Absorption of CO2 in high acrylonitrile content copolymers: dependence on acrylonitrile content

In continuation of our goal to determine the ability of CO2 to plasticize acrylonitrile (AN) copolymers and facilitate melt processing at temperatures below the onset of thermal degradation, a systematic study has been performed to determine the influence of AN content on CO2 absorption and subsequent viscosity reduction. Our previous report focused on the absorption of CO2 in a relatively thermally stable 65 mol% AN copolymer. In this study, the ability for CO2 to absorb in AN copolymers containing 85–98 mol% acrylonitrile was determined, and subsequent viscosity and equivalent processing temperature reductions were evaluated. Eighty five and 90 mol% acrylonitrile/methyl acrylate (AN/MA) copolymers were found to absorb up to 5.6 and 3.0 wt% CO2, corresponding to reductions of Tg of 37 and 27 °C, and subsequent viscosity reductions of 61 and 56%, respectively. CO2 absorption in these copolymers was found to occur immediately, in contrast to the time dependent absorption observed in the 65 mol% copolymer. An Arrhenius scaling analysis was used to determine the equivalent reductions in processing temperature resulting from the viscosity reductions, and reductions of up to 25 and 9 °C were observed for the 85 and 90 mol% AN copolymers. Based on the specific conditions used for absorption, no significant CO2 uptake was observed for AN copolymers containing greater than 90 mol% acrylonitrile. Higher temperatures than those used here may be required to absorb CO2 into AN copolymers containing greater than 90 mol% AN.