The morphology of semicrystalline polymers. Part I. The effect of temperature on the oxidation of polyolefins

Abstract

Oxidation rates of several uninhibited polyolefins were determined in the temperature range 40–140°C. The logerithm of the induction period increased linearly with 1/T, no changes in slope being noted in the melting range with polythylene. At the lower temperatures branched polythylenes were more susceptible to oxidation than the linear types. In the solid statem, oxygen uptake of both modifications were substantially less than that observed for the molten polymer. The amount of oxygen reacting in the solid state was shown to be inversely proportional to the per cent crystallinity, which indicates that reaction with oxygen takes place only in the amorphous region of these semicrystalline polymers. Isotactic polypropylene was only slightly less reactive than the atactic form, and both were more reactive than polyethylene. The effect of temperature on the activity of several moderately effective anotioxidants in branched polythylene was measured. These data also conform to linear Arrhenius‐type plots. Activation energies were specific, however, for each antioxidant and varied considerably; thus, an antioxidant rated as relatively ineffective under accelerated testing conditions could be quite effective within the temperature range over which it would normally be used as a polythylene protectant. Carbon black, which is comparable with some to the less effective thermal antioxidants under accelerated test conditions, provided an unexpected high order of protection for polyethylene below the melting point. This increased protection in the solid state was attributed to the impermeability of the crystalline phase to oxygen and increased concentration of the bulky carbon (antioxidant) particles in the amorphous region.

Review on the thermo-oxidative degradation of polymers during processing and in service

“…As a result it can be expected that PE only degrades in the amorphous phase. Experimentally this is confirmed by Hawkins et al [80] and Winslow et al [81], they showed that with increasing crystallinity the oxidation rate of PE decreases. At the moment there is no doubt that oxidation in polyethylene and polypropylene is restricted to the amorphous phase [51], which is the case for the majority of all polymers.…”

Chapter II Materials and Methods

“…Figure 37 illustrates the non -Arrhenian behavior of the induction time for pure PE and composite PENC at the three studied temperatures. It can be seen that experimental results correspond well with available literature data for polyethylene thermal degradation [140,153,154,155,156,157,158,159,160] . Finally, our results confirmed that induction time values follow a non Arrhenian behavior.…”

Effect of Temperature and Mechanical Stress on Barrier Properties of Polymeric Films Used for Food Packaging

“…If the mechanism of the reaction at higher or lower temperatures should differ, this too would alter the slope of the curve. Numerous examples of non-linear Arrhenius plots, the consequence of a change in mechanism, can be found in the literature [29][30][31][32].…”