Thermochemical and kinetic studies on the effects of cobalt salicylate on the oxidative degradation of polystyrene

Abstract

The effect of cobalt salicylate on the oxidative degradation and ignition of polystyrene has been studied. It was found that cobalt salicylate sensitizes both the degradation and ignition of polystyrene by facilitating electron-transfer processes in the propagation step. From thermochemical and kinetic studies it was found that the cobalt ion, owing to its ability to exist in variable valence states, promotes electron transfer in the propagation step of polymer degradation, increasing the rate of propagation and consequently the overall rate. Using solid-phase thermal ignition theory, an attempt has been made to explain the sensitization of ignition by the cobalt ion.In an earlier paper [1] we have shown that transition metal salicylates (Msal), when added in small quantities, sensitize the polymer ignition process and also the oxidative degradation of the polymer at 400 ~ In the above-mentioned paper [I ] no detailed kinetic analysis was made, and only the average ratedata were presented for comparison purposes. To acquire a deeper knowledge about the mechanism of action of the metal salicylates (Msal), information on the thermochemical and kinetic aspects would be quite useful and rewarding. The present paper aims at fulfilling this task by considering the ignition and degradation of polystyrene (PS) containing cobalt salicylate (Cosal) as an additive. ExperimentalThe preparation of PS, Cosal and PS + Cosal have been described elsewhere [l ]. Thermogravimetric (TG) analyses were performed on a home-made TG assembly, the description of which is given elsewhere [1 ].The differential thermal analysis (DTA) was carried out on an assembly described elsewhere [2]. The area under the endotherm/exotherm in the DTA curve was used to estimate the enthalpy associated with the process. The area measurements under the peaks were calibrated in units of J/degree s-1, using standard substances such as tin, benzoic acid and ammonium nitrate. The calibration constant obtained was 0.1458 _+ 0.0028 J/degree s -1.An assembly similar to the DTA assembly was used for ignition temperature measurements. The heating rate employed was 170~

Thermal stabilities of copolymers of styrene with lithium, sodium and potassium acrylates and methacrylates

“…The order of reaction for the main decomposition step of all the investigated copolymers was equal to one, similarly as for the comparative PS and in accord with the common observation that the degradation of vinyl polymers usually follows first-order kinetics [13].…”