Foaming in CO2 and Post-Foaming Characterization of Rubbery Poly(ethylene-co-vinyl acetate-co-carbon monoxide)

Foaming of polymers with compressed fluids like carbon dioxide is an industrially important and attractive alternative to generate porous polymeric matrices which find use in a wide range of applications from insulation materials to footwear. In this poster, we will present results of foaming of a series of polyethylene copolymers, namely poly(ethylene-co-vinyl-acetate-co-carbon monoxide) (EVACO) with differing compositions. The assessed polymers were EVACO-0010 (90 wt % ethylene, 10 wt % carbon monoxide), EVACO-1010 (80 wt % ethylene, 10 wt % vinyl acetate, 10 wt % carbon monoxide), and EVACO-2010 (70 wt % ethylene, 10 wt % vinyl acetate, 10 wt % carbon monoxide).

Foaming experiments were conducted isothermally in a free-foaming mode in a special foaming cell. Polymer samples (1mm-thick, 10 mm x 30 mm) were loaded in the foaming cell on a Teflon tray that minimizes direct contact of the sample with the cell body. Cell temperature was measured and controlled with an RTD 100. After closure of the cell, the cell was first purged with carbon dioxide, and then filled with carbon dioxide to a target pressure. In this study all foaming experiments were conducted after saturation in carbon dioxide at 200 bar for 1 h at a set of foaming temperatures followed by rapid depressurization. The saturation temperatures were selected based on the results of a parallel study in which melting and crystallization temperatures were identified for these polymers exposed to carbon dioxide. The foaming temperature ranges were from 92 to 112 ^oC (for EVACO-0010), from 72 to 90 ^oC (for EVACO-1010) and from 46 to 66 ^oC (for EVACO-2010).

The generated foams were characterized with respect to their foam bulk densities and pore morphologies. Bulk foam densities were determined by measuring the mass of a foam sample in air and then submerged in water to assess its volume and thus the density. Pore size determinations were carried out with a benchtop SEM unit using freeze-fractured, sputter coated samples. The SEM micrographs were further analyzed using ImageJ software to generate pore size distribution in the foams generated at different temperatures from different EVACO samples which will be presented in the poster.