Study of the Alcoholysis of Ethylene-Vinyl Acetate Copolymers with Methanol in the Extrusion Process

Abstract

We investigated the sodium methanolate (NaOMe) catalyzed transesterification of ethylene-vinyl acetate copolymers (EVA) of different compositions with the less compatible methanol (MeOH). The experiments were carried out in a twin-screw extruder with a specially designed reaction zone. The residence time was about 150 seconds. The influence of catalyst quantity on conversion yield was determined for different amounts of added alcohol. Increasing catalyst concentrations accelerated transesterification to such an extent that the state of equilibrium could be achieved during the residence time in the extruder. The dependence of equilibrium conversions on the starting molar ratio MeOH/VA were determined over a broad range, and the equilibrium constant of methanolysis was calculated for K = 3.3. Based on an overall reaction rate derived from the general reaction scheme and which considers a mass transfer for catalyst in the EVA melt, it is possible to calculate the rate constants k ₁ = 33.1 and k _?1 = 8.0 L²˙mol^?2˙min^?1. The methanolysis of EVA in the extrusion process was shown to be a useful method suitable for industrial application. The results of our investigations allow for accurate modification of EVA products.