Miscibility and crystallization behavior of Poly(butylene terephthalate)/Poly(ethylene terephthalate-co-1,4-cyclohexylene dimethylene terephthalate) blends

Abstract

The miscibility and crystallization behavior of a series of polymer blends containing different content of poly(butylene terephthalate) (PBT) and poly(ethylene terephthalate-co-1,4-cyclohexylene dimethylene terephthalate) (P(ET/CT)) have been studied. It is confirmed through DSC, SAXS and SEM that PBT is miscible with P(ET/CT) with different CT content. When the mole content of CT is 37 %, P(ET/CT) (abbreviated as P(ET/CT37 %)) is fully amorphous. But, as the mole ratio of CT is 66 %, P(ET/CT) (abbreviated as P(ET/CT66 %)) possesses crystallizability. Compared to the extremely fast crystallization of PBT, the crystallizability of P(ET/CT66 %) is so weak that non-isothermal crystallization (at a cooling rate of 10 °C/min) can hardly occur. Upon blending, however, it is interesting to find that the P(ET/CT66 %) could be involved in the crystallization of the blends within the entire composition range. In the DSC cooling curves, a double-peak crystallization could be observed, in which the Tc1 is attributed to the crystallization of PBT and the Tc2 to that of P(ET/CT66 %). Further, the two glass transition temperatures of the blends after crystallization confirm the occurrence of crystallization-induced phase separation at higher P(ET/CT) content. Therefore, the excluded P(ET/CT66 %) local domain or aggregation is regarded as the prerequisite of the P(ET/CT66 %) crystallization, and the previously formed PBT crystals act as its nucleating agent.