Radiation Induced Long Chain Branching in High‐Density Polyethylene through a Reactive Extrusion Process

A reactive extrusion process is developed for the modification of the rheological properties of a high density polyethylene (HDPE) by inducing long chain branching (LCB) using a photoinitiator and ultraviolet (UV) light. A central composite response surface design is selected to design the experimental runs at different photoinitiator concentrations, polymer flow rates, and extruder screw speeds. The selected processing factors at the specified levels produce negligible amounts of gel as indicated by extraction experiments. Linear viscoelastic properties at low frequencies indicate the presence of long chain branches. Both zero shear viscosity and relaxation time of the modified samples are enhanced with the branching. According to further molecular characterization, the molecular weight averages are slightly increased, however, the polydispersity index (PDI) of the modified samples remains the same.