A deformation-resistant thermoplastic composite material and a method of making the same

Abstract

The application discloses a kind of deformation-resistant thermoplastic composite material and preparation method thereof, belong to high polymer composite material preparation technical field, to solve the existing thermoplastic composite material under high load prone to creep, fiber infiltration is insufficient and the problems such as insufficient part size stability.The application uses cyclic butylene terephthalate oligomer as low-viscosity precursor, introduces bifunctional catalytic crosslinking agent, and carries out in-situ reactive molding with glass fiber reinforcement.The method utilizes the low melt viscosity of cyclic butylene terephthalate oligomer, realizes the sufficient infiltration of fiber reinforcement before polymerization and viscosity increase, and constructs a covalent crosslinking network containing dynamic ester exchange bond in-situ during ring-opening polymerization.The obtained composite material has low porosity and good interface bonding, and significantly improves the anti-creep performance and dimensional stability while maintaining the toughness of thermoplastic materials.

Description

Technical Field

[0001] This invention relates to the field of polymer composite material preparation technology, and in particular to a deformation-resistant thermoplastic composite material and its preparation method. Background Technology

[0002] Thermoplastic resin-based composites have been widely used in the automotive, aerospace, and electronics industries due to their advantages such as recyclability, short production cycles, and good impact resistance. However, as applications expand towards high-temperature, long-term load-bearing, and precision structural components, traditional thermoplastic resin-based composites have revealed significant limitations:

[0003] (1) Traditional thermoplastic resins transfer stress through the physical entanglement of linear molecular chains. Under high temperature or long-term constant load, the molecular chains are prone to unentanglement and slippage, resulting in irreversible creep deformation of the material, which cannot meet the dimensional stability requirements of precision structural parts.

[0004] (2) The melt viscosity of engineering plastics is usually as high as thousands or even tens of thousands of Pascals per second, making it difficult to completely wet high-content continuous fiber bundles and fabrics. It is easy to leave micropores at the interface. These defects are the source of micro-deformation and failure of materials under stress.

[0005] (3) Although the existing in-situ polymerization technology has solved the wetting problem, the polymerization process is accompanied by significant volume shrinkage, and due to the formation of a structure with extremely low or no cross-linking, the huge thermal residual stress generated during the cooling process cannot be released.

[0006] Prior art CN119955284A discloses a glass fiber reinforced polycarbonate composite material and its... The core of the preparation method and application is to use the skeleton support provided by polyurethane and glass fiber to improve the mechanical properties and transparency of the composite material. However, the matrix formed by this technology has a linear molecular structure. Under high temperature or long-term high load, the molecular chains are prone to slippage and deentanglement, which makes it difficult for the material to meet the requirements of precision structural parts in terms of creep resistance and dimensional stability. In addition, the deep wetting effect of high viscosity resin melt on high content continuous fiber bundles is not good.

[0007] Therefore, developing a deformation-resistant composite material that can maintain low viscosity to achieve perfect wetting, lock deformation at the molecular level through chemical means, and has an internal stress relief mechanism is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0008] The present invention aims to solve the problems of existing thermoplastic composite materials being prone to creep under high loads, insufficient fiber impregnation leading to micropores, and insufficient dimensional stability of parts.

[0009] The specific technical solution is as follows: A deformation-resistant thermoplastic composite material, comprising a thermoplastic resin matrix system and a reinforcing material, glass fiber cloth; the thermoplastic resin matrix system comprises the following raw materials in parts by weight: 92-98 parts of cyclic butylene terephthalate oligomer, 2-5 parts of bifunctional catalytic crosslinking agent, 1-2 parts of modified silica, 0.2-0.5 parts of antioxidant, and 0.2-0.5 parts of lubricant; the bifunctional catalytic crosslinking agent is a hyperbranched epoxy functionalized polymer supported on a metal catalyst; the metal catalyst is zinc acetylacetone.

[0010] Furthermore, the surface density of the glass fiber cloth is 300-600 g / m². 2 The fiber volume fraction in the composite material is 45%-60%.

[0011] Furthermore, the cyclic butylene terephthalate oligomer has a melting point of 135-145℃ and a melt viscosity of less than 30 mPa·s; the modified silica is amorphous silica with a surface treated with silane and a particle size of 1-3 μm; the antioxidant is one or a combination of antioxidant 1010 or antioxidant 168; and the lubricant is pentaerythritol tetrastearate.

[0012] Further, the preparation steps of the bifunctional catalytic crosslinking agent include: taking pentaerythritol and 2,2-di(hydroxymethyl)propionic acid in a molar ratio of 1:15, adding 0.1 wt% of p-toluenesulfonic acid of the total weight of the reactants, passing a nitrogen gas stream, and performing a melt polycondensation reaction at 140°C for 5 hours to obtain a hydroxyl-terminated hyperbranched polyester polymer; dissolving the obtained hydroxyl-terminated hyperbranched polyester polymer in tetrahydrofuran, with the solid content controlled at 25 wt%; and adding 5 times the molar amount of epichlorohydrin based on the molar amount of hydroxyl groups in the hydroxyl-terminated hyperbranched polyester polymer. Under stirring conditions, a 30wt% sodium hydroxide aqueous solution was added dropwise, and the reaction was carried out at 60℃ for 6 hours. The amount of sodium hydroxide used was 2.5 times the molar amount of hydroxyl groups in the hydroxyl-terminated hyperbranched polyester polymer. After the reaction was completed, the polymer was washed with deionized water, dried, and rotary evaporated to obtain an epoxy-terminated hyperbranched polyester polymer. The obtained epoxy-terminated hyperbranched polyester polymer was mixed with zinc acetylacetonate at a weight ratio of 10:1 in anhydrous ethanol, and the system concentration was controlled at 30wt%. The mixture was refluxed and stirred at 80℃ for 2 hours. After removing the solvent and drying, a bifunctional catalytic crosslinking agent was obtained.

[0013] Furthermore, the method for preparing the deformation-resistant thermoplastic composite material includes the following steps: S1: The cyclic butylene terephthalate oligomer, bifunctional catalytic crosslinking agent, modified silica, antioxidant and lubricant are mixed evenly to obtain precursor powder; S2: The precursor powder is melt-dispersed to prepare a reactive melt and then transported to the impregnation area; S3: The surface-treated glass fiber cloth is introduced into the reactive melt in the impregnation area for impregnation treatment to obtain a prepreg tape; S4: The prepreg tape is placed in a high-temperature environment for in-situ ring-opening polymerization, followed by dynamic annealing. S5: Cool and shape the treated material and cut it in an orientation to obtain a deformation-resistant thermoplastic composite material.

[0014] Furthermore, in step S1, the precursor powder is mixed using a two-way composite motion mixing method for 1-2 hours, while maintaining an ambient relative humidity below 50% during the mixing process.

[0015] Furthermore, the melting and dispersion temperature in step S2 is 140-155°C, and the residence time of the precursor powder in the melting and dispersion process is 10-15 minutes.

[0016] Further, the surface treatment process in step S3 is as follows: prepare an ethanol-water solution containing 1.0 wt% γ-epoxypropoxypropyltrimethoxysilane, wherein the volume ratio of ethanol to water in the ethanol-water solution is 3:5; adjust the pH of the solution to 4-5 with acetic acid, and stir at room temperature for 45 minutes; immerse the glass fiber cloth in the solution for 5 minutes, and then dry it at 110°C for 20 minutes.

[0017] Furthermore, the temperature of the in-situ ring-opening polymerization reaction in step S4 is 190-205℃, and the holding time is 5-15 minutes; the temperature of the dynamic annealing treatment is 180-190℃, and the holding time is 5-20 minutes.

[0018] Furthermore, the cooling and shaping rate in step S5 is 3-8℃ / min, cooling to below 80℃; the directional cutting control cuts in the direction that the short side is parallel to the production line travel direction and the long side is parallel to the weft direction.

[0019] Compared with the prior art, the present invention has the following beneficial effects: (1) This invention introduces a bifunctional catalytic crosslinking agent to simultaneously construct a three-dimensional crosslinking network in situ during the ring-opening polymerization of cyclic butylene terephthalate (CBT) to form linear polybutylene terephthalate (PBT) segments. This crosslinking structure restricts the slippage of molecular chains in crystalline and amorphous regions, enabling the material to exhibit thermosetting-like creep resistance under high temperature and high load conditions. Simultaneously, by utilizing the extremely low viscosity of CBT oligomers in the molten state, sufficient impregnation of high-density continuous fiber fabrics can be completed before the catalyst triggers rapid thickening and polymerization, allowing the resin to effectively fill the gaps between fiber bundles. This results in a composite material structure with low porosity and good interfacial bonding, thereby improving the overall mechanical properties and deformation stability of the material.

[0020] (2) The crosslinked network constructed in this invention contains dynamic covalent bonds that can undergo transesterification. During the annealing process, the material is heated to a temperature above the topological freezing temperature of the crosslinked network but below the melting point of PBT crystals. At this time, the overall structure of the material remains solid, but under the action of the metal catalytic center in the bifunctional catalytic crosslinking agent, the ester bonds in the network can undergo reversible transesterification, redistribute the crosslinking points, and release the residual internal stress generated by polymerization and thermal shrinkage, thereby improving the dimensional stability and long-term service performance of the composite material.

[0021] (3) The present invention uses the synergistic design of CBT in-situ polymerization, hyperbranched crosslinking structure construction and continuous fiber reinforcement to enable the bifunctional catalytic crosslinking agent to play both network construction and transesterification catalysis roles. While maintaining the processability of the thermoplastic matrix, it introduces a thermosetting-like network constraint effect, so that the composite material has high mechanical strength, good heat resistance and excellent creep resistance, and is suitable for structural application fields with high requirements for dimensional stability and long-term load performance. Attached Figure Description

[0022] Figure 1 This is a process flow diagram for preparing a deformation-resistant thermoplastic composite material according to the present invention; Figure 2 The synthetic route for preparing the bifunctional catalytic crosslinking agent of this invention is shown in the diagram. Figure 3 Fourier transform infrared spectra of the hydroxyl-terminated hyperbranched polyester polymer and the epoxy-terminated hyperbranched polyester polymer prepared in Example 1 of this invention. Figure 4 This is a comparison chart of the test results of microporosity, creep resistance and heat distortion temperature of the embodiments and comparative examples of the present invention; Figure 5 Comparison chart of the test results of bending strength, bending modulus and impact strength of the embodiments and comparative examples of the present invention. Detailed Implementation

[0023] The following embodiments further explain and illustrate the technical solutions of the present invention. It should be specifically noted that each specific embodiment is a concretization and explanation of the technical solution and should not be considered as a limitation on the scope of protection of the present invention. Those skilled in the art still have the right to modify the technical solutions of these embodiments and make equivalent substitutions for some or all of the technical features, and these modifications or substitutions do not change the essence of the corresponding technical solutions, nor do they cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions described in the present invention.

[0024] This invention proposes a deformation-resistant thermoplastic composite material and its preparation method, wherein the composite material is composed of a thermoplastic resin matrix system and a reinforcing material. The reinforcing material is glass fiber cloth with an areal density of 300-600 g / m³. 2 The fiber volume fraction in the composite material is 45%-60%. The thermoplastic resin matrix system is made from the following raw materials in parts by weight: 92-98 parts of CBT oligomer, 2-5 parts of bifunctional catalytic crosslinking agent, 1-2 parts of modified silica, 0.2-0.5 parts of antioxidant, and 0.2-0.5 parts of lubricant.

[0025] The CBT oligomer has a melting point of 135-145℃ and a melt viscosity of less than 30 mPa·s.

[0026] The modified silica is amorphous silica with a surface treated with silane and a particle size of 1-3 μm, used to reduce polymerization shrinkage, improve dimensional stability and flexural modulus.

[0027] The antioxidant is one or a combination of antioxidant 1010 and antioxidant 168, used to inhibit thermo-oxidative degradation and yellowing during high-temperature polymerization.

[0028] The lubricant is pentaerythritol tetrastearate, used to improve the stability of continuous molding.

[0029] The bifunctional catalytic crosslinking agent is a hyperbranched epoxy functionalized polymer with a complexed metal catalyst. The supported metal catalyst can subsequently initiate the ring-opening polymerization of CBT and also serves as a catalyst for dynamic transesterification at high temperatures. Simultaneously, its epoxy groups react with the carboxyl / hydroxyl groups at the chain ends of PBT obtained after the ring-opening polymerization of CBT during the polymerization process, forming permanent or dynamic crosslinking sites. The hyperbranched structure provides a high density of reaction sites and a rigid core. (See attached image) Figure 2 As shown, the preparation process is as follows: (1) Hyperbranched nucleus synthesis: Pentaerythritol and 2,2-di(hydroxymethyl)propionic acid (DMPA) were added to a reactor equipped with mechanical stirring, nitrogen protection, and a water separator in a molar ratio of 1:15. Pentaerythritol served as the core molecule, and 2,2-di(hydroxymethyl)propionic acid served as the branching monomer. 0.1 wt% of p-toluenesulfonic acid was added as a catalyst, and the reaction was carried out at 140°C for 5 hours via melt polycondensation. During the reaction, nitrogen gas was continuously introduced, and the water generated in the reaction was continuously removed through the water separator. The reaction continued until no water was generated, yielding a hydroxyl-terminated hyperbranched polyester polymer (HBP-OH). At this point, the polymer had a spherical or quasi-spherical structure with highly reactive hydroxyl groups densely distributed on its surface.

[0030] (2) Terminal functionalization: The above HBP-OH was dissolved in tetrahydrofuran, with the solid content controlled at 25 wt%. Based on the molar amount of hydroxyl groups in HBP-OH, 5 times the molar amount of epichlorohydrin was added. Under stirring conditions, a 30 wt% sodium hydroxide aqueous solution was slowly added dropwise, with the amount being 2.5 times the molar amount of hydroxyl groups. The reaction temperature was controlled at 60℃, and the reaction was carried out for 6 hours. First, the hydroxyl groups on the surface of HBP-OH attacked epichlorohydrin under alkaline conditions, forming a chlorohydrin intermediate through ring opening; subsequently, under the action of excess sodium hydroxide, the intermediate underwent an intramolecular dehydrochlorination ring-closure reaction, regenerating epoxy groups. After the reaction was completed, the byproduct sodium chloride was removed by washing with deionized water multiple times, and the solvent was removed by drying and rotary evaporation to obtain the terminal epoxy hyperbranched polyester polymer (HBP-EP).

[0031] (3) Catalyst Complexation: HBP-EP and zinc acetylacetonate were mixed in anhydrous ethanol at a weight ratio of 10:1, with the system concentration controlled at 30 wt%. The mixture was refluxed and stirred at 80 °C for 2 hours. Utilizing the internal cavities formed by the highly branched topology of the hyperbranched polyester polymer and the Lewis acid-base interactions between the numerous polar ester / ether bonds in the backbone and zinc ions, zinc acetylacetonate molecules were physically captured and anchored within the free volume of the polymer. This process is mainly based on the supramolecular encapsulation effect between the host and guest. After solvent removal and drying, zinc acetylacetonate was locked inside HBP-EP in a molecularly dispersed state, yielding a bifunctional catalytic crosslinking agent.

[0032] The specific preparation process is as follows, see attached. Figure 1 The following is a flowchart of the preparation process: S1. Premixed precursor powder Add CBT oligomer, bifunctional catalytic crosslinking agent, modified silica, antioxidant, and lubricant to a two-dimensional mixer in the specified proportions. Turn on the equipment and perform bidirectional composite mixing for 1-2 hours to achieve macroscopically uniform dispersion of trace catalysts and additives in the matrix powder. Maintain an ambient relative humidity below 50% during the mixing process to prevent CBT from absorbing moisture and affecting its molecular weight. Immediately seal and store the mixed powder for later use.

[0033] S2. Preparation of reactive melts The uniformly mixed precursor powder is continuously fed into a co-rotating twin-screw extruder for melt dispersion. The temperature is controlled within the range of 140-155℃ to ensure complete melting of CBT to form a low-viscosity melt. Within this temperature range, the catalyst activity in the bifunctional catalytic crosslinking agent is low, and the system remains in a oligomerized state. The melt residence time is controlled within 10-15 minutes to avoid significant prepolymerization that would lead to an increase in viscosity. This stage forms an ultra-low viscosity reactive impregnated melt. The melt is continuously fed into the impregnation tank through a closed conveying pipeline while maintaining nitrogen protection to prevent moisture absorption and oxidation.

[0034] S3. Glass fiber impregnation (1) Prepare an ethanol-water solution containing 1.0 wt% γ-epoxypropoxypropyltrimethoxysilane (KH-560), wherein the volume ratio of ethanol to water in the ethanol-water solution is 3:5. Adjust the pH of the solution to 4-5 with acetic acid, and stir and hydrolyze for 45 minutes at room temperature to fully hydrolyze the methoxy groups to generate silanol. Completely immerse the glass fiber cloth in the above solution for 5 minutes to allow the silanol molecules to be uniformly adsorbed on the fiber surface. Then remove excess liquid by roller pressing and dry in a 110°C hot air oven for 20 minutes. During the drying process, the silanol groups undergo a condensation reaction, forming silicon-oxygen-silicon covalent bonds with the hydroxyl groups on the glass fiber surface, while some silanol self-condenses to form a dense interface layer. An epoxy-containing organosilane interface layer is formed on the surface of the treated glass fiber, providing reactive sites for the subsequent resin system.

[0035] (2) The dried glass fiber cloth is introduced into the impregnation tank through guide rollers. The temperature of the impregnation tank is controlled at 145-155℃ to maintain the low viscosity of the melt. The contact time between the glass fiber cloth and the melt in the impregnation tank is controlled at 2 minutes. Taking advantage of the extremely low viscosity of CBT melt, it can quickly penetrate into the interior of the fiber bundle and the gaps between the monofilaments to achieve complete impregnation. During the impregnation process, the resin content is controlled by high-temperature extrusion rollers to adjust the fiber volume fraction and remove air bubbles. The impregnation zone adopts a closed structure and maintains a slightly positive pressure nitrogen environment to inhibit oxidation and moisture introduction. This step replaces the traditional solvent impregnation process, eliminating solvent evaporation problems and avoiding micropore formation.

[0036] S4. In-situ polymerization and dynamic annealing (1) The impregnated prepreg tape is continuously fed into a high-temperature polymerization oven for in-situ ring-opening polymerization. The temperature is raised to 190-205℃ and held for 5-15 minutes. At this temperature, the zinc catalyst is fully activated, initiating the ring-opening polymerization of CBT to generate high molecular weight PBT. At the same time, the terminal epoxy groups in the bifunctional catalytic crosslinking agent react with the PBT chain ends to form crosslinking nodes and construct a three-dimensional network structure.

[0037] (2) After the polymerization reaction is complete, maintain the temperature at 180-190℃ for 5-20 minutes. At this time, the material has solidified, but internal stress is generated due to polymerization shrinkage. Under the catalysis of zinc ions, the ester bonds in the network undergo a reversible transesterification reaction, realizing topological rearrangement. This process effectively releases the residual internal stress generated by polymerization shrinkage and traction, and improves dimensional stability.

[0038] S5. Cooling, shaping, and directional cutting The material is cooled to below 80°C using cooling rollers at a rate of 3-8°C / min, achieving structural freezing and forming a continuous thermoplastic fiberglass composite board. It is then slit using an automated cutting machine. The cutting direction is controlled so that the short side is parallel to the production line's travel direction and the long side is parallel to the weft direction. During continuous production, the residual stress in the warp direction is higher than that in the weft direction. Through this specific cutting direction, combined with a dynamic annealing release mechanism, dual deformation control is achieved, significantly reducing the risk of warping.

[0039] Example 1 Preparation of bifunctional catalytic crosslinking agent: 13.6 parts pentaerythritol and 201 parts DMPA were added to a reactor. 0.2 parts p-toluenesulfonic acid were added, and nitrogen gas was introduced. The mixture underwent melt polycondensation at 140°C for 5 hours to obtain HBP-OH. The obtained HBP-OH was dissolved in 850 parts tetrahydrofuran, and 879 parts epichlorohydrin were added. Under stirring, 507 parts 30wt% sodium hydroxide aqueous solution was slowly added dropwise, and the reaction was carried out at 60°C for 6 hours. After the reaction was completed, the mixture was washed repeatedly with deionized water, dried, and rotary evaporated to obtain HBP-EP. The obtained HBP-EP was mixed with 40 parts zinc acetylacetonate in 1026 parts anhydrous ethanol, and refluxed and stirred at 80°C for 2 hours. After removing the solvent and drying, the bifunctional catalytic crosslinking agent was obtained.

[0040] Raw materials for preparing thermoplastic composites: 95 parts CBT oligomer (melting point 135-145℃, melt viscosity <30mPa·s), 3 parts bifunctional catalytic crosslinking agent, 1.5 parts modified silica with a particle size of 1-3μm, 0.3 parts antioxidant 1010, 0.3 parts pentaerythritol tetrastearate, density 450g / m³ 2 200 portions of fiberglass cloth. The preparation process is as follows: (1) CBT oligomer, bifunctional catalytic crosslinking agent, modified silica, antioxidant 1010 and pentaerythritol tetrastearate were added to a two-dimensional mixer and mixed in a two-way composite motion for 1.5 hours.

[0041] (2) The mixed powder is continuously fed into a co-rotating twin-screw extruder for melt dispersion. The temperature is controlled at 148°C and the melt residence time is 12 minutes to obtain a low-viscosity melt. The melt is continuously fed into the impregnation tank through a closed conveying pipeline while maintaining nitrogen protection.

[0042] (3) Prepare an ethanol-water solution containing 1.0 wt% KH-560, wherein the volume ratio of ethanol to water in the ethanol-water solution is 3:5. Adjust the pH of the solution to 4-5 and stir at room temperature for 45 minutes. Completely immerse the glass fiber cloth in the above solution for 3 minutes. Then remove excess liquid and dry in a hot air oven at 110°C for 20 minutes. Introduce the dried glass fiber cloth into the impregnation tank through guide rollers, with the impregnation tank temperature at 150°C. Control the contact time between the glass fiber cloth and the melt in the impregnation tank to 2 minutes.

[0043] (4) The impregnated prepreg tape is continuously fed into the high-temperature polymerization oven and heated to 200°C for 10 minutes. Then the temperature is maintained at 185°C for 15 minutes.

[0044] (5) The material is cooled to below 80°C by cooling rollers at a rate of 5°C / min to form a continuous thermoplastic fiberglass composite board. Then, it is cut by an automatic cutting device.

[0045] Fourier transform infrared (FT-IR) structural characterization (1) Parameter setting and detection process: The chemical structure of HBP-OH and HBP-EP prepared in Example 1 was analyzed using a high-sensitivity Fourier transform infrared spectrometer. The test used an ATR total reflectance assembly for direct sampling, and the scanning range was set to 4000 cm⁻¹. -1 Up to 500cm -1 The mid-infrared region has a spectral resolution of 4 cm⁻¹. -1 .

[0046] (2) Characterization results: as shown in the appendix Figure 3 As shown, comparing the two spectral curves clearly reveals the chemical transformation process of the functional groups. The spectra of the two samples are at 1732 cm⁻¹. -1 The surrounding area shows extremely strong absorption peaks, corresponding to the characteristic stretching vibrations of the ester carbonyl group (C=O) in the hyperbranched polyester backbone, indicating that the polymer backbone remained intact and did not degrade during the modification process. The HBP-OH curves are in the range of 3200-3600 cm⁻¹. -1 A significant broad and strong absorption band exists in the region, attributed to the stretching vibration of the terminal hydroxyl group (-OH). However, this broad peak has largely disappeared in the HBP-EP curve, indicating that the hydroxyl groups on the reactant surface have participated in the reaction and been consumed. Furthermore, the HBP-EP curve shows a peak at 910 cm⁻¹ in the fingerprint region. -1 A new, sharp absorption peak is clearly visible, which is attributed to the characteristic breathing vibration peak of the epoxy group. In summary, the disappearance of the hydroxyl peak and the formation of the epoxy peak shown in this spectrum strongly confirm that the hydroxyl groups at the ends of the hyperbranched polyester polymer have been successfully converted into epoxy functional groups, proving the successful construction of the bifunctional catalytic crosslinking agent molecular structure described in this invention.

[0047] Example 2 The bifunctional catalytic crosslinking agent was taken from the same batch as in Example 1. Raw materials for the thermoplastic composite material preparation: 98 parts CBT oligomer (melting point 135-145℃, melt viscosity <30 mPa·s), 5 parts bifunctional catalytic crosslinking agent, 2 parts modified silica with a particle size of 1-3 μm, 0.5 parts antioxidant 168, 0.5 parts pentaerythritol tetrastearate, density 600 g / m³ 2 310 parts of glass fiber cloth. The preparation process is as follows: resin precursor powder premixed for 2 hours; melt dispersion temperature 155℃, melt residence time 15 minutes; impregnation tank temperature 155℃; in-situ ring-opening polymerization reaction temperature 205℃, time 15 minutes; after the reaction is completed, the temperature is maintained at 190℃ for 20 minutes; cooling and shaping rate 8℃ / min; the rest of the process is the same as in Example 1.

[0048] Example 3 The bifunctional catalytic crosslinking agent was taken from the same batch as in Example 1. Raw materials for the thermoplastic composite material preparation: 92 parts CBT oligomer (melting point 135-145℃, melt viscosity <30 mPa·s), 2 parts bifunctional catalytic crosslinking agent, 1 part modified silica with a particle size of 1-3 μm, 0.1 parts antioxidant 1010, 0.1 parts antioxidant 168, 0.2 parts pentaerythritol tetrastearate, density 300 g / m³. 2 152 parts of glass fiber cloth. The preparation process is as follows: resin precursor powder is premixed for 1 hour; melt dispersion temperature is 140℃, melt residence time is 10 minutes; impregnation tank temperature is 145℃; in-situ ring-opening polymerization reaction temperature is 190℃, time is 5 minutes, after the reaction is completed, the temperature is maintained at 180℃ for 5 minutes; cooling and shaping rate is 3℃ / min; the rest of the process is the same as in Example 1.

[0049] Comparative Example 1 Same as Example 1, except that a hyperbranched epoxy polymer without a metal catalyst is used instead of a bifunctional catalytic crosslinking agent.

[0050] Comparative Example 2 Same as Example 1, except that a conventional bisphenol A type epoxy resin is used instead of a bifunctional catalytic crosslinking agent.

[0051] Comparative Example 3 Same as Example 1, except that no bifunctional catalytic crosslinking agent is added.

[0052] Performance testing The prepregs obtained in the examples and comparative examples were hot-pressed into laminates with a thickness of about 3-4 mm by multi-layer stacking, and then cut into the required samples according to various test standards.

[0053] 1. Microporosity testing Refer to GB / T 1033.1-2008 "Determination of density of non-foamed plastics - Part 1: Impregnation method, liquid pyrometer method and titration method".

[0054] Sample preparation: Cut the board into small pieces of 10×10×5mm, keeping the surface flat.

[0055] Specific steps: Use a precision balance to determine the dry weight W1 of the sample. Immerse the sample in distilled water and determine the volume of liquid displaced or the wet weight W2 after immersion in liquid. Calculate the actual density ρ. r =W1×ρ r / (W2-W1), the theoretical density ρ is calculated from the volume fraction of resin and glass fiber. t .according to =(1 ρ r / ρ t Calculate the microporosity (%) by multiplying the result by 100%. Test 3 samples in each group and take the average value.

[0056] 2. Creep resistance test Refer to GB / T 41061 2021 Test Method for Creep Properties of Fiber Reinforced Plastics.

[0057] Sample preparation: Cut the board into 10×5×3mm samples.

[0058] Specific steps: Using a dynamic thermomechanical analyzer, apply a constant stress of 5 MPa at a constant temperature of 150℃, and record the creep strain ε=ΔL(t) / L0 after 1000 minutes, where ΔL(t) is the increase in sample length at time t, and L0 is the initial gauge length. Three samples are tested in each group, and the average value of the results is taken.

[0059] 3. Heat distortion temperature test Refer to GB / T 1634.1-2025 "Determination of temperature of deformation under load for plastics - Part 1: General test method".

[0060] Sample preparation: The plate was cut into 80×10×4mm samples with a smooth surface.

[0061] Specific steps: Place the sample in the HDT instrument fixture, apply a static load of 1.8 MPa, and heat at a rate of 2 °C / min. Record the temperature (°C) at which the sample produces a bending deformation of 0.25 mm. Test 3 samples per group and take the average value.

[0062] 4. Mechanical performance testing (1) Bending strength / bending modulus test Refer to GB / T 1449-2005 "Test Method for Bending Properties of Fiber Reinforced Plastics".

[0063] Sample preparation: Cut the plate into 80×10×4mm samples. The sample surface should be flat and free of obvious defects.

[0064] Test Procedure: A three-point bending test was performed using an electronic universal testing machine. The span was set to 64 mm, and the loading rate was 2 mm / min. The maximum load at which the specimen fractured was recorded, and the bending strength (MPa) was calculated. The bending modulus (MPa) was calculated based on the slope of the linear stage of the load-deflection curve. Five samples were tested in each group, and the average value of the results was taken.

[0065] (2) Tensile strength / elongation at break test Refer to GB / T 1040.2-2022 "Determination of tensile properties of plastics - Part 2: Test conditions for molded and extruded plastics".

[0066] Sample preparation: The plate is processed into dumbbell-shaped specimens with a total length of about 150 mm and a gauge length of 50 mm.

[0067] Test Procedure: Tensile tests were conducted using an electronic universal testing machine. The test temperature was 23℃, and the loading rate was 5 mm / min. The maximum load and elongation at break were recorded, and the tensile strength (MPa) and elongation at break (%) were calculated. Five samples were tested in each group, and the average value of the results was taken.

[0068] (3) Impact strength test Refer to GB / T 1043.1-2008 "Determination of impact properties of simply supported plastic beams - Part 1: Non-instrumental impact test".

[0069] Sample preparation: Cut the plate into 80×10×4mm specimens and process a V-shaped notch in the middle of the specimen with a notch depth of 2mm.

[0070] Test Procedure: The test is conducted using a simply supported beam impact testing machine. The specimen is placed horizontally on the support, and the impact pendulum is released from a specified height to deliver a single impact to the back of the notched specimen. The impact energy consumed at specimen fracture is recorded, and the impact strength (kJ / m²) is calculated based on the specimen's cross-sectional area. 2 Five samples were tested in each group, and the average result was taken.

[0071] Table 1. Test results of microporosity, creep resistance, and heat distortion temperature for the examples and comparative examples.

[0072] Table 2. Mechanical property test results of the examples and comparative examples.

[0073] Results Analysis (1) As can be seen from Tables 1 and 2, Examples 1-3 all exhibited excellent and stable comprehensive performance. All three groups of samples had low microporosity, as shown in the attached table. Figure 4 This demonstrates that using CBT low-viscosity melt for fiber impregnation can achieve good internal penetration of the fiber bundle, thereby forming a dense structure. The low porosity effectively reduces internal defects in the material, resulting in high mechanical load-bearing capacity of the composite material under bending, tensile, and impact loads. Simultaneously, all three sets of examples exhibited low creep strain values, as shown in the attached figure. Figure 5 This indicates that the material exhibits excellent resistance to deformation under long-term high-temperature stress, which is related to the three-dimensional network structure formed in the system and the dynamic rearrangement mechanism of ester exchange. This structure can release some internal stress and maintain network stability under high-temperature conditions, thereby improving the material's dimensional stability and heat resistance. Overall, Example 1 shows the best performance across all performance indicators, indicating that the content of the catalytic crosslinking agent, the filler ratio, and the process conditions are in a relatively ideal balance, enabling the material to simultaneously possess high strength, high stiffness, good heat resistance, and excellent creep resistance.

[0074] (2) Comparative Example 1 showed some performance degradation. Although a hyperbranched structure was still introduced into the system, the catalytic efficiency of CBT ring-opening polymerization and subsequent dynamic transesterification reaction was significantly reduced due to the lack of a metal catalyst, resulting in a lower network density in the system. This structural difference made the material more prone to creep deformation under long-term high-temperature loading, and the internal stress generated during polymerization was difficult to release through dynamic rearrangement, thus reducing both heat resistance and mechanical properties. In addition, the insufficient network structure also affected the interfacial bonding strength after melt wetting, resulting in lower flexural strength and impact strength than the example.

[0075] (3) Compared with the examples, the performance degradation of Comparative Examples 2 and 3 was more significant. Comparative Example 2 used traditional epoxy resin as an additive component. This system mainly provides static crosslinking but lacks dynamic transesterification regulation capability. It is prone to generating large residual internal stress during polymerization shrinkage, thus exhibiting poor performance in terms of heat resistance and creep resistance. Comparative Example 3 did not introduce any catalytic crosslinking component. The system mainly relies on the linear structure of PBT to provide mechanical properties. It lacks an effective three-dimensional network reinforcement structure, making the material more prone to deformation under high-temperature loads. At the same time, the interfacial bonding strength is reduced, resulting in a significant decrease in flexural strength, tensile strength, and impact strength. The higher porosity also further weakens the overall structural stability of the material.

[0076] In summary, this invention introduces a hyperbranched polyester polymer structure with dual catalytic and crosslinking functions into the CBT in-situ polymerization system. This structure ensures low-viscosity impregnation properties of the melt while constructing a stable three-dimensional network structure, and combines this with a dynamic transesterification mechanism to release internal stress. This structural design significantly reduces material porosity, improves heat resistance and creep resistance, while also maintaining high flexural strength, tensile strength, and impact toughness, thus obtaining a deformation-resistant thermoplastic glass fiber composite material with excellent comprehensive performance and good dimensional stability.

Claims

1. A deformation-resistant thermoplastic composite material, characterized in that, The composite material is composed of a thermoplastic resin matrix system and a reinforcing material, glass fiber cloth. The thermoplastic resin matrix system includes the following raw materials in parts by weight: 92-98 parts of cyclic butylene terephthalate oligomer, 2-5 parts of bifunctional catalytic crosslinking agent, 1-2 parts of modified silica, 0.2-0.5 parts of antioxidant, and 0.2-0.5 parts of lubricant. The bifunctional catalytic crosslinking agent is a hyperbranched epoxy functionalized polymer supported on a metal catalyst. The metal catalyst is zinc acetylacetone.

2. The deformation-resistant thermoplastic composite material as described in claim 1, characterized in that, The surface density of the glass fiber cloth is 300-600 g / m². 2 The fiber volume fraction in the composite material is 45%-60%.

3. The deformation-resistant thermoplastic composite material as described in claim 1, characterized in that, The cyclic butylene terephthalate oligomer has a melting point of 135-145℃ and a melt viscosity of less than 30 mPa·s; the modified silica is amorphous silica with a surface treated with silane and a particle size of 1-3 μm; the antioxidant is one or a combination of antioxidant 1010 or antioxidant 168; and the lubricant is pentaerythritol tetrastearate.

4. The deformation-resistant thermoplastic composite material as described in claim 1, characterized in that, The preparation steps of the bifunctional catalytic crosslinking agent include: taking pentaerythritol and 2,2-di(hydroxymethyl)propionic acid in a molar ratio of 1:15, adding 0.1 wt% of p-toluenesulfonic acid of the total weight of the reactants, introducing a nitrogen gas flow, and performing a melt polycondensation reaction at 140°C for 5 hours to obtain a hydroxyl-terminated hyperbranched polyester polymer; dissolving the obtained hydroxyl-terminated hyperbranched polyester polymer in tetrahydrofuran, with the solid content controlled at 25 wt%; and adding 5 times the molar amount of epichlorohydrin based on the molar amount of hydroxyl groups in the hydroxyl-terminated hyperbranched polyester polymer, while stirring... Under stirring conditions, a 30wt% sodium hydroxide aqueous solution was added dropwise, and the reaction was carried out at 60℃ for 6 hours. The amount of sodium hydroxide used was 2.5 times the molar amount of hydroxyl groups in the hydroxyl-terminated hyperbranched polyester polymer. After the reaction was completed, the polymer was washed with deionized water, dried, and rotary evaporated to obtain the epoxy-terminated hyperbranched polyester polymer. The obtained epoxy-terminated hyperbranched polyester polymer was mixed with the zinc acetylacetonate at a weight ratio of 10:1 in anhydrous ethanol, and the system concentration was controlled at 30wt%. The mixture was refluxed and stirred at 80℃ for 2 hours. After removing the solvent and drying, the bifunctional catalytic crosslinking agent was obtained.

5. A method for preparing a deformation-resistant thermoplastic composite material according to any one of claims 1-4, characterized in that, Includes the following steps: S1: The cyclic butylene terephthalate oligomer, bifunctional catalytic crosslinking agent, modified silica, antioxidant and lubricant are mixed evenly to obtain precursor powder; S2: The precursor powder is melt-dispersed to prepare a reactive melt and then transported to the impregnation area; S3: The surface-treated glass fiber cloth is introduced into the reactive melt in the impregnation area for impregnation treatment to obtain a prepreg tape; S4: The prepreg tape is placed in a high-temperature environment for in-situ ring-opening polymerization, followed by dynamic annealing. S5: Cool and shape the treated material and cut it in an orientation to obtain a deformation-resistant thermoplastic composite material.

6. The method for preparing a deformation-resistant thermoplastic composite material as described in claim 5, characterized in that, In step S1, the precursor powder is mixed using a two-way compound motion mixing method for 1-2 hours, while maintaining an ambient relative humidity below 50% during the mixing process.

7. The method for preparing a deformation-resistant thermoplastic composite material as described in claim 5, characterized in that, The melting and dispersion temperature in step S2 is 140-155℃, and the residence time of the precursor powder in the melting and dispersion process is 10-15 minutes.

8. The method for preparing a deformation-resistant thermoplastic composite material as described in claim 5, characterized in that, The surface treatment process described in step S3 is as follows: prepare an ethanol aqueous solution containing 1.0 wt% γ-epoxypropoxypropyltrimethoxysilane, wherein the volume ratio of ethanol to water in the ethanol aqueous solution is 3:5; adjust the pH of the solution to 4-5 with acetic acid, and stir for 45 minutes at room temperature; immerse the glass fiber cloth in the solution for 5 minutes, and then dry it at 110°C for 20 minutes.

9. The method for preparing a deformation-resistant thermoplastic composite material as described in claim 5, characterized in that, The in-situ ring-opening polymerization reaction in step S4 is carried out at a temperature of 190-205℃ for 5-15 minutes; the dynamic annealing treatment is carried out at a temperature of 180-190℃ for 5-20 minutes.

10. The method for preparing a deformation-resistant thermoplastic composite material as described in claim 5, characterized in that, The cooling and shaping rate in step S5 is 3-8℃ / min, cooling to below 80℃; the directional cutting control cuts the cutting direction so that the short side is parallel to the production line travel direction and the long side is parallel to the weft direction.

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