Non-isothermal crystallization and thermo-mechanical properties of poly(butylene adipate-co-ethylene terephthalate) random copolyesters

•Polybutylene adipate (PBA) is a degradable polyester which is available on the market place and used in many industrial applications, but modifications are necessary for some application.•Copolymerization with nondegradable aromatic polyethylene terephthalate leads to the formation of random tetrapolymers and a reduction in BA sequence length distribution.•PBA shows polymorphic crystalline structure. Our findings indicate that the reduction in sequence length distribution alters the polymorphism, crystallization kinetics, and crystalline size of PBA. Random aliphatic-aromatic copolyesters are synthesized through melt polycondensation of bis(2-hydroxybutyl) adipate (BHBA) with 0–15 mol% of bis(2-hydroxyethyl) terephthalate (BHET) oligomers. Regarding the random ester-interchange reactions, the sequence length distribution of butylene adipate (BA) units reduces with increasing BHET. Crystallization of copolyesters is investigated by differential scanning calorimetry. Crystallization peak temperatures (Tc) and melting peaks (Tm1, Tm2, and Tm3) of all samples decrease with increasing cooling rate. Moreover, increasing BHET results in the reduction of crystallinity. Regarding the results of Avrami, Tobin, Ozawa, and Mo's models for non-isothermal crystallization, the crystallization rate decreases as the BHET content increases. Using the isoconversional method of Friedman, it is revealed that copolymerization leads to a reduction of the absolute enthalpy of crystallization. According to the wide-angle X-ray diffraction (WAXD) results, the crystalline dimensions reduce with copolymerization, and flawed crystals are developed in copolyesters.