Polypropylene photo-oxidation

PP. Embrittlement times always change most rapidly in mildly oxidised polymers containing little or no carbonyl. This finding is consistant with the observation that added long chain dialkyl ketones are not sensitisers for polypropylene photo-oxidation (30) although aromatic ketones are (22, 30). 

G.A. George and M. Ghaemy, The effect of stabilizers on integrated chemiluminescence in the early stages of polypropylene photo-oxidation, Polym. Degrad. Stab. 1991, 34, 37-53. 

Blais, P., Carlsson, D.J., Wiles, D.M. Surface changes during polypropylene photo-oxidation a study by infrared spectroscopy and election microscopy. J. Polym. Sci. 

Degradation of polyolefins such as polyethylene, polypropylene, polybutylene, and polybutadiene promoted by metals and other oxidants occurs via an oxidation and a photo-oxidative mechanism, the two being difficult to separate in environmental degradation. The general mechanism common to all these reactions is that shown in equation 9. The reactant radical may be produced by any suitable mechanism from the interaction of air or oxygen with polyolefins (42) to form peroxides, which are subsequentiy decomposed by ultraviolet radiation. These reaction intermediates abstract more hydrogen atoms from the polymer backbone, which is ultimately converted into a polymer with ketone functionahties and degraded by the Norrish mechanisms (eq. 

In our study we have found that UV-light greatly accelerates the rate of ozone attack at the polypropylene surface. Presented results were undertaken to determine mechanism of the photo-oxidation of polypropylene surface upon UV-irradiation of polymer films in ozone. 

The photo-oxidative degradation of polypropylene (PPH) can be largely summarized by the reactions 1 to h ( l,2j. During the... 

Substituted tetramethylpiperidines and their oxidation products appear to act as UV stabilizers for polypropylene by weakly scavenging PP, PPO2 and possibly other radicals involved in the photo-oxidation. Their weak scavenging ability is off-set by the... 

Table 3 Comparison of embrittlement times during photo-oxidation with catalyst residues for polypropylene samples ...

Bagheri, R. Chakraborty, K.B. Scott, G. Mechanisms of antioxidant action behavior of a hindered piperidine and related oxidation products during processing and photo-oxidation of polypropylene. Polym. Deg. Stab. 1982, 4 (1), 1-16. 

O Donnell, B. White, J.R. Stress-accelerated photo-oxidation of polypropylene and glass fibre-reinforced polypropylene. Polym. Degrad. Stab. 1994, 44, 211-222. 

Valenza, A. La Mantia, F.P. Recycling of polymers. Part 1. Photo-oxidized polypropylene. Polym. Degrad. Stab. 1987,19, 135-145. 

The content of aldehyde groups in the final product of polypropylene photodegradation is 7%. In the case of polyethylene degradation these groups are completely absent [6]. The relatively lower amount of aldehyde groups in the products of polyolefine photo-oxidation is due to the fact that they absorb radiation and subsequently react as above [278]. 

A number of volatile compounds are obtained apart from the crosslinked products in the final oxidation process. With polyolefines, water, formaldehyde, acetaldehyde, acetone, methanol, hydrogen peroxide, carbon monoxide, and carbon dioxide were identified [Refs. 75, 76, 122, 292, 424, 425, 449, 487, 560, 608]. Table 5 shows the percentage content of particular volatile products formed during the photo-oxidative degradation of polypropylene [122]. 

A. Zahradnickova, J. Sedlar, and D. Dastych, Peroxy acids in photo-oxidized polypropylene, Polym. Deg. Stab. 1991, 32, 155-176. 

T. Kurumada, H. Ohsawa, T. Fujita, and T. Toda, The effect of A-substituents of hindered amine on photo-oxidation of polypropylene, J. Polym. Sci. Polym. Chem. Ed. 1984, 22, 277-281. 

Secondary HAS already decompose polypropylene hydroperoxide in the solid phase at ambient temperatures [200]. The process appears to be sufficiently rapid for the destruction of ROOH during the dark period, after the photo-oxidation phase. This enhances the photostability of PP in the repeated photo-oxidation. 

The photo-oxidative degradation of polypropylene and stabilization by hindered amines has been reviewed. A study has appeared of the effect of P-carotene on the photoreactivity of anthracene in hexane solution and a kinetic scheme has been proposed to account for the photochemical and photophysical processes that occur on irradiation at 365 nm. Quenching rate constants have been determined between /S-carotene and singlet oxygen. Some characteristics have been communicated of the sensitized photo-oxidation of abietic acid contained in a vinyl butyl ether-butyl methacrylate-methacrylic acid copolymer. At 400 nm... 

They found that the quantum yield for C—H bond rupture was 10—100-fold higher than for C—C bond rupture. In the photo-oxidation of radiation-modified polyethylene, the formation of carbonyl groups was associated with diene formation in the polymer. Frank has reported on the lifetimes of free radicals during the intermittent exposure of polypropylene. 

Vink has produced evidence in total conflict with previous experience which is suggested to show that the photo-oxidation of polypropylene is a bulk reaction rather than a surface phenomenon. ESCA studies, however, have shown that the photo-oxidation of polypropylene is clearly a surface phenomenon.In a recent study by Kollmann and Wood the photo-oxidation of polypropylene was found to be dependent upon the intensity of the light source. Thus, for unstabilized polymer the rate was proportional to I , whereas for stabilized polymer the rate was proportional to 1O 8-0.9 Thej-e appears to be some conflict in the literature as to whether chemical changes during the photo-oxidation of polyolefins correlate with the changes in mechanical properties.This has always been a difficult... 

Photoactive Additives.—Ferric compounds, in particular, the chloride, continue to attract much interest as photosensitizers for thermoplastics. " From e.s.r. work the mechanism appears to involve a redox reaction resulting in the formation of active hydroxy-radicals. Photodegradable polyethylene film has been developed by doping it with radiation-modified atactic polypropylene and hydroxyethyl-ferrocene. Several workers have studied the dye-sensitized photo-oxidation of polyisoprene and di-n-butyl sulphide embedded in Augustyniak and... 

The photostabilization of polymers continues to be a rapidly advancing area of scientific and technological interest. Carlsson and Wileshave written several reviews on photostabilizing mechanisms in polymers, while Swasey has given an updated guide to stabilization, and Reid has discussed the effects of stabilizers in vinyl polymers. Nemzek and Mayo have predicted the service life of polypropylene, and Bredereck has reviewed the photostabilization of PVC. Several comprehensive review articles have appeared. Pospisil has reviewed in considerable depth the photo-oxidation mechanisms of phenolic anti-oxidants, Shlyapintokh has reviewed the kinetics of stabilizer distribution, Vink has... 

The mechanism of oxidation of short-chain hydrocarbons is widely known imder the name of Bolland s cycle (Scheme 7) (Bolland 1949). Oxidation of polyethylene and polypropylene has been extensively studied (Lacoste and Carlsson 1992). More recently, the thermal and photo-oxidation of UHMWPE has been investigated (Costa, Luda, and Trossarelli 1997a). These processes are mostly similar to oxidation of high-density polyethylene (HOPE), with some exceptions, mainly because of the low mobility of the polymeric chains in UHMWPE. 

How does commercial polypropylene degrade photo-oxidatively ... 

Diagne, M., Gueye, M., Vidal, L., and Tidjani, A. 2005. Thermal stability and fire retardant performance of photo-oxidized nanocomposites of polypropylene-grayi-maleic anhydride/clay. Polymer Degradation and Stability 89 418-426. 

Some molecular structures are much more reactive than others. Polypropylene, for example, is significantly more susceptible to photo-oxidation than is polyethylene. Furthermore, for some materials, it is feasible to upgrade the material during reprocessing (such as in solid-stating of recycled PET), while for others it is not. 

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