Void distributions and permeability prediction for rotationally moulded polymers

An experimental study of void distributions for rotationally moulded polyethylene is presented. The effects of key variables such as maximum process temperature and nominal wall thickness (via powder mass) are studied. Analytical models and finite element mass diffusion models for the permeability of heterogeneous polymers with air voids are presented and comparatively assessed. The FE method allows modelling of realistic (measured) void distributions. A preliminary estimation method for void volume fraction and mean void radius is presented. This approach is based on hot plate measurements and is shown to give good correlation with the rotationally moulded material for different process temperatures. Key objectives of the present work are (i) to develop an understanding of the factors affecting gas permeability in rotationally moulded polymers and (ii) to develop experimental and computational methods to help design low permeability rotomoulded polymer liners.