Thermal and thermo‐oxidative degradation study of a model LDPE/EVA based TPE system: Effect of nano silica and electron beam irradiation

Abstract

The effect of nano-silica on the thermal degradation behavior of Low density polyethylene-poly(ethyleneco-vinyl acetate) (LDPE-EVA) based thermoplastic elastomeric (TPE) system was monitored using thermo gravimetric analysis (TGA) in nitrogen and oxygen atmospheres (air), respectively. The pristine nano silica was melt-blended with the LDPE-EVA system at different loadings by varying the sequence of addition. In one of the compositions, coupling agent (Si69) was used. In nitrogen, thermal stability of such systems remained unchanged. However, in oxygen atmosphere, the TGA thermograms reflected a dramatic change. A two staged degradation was observed for all the samples. The enhancement in thermal stability particularly upto the low conversion levels was interpreted in terms of the barrier effect of silica particles on the O 2 flow into the sample. The activation energies of degradation up to lower range of conversions were determined by nonisothermal and isothermal kinetic analyses. These were found to register a similar trend for various systems studied. Upon electron beam irradiation of such filled LDPE/EVA systems at controlled doses (20 and 40 kGy), the thermal stabilities were enhanced marginally. Overall, the thermal stabilities of the TPE nanocomposites are the function of sequence and extent of nano silica addition, presence of coupling agent and extent of irradiation.

Dynamic mechanical analysis and thermal properties of LLDPE/EVA/modified silica nanocomposites

“…As shown in TEM image, nanoparticles could play a compatibilizing role for EVA and LLDPE phases leading to increase the chance for grafting reactions in the course of degradation process [25]. however, the weight loss is highly impeded at higher temperatures.…”

“…Hiu et al, have also investigated the effect of nanosilica modified by bis(triethoxy silyl propoyl) tetrasulfate on the thermal stability of LDPE/EVA. They observed an increase in the onset temperature of degradation under O 2 atmosphere for the samples containing nanosilica[25]. The second probable reason for the mentioned phenomenon is detachment of the modification groups from the nanosilica surface leading to acceleration of peroxide formation.…”