Melt Densification of Polymeric Powder Beds Filled with Natural Fibres

Abstract

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.

Thermal, Mechanical, Morphological and Aesthetical Properties of Rotational Molding PE/Pine Wood Sawdust Composites

“…The internal air temperature of the mold shows a typical curve, with a rapid increase in the temperature followed by a plateau observed between 120 and 160 °C, which represents the moment of melting and adhesion of the PE/wood to the mold surface. The presence of natural fibers causes a delaying effect on plastic particle coalesce during the sintering process, as observed in the plot [ 58 ]. When the cooking stage is completed and PIAT is reached (setup at 200 °C) the mold is transferred to the cooling chamber; the temperature drops and a small plateau occurs due to the crystallization of PE.…”

Rotomolding and polyethylene composites with rotomolded lignocellulosic materials: A review

“…Heating and rotating the mold: The mold is heated in an oven and rotated through two or more axes until the material melts and its particles are sintered, forming a single solid mass that coats the mold wall. 11,72 Bubble removal and melt densification can be controlled according to the particle geometry of the polymer and its melt rheology, which typically exhibits Newtonian fluid behavior. 10,73 The biaxial rotation of the equipment axes, where the molds are installed, allows the melted material to adhere to the inner wall of the mold, forming the object with the desired thickness.…”

“…The entire cooling process is accompanied by biaxial rotation of the mold. 26,72 Stage 4. Demolding: Once mold rotation is complete and the part has solidified, the mold is opened and taken to a demolding station where the final part is removed.…”