Use of virgin/recycled polyethylene blends in rotational moulding

Aiming to further plastics recycling via rotational moulding plastics processing, blends of virgin and recycled polyethylene sourced from post-consumer plastics were developed. Three different kinds of recycled high density polyethylene – from bottles, pipes and mixed household waste – were compounded with virgin medium density polyethylene in an extruder. The ideal amount of recyclate was chosen based upon the impact resistance of different contents (25, 50 and 75%) of recycled plastic with the 50/50 blend found to have the best performance. Compression-moulded and rotationally-moulded samples were analysed through falling dart impact test, flexural test, melt flow rate and differential scanning calorimetry analysis. The impact results of the compression-moulded samples showed an increase in the impact resistance of the blends with a higher melt flow index and lower degree of crystallinity. The rotationally-moulded specimens displayed much lower impact resistance than the pure virgin plastic and a 20–30% reduction in the flexural moduli, which were ascribed to the crystalline structure of the part and issues in the blends’ rotomoulding process. It was concluded that blending virgin and recycled polyethylene for rotational moulding can be an effective way to further plastics recycling inside the Circular Economy context.

Morphology of Rotationally Moulded Microfibril Reinforced Composites and its Effect on Product Performance

Rotational moulding (rotomoulding) is one of the fastest growing plastics manufacturing processes using linear polyethylenes dominantly as raw materials. However, due to their modest mechanical properties, rotational moulders worldwide are keen to develop stronger and stiffer materials. In the present study, an attempt was undertaken to apply the concept of microfibril reinforced composites (MFCs) for improving the material performance. Melt blended and subsequently cold drawn and undrawn linear medium density polyethylene (LMDPE) with either poly(ethylene terephthalate) or poly(ethylene naphthalate) possessing MFC structure were mixed with neat LMDPE and thereafter processed via rotational moulding. The rotomoulded samples were characterised morphologically and tested mechanically. The obtained unsatisfactory mechanical characteristics led to the subsequent morphological study which revealed some interesting phenomena for the rotomoulded products containing MFC blends.