in humid and hot environments, providing superior long-term protection, and further enhancing hydrolysis resistance and anti-yellowing properties.

[0098] Comparing Examples 1 and 2 with Example 3 (4-CBA = 8 ppm, initial b* = 5.7), Example 3, after aging, showed a Δb* of 3.6, which was still significantly better than Comparative Example 2 (Δb* = 6.5), which used the ester-free antioxidant Irganox 1330 but with v-PTA as the raw material. This demonstrates that even when the 4-CBA content of v-PTA is close to the upper limit of control, its anti-yellowing performance is still superior to that of petrochemical v-PTA. Example 1, using the ester-containing antioxidant Irganox 1010, also showed better ΔAV and Δb* than Comparative Example 2. This indicates that as long as the 4-CBA content is controlled below 10 ppm, even recycled raw materials with slightly inferior base color can achieve superior anti-yellowing performance compared to petrochemical materials, resulting in products with better hydrolysis resistance and aging resistance.

[0099] Compared to Comparative Example 3, Comparative Example 3 added 0.8% of a hydrolysis-resistant agent to the reaction system. Although the ΔAV value was better and the water resistance was stronger, the Δb* value was as high as 9.5, indicating that its appearance stability was still very poor and the aging process was obvious. This is likely because 4-CBA generates free radicals that initiate directional oxidation of the polyether soft segments, leading to yellowing. This reaction cannot be alleviated by adding a hydrolysis-resistant agent. The hydrolysis-resistant agent can only inhibit ester bond hydrolysis, but cannot block the chain oxidation initiated by 4-CBA, ultimately leading to color difference changes and overall product defects. On the other hand, the hydrolysis-resistant agent itself may have yellowing properties. The addition of 0.8% hydrolysis-resistant agent in Comparative Example 3 is also the reason for the high Δb value of the product. Therefore, this invention only needs to control the 4-CBA content of the raw material r-PTA to below 10ppm to achieve high hydrolysis resistance and aging resistance of thermoplastic polyester elastomer products without adding a hydrolysis-resistant agent and using inferior ester-containing antioxidants. It is especially suitable for making industrial products for humid and hot environments, such as automotive parts and optical cable sheaths.

[0100] Comparing Example 4 and Comparative Example 4, both using raw material r-PTA-1, Example 4 added 0.1% hydrolysis resistant agent, while Comparative Example 4 added 0.5%. Comparative Example 4 had a better ΔAV value and stronger water resistance, but its Δb* value reached 6.6. This is likely because, on the one hand, excessive hydrolysis resistant agent itself may have yellowing properties, and on the other hand, high dosage may have side reactions with the TPEE system, exacerbating color difference changes during aging. At the same time, its initial base color b*=6.3 is higher than that of Example 4 (5.6), indicating that excessive hydrolysis resistant agent is the direct cause of yellowing.

[0101] The above description is an explanation of the present invention and not a limitation thereof. The present invention can be modified in any form without departing from its spirit.

Claims

1. A hydrolysis-resistant thermoplastic polyester elastomer, characterized in that: The thermoplastic polyester elastomer is copolymerized from hard and soft segments. The hard segments are derived from recycled terephthalic acid (r-PTA) that has a 4-CBA content of less than or equal to 10 ppm and a p-methylbenzoic acid (p-TA) content of less than or equal to 30 ppm. The initial terminal carboxyl group content of the thermoplastic polyester elastomer is 4 to 20 mol / t, and the content of the hydrolysis-resistant stabilizer used in the preparation process is 0 to 0.1 wt%. The recycled terephthalic acid (r-PTA) has specific stable carbon isotope characteristics, and its δ... 13 The C value is distributed in the range of -24‰ to -27‰; the thermoplastic polyester elastomer contains an antioxidant, which comprises a hindered phenolic compound whose molecular structure does not contain ester bonds, and the relative molecular mass of the antioxidant is greater than 700 g / mol; the soft segment is derived from a polyether polyol unit, which is selected from at least one of polytetrahydrofuran ether diol (PTMEG), polyethylene glycol (PEG), polypropylene glycol (PPG), or copolymers thereof, and the number average molecular weight (Mn) of the polyether polyol is 600 to 3000 g / mol.

2. The hydrolysis-resistant thermoplastic polyester elastomer according to claim 1, characterized in that: After the thermoplastic polyester elastomer was treated in a boiling water environment at 100°C for 168 hours, the end carboxyl group increment ΔAV≦15mol / t and the color difference change value Δb*≦5.

0.

3. The hydrolysis-resistant thermoplastic polyester elastomer according to claim 1, characterized in that: The antioxidant is 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene.

4. The hydrolysis-resistant thermoplastic polyester elastomer according to claim 1, characterized in that: The thermoplastic polyester elastomer has a Shore hardness (Shore D) of 20D to 75D, and the mass ratio of its hard segment to soft segment is 20:80 to 80:

20.

5. The hydrolysis-resistant thermoplastic polyester elastomer according to claim 1, characterized in that: The recycled terephthalic acid (r-PTA) has a 4-CBA content of less than or equal to 5 ppm and a p-methylbenzoic acid (p-TA) content of less than or equal to 20 ppm; after the thermoplastic polyester elastomer is treated in boiling water at 100°C for 168 hours, its terminal carboxyl group increment ΔAV≦12mol / t and its color difference change value Δb*≦4.

0.

6. The hydrolysis-resistant thermoplastic polyester elastomer according to any one of claims 1 to 5, characterized in that: The thermoplastic polyester elastomer is molded into automotive constant velocity joint sleeves, foam materials, functional films, or monofilaments and fibers.

7. A method for preparing the hydrolysis-resistant thermoplastic polyester elastomer according to any one of claims 1 to 5, characterized in that, Includes the following steps: (1) Hard segment esterification: Regenerated terephthalic acid (r-PTA) is mixed with 1,4-butanediol (BDO) and the first part of the catalyst, and the esterification reaction is carried out under an inert atmosphere until the reaction system is clear and transparent; (2) Soft segment introduction and antioxidant addition: Polyether polyol and antioxidant are added to the product of step (1), and the remaining catalyst is added to carry out transesterification reaction; (3) Polycondensation: Pre-polymerization and final polymerization reactions are carried out under vacuum conditions until the predetermined torque value is reached.