Irradiation processing to modify HDPE molecular architecture: Correlation with irradiation conditions and polymer grade
Elham Moradkhani, Mehdi Entezam, Mostafa Ahmadi, Hossein Ali Khonakdar, Holger Ruckdäschel, Volker Altstädt
Abstract
Irradiation process is an effective technique to modify the molecular architecture, and therefore, the processability and thermo-mechanical properties of polyolefins. In this study, the utility of irradiation dose and atmosphere, heat treatment of the raw material prior to irradiation and the polymer grade, as the most important parameters to influence the irradiation performance in terms of modifying the molecular characteristics, rheological, and thermo-mechanical properties of high-density polyethylene are comprehensively investigated. According to the SEC analysis and linear viscoelastic rheology results, long chain branch formation is predominant at doses below 25 kGy, which is strongly influenced by the polymer grade but not by the heat treatment. Rheological analyses also suggest a star like molecular architecture for branched HDPE chains. Unexpectedly, Ziegler-Natta catalyzed HDPE grades were found to be branched significantly more than Philips catalyzed ones, which highlights the dominance of chain mobility factor over the presence of unsaturated bonds. The extent of crystallinity and tensile mechanical properties also change upon irradiation, in agreement with the extent of molecular architecture modification. These results provide a useful guideline to control the extent of the irradiation induced LCB in HDPE.