Kinetics and thermal crystallinity of recycled PET. I. Dynamic cooling crystallization studies on blends recycled with engineering PET

The recycled poly(ethylene terephthalate) (R-PET) from the recovery of a blow-molded bottle is studied with its crystalline behavior in terms of glass transition temperature (Tg), crystallization temperature (Tc), melting temperature (Tm), and its dynamic crystallization kinetics. These crystalline behaviors offer an explanation of the better mechanical properties of the R-PET. Thermal cycles of the processes of the R-PET and its blending specimens with engineering PET (E-PET) show the importance of the thermal treatment of the plastic PET in the improvements of mechanical strength and increased crystallinity. Tenfold and fivefold increases, respectively, of elongation and impact strength are observed in the specimen of R-/E-PET of 20/80 weight ratio blend, better than that of E-PET alone. A nearly 20-fold increase of the crystallization rate constant (K) at 190°C for the same R-/E-20/80 blend is observed. The Avrami exponent (“n”) is found to be variable with temperature. The changing crystallization mechanisms are mainly the result of the competition between the nucleating and growing of crystallites in response to the temperature-controlling factor at the melt state.