Formation of segregation morphology in crystalline/amorphous polymer blends: Molecular weight effect

In a melt-miscible crystalline/amorphous polymer blend, crystallization is accompanied with the segregation of amorphous diluent. Depending on the distance of segregation, various types of segregation morphology, including interlamellar, interfibrillar, and interspherulitic, may be created. In this study, we systematically investigated the effects of molecular weight (MW) of both crystalline and amorphous component on the formation of segregation morphology in polycaprolactone (PCL)/poly(vinyl chloride) (PVC) blends. Optical microscopy and small-angle X-ray scattering (SAXS) revealed that the extent of interfibrillar morphology increased with decreasing MW of PCL (M-PCL). However, in the blends containing oligomeric PCL, interfibrillar segregation also involved the exclusion of uncrystallizable PCL short chains. The volume fraction of PVC expelled into the interfibrillar regions was calculated from SAXS Linear crystallinity and bulk crystallinity. The results indicated that the transport of PVC into interfibrillar regions was facilitated by decreasing M-PCL for PCL/PVC 80/20 blend. However, the extent of PVC expelled interfibrillarly was relatively unaffected by M-PCL for the 70/30 and 60/40 blends. The variation of crystal growth rate with M-PCL played a key role in controlling the segregation distance of PVC. Increasing the molecular weight of PVC (M-PVC) was found to shorten the segregation distance. The dependence of growth rate on M-PVC again governed the length scale of PVC segregation.