EPDM Elastomers as Impact Modifiers for Contaminated, Recycled HDPE

Abstract

The value of recycled high-density polyethylene (HDPE) is lowered if it contains impurities of PP, PS or PET, hut the embrittlement (partial loss of ductility and toughness) that arises when HDPE is blended with these more rigid polymers can be counteracted by the addition of an impact modifier. In this work, two EPDM grades with different monomer compositions have been evaluated as impact modifiers to upgrade recycled HDPE. Both elastomers improved the tensile impact strength and elongation at yield, at the expense of reduced modulus and yield strength. These effects were more pronounced for an amorphous EPDM with 58 wt% ethylene than for a semicrystalline EPDM with 72 wt% ethylene. The reduced impact strength and yield elongation caused by up to 10% polystyrene or PET could be compensated for by adding an amount of amorphous EPDM equal to half the weight of the contaminant polymer. The effect of EPDM modification on the morphology of the HDPE phase was studied by differential scanning calorimetry. The thermal history of the material is shown to be an important factor, influencing the ability of the HDPE to crystallise.