Pore Structure of Plastic Powder Compacts

Abstract

The pore structure of hot-pressed polystyrene and polyvinyl chloride powder compacts prepared at 40-100°Cand 1-8t/cm2 was studied by means of mercury porosimeter. Most polystyrene compacts have two peaks in the open pore size distribution curve, one at 0.01μ and the other at 1-5μ inradius. It has been found that the first peak corresponds to the pore on the surface of starting powder particle and the second to interparticle voids. The latter has been found to shift to smaller radius with increasing compacting pressure and/or temperature. The effects of compacting conditions on open and total pore volumes were studied. And it has been shown that the compacting pressure at which the open pore volume remains unchanged with further increase of pressure decreases as compacting temperature is raised.The increase in the open pore volume was observed on heating the polyvinyl chloride powder compacts prepared at room temperature. This might be explained by irreversible displacement of particles due to the expansion or stretching of particles and other factors. Different features both in the pore structure and its dependence on compacting conditons were observed between the poly-styrene and polyvinyl chloride powder compacts. This would be ascribed to the differences in their softening characteristics and powder parameters.On the basis of the experimental results and discussion, the mechanism of pore volume variation has been presented, and it is suggested that the deformation caused by softening and compression of powder particles is one of the most important factors to be considered in plastic powder compact.