The Melting Behavior of Poly(Ethylene Terephthalate)/SiO2 Nanocomposites

The melting and recrystallization behavior of poly(ethylene terephthalate) (PET)/SiO₂ nanocomposites after isothermal crystallization from the melt was studied by step-scan differential scanning calorimetry (SDSC). The influences of SiO₂ contents, crystallization temperature, and crystallization time on the melting process were examined. Two melting endotherms (in the SDSC C_P.A curves, reversible part) and one recrystallization exotherm (in the SDSC C_P.IsoK curves, irreversible part) of PET/SiO₂ nanocomposites after isothermal crystallization were observed during the melting process. All are ascribed to the melting–recrystallization mechanism. The low-temperature endotherm is attributed to the melting of initial crystals formed during the isothermal treatment and the high temperature endotherm to the melting of recrystallization materials. The reason why more recrystallization happened with the increase of SiO₂ content is given and the process of recrystallization was described in detail. The effects of crystal perfection and recrystallization were minimized by increasing crystallization temperature and time.