Effect of short-chain branching on melt fracture behavior of metallocene and conventional poly(ethylene/α-olefin) copolymers

A phenomenon that can represent a great problem in melt processing is extrudate distortion. This effect can range in intensity from a loss of gloss to gross distortion and is the factor that limits the production rate in certain processes such as the blown film extrusion of linear low-density polyethylene (LLDPE). The aim of this work was to investigate the effects that molecular weight distribution and short-chain branch length have on the observed melt fracture phenomena for poly(ethylene/α-olefin) resins with similar weight comonomer content and molecular weight. The flow stability analysis conducted in this study has shown that, even increasing of few carbon atoms the short-chain branch length of the resins, the surface melt fracture phenomena are reduced and/or eliminated. Moreover, the comparison between the metallocene (mLLDPE) and conventional LLDPE samples, with the same comonomer (hexene), showed that the metallocene-catalyzed resin exhibits early onset and more severe melt fracture, due to its narrower molecular weight distribution. POLYM. ENG. SCI., 52:1968–1977, 2012. © 2012 Society of Plastics Engineers