Formation of shish-like fibril crystals from the melt of blends of cyclic and linear polyethylene under shear flow

The role of chain entanglements in shear-induced crystallization is one of the most important unsolved problems. The entanglements formed by topologically distinct cyclic and linear polymers are particularly notable. The shear-induced crystallization behavior of a blend of cyclic polyethylene (C-PE) and linear polyethylene (L-PE) was investigated. Using C-PE as a matrix and L-PE as an additive, we changed the molecular weight and blend ratio of C-PE and L-PE and measured the formation rate of shish-like fibril crystals, I. In both blend systems of C-PE(230k)/L-PE(42k) and C-PE(230k)/L-PE(104k), where the values in parentheses represent the molecular weight, I reached a maximum at a certain weight fraction of L-PE, Phi(L-PE). As the Phi(L-PE) was increased, that is, the entanglement density was increased, the formation of the oriented melt was promoted while crystallization was simultaneously suppressed by entanglements. The maximum value of I was observed owing to these two competing factors. Similar behavior was observed in the blend systems of C-PE(230k)/L-PE(42k), C-PE(130k)/L-PE(42k), and C-PE(86k)/L-PE(42k).

Automated summary

The role of chain entanglements in shear-induced crystallization is a major unsolved problem. In this study, the shear-induced crystallization behavior of a mixture of cyclic polyethylene (C-PE) and linear polyethylene (L-PE) with different molecular weights and blend ratios was investigated. It was found that increasing entanglement density promoted the formation of oriented melt, while simultaneously suppressing crystallization. These competing factors resulted in the maximum formation rate of shish-like fibril crystals.