Polypropylene oxidative degradation

Oxidative degradation of polypropylene chemically incorporates oxygen to the polymeric chains. Why would an isotactic polypropylene be less susceptible to this type of degradation than one that is atactic ... 

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

I. Blakey, Thesis Aspects of oxidative degradation of polypropylene, Queensland University of Technology, Brisbane, Australia, 2001. 

Simulation programs for the ESR line shapes of peroxy radicals for specific models of dynamics have been developed for the study of oxidative degradation of polymers due to ionizing radiation [66]. The motional mechanism of the peroxy radicals, ROO, was deduced by simulation of the temperature dependence of the spectra, and a correlation between dynamics and reactivity has been established. In general, peroxy radicals at the chain ends are less stable and more reactive. This approach has been extended to protiated polymers, for instance polyethylene and polypropylene (PP) [67],... 

In addition to acting as photostabilizers for polypropylene, nickel complexes also inhibit their direct thermal oxidative degradation by molecular oxygen. The salicylate complex (26), thought to be square planar, was more effective than the analogous cobalt(II) and copper(II) complexes.83 Iron(III) and chromium(II) analogues were almost inactive. Complexes (25) and (27) were roughly... 

Oxidative degradation of polyethylene (PE) and polypropylene (PP) can occur at all stages of their lifecycle (polymerisation, storage, processing, fabrication and in-service). The auto-oxidation process of polyolefins is best described by the classical free-radical-initiated chain reaction outlined in Scheme 1 [1]. Impurities initially present in the polymers during polymerisation or melt processing, exert profound effects on the behaviour of the final polymer article in service. 

Abstract The oxidation of polymers such as polypropylene and polyethylene is accompanied by weak chemiluminescence. The development of sensitive photon counting systems has made it comparatively easy to measure faint light emissions and polymer chemiluminescence has become an important method to follow the initial stages in the oxidative degradation of polymers. Alternatively, chemiluminescence is used to determine the amount of hydroperoxides accumulated in a pre-oxidised polymer. Chemiluminescence has also been applied to study how irradiation or mechanical stress affects the rate of polymer oxidation. In recent years, imaging chemiluminescence has been established as a most valuable technique offering both spatial and temporal resolution of oxidation in polymers. This technique has disclosed that oxidation in polyolefins is non-uniformly distributed and proceeds by spreading. 

During weathering, phenolic antioxidants are photooxidized into hydroperoxycy-clohexadienones, such as 59 (Pospisil, 1993 Pospisil, 1980). The presence of peroxidic moieties in 57 and 59 renders them thermolabile at temperatures exceeding 100 °C and photolysable under solar UV radiation. Both processes account for homolysis of the peroxidic moieties. As a result, the oxidative degradation of the polymeric matrix is accelerated by formed free-radical fragments (tests were performed with atactic polypropylene and acrylonitrile-butadiene-styrene terpolymer (ABS) (PospiSil, 1981 PospiSil, 1980). Low-molecular-weight products of homolysis, such as 60 to 63 are formed in low amounts. 

Oxidative degradation can also occur in other polymers including natural rubber, polystyrene, polypropylene, nylons, polyurethanes, and most natural and naturally derived polymers. With the exception of fluo-ropolymers, most polymers are susceptible to oxidation, particularly at elevated temperature or during exposure to ultraviolet hght. Oxidation usually leads to increasing brittleness and deterioration in strength. 

The role of singlet oxygen in the oxidative degradation of polymers has been pointed out by several authors,e.g.for polyethylene (36.56),polypropylene (59)>polystyrene (57>60), poly(vinyl chloride)(58,61) cmd rubber (62-66) and reviewed by Rabek cmd R nby (54> 55) ... 

Ethanox 376 is a stabilizer that provides heat stability by preventing thermo-oxidative degradation during processing and service life. It provides compatibility with resins and extraction resistance. It can be applied in polyolefins, such as polyethylene, polypropylene, polybutene-1 and other polymers such as engineering plastics, styrenes, polyurethanes, saturated and unsaturated elastomers, styrenics, rubber modified styrenics, segmented block copolymers, and PVC. 

Non-discoloring, sulfur containing phenolic antioxidant and stabilizer that provides long-term heat stability by preventing thermo-oxidative degradation. Used for the process stabilization of polyethylene wire and cable resins for polyethylene during extruder compounding. Can also be applied in styrenic polymers, polypropylene, elastomers such as EPDM and SBR and for carboxylated SBR latex, polybutadiene rubber and polyisopropene rubber. 

Girois, S. Delprat, P. Audouin, L. Verdu, J. Oxidation thickness profiles during the photooxidation of non-photostabilized polypropylene. Polym. Degrad. Stab. 1997, 56, 169-177. 

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. 

During oxidative degradation, a concentration gradient always develops at a film surface. Inasmuch as the depth profile depends on permeabilities and reaction rates, the effect is more noticeable in photooxidations than in thermal oxidations. An unusually marked skin effect observed in photooxidized polypropylene has been ascribed (14) to the action of chronophores located at or near the surface. 

Blakey, I. (2001) Aspects of the oxidative degradation of polypropylene. Thesis, School of Physical... 

Gugumus F. Re-examination of the thermal oxidation reactions of polymers 3. Various reactions in polyethylene and polypropylene. Polym Degrad Stab 2002 77(1) 147-55. 

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