The antioxidant effect in controlling thermal degradation of a low density polyethylene blown film

Abstract

It is well known that antioxidants are widely used to prevent thermal degradation of high density and linear low density polyethylene. Antioxidants are not always present in low density polyethylene and only small amounts are usually added to these resins. In this work the effect of an antioxidant system on a low density resin having MFI (190 °C/2.16 kg)=2 g/10′ and density 0.9230 g/cm 3 has been studied. Its effect on melt viscosity has been studied by means of a batch mixer and the torque vs time behaviour has been analysed. The results show that a maximum in the torque vs time curve can be seen for the material containing antioxidant. In contrast, the material without antioxidant does not show any maximum in the torque vs time curve and, after a certain time, directly undergoes chain scission. The presence of the antioxidant in a low density polyethylene seems to change the kinetics of two competitive phenomena: long chain branching formation/crosslinking and chain scissions. The antioxidant works essentially by stopping the peroxides formation. This effect slows the molecular weight decrease but does not influence long chain branching formation or crosslinking.