Permeation of Volatile Organic Compounds through EVOH Thin Film Membranes and Coextruded LLDPE/EVOH/LLDPE Geomembranes: Fid-Bau Portal

Permeation of Volatile Organic Compounds through EVOH Thin Film Membranes and Coextruded LLDPE/EVOH/LLDPE Geomembranes

McWatters, Rebecca S. / Rowe, R. Kerry

Abstract

Coextruded geomembranes with an inner ethylene vinyl alcohol (EVOH) layer are gaining attention as potential improved barriers to volatile organic compounds (VOCs) when used in barrier systems that would traditionally use high-density polyethylene (HDPE) geomembranes. The permeation characteristics of nine common VOCs in aqueous solutions through the EVOH layer are investigated for two thin films: a 0.015-mm-thick, 32 mol% EVOH and a 0.02-mm-thick, 44 mol% EVOH. The VOCs included aromatic hydrocarbons [benzene, toluene, ethylbenzene, and xylenes (BTEX)] and chlorinated hydrocarbons [1,2-dichloroethane (1,2-DCA), dichloromethane (DCM), trichloroethylene (TCE), and tetrachloroethylene (PCE)]. The BTEX permeation coefficients, $P_{g}$ , range from $1.4 \times 10^{- 14} to 25 \times 10^{- 14} m^{2} \cdot s^{- 1}$ depending on the contaminant and mol% EVOH. When a 0.02-mm-thick, 38 mol% EVOH thin film layer is coextruded with linear low-density polyethylene (LLDPE) to form a 0.53-mm-thick geomembrane, the BTEX permeation values of the EVOH thin film itself are reduced to $P_{g} = 0.4 \times 10^{- 14} to 0.7 \times 10^{- 14} m^{2} \cdot s^{- 1}$ . The higher permeation coefficients for the thin films as compared with the film contained in the coextruded LLDPE/EVOH/LLDPE geomembrane are attributed to interactions between the water in the aqueous solution and the EVOH layer, an interaction that is prevented by the presence of the LLDPE in the coextruded geomembrane. These $P_{g}$ values are two to four orders of magnitude lower than values that have been observed for LLDPE and HDPE geomembranes. The effect of temperature on VOC permeation was also studied for the 32 mol% EVOH thin films at $23, 30, 40, and 50 \pm 1 ° C$ . An Arrhenius relationship was developed that allows the evaluation of the permeation characteristics at temperatures 23–50°C and, by extrapolation, an estimation of the values for temperatures a little higher or lower than the test temperatures.