Synthesis of metals stearate and thermal degradation study of polystyrene metals stearate blends

Abstract

Transition metals had been reported to act as effective pro oxidative additive for polymers. This study deals with the synthesis and characterization of three active transition metals complexes such as cobalt stearate, cupric stearate, and ferric stearate. A derivative of active transition metals stearate were synthesized by increasing the pH of metal acetate solution stirred with stearic acid in the presence of sodium hydroxide (NaOH) at 80 oC. The formula for the trimer as prepared is [CH3 (CH2)nCOO]M (M= metal). The melting points of the additives were obtained by differential scanning calorimetry (DSC) which resulted 94.33 oC, 99.85 oC and 66.90 oC respectively. Thermogravimetric analysis (TGA) was also conducted to study the thermal stabilities of the additives. The study also involved the investigation of the effect of the oxidative additives on the degradation process of general purpose polystyrene (GPPS). The additives were blended with GPPS with the formulation 0.05-0.20 wt %. Studies on the effects of additives were then carried out by exposing the samples into the oven at 70 oC, 90 oC and 100 oC respectively for 50 hours. The chemical and mechanical changes induced by this exposure were followed by fourier transform infrared spectroscopy (FTIR), melt flow index (MFI), tensile test, TGA and DSC. Surface morphologies of degraded samples were observed by using scanning electron microscopy (SEM). The FTIR result indicates that carbonyl compound had the most significant changes for cobalt stearate at 1756.8-1800 cm-1. The absorption around band 1756.8 cm-1 which can be assigned to the stretching of C=O functionalities, increased in intensity and broadened substantially, indicating the presence of the most effective oxidation product which is cobalt stearate. The thermo oxidative degradation in presence of metals stearate was found that all the additives effective were at 0.2 wt % according to the following arrangement cobalt> cupric>ferric in 90 oC air exposure.