Radiation degradation mechanisms

Further Investigations Involving analytical techniques such as epr and mass spectroscopy are needed to reveal the radiation degradation mechanism of the itaconate copolymers. 

Additionally, organotin mercaptides can act as antioxidants, as they can sequester free-radical degradation mechanisms (48). The one drawback of mercaptide-based tin stabilizers is the discoloration of the sulfur after exposure to uv-radiation. Special precautions or formulations need to be developed for outdoor apphcations. 

Cheng et al. [116] reported that the structure of primaquine phosphate irradiated with 0.7—10 Mrad remained unchanged. The energy transfer action of the quinolyl group was considerable due to its resonance stabilization. Radiation-induced degradation of polyl(vinyl alcohol) decreased in the presence of primaquine phosphate but the degradation mechanism was unaffected. The content of primaquine phosphate showed linear relationship with degradation parameters of poly(vinyl alcohol). 

Understanding of the mechanism of radiation degradation of polymer molecules is essential for development of improved and new industrial processes, for radiation-induced modification of polymer properties, and for selection of polymers for use in radiation environments. This means that the detailed chemical reactions resulting from absorption of radiation must be known. This fundamental understanding must enable us to relate the chemical structure of a polymer to changes in its chemical, physical and material properties. Such structure-property relationships require a great deal of research work, but they are the key to further advancement on a scientific basis. 

Thus, there are three possible pathways for the radiation degradation of polymer molecules neutral radical, cation-radical and/or anion-radical intermediates. Interest in the formation of these three types of reaction intermediates has fluctuated over the years with the utilization of different techniques and with the particular interests of different investigators. It is likely that all three species will be produced, but their relative importance in the degradation mechanism will depend on the chemical structure of the polymer. Evidence for their involvement will depend on the experimental methods used and the temperature and time scale of observation. In this paper we illustrate our investigations of many of the fundamental aspects of the radiation degradation of polymers through studies of series of polymers and copolymers. 

Mao, Y. Schoeneich, C. Asmus, K. D. Radical mediated degradation mechanisms of halogenated organic compounds as studied by photocatalysis at Ti02 and by radiation chemistry, in Photocatalytic Purification and Treatment of Water and Air D. F. Ollis H. Al-Ekabi, eds., Elsevier Science Publishers B.V. Amsterdam, 1993, p. 49. 

Pulse radiolysis studies concerning the polymerization as well as the degradation, crosslinking and radiation resistance of polymers are surveyed. Initiation mechanisms of the radiation-induced polymerization of styrene and other monomers are discussed on the basis of the direct measurements of the reaction intermediates. Optical and kinetic data on the short-lived chemical intermediates produced in the solution of polymers and in the rigid polymers are surveyed and discussed with special reference to the degradation mechanism of polymers. 

Resins may influence phototendering of rayons. Wood (26) has reported that viscose rayon fabrics treated with urea formaldehyde or thiourea formaldehyde resin are protected from the degradative effects of mercury vapor lamp radiation. The mechanism of the protective effect is not fully understood as yet. Possibly resins can quench free radicals formed during irradiation. Work with resin-treated cotton indicates that simultaneous scission of cellulose chain molecules and resin-cellulose bonds occurs on exposure to light (63). 

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