Studies on the oxidative degradation of nylons by nitrogen dioxide in supercritical carbon dioxide

Oxidative degradation of nylons was carried out using nitrogen dioxide (NO2) as the oxidizing agent and supercritical carbon dioxide (scCO2) as the reaction medium. Seven typical nylons were studied: three ring opening polymerization type nylons (nylon-6, -11 and -12) and four condensation co-polymerization type nylons (nylon-4/6; -6/6; -6/9 and -6/12). All the nylons decomposed in the NO2/scCO2 system under relatively mild conditions (140 °C, 1 h, and 10 MPa) and provided aliphatic α, ω-diacids such as succinic, glutaric and adipic acids in good yields. The product distribution of these α, ω-diacids strongly depended on the reaction conditions such as temperature, time and amount of NO2, but not on the total pressure. Furthermore, the proportions of the products were affected by the type of nylon. A mechanism is proposed and a detailed discussion regarding the degradation of nylon in the NO2/scCO2 system is provided.