Thermal, physico-mechanical, and morphological properties of HDPE graft-copolymerized with polystyrene

In this study, polystyrene was graft-copolymerized onto high-density polyethylene (HDPE) by in situ polymerization of styrene monomer to change the physico-mechanical and thermal properties of HDPE. The grafting was carried out in a Brabender-type static mixer by injecting styrene monomer directly into the molten HDPE in the presence of a free-radical initiator (lauroyl peroxide or LP). The effect of wt% of styrene and initiator concentrations on thermal, physico-mechanical, and morphological properties of HDPE was investigated. The neat and modified HDPE was characterized by differential scanning calorimetry, thermogravimetric analysis, scanning electron microscopy, Fourier transform infrared spectroscopy, scanning electron microscopy, and also by tensile strength and contact angle measurements. It was found that the increase in wt% of styrene and LP dosage reduced elongation at break, hygroscopic expansion and also the melting, and the crystallization temperatures of HDPE but increased its tensile strength. The tensile strength was increased from 14.6MPa for the neat HDPE to 20.6MPA for the 10 wt% of styrene grafted onto HDPE using 0.8% LP. Scanning electron microscopy results show that there was no phase separation, and the grafted polystyrene became integral part of HDPE. The results demonstrate that styrene could be used in melt compounding to improve various properties of HDPE.