PBT and ethylene terephthalate are both semi-crystalline thermoplastic polyesters, the difference being mainly due to the difference in glycol used in the polymerization. Compared with PET, the higher raw material butanediol price, small production scale, low melting point, and mechanical properties are slightly weaker than PET, it seems that PBT can not compete with PET.
However, due to the use of linear four-carbon alcohols, the flexibility of the polymer chain is enhanced, which is manifested by a rapid crystallization rate, which makes the cycle time of injection molding shortened during the processing of PBT engineering plastics, and the yield of the mold blank improve. The good crystallization properties during the molding process result in better stability of the product and thus higher economic benefits.
In addition, the use of four carbon alcohols also makes PBT fibers have better elasticity and flexibility, and are well used in fibers and toothbrushes. PBT is a product of melt polycondensation of dimethyl terephthalate or terephthalic acid and butanediol. By controlling the polymerization time and the degree of vacuum, a product with a relative molecular mass of 17,000-40000 can be obtained. The relative molecular mass can be obtained by further solid phase polycondensation. PBT has a glass transition temperature (24 ° C) close to room temperature, lower than PET (76 ° C), close to polyamide (40 ° C); melting point is lower than PET close to polyamide; crystallization rate is 15 times that of PET, and similar to polyamide 66 . The difference in basic physical properties between PBT and PET makes them different in processing behavior and application. The low crystallization and high orientation behavior of PET in post-processing is suitable for fiber and film, while the fast-crystallizing PBT is suitable. Engineering plastics.
