Radiation effects on liquid paraffins as polymer model compounds

Abstract

The effects of gamma rays on n-C16H34 and C30H62 have been studied under vacuum and oxygenated conditions. Aromatic compounds were dissolved in various liquids to investigate the protection mechanism. The radiolysis and protection mechanisms were explored from product analysis. Gas products were analysed by gas chromatography (GC), and combinations of GC, gel permeation chromatography (GPC) and mass spectrometry (MS) were used to analyse the liquid products. Hydrogen gas was the main component of the gas product regardless of the irradiation conditions. Oligomerization was dominant under vacuum, whereas chain-scission was dominant under oxidation condition. Double bond enrichment of the oligomeric products is the main source of H2 formation as shown by vacuum radiolysis. The scission products under vacuum were saturated alkanes, and the presence of O2 during oxidation did not affect the scission pattern. Energy (excitation and charge) transfer to the aromatic molecules reduces the solvent excitation that preceeds the formation of radiolysis products. In vacuum radiolysis, reactions of additive-solvent molecules to form adduct compounds were observed. Mass analysis showed that the adduct compounds had fewer double bonds due to hydrogenation, and the protection efficiency depended on the degree of aromaticity. The low O2 uptake [G(O2) ≈ 6.0] indicates that liquid oxidation does not exhibit chain kinetics. More than 90% of the consumed O2 was converted into the oxidation products in the liquid phase, mainly carboxylic acids. Hydroaromatic compounds are energy- and charge-scavengers, but they are selectively oxidized leading to large O2 uptake and corresponding ketone formation. The G values of products in the vacuum radiolysis of liquid paraffins were hardly comparable to those in the polymeric systems. However, similar tendencies can be seen, and the comparable G(O2) in the radiation-induced oxidation indicates that the chemical reactions taken place in the liquid paraffins reflect those in the amorphous part of polymers. The results of mechanical testing on radiation-oxidized polypropylene (PP) matrix (stabilized and unstabilized) confirmed that alkane radiolysis and the protection mechanism also occurred in the practical application of polymers. © 1999 Society of Chemical Industry