Photo-thermal degradation polypropylene

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. 

MarciniSin, A., Hricova, M., Ujhelyiova, A., et al. Effect of inorganic (nano)fillers on the UV barrier properties, photo and thermal degradation of polypropylene fibres. Fibres Text East Eur. 17, 29-35 (2009)... 

Thermoplastic based binders are by far the most widely used. These forms of binder usually contain a wax as a major component and a thermoplastic as the minor component. Additives are usually added for lubrication, viscosity control, wetting and improving powder-binder interaction. Debinding of such binders is normally achieved via thermal degradation, wicking, solvent extraction or even photo-degradation. Thermoplastics commonly used include polyethylene, polystyrene, polypropylene and ethylene vinyl acetate. Table 2 highlights some of the common thermoplastics used in PIM or MIM processes. 

Interest in the susceptibility of polypropylene (PP) to degradation, especially by heat, light, oxygen and combinations of these agencies, has kept pace with the increasing commercial application of this material. The purely photo (1-5) and thermal reactions (0 which occur, have been studied in isolation from one another, and it is clear that similar radicals are involved as intermediates in the overall processes. Previous work on acrylate and methacrylate polymers and copolymers (7-8) has demonstrated that the superficial differences in overall degradation mechanism may be attributed to the different ways in which the same primarily produced radicals react in the solid and liquid... 

N.S. Allen, A. Chirinos-Padron, and J.H. Appleyard, Photo-stabilizing action of metal chelates in polypropylene. Part III. Thermal antioxidant action and its relationship to photo-stabilization, Polym. Degrad. Stab. 1983, 5, 55-63. 

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. 

FTIR techniques in combination with or as complement to other measurement techniques have been used in a wide range of photochemistry studies on polymers. These include bisphenol-A polycarbonate [173], polycarbonate coatings on mirrors [174], PMMA [175], poly( -butyl acrylate) [176] and polypropylene [177]. DSC and FTIR studies have been used in conjunction to investigate the nature of y-radiation-induced degradation and its effect on the 19°C and 30°C phase transitions in PTFE [178]. IR studies of the hydrolysis of melamine-formaldehyde crosslinked acrylic copolymer films have shown that copolymer-melamine formaldehyde crosslinks are broken and that crosslinks between melamine molecules are formed [179]. The thermal and photo-degradation mechanisms in an IR study of cured epoxy resins were found to be related to the autoxidative degradation processes for aliphatic hydrocarbons [180]. 

AUen NS, Parkinson A, Loffelman IT, Susi PV. Photo-stabilising action of A /i-hydroxybenzo-ate compound in polyolefins. Part I thermal and photochemical behaviour in polypropylene film. Polym Degrad Stab 1983 5 241-b6. 

Hydroperoxide groups formed at high processing temperatures in polyethylene (160 °C) [125, 848, 1918, 2279] and polypropylene (135 °C) [443, 1879,1975,2339] are associated (adjacent) with each other, and are rapidly thermally- and/or photo-decomposed into free radicals which initiate the degradation process. 

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