Effects of processing variables on polypropylene degradation and long chain branching with UV irradiation

A technique has been developed to modify the melt properties of polypropylene (PP). Photoinitiators along with UV irradiation were employed to introduce long chain branching (LCB) and/or crosslinking (CL). Statistically designed experiments were carried out to study the effect of processing conditions, such as photoinitiator concentration, duration of irradiation, UV lamp intensity, cooling air pressure, and photoinitiator type, on rheological properties, molecular weight characteristics and branching level. Samples were evaluated through linear viscoelastic (LVE) measurements, extensional rheometry, gel content, gel permeation chromatography (GPC), and differential scanning calorimetry (DSC). Results clearly indicated that PP can be successfully modified in order to enhance strain hardening behaviour without significant gel formation.