Kinetic study on the thermal degradation of ethylene–norbornene copolymers under the effect of Fe and Mn stearates

Abstract

A kinetic study on the thermal degradation of ethylene–norbornene cyclic olefin copolymers (COCs), pristine and formulated with iron and manganese stearate, was performed. Three different COCs with cyclic structure (norbornene) contents of 30 mol% (COC30), 38 mol% (COC38), and 55 mol% (COC55) were analyzed. The thermal degradation order (n), activation energy (E a), and pre-exponential factor (A) were evaluated using multiple heating rates based on three different “model-free” methods: Flynn–Wall–Ozawa, Kissinger–Akahira–Sunose (KAS) and Friedman (FR). The thermal stability of virgin and formulated COC films with ferric and manganese stearates were calculated using a non-isothermal thermogravimetric analysis (TGA) and derivative thermogravimetric analysis. The reaction order of the thermodegradation of the tested copolymers was close to unity according to the KAS and FR methods. The calculated E a for pristine copolymers increased from 232 to 254 kJ mol−1 when the content of cyclic norbornene units in the pure copolymers was diminished from 55 to 30 mol%. The calculated E a for the stearate-formulated COC copolymers had values between 214 and 238 kJ mol−1. TGA curves of the thermal degradation in a nitrogen atmosphere show a one-step reaction in the range of temperatures between 30 and 600 °C. It was found that manganese stearate is more efficient than ferric stearate in initiating the thermodegradation of COC38 and COC55 copolymers.