Mutual influence of the morphology and growth kinetics in binary crystalline blends of poly(butylene terephthalate) and polyarylate

The spherulitic morphology and crystallization behaviors of binary crystalline blends of poly(butylene terephthalate) (PBT) and polyarylate (PAr), based on bisphenol A, (27:73 isophthalic:terephthalic acids), are investigated herein. PBT and PAr crystallize simultaneously or sequentially; various crystallization behaviors and morphologies are observed. In the PBT-rich blends, PAr does not crystallize; the PBT spherulites coarsen as the PAr concentration increases. Non-crystallizable PAr is trapped inside the spherulites. The PBT spherulitic growth rate decreases when PAr is added and remains constant thereafter. For the 50/50 blends, PBT and PAr crystallize simultaneously, and their spherulites co-exist separately. The spherulitic growth rate of PBT increases with time while PAr is crystallizing, but it remains constant if PAr crystallizes prior. At a crystallization temperature of 250 °C, only PAr crystallizes; the non-crystallizable PBT is expelled from the PAr spherulites because the crystallization rate of PAr is low. The spherulites of PAr do not fill the space in the final crystallization stage. The crystallization rate of the binary crystalline PBT/PAr blends was notably influenced by the prior crystallization of the other component, and was due to the change of the amorphous composition in addition to the constraints of the crystals on the chain mobility.