Abstract
Summary: The diffusion of styrene into linear low density polyethylene in a solution of supercritical CO~2~ was investigated using NMR microimaging. For both pure styrene and styrene dissolved in supercritical CO~2~, the diffusion was found to follow Fickian kinetics. Supercritical CO~2~ was found to enhance the rate and extent of diffusion of styrene into the substrate by up to three times under the conditions of this investigation, compared to pure styrene. NMR imaging was used to measure the concentration profiles of the styrene penetrants in real time, and the results were fitted to a Fickian model for diffusion. At a CO~2~ pressure of 150 bar and temperature of 40βΒ°C, the diffusion coefficient of a 30 wtβ% solution of styrene into LLDPE was calculated to be 1βΓβ10^β11^ m^2^βΒ·βs^β1^. This is significantly faster than the diffusion coefficient measured for pure styrene diffusion at 40βΒ°C (3βΓβ10^β12^ m^2^βΒ·βs^β1^). The diffusion coefficients determined by gravimetric analysis were slightly higher than those determined by the imaging method. This was probably due to residual styrene and/or polystyrene adhering to the surface of the films in the gravimetric technique.
NMR image of styrene in linear low density polyethylene following supercritical fluid enhanced impregnation.
imageNMR image of styrene in linear low density polyethylene following supercritical fluid enhanced impregnation.