Thermal oxidation of Linear Low Density Polyethylene

Abstract

The oxidative stability of Linear Low Density Polyethylene (LLDPE) melts was studied under static and dynamic conditions. Static oxidation of two types of LLDPEs (n-hexene and 4-methyl-pentene-1 comonomers) containing different amounts of comonomer units was carried out at 150°C. The oxidizability of the samples was characterized by the induction period (ti,O2) and the maximum rate of oxygen uptake (WO2,max). The induction period was found to be inversely proportional to the vinyl content of the polymer while WO2,max was proportional to the amount of chain branching.Dynamic degradation during moulding in a closed mixing chamber at 200°C was studied on stabilized LLDPE containing a degree of branching of 6,5 n-butyl/1000 C and HDPE containing no short chain branching. The degradation of LLDPE involved chain scission (and oxygen uptake), and that of HDPE, chain scission and crosslinking. The degradation of LLDPE melt resulted in only a slight change in the physical properties of the solidified polymer but, in the case of HDPE, a considerable decrease in structural order was found. As a result of moulding, the remaining stability decreased drastically, while mechanical properties revealed a considerable decrease only after the stabilizer was used up.