Polymer melting and polymer powder sintering by thermal analysis

Sintering of polymeric powders is a peculiar characteristic of many processing technologies, including rotational moulding and selective laser sintering (SLS). During polymer sintering, viscosity reduction in the melt state promotes densification of polymer powders, through a double stage mechanism, involving powder coalescence and bubble removal. In particular, sintering of semi-crystalline polymers is strongly influenced by the melting behaviour. Nevertheless, melting itself in absence of pressure is not necessarily accompanied by powder sintering, unless low viscosities are achieved. In this work, the melting and sintering behaviour of recycled high density polyethylene (rHDPE) have been analysed through differential scanning calorimetry (DSC) and Thermomechanical Analysis (TMA). Efficient models capable of describing the melting temperature distribution and rate of sintering of rHDPE powders have been developed, highlighting the inherent differences between the two distinct processes.