High‐temperature crystallization of immiscible polymer blends induced by the shear flow in injection molding

The crystallization behavior of a polymer blend is thoroughly investigated by considering its melt‐flow history. Poly(ethylene terephthalate) (PET) is found to crystallize at high temperature through shear flow during injection molding when blended with immiscible polyamide 6. Wide‐angle X‐ray scattering experiments reveal that the PET in the blend is better oriented than pure PET because phase separation enhances shear stress during injection molding. Differential scanning calorimetry shows that the crystallization temperature (Tc) of PET (blend) is sensitive to its melt‐flow history. PET (blend) crystallizes at a temperature lower than that of pure PET in pellets prior to injection molding; however, following injection molding, the Tc of PET (blend) is higher than that of pure PET. In particular, high shear conditions, such as in low‐temperature molding, facilitate the high‐temperature crystallization of PET. Therefore, phase separation enhances molecular‐chain orientation and promotes the crystallization of PET. Thorough investigations of polymer crystallization that consider melt‐flow history are conducted for immiscible blends of poly(ethylene terephthalate) and polyamide 6. The crystallization behavior of the polymers in the blend is strongly affected by the processing history, and high‐temperature crystallization of the polymers in the blend is observed after injection molding. Highly orientated polymer chains, generated by phase separation and shear flow during injection molding, promote the crystallization of the polymers in the blend.