Esterified crosslinked thermoplastic elastomer and method for producing the same

Abstract

The application discloses an esterification crosslinking type thermoplastic elastomer and a preparation method thereof, and belongs to the technical field of polymer material modification. The elastomer is prepared from a thermoplastic polyester elastomer matrix, a star topological construction agent, an acid anhydride type multifunctional crosslinking agent, a multi-epoxy functional chain expansion agent, an ionic crosslinking synergist and an antioxidant. The star topological construction agent and the ionic crosslinking synergist are introduced to construct a star topological-ionic hybrid network in the matrix in situ, and a double dynamic network of a covalent ester bond and an ionic coordination bond is formed. The material significantly reduces high-temperature compression permanent deformation, improves melt strength, solves the melt sag problem, and maintains excellent recyclability.

Description

Technical Field

[0001] This invention belongs to the field of polymer material modification technology, specifically relating to an esterified crosslinked thermoplastic elastomer and its preparation method. Background Technology

[0002] Thermoplastic polyester elastomer (TPEE) is widely used in automotive dust covers, intake pipes, and sealing strips due to its excellent mechanical strength, heat resistance, and oil resistance. However, under long-term compression conditions at high temperatures (such as above 100°C), ordinary TPEE is prone to significant compression set and creep due to the softening of hard crystal segments and the relaxation of amorphous regions, leading to seal failure.

[0003] To solve the above problems, existing technologies typically employ the following two methods:

[0004] (1) Chemical crosslinking method: crosslinking is carried out using peroxides or high-energy rays. Although this method can significantly reduce compression deformation, the carbon-carbon crosslinking bonds formed are irreversible, causing the material to lose its thermoplasticity. The waste generated cannot be recycled, and gel points are easily generated during processing, affecting the appearance of the product.

[0005] (2) Dynamic vulcanization or transesterification crosslinking: Transesterification is used to introduce ester bonds between TPEE molecular chains. This method preserves the recyclability of the material. However, the simple transesterification reaction is slow and requires a long reaction time. The ester bond network formed is slow to dissociate in the molten state or has too high viscosity, which leads to a lag in the establishment of melt strength during extrusion processing. This easily results in the phenomenon of "melt sagging", making it difficult to prepare large-diameter hoses or sealing strips with complex cross-sections, and resulting in poor dimensional stability.

[0006] Therefore, there is an urgent need in the existing technology for a thermoplastic elastomer material that can significantly reduce high-temperature compression set, overcome the problems of slow simple esterification crosslinking reaction and low melt strength, and maintain excellent recyclability. Summary of the Invention

[0007] The purpose of this invention is to provide an esterified crosslinked thermoplastic elastomer and its preparation method, so as to solve the problems of large compression set of existing thermoplastic polyester elastomers at high temperatures, as well as the problems of low melt strength and poor extrusion dimensional stability in existing esterification crosslinking modification technologies.

[0008] To achieve the above objectives, this invention adopts a "superimposed enhancement" design concept. On the basis of traditional esterification covalent crosslinking, metal ion coordination physical crosslinking is introduced to construct a dual dynamic network of "covalent ester bond + ionic coordination bond". At the same time, this invention introduces a star-shaped topology building agent with high functionality polyhydroxy compound as the topology center, and in combination with acid anhydride and metal ions, constructs a "star-shaped topology-ionic hybrid network" in situ in the TPEE matrix.

[0009] The specific technical solution is as follows:

[0010] An esterified crosslinked thermoplastic elastomer, comprising, by weight:

[0011] (A) Thermoplastic polyester elastomer matrix: 100 parts;

[0012] (B) Star-shaped topology building agent: 0.1–0.8 parts;

[0013] (C) Anhydride-type multifunctional crosslinking agent: 0.3–1.5 parts;

[0014] (D) Polyepoxy functional chain extender: 0.5–2.5 parts;

[0015] (E) Ionic crosslinking synergist: 1.0–4.0 parts;

[0016] (F) Compound antioxidant: 0.2 to 1.0 parts.

[0017] Furthermore, the thermoplastic polyester elastomer matrix is ​​a polybutylene terephthalate-polytetrahydrofuran ether copolymer, grade 5556, with a hardness of 55D.

[0018] Furthermore, the anhydride-type multifunctional crosslinking agent is one or more of pyromellitic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic acid dianhydride, and trimellitic anhydride.

[0019] Furthermore, the anhydride-type multifunctional crosslinking agent is pyromellitic dianhydride.

[0020] Furthermore, the polyepoxy functional chain extender is a styrene-acrylate copolymer type epoxy chain extender, with the brand name Joncryl ADR-4368.

[0021] Furthermore, the ionic crosslinking synergist is a compound of organic zinc salt and organic magnesium salt.

[0022] Furthermore, the ionic crosslinking synergist is composed of zinc acetate and magnesium stearate in a mass ratio of 1:1 to 1:3.

[0023] Furthermore, the compound antioxidant is a 1:1 mixture of antioxidant 1010 and antioxidant 168.

[0024] Furthermore, the preparation method of the esterified crosslinked thermoplastic elastomer includes the following steps:

[0025] (1) Raw material pretreatment: The thermoplastic polyester elastomer matrix is ​​dried by blowing at 100-120℃ until the moisture content is less than 0.05% to obtain the dried TPEE matrix;

[0026] (2) Premixing: The dried thermoplastic polyester elastomer matrix is ​​mixed with star-shaped topological building agent, ionic crosslinking synergist and compound antioxidant in a high-speed mixer for 20-30 minutes to obtain a premix;

[0027] (3) Reactive extrusion: The premixed material is added to the main feed port of a 35mm twin-screw extruder, and the anhydride-type multifunctional crosslinking agent and the polyepoxy functional chain extender are added to the extruder through the side feed port respectively;

[0028] (4) Extrusion process control: The screw speed of the extruder is 200-500 rpm, the barrel temperature is set to 180℃-230℃, and the residence time of the material in the extruder is 40-120 seconds;

[0029] (5) Post-processing: The extruded strip is cooled with water, granulated and dried to obtain the finished esterified cross-linked thermoplastic elastomer.

[0030] Furthermore, the barrel temperature is: Zone 1 180-190℃, Zone 2 190-205℃, Zone 3 205-220℃, and Zone 4 220-230℃.

[0031] Raw material selection explanation (key innovation):

[0032] (1) Component B is selected from dipentaerythritol (Di-PE) or tripentaerythritol. These small molecules contain 6 or more primary hydroxyl groups, have high reactivity, and serve as the "core" of the star network.

[0033] (2) Component C is pyromellitic dianhydride (PMDA). One end of it reacts with component B, and the other end reacts with the hydroxyl group at the TPEE end, thus acting as a "bridge".

[0034] (3) Component E is selected as a zinc acetate / magnesium stearate compound.

[0035] Reaction mechanism (principle):

[0036] (1) Star-shaped core formation: In the early stage of melt extrusion, pyromellitic dianhydride PMDA (C) preferentially reacts with highly active dipentaerythritol (B) and TPEE (A) end groups to generate a "star-shaped prepolymer" with dipentaerythritol as the center and multiple TPEE molecular chains radiating outward.

[0037] (2) Super ion cluster locking: A large number of carboxyl groups (-COOH) are densely distributed around the star nucleus due to the ring-opening reaction of PMDA. These high-density carboxyl groups capture ion crosslinking synergists (E) to form "super ion clusters" with extremely high binding energy, which firmly lock the star structure.

[0038] (3) Network closure: The last added polyepoxy functional chain extender (D) reacts with the remaining carboxyl groups to complete the final three-dimensional network closure.

[0039] The beneficial effects of this invention are:

[0040] (1) Significantly solves the technical problem of large compression set of thermoplastic polyester elastomer (TPEE) at high temperature: Existing TPEE is prone to creep at high temperature due to softening of hard segments, while the present invention greatly improves the high temperature resilience of the material by constructing a dual dynamic network of "covalent ester bond + ionic coordination bond".

[0041] (2) It overcomes the processing defects of low melt strength and easy "melt sagging" in traditional esterification crosslinking modification: the existing transesterification reaction rate is slow, resulting in a lag in the establishment of melt strength during extrusion. This invention introduces a high-functionality star-shaped topology building agent (Di-PE) to rapidly build a star-shaped long-branched structure in the early stage of the reaction, which significantly improves the melt strength.

[0042] (3) The advantages of high-functionality star kernels in constructing dense networks have been verified.

[0043] (4) This confirms the indispensability of anhydride crosslinking agents (PMDA) as network hubs.

[0044] (5) It maintains excellent material recyclability. Detailed Implementation

[0045] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Meanwhile, unless otherwise specified, the raw materials, reagents, or devices used in the following embodiments can be obtained from conventional commercial channels or by existing known methods. Some raw material specifications and sources are as follows:

[0046] (A) TPEE matrix: grade 5556, hardness 55D, melt index 7.8 g / 10min (220℃, 2.16kg), purchased from Changchun Chemical.

[0047] (B) Star-shaped topology building agent (polyhydroxy core): Dipentaerythritol (Di-PE), purity 90%, hydroxyl value ≥1300mgKOH / g, commercially available industrial grade.

[0048] (C) Anhydride type multifunctional crosslinking agent: Pyromellitic dianhydride (PMDA), purity ≥99%, powder, commercially available industrial grade.

[0049] (D) Poly-epoxy functional chain extender: Styrene-acrylate copolymer type epoxy chain extender, brand name JoncrylADR-4368, purchased from BASF.

[0050] (E) Ion crosslinking synergist:

[0051] Zinc acetate (Zn(OAc)2·2H2O), analytical grade, commercially available.

[0052] Magnesium stearate, industrial grade, commercially available.

[0053] Compounding method: Mix zinc acetate and magnesium stearate at a mass ratio of 1:2 and grind them evenly before use.

[0054] (F) Compound antioxidants: Antioxidant 1010 and antioxidant 168 are compounded in a 1:1 ratio and are commercially available.

[0055] Example 1

[0056] An esterified crosslinked thermoplastic elastomer and its preparation method:

[0057] (A) TPEE matrix: 100 parts;

[0058] (B) Di-PE: 0.1 parts;

[0059] (C)PMDA: 0.3 parts;

[0060] (D)ADR-4368: 0.5 copies;

[0061] (E) Ionic crosslinking synergist: 1.0 part;

[0062] (F) Compound antioxidant: 0.2 parts;

[0063] A method for preparing esterified crosslinked thermoplastic elastomers includes the following steps:

[0064] (1) Raw material pretreatment: The TPEE matrix (A) was dried by blowing at 100°C until the moisture content was less than 0.05% to obtain the dried TPEE matrix (A);

[0065] (2) Premixing: The dried TPEE matrix (A) is mixed with Di-PE (B), ionic crosslinking synergist (E) and compound antioxidant (F) in a high-speed mixer for 20 min to obtain a premix;

[0066] (3) Reactive extrusion: Add the premix to the main feed port of a 35mm twin-screw extruder, and add PMDA(C) and ADR-4368(D) to the extruder through the side feed ports respectively;

[0067] (4) Extrusion process control: The screw speed of the extruder is 200 rpm, the barrel temperature is set to 180℃~220℃, specifically, 180℃ in zone 1, 190℃ in zone 2, 205℃ in zone 3, and 220℃ in zone 4, and the residence time of the material in the extruder is 40 seconds.

[0068] (5) Post-processing: The extruded strip is cooled with water, granulated and dried to obtain the finished esterified cross-linked thermoplastic elastomer.

[0069] Example 2

[0070] (A) TPEE matrix: 100 parts;

[0071] (B) Di-PE: 0.5 parts;

[0072] (C)PMDA: 1.2 parts;

[0073] (D)ADR-4368: 2.0 copies;

[0074] (E) Ionic crosslinking synergist: 3.0 parts;

[0075] (F) Compound antioxidant: 0.5 parts;

[0076] A method for preparing esterified crosslinked thermoplastic elastomers includes the following steps:

[0077] (1) Raw material pretreatment: TPEE matrix (A) is dried by blowing at 120°C until the moisture content is less than 0.05% to obtain dried TPEE matrix (A);

[0078] (2) Premixing: The dried TPEE matrix (A) is mixed with Di-PE (B), ionic crosslinking synergist (E) and compound antioxidant (F) in a high-speed mixer for 30 min to obtain a premix;

[0079] (3) Reactive extrusion: Add the premix to the main feed port of a 35mm twin-screw extruder, and add PMDA(C) and ADR-4368(D) to the extruder through the side feed ports respectively;

[0080] (4) Extrusion process control: The screw speed of the extruder is 500 rpm, the barrel temperature is set to 190℃~225℃, specifically, 190℃ in zone 1, 200℃ in zone 2, 210℃ in zone 3, and 225℃ in zone 4. The residence time of the material in the extruder is 80 seconds.

[0081] (5) Post-processing: The extruded strip is cooled with water, granulated and dried to obtain the finished esterified cross-linked thermoplastic elastomer.

[0082] Example 3

[0083] (A) TPEE matrix: 100 parts;

[0084] (B) Di-PE: 0.8 parts;

[0085] (C)PMDA: 1.5 parts;

[0086] (D)ADR-4368: 2.5 copies;

[0087] (E) Ionic crosslinking synergist: 4.0 parts;

[0088] (F) Compound antioxidant: 1.0 part;

[0089] A method for preparing esterified crosslinked thermoplastic elastomers includes the following steps:

[0090] (1) Raw material pretreatment: TPEE matrix (A) is dried by blowing at 120°C until the moisture content is less than 0.05% to obtain dried TPEE matrix (A);

[0091] (2) Premixing: The dried TPEE matrix (A) is mixed with Di-PE (B), ionic crosslinking synergist (E) and compound antioxidant (F) in a high-speed mixer for 30 min to obtain a premix;

[0092] (3) Reactive extrusion: Add the premix to the main feed port of a 35mm twin-screw extruder, and add PMDA(C) and ADR-4368(D) to the extruder through the side feed ports respectively;

[0093] (4) Extrusion process control: The screw speed of the extruder is 500 rpm, the barrel temperature is set to 190℃~230℃, specifically, 190℃ in zone 1, 205℃ in zone 2, 220℃ in zone 3, and 230℃ in zone 4. The residence time of the material in the extruder is 120 seconds.

[0094] (5) Post-processing: The extruded strip is cooled with water, granulated and dried to obtain the finished esterified cross-linked thermoplastic elastomer.

[0095] Comparative Example 1

[0096] Comparative Example 1 served as the control group for Example 2. Based on Example 2, component (B) Di-PE was removed, while other components and processes remained completely consistent with those in Example 2, ultimately yielding the finished esterified crosslinked thermoplastic elastomer.

[0097] Comparative Example 2

[0098] Comparative Example 2 served as the control group for Example 2. Based on Example 2, component (E) ionic crosslinking synergist was removed, while other components and processes remained completely consistent with those in Example 2, ultimately yielding the finished esterified crosslinked thermoplastic elastomer.

[0099] Comparative Example 3

[0100] Comparative Example 3 served as the control group for Example 2. Based on Example 2, component (B) Di-PE (6-functionality) was replaced with an equimolar amount of trimethylolpropane (TMP, 3-functionality), while maintaining the same number of hydroxyl groups. Other components and processes remained completely consistent with those in Example 2, ultimately yielding the finished esterified crosslinked thermoplastic elastomer.

[0101] Comparative Example 4

[0102] Comparative Example 4 served as the control group for Example 2. Based on Example 2, component (C) PMDA was removed, while other components and processes remained completely consistent with those in Example 2, ultimately yielding the finished esterified crosslinked thermoplastic elastomer.

[0103] The performance of the finished esterified crosslinked thermoplastic elastomers obtained in Examples 1 to 3 and Comparative Examples 1 to 4 was tested. The performance testing process is as follows, and the test results are shown in Table 1:

[0104] (1) Tensile properties: tested according to GB / T 528 standard, tensile rate 50mm / min.

[0105] (2) Compression set: Tested according to GB / T 7759 standard. Test conditions: 100℃ × 22 hours, compression rate 25%. The smaller the value, the stronger the resistance to deformation.

[0106] (3) Melt flow rate (MFR): Tested according to GB / T 3682 standard, 230℃, 2.16kg.

[0107] (4) Melt sag: used to characterize the dimensional stability of extrusion.

[0108] A. Test method: Using a melt flow indexer, at 230℃, remove the weights and allow the melt to be extruded naturally under gravity. Record the time (t1) required for the melt strip to reach a length of 10cm and the rate of change in the diameter of the melt strip after extrusion.

[0109] B. Simplified characterization: This embodiment uses "qualitative melt strength scoring". The material is extruded in a single-screw extruder (length-to-diameter ratio 25:1, die diameter 5mm, temperature 230℃), and the sag of the extruded strip at 10cm away from the die is observed.

[0110] C. Scoring Criteria:

[0111] Grade A (Excellent): The extruded strip is straight with almost no sagging and maintains good cross-sectional roundness.

[0112] Grade B (Good): The extruded strip is slightly bent and drooping.

[0113] Grade C (Poor): The extruded strip sags severely and becomes thin, with the cross-section turning into an ellipse.

[0114] (5) Recycling performance: After the injection molded sample is crushed, 100% of the material is recycled and re-injected, and the tensile strength retention rate is tested.

[0115]

[0116] Analysis of the data in Table 1:

[0117] 1. Analysis of Examples 1-3:

[0118] Compression set: With the increase of crosslinking components, the compression set decreased significantly from 32% to 21%. Compared with ordinary TPEE (typically >50%), the "star-shaped ion hybrid network" of the present invention greatly improves high-temperature resilience. Example 2, as a preferred formulation, achieves an excellent resistance to deformation of 24% while maintaining good processability.

[0119] Melt stability: The MFR of Examples 1-3 decreased progressively (4.5->1.5), and the melt sag was Grade A (excellent) for all three. This verifies that the star-shaped topology can rapidly build melt strength and solves the sag problem caused by the slow transesterification reaction in traditional methods.

[0120] 2. Comparative Example 1 Analysis (The Role of the Astral Nucleus):

[0121] Data comparison: Comparative Example 1 removed Di-PE, MFR increased to 6.2, and melt shrinkage rating was C (poor).

[0122] Conclusion: This directly proves that star-shaped topological building blocks (Di-PE) are key to solving melt sagging. Without a star-shaped core, molecular chains cannot form effective long-chain entanglements, resulting in insufficient melt strength to support its own weight.

[0123] 3. Comparative Example 2 Analysis (Effect of Ionic Crosslinking):

[0124] Data comparison: Comparative Example 2 removed the ionic crosslinking agent. Although it had covalent crosslinking, its compression set was as high as 42%, which was much worse than the 24% of Example 2.

[0125] Conclusion: This study demonstrates that simple covalent crosslinking is insufficient to resist creep at high temperatures. The "super ionic clusters" formed by the ionic crosslinking synergist play a crucial physical anchoring role and are the core factor in reducing compression set. Furthermore, due to the lack of dynamic reversibility of ionic bonds, its recovery retention rate (88%) is slightly lower than that of Example 2 (95%).

[0126] 4. Comparative Analysis of Example 3 (Effect of Functionality):

[0127] Data comparison: Using 3-functionality TMP instead of 6-functionality Di-PE, the compression set (36%) and melt shrinkage (Grade B) were both inferior to those in Example 2.

[0128] Conclusion: This study validates the importance of high functionality (6-functionality) for constructing high-density networks. More "arms" mean stronger molecular chain gripping ability and a more sophisticated stress transfer network.

[0129] 5. Comparative Example 4 Analysis (The Bridging Role of PMDA):

[0130] Data comparison: After removing PMDA, the performance was the worst. Compression set was as high as 65% (close to the raw material level), and melt shrinkage was grade C.

[0131] Conclusion: This confirms that PMDA is the key component of the entire reaction system. Without it, the star-shaped nucleus cannot connect to the matrix, ionic crosslinking sites cannot form, and the system fails to form an effective network.

[0132] In summary, the above data analysis fully demonstrates that the synergistic effect of constructing a star-shaped framework with Di-PE and constructing ionic crosslinking with PMDA / metal salt has successfully solved the two major technical problems of large high-temperature compression deformation and low extruded melt strength of TPEE, while maintaining excellent recycling performance.

[0133] It should be noted that, in this document, terms such as “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0134] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. An esterified crosslinked thermoplastic elastomer, characterized in that, By weight, it includes: Thermoplastic polyester elastomer matrix: 100 parts; Star topology builder: 0.1–0.8 parts; Anhydride-type multifunctional crosslinking agent: 0.3–1.5 parts; Polyepoxy functional chain extender: 0.5–2.5 parts; Ionic crosslinking synergist: 1.0–4.0 parts; Compound antioxidant: 0.2–1.0 parts; The thermoplastic polyester elastomer matrix is ​​polybutylene terephthalate-polytetrahydrofuran ether copolymer, grade 5556, with a hardness of 55D; The anhydride-type multifunctional crosslinking agent is pyromellitic dianhydride; The polyepoxy functional chain extender is a styrene-acrylate copolymer type epoxy chain extender, with the brand name JoncrylADR-4368; The star-shaped topology builder is dipentaerythritol; The ionic crosslinking synergist is composed of zinc acetate and magnesium stearate in a mass ratio of 1:1 to 1:

3. The preparation method of the esterified crosslinked thermoplastic elastomer includes the following steps: (1) Raw material pretreatment: The thermoplastic polyester elastomer matrix is ​​dried by blowing at 100-120℃ until the moisture content is less than 0.05% to obtain the dried TPEE matrix; (2) Premixing: The dried thermoplastic polyester elastomer matrix is ​​mixed with star-shaped topological building agent, ionic crosslinking synergist and compound antioxidant in a high-speed mixer for 20-30 minutes to obtain a premix; (3) Reactive extrusion: The premixed material is added to the main feed port of a 35mm twin-screw extruder, and the anhydride-type multifunctional crosslinking agent and the polyepoxy functional chain extender are added to the extruder through the side feed port respectively; (4) Extrusion process control: The screw speed of the extruder is 200-500 rpm, the barrel temperature is set to 180℃-230℃, and the residence time of the material in the extruder is 40-120 seconds; (5) Post-processing: The extruded strip is cooled with water, granulated and dried to obtain the finished esterified cross-linked thermoplastic elastomer.

2. The esterified crosslinked thermoplastic elastomer according to claim 1, characterized in that, The compound antioxidant is a mixture of antioxidant 1010 and antioxidant 168 in a 1:1 ratio.

3. A method for preparing an esterified crosslinked thermoplastic elastomer according to any one of claims 1 to 2, characterized in that, Includes the following steps: (1) Raw material pretreatment: The thermoplastic polyester elastomer matrix is ​​dried by blowing at 100-120℃ until the moisture content is less than 0.05% to obtain the dried TPEE matrix; (2) Premixing: The dried thermoplastic polyester elastomer matrix is ​​mixed with star-shaped topological building agent, ionic crosslinking synergist and compound antioxidant in a high-speed mixer for 20-30 minutes to obtain a premix; (3) Reactive extrusion: The premixed material is added to the main feed port of a 35mm twin-screw extruder, and the anhydride-type multifunctional crosslinking agent and the polyepoxy functional chain extender are added to the extruder through the side feed port respectively; (4) Extrusion process control: The screw speed of the extruder is 200-500 rpm, the barrel temperature is set to 180℃-230℃, and the residence time of the material in the extruder is 40-120 seconds; (5) Post-processing: The extruded strip is cooled with water, granulated and dried to obtain the finished esterified cross-linked thermoplastic elastomer.

4. The method for preparing an esterified crosslinked thermoplastic elastomer according to claim 3, characterized in that, The barrel temperatures are: Zone 1 180-190℃, Zone 2 190-205℃, Zone 3 205-220℃, and Zone 4 220-230℃.

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