A PROCESS TO PRODUCE MICROCELLULAR PVC

A novel process to produce microcellular PVC foams with a very homogeneous cell distribution and cell densities ranging from 10(7) to 10(9) cells/cm3 is described. Microcellular PVC foams with relative densities (density of foam divided by the density of unfoamed polymer) ranging from 0. 15 to 0.94 have been produced. In this paper, experimental results on bubble nucleation and growth are presented. It was found that the bubble nucleation density increases with-foaming temperature and eventually reaches a limiting value, while the average bubble diameter is relatively independent of the foaming temperature. A majority of the cell growth was found to occur in the early stages of foaming.