The dependence time of melting behavior on rheological aspects of disentangled polymer melt: a route to the heterogeneous melt

To enhance the time scale for entanglement recovery, ultra high molecular weight polyethylene (UHMWPE) with a molecular weight of approximately 9.2 × 106 gmol−1 has been used. Rheological experiments were performed to monitor the melting kinetics of the disentangled melt prepared via solution casting. The successive frequency and strain sweep experiments showed that the processes of recovery of entanglements were quite clear in our experiments. It was observed that the entangled state influenced the border of the linear viscoelastic regime and the non-linear region. Complete re-entanglement time obtained by dynamics time-sweep experiment changed with the entanglement density and became unexpectedly longer in the disentangled sample. Meanwhile, the time-sweep experiments performed in the disentangled melt displayed that the gradual increasing of storage modulus in the initial has lagged behind and the time required for the modulus build up was relevant to the heating rate on melting. We suggested that an unusual behavior of melting kinetics of the disentangled sample caused the resultant heterogeneous melt having differences in local chain mobility, and hence an “immediate” loss in the disentangled state did not occur. Therefore, the level-off storage modulus on the onset of the following time-sweep experiment may be associated with the mixing of the distinguishable state of the heterogeneous distribution on melting.