Tubular Film Extrusion Stability of Metallocene Linear Low Density Polyethylene

Abstract The bubble stability of tubular film extrusion in metallocene linear low density polyethylene(m-LLDPE) and metallocene linear low density polyethylene/linear low density polyethylene(m-LLDPE/LLDPE) blend was investigated. Unstable bubble characteristics in m-LLDPE were found at low draw down ratio (DR) with a symmetric periodic bubble instability at low blow up ratio (BUR) and a helical instability at high blow up ratio. However, m-LLDPE showed better operation windows in tubular film extrusion than that of LLDPE, especially in bubble instability at low BUR. Both bubble instability and helical instability in LLDPE tubular film extrusion were enhanced by the blending with m-LLDPE. m-LLPE possesses higher melt elasticity as compared to m-LLDPE and LLDPE due to the long chain branching introduced by 1-octene co-monomer during polymerization. Blending resulted in broadening of molecular weight distribution (MWD) and thus increase in activation energy.