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, Φ_L-PE. As the Φ_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).