The effect of long chain branching on the processability of polypropylene in thermoforming

Linear polypropylene was modified by reaction with peroxydicarbonates in a twin screw extruder to obtain varied degrees of long chain branching. The melt strength and the elasticity of the modified polymers were found to increase with the modification. The processability in foaming and thermoforming processes improved with branching and showed an optimum, beyond which higher degrees of long chain branching appeared not to help any further. The branched PP samples showed distinct strain hardening in the elongational viscosity, which was absent from the original linear melts. Melt strength, elasticity and strain hardening increased with the increase of the number of long chain branches on the main chain. The effect of molecular weight and molecular weight distribution of the precursor on the improvement of the processability of the polymer was examined.