Photodegradation of polypropylene

The polymers obtained by polymerization in the presehce of metal catalysts contain metal residues which cannot be removed so readily. It is also well known that transition metal ions act as sensitizers for the photooxidation of polyolefins (29). Kujirai et al. (30) found that photodegradation of polypropylene depends on the oxygen concentration and on the residues of the polymerization catalyst, and they concluded that oxidative photodegradation is sensitized by the initiator metal residues (ash). Very recently Scott (31) used transition metal ions as sensitizers to develop photodegradable polymers. 

Polypropylene usually exhibits an ultraviolet absorption extending beyond 290 nm, although the pure polymer is not expected to show an absorption beyond 200 nm. Photodegradation of polypropylene is thus likely to be initiated by impurities such as hydroperoxides or ketonic oxidation products formed during the processing of the sample. Such behaviour is similar to that already discussed for polyethylene. 

Hydroperoxide photolysis by sunlight in the presence of air is considered to be the major source of free radicals and backbone scission during the photodegradation of polypropylene [37]. 

Mailhot B, Morlat S, Gardette JL, Boucard S, Duchet J, Gerard JF. Photodegradation of polypropylene nanocomposites. Polym Degrad Stab 2003 82(2) 163-7. 

Ozone accelerates the photodegradation of polypropylene [1359, 1777], 1,2-polybutadiene [1362] and water soluble polymers such as poly(ethylene glycol), carboxymethyl cellulose, poly(vinyl alcohol) and polyacrylamide [1041]. 

UV/VIS derivative spectroscopy has been found to be very useful for studying photodegradation of polypropylene [46,61], poly(vinyl chloride) [1792, 1888] and polyamides [47]. 

White, J.R., Shyichuk, A.V., Turton, T.J., Syrotynska, I.D. Effect of stabilizer and pigment on photodegradation of polypropylene as revealed by macromolecule scission and crosslinMng measurements. Polym. Degtad. Stab. 91, 1755-1760 (2006)... 

Tidjani, A. Photodegradation of polypropylene under natural and accelerated conditions. J. Appl. Polym. Sci. 64, 2494-2503 (1997)... 

Oxidative Photodegradation and XJV Stabilization of Polyolefins 95 Table 4. Oxidative photodegradation of polypropylene... 

However, this mechanism requires further experimental evidence. To conclude, the postulated mechanism of oxidative photodegradation of polypropylene (scheme of Table 4) would consist of two phases ... 

B. Mailhot, S. Morlat, J.L. Gardette, S. Boncard, J. Duchet, J.F. Gerard, Photodegradation of polypropylene nanocomposites , Polym. Degr. Stab., 2003, 82, 163-167... 

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