René Arnaud

Photo-oxidation of ethylene-propylene copolymers in the solid state

Abstract The photo-oxidation of various ethylene-propylene copolymers (EPM) (40–76 weight % ethylene) has been compared with the photo-oxidation of physical mixtures of polyethylene and polypropylene. The photo-chemical behaviour of the PE-PP mixtures changes gradually from pure LDPE to pure isotactic PP. The photo-chemical behaviour of EPM copolymers is quite different. In EPM copolymers, isolated hydroperoxides absorbing at 3550 cm −1 appear on the propylene units surrounded by polyethylene sequences. Associated hydroperoxides are formed on the polyethylene segments. The rate of hydroperoxidation of EPM is an increasing function of the propylene content; at the same propylene content, this rate is higher in EPM than in physical mixtures. Even at high propylene contents, the carbonyl region of the ir spectra of photo-oxidized EPM bears much more resemblance to that of photo-oxidized polyethylene. This results from the formation of isolated hydroperoxides on tertiary carbon atoms. The hydroxyl region shows a sharp band at 3615 cm −1 , indicating the formation of isolated tertiary alcohols. In the EPM samples, the formation of vinyl groups is favoured in comparison with PE; in contrast to the ketones formed in PP, those which appear in EPM are converted into shorter ketones and vinyl groups through Norrish type II processes.

Octene-1 linear low density polyethylene photooxidation

Abstract Low-temperature thermooxidation and photooxidation at long wavelengths ( λ > 300 nm) of octene-1 linear low density polyethylene have been examined. It is shown that both oxidations proceed according to mechanisms which are very similar to those thought to occur in free radical low density polyethylene presenting a low content of vinylidene unsaturation. Hydroperoxidation in the α-position to the vinylidene groups gives rise to isolated hydroperoxide groups that absorb at 3550 cm −1 and are stable at 85°C. A parallel hydroperoxidation occurs on the saturated chain affording hydrogen-bonded hydroperoxides which are fairly unstable at 85°C. In photooxidation at long wavelengths both hydroperoxides are produced and readily photolysed. Variations in the number of branch points which provoke large variations in density have no significant influence on the photooxidation rate.

Cadmium sulphide photocatalytic oxidation of crosslinked polyethylene

Abstract The photo-oxidation of crosslinked polyethylene (XLPE) modified by cadmium sulphide is investigated and compared to a photothermal oxidation and a zinc oxide-photocatalytic oxidation of XLPE. Cadmium sulphide is shown to afford a photochemical protection of hydroperoxides and ketones, but to a lesser extent than zinc oxide. Cadmium sulphide is also shown to act as a poor photocatalyst. The pigment absorbs wavelengths