Permeation mechanisms of xylene in blow-molded bottles of pure polyethylene, polyethylene/polyamide and polyethylene/ modified polyamide blends

Abstract

The hydrocarbon permeation mechanisms of polyethylene/ modified polyamide (PE/ MPA). PE/PA blends and pure PE, were investigated over a range of testing temperatures. In addition to the permeation resistance to xylene, the weight of xylene absorbed per gram of dry polymers (Sx) and the diffusion coefficient (D) of xylene in these bottles were determined. At each fixed testing temperature, the steady permeation rates (Ps) and D of xylene in PE/MPA bottles is significantly lower than those of pure PE bottles, and that of PE/PA bottles is slightly lower. This significantly improved permeation resistance of PE/MPA to xylene at each testing temperature is mainly attributed to the significantly reduced diffusion coefficient of xylene in PE/ MPA bottles, but not due to the slight change in the amount of xylene absorbed in these three bottles. The temperature dependence of steady permeation rates and diffusion coefficient of xylene in each bottle is very similar, and, in fact, some clear “transition” points were found on the plots of Ps and D versus testing temperatures for PE. PE/PA and PE/MPA bottles. These interesting behaviors along with the temperature dependence of Sx in each bottle were discussed and correlated with the free volume, molecular relaxation motions of these polymers and the vapor pressure of xylene at varying testing temperatures.