Melt strength and thermal properties of organic peroxide modified virgin and recycled HDPE

Commercial blow moulding grade recycled high density polyethylene (r-HDPE) and blow moulding grade virgin HDPE were reactively extruded with various compositions (0.00 to 0.15%) of different peroxides in a twin screw extruder. The aim was to improve the melt strength properties of a blow moulding grade HDPE homopolymer ¿ a polymer resin comprising a significant part of the post consumer recycled plastic stream in Australia. Melting behaviour and crystallinity were investigated by modulated differential scanning calorimetry (MDSC). Uniaxial melt extensional (UME) measurement of the modified materials was carried out using Göttfert Rheotens melt strength tester to measure melt quality of the material. Melt strength and zero shear viscosity were also measured to assess and correlate changes in melt properties due to peroxide modification. Melt strength and zero shear viscosity of both recycled and virgin material were enhanced with the increase in composition of peroxide. However, addition of peroxide also brought with it flow instabilities like draw resonance and necking, both of which lead to limitations in polymer processing.