Effects of Fillers on the Crystallization and Degradation Behavior of Poly(ethylene terephthalate): A Review

Poly(ethylene terephthalate) (PET) is an important semicrystalline polymer, but its relatively slow crystallization restricts processing efficiency and dimensional stability. The incorporation of fillers is an effective means of promoting PET crystallization, while the resulting polymer–filler interface may also alter chain stability during processing and subsequent use. Crystallization involves segmental motion and chain ordering, whereas degradation changes the molecular structure of PET through reactions such as chain scission. Although these processes are closely related at the molecular scale, they have generally been discussed separately. This review summarizes the effects of inorganic particles, layered materials, carbon materials, fibers, and organic nucleating agents on the crystallization and degradation behavior of PET. The discussion addresses heterogeneous nucleation, crystal growth, interfacial chain organization, and the influence of filler dispersion and surface condition. Particular attention is given to the effects of filler interfaces on hydrolysis, thermal and oxidative degradation, and changes occurring during repeated melt processing. High-temperature thermal decomposition is distinguished from molecular-weight loss under processing and aging conditions. The retention of fillers during mechanical recycling is also considered. By examining crystallization and degradation together, this review clarifies how filler-induced crystal formation is related to PET chain stability and provides guidance for the selection and use of fillers in PET materials.