Rotational moulding of expanded polyethylene by pellets

An innovative method of rotational moulding expanded polyethylene by pellets was reported. Experiments were carried out in a laboratory scale uniaxial machine, which was capable of measuring in-mould air temperature in the cycle. The polymeric material used was linear low-density polyethylene. The foaming material used is endo-thermal chemical blowing agent. Before moulding, the polyethylene material and the chemical-foaming agent were first melt blended by a single-screw extruder and were then cut into pellets of 2-3 mm in diameter. Pellets were then dry-blended with pure LLDPE powder by a mixer for moulding. Characterization of moulded part properties was performed after moulding. An optical microscopy equipped with an image analysis system was also employed to determine the bubble distribution in foamed parts. The purpose of this study is to access the mouldability of rotational moulding expanded polyethylene by pellets, and to investigate how the foaming agent and processing conditions can influence the moulding process and the final product quality. It was found that the rotational moulding of expanded parts by pellets saves the cost of powder grinding as well as improves the impact property of moulded parts, but is counteracted by uneven inner surfaces.