Melt densification of polymeric powder beds filled with natural fibres

An experimental study of the melt densification of polyethylene powders filled with natural fibres is presented. The aim was to understand the underlying principles applicable to the consolidation of thermoplastic polymer-natural fibre systems processed by rotational moulding. This process has been developed at POLYCOM and has been reported previously in the literature. A sintering oven with PID-controlled temperature was equipped with a stereo microscope and image acquisition facilities. Sintering sequences were studied using image analysis procedures. Initial studies with two kinds of polymer particle and one type of fibre were carried out in order to identify some of the governing processes. Other studies included the use of multi-particle beds with many fibres having different concentrations, and the measurement of powder permeability and density. The influence of sintering temperature and time on the sintered specimens' density is also reported. Natural fibres induce voids in the sintered specimens and retard coalescence between the polymer particles. The experimental results were in good agreement with previous data obtained from the rotational and compression moulding of natural fibre reinforced thermoplastics.