Dino talks about the structure and performance of thermoplastic polyester

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Plastic polyester PET and PBT are crystalline polymers, but their crystallinity is low (less than 30%). The amorphous density of PET is 1.335g/cm3, the crystal density is 1.445g/cm3, usually the crystallinity is 20%-30%, the melting point is 256℃, Tg69℃; the amorphous density of PBT is 1.227g/cm3, and the crystal density is 1.396g/ cm3, usually 25%-30% crystallinity, melting point 2227℃, Tg45℃.
 

PET and PBT have low Tg, and the corresponding heat distortion temperature under high load is not high, which limits the application of pure resin. After heat treatment or reinforcement with GF, the thermal deformation temperature rises significantly, and the mechanical and thermal properties of GF-reinforced PET and PBT are significantly improved. Therefore, 80% of PBT is applied after modification, and 97% of which is reinforced with GF. The characteristics of PET and PBT after enhancement are as follows.

    (1) Excellent comprehensive performance, high mechanical strength, tensile strength greater than 130MPa, bending elastic modulus greater than 8800MPa, cantilever impact strength (notch) greater than 80J/m, long-term high load deformation is small. High heat resistance, heat distortion temperature greater than 200°C, long-term use temperature 120°C, short-term use temperature 200°C. Low water absorption and excellent friction and abrasion resistance. The mechanical strength of 30% GF reinforced PBT has surpassed MPPO reinforced with the same GF dosage, and the long-term use temperature has exceeded that of PA, PC and POM reinforced with 30% GF, and the notched impact strength is only slightly lower than that of PC and PA. Table 2—165 and Table 2-166 list the performance comparison of unreinforced and reinforced PET, PBT and other engineering plastics.

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    (2) Excellent electrical performance. The electrical performance of 30% GF reinforced PBT exceeds that of PA, PC and POM reinforced by the same amount of GF, which is particularly suitable for replacing thermoset plastics. Good corrosion resistance and flame retardancy.

    (3) The density is higher (greater than 1.5g/cm3), and the price per unit volume is higher.

    (4) Easy to hydrolyze, it will be improved if the terminal carboxyl group is reduced.

    (5) Molded products are easy to warp. Alloying with amorphous polymers or filling fillers with low aspect ratios can be improved.

    (6) Reinforced PET has a high crystallization temperature (the mold temperature needs to be 130°C), and the molding efficiency is low. However, the use of copolymers and nucleating agents may reduce the mold temperature to 70°C.

    Table 2—167 lists the properties of PET and PBT

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    The blending method is used to form a polymer alloy, which can improve the performance of PBT and PET. Such as blending with EVA to improve the hot water resistance of PBT, blending with PU and abs to improve the notched impact strength of PBT, blending with PTFE to improve the abrasion resistance of PBT, and blending with PET, PC or polycarbonate polyurethane (PC-PU) The blending of rubber, etc. improves flexibility and stress crack resistance.