Thermal oxidative degradation polypropylene

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... 

Ostwald and Turi [471] noted that the molecular weight distribution found during thermal oxidation of polypropylene below the melting point was broader than that found for a degradation carried out above the... 

M. Celina and G.A. George, Heterogeneous and homogeneous kinetic analysis of the thermal oxidation of polypropylene, Polym. Degrad. Stab. 1995, 50, 89-99. 

The Effect of Transition Metal Compounds on the Thermal Oxidative Degradation of Polypropylene in Solution... 

Nakatani H., Suzuki S., Tanaka T. and al. "New kinetic aspects on the mechanism of thermal oxidative degradation of polypropylenes with various tacticities". (2005). Polymer. V.46. No ll.PP.12366-12371. 

Studies of thermal and fiie resistant properties of the polypropylene/multi-walled carbon nanotube composites (PP/MWCNT) prepared by means of melt intercalation are discussed. The sets of the data acquired with the aid of non-isothermal thermogravi-metric (TG) experiments have been treated by the model kinetic analysis. The thermal-oxidative degradation behavior of PP/MWCNT and stabilizing effect caused by addition of multi-walled carbon nanotube (MWCNT) has been investigated by means of thermogravimetric analysis (TGA) and election paramagnetic resonance (EPR) spectroscopy. 

Polymer/fullerene [Ceol nanocomposites can be considered environmentally friendly alternatives to some traditional flame retardants. The presence of Ceo can markedly delay thermal oxidative degradation and reduce the flammability of polypropylene at very low loadings. It can decrease the heat release rate of polymeric materials by trapping the free radicals created through thermal degradation and combustion, and subsequently forming three-dimensional gelled networks. This network can increase the melt viscosity and consequently slow down combustion. Furthermore, the incorporation of Qo does not affect the physical properties of the polymer. 

Yongcheng, Y, Thermal oxidation of polypropylene containing hindered piperidine compounds. Polym Degrad Stab 1992 37(l) ll-7. 

The literature describes the mechanism of photo-oxidative degradation in isotactic and atactic polypropylene well (Figure 5.25). However, the initiation step - the formation of primary radicals - has not been precisely explained. Photo-oxidative degradation in polypropylene, like thermal-oxidative degradation, also leads to the formation of hydrogen peroxides, ketones, esters, and acids. Figure 5.26 [653]. Simultaneously, molecular weight decreases. Table 5.2. 

Celina, M., George, G.A. Physical spreading and heterogentity in the thermal oxidation of polypropylene. Polymer Degradation and Stability, 42 (1993), p. 335 - 344... 

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. 

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. 

Polymeric hydroperoxides are the major product of low temperature oxidation [Refs. 46, 113,115, 148, 189, 191, 193,195,196, 300]. Yields of hydroperoxides in oxidized polypropylene exceed 40%, and more than half that amount is contained in low molecular weight degradation products. It was shown that isolated hydroperoxide groups in thermally oxidized polypropylene constitute less than 10% of the total hydroperoxide concentration, and the majority of the polypropylene hydroperoxide groups occur in dimers, trimers, or longer sequences [148]. 

Figure 10.3 Carbonyl absorption of polypropylenes vs. the thermal oxidation time at I00°C (from Kelen, T, Polymer Degradation, Van Nostrand Rheinhold, 1983).

Polypropylene (PP) has wide acceptance for use in many application areas. However, low thermal resistance complicates its general practice. The new approach in thermal stabilization of PP is based on the synthesis of PP nanocomposites. This paper discusses new advances in the study of the thermo-oxidative degradation of PP nanocomposite. The observed results are interpreted by a proposed kinetic model, and the predominant role of the one-dimensional diffusion type reaction. According to the kinetic analysis, PP nanocomposites had superior thermal and fireproof behavior compared with neat PP. Evidently, the mechanism of nanocomposite flame retardancy is based on shielding role of high-performance carbonaceous-silicate char which insulates the underlying polymeric material and slows down the mass loss rate of decomposition products. 

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