Processing and characterization of HDPE and MDPE processed by rotational moulding

Abstract

Rotational moulding otherwise called as roto moulding is a process used to produce hollow plastic products with nearly stress free objects with the help of a bi axial rotational moulding machine which rotates the mould in two axes with minimum speed of rotation. Plastic granules pulverized into fine powders are used to produce hollow parts such as water tanks, fuel tanks, kayak boats, refrigerated panel etc. The present work investigates the mouldability of High Density Poly Ethylene (HDPE) and Medium Density Poly Ethylene (MDPE) powders by rotational moulding process. A lab model roto moulding machine has been fabricated. There are two rotating frames – an inner and an outer frame – both rotating about two mutually perpendicular axes. The driving torque is given by a motor. The machine was designed to accommodate a rectangular shape stainless steel mould. Both MDPE and HDPE were processed at three different internal air temperature and the mechanical properties were estimated as per ASTM standards. Both tensile and impact strength were observed to be improved by the increase in internal air temperature. Hardness values observed shows no significant effect on internal air temperature. The MDPE products showed higher impact strength while HDPE products showed higher tensile strength. The morphology of the MDPE and HDPE powders and the microstructure of the products were studied under optical microscope.