Gross melt fracture of polyethylene. II: Effects of molecular structure

The effect of molecular structure (MW, MWD and LCB) on the critical tensile stress (sigma(c)) for the onset of gross melt fracture (OGMF), proposed in Part I (1) as a material-dependent criterion for fracture, was determined for a group of polyethylenes varying in structure. These included linear low and high-density polyethylenes and several materials produced using metallocene and constrained geometry catalysts. It was found that the critical stress is independent of M-w, for constant poly dispersity but increases with increasing long chain branching and polydispersity. The addition of boron nitride particles had no effect on the sigma(c) up to a level of 0.5% by weight.