Foam processing of polyethylene ionomers with supercritical CO2

Via a batch process, the foam processing of polyethylene-based ionomers having two different degree of the neutralization has been conducted using supercritical CO2. The cellular structures obtained from various ranges of foaming temperature-CO2 pressure were investigated by using field emission scanning electron microscopy. For comparison, the corresponding nano-composite also has been examined. The ionic cross-linked structure in the ionomer exhibited significant contribution to retard the cell growth and coalescence of cell, especially in ionomer having higher degree of the neutralization. For nano-composite foaming, experimentally, nano-clay particles led to an increase in cell density after foaming. However, the dispersed nano-clay particles did not act as nucleating sites for cell formation. The competitive phenomenon between the cell nucleation and the cell growth including the coalescence of cell was discussed in the light of the interfacial energy and the relaxation rate as revealed by the modified classical nucleation theory and rheological measurement, respectively. (C) 2009 Elsevier Ltd. All rights reserved.