Polymer radiation degradation, applications

Areas of application of radiation degradation of polymers can be usefully classified into (1) modification of polymers, e.g. molar mass or structure, (2) radiation-sensitive polymers, and (3) radiation-resistant polymers. Within the constraints of the required material properties of the polymers, either maximization or minimization of the response to radiation is usually the objective. 

When the ESR spectrum has been analyzed into spectral components assigned to particular radicals, the individual spectra are simulated, taking into consideration (1) g value, (2) hyperfine splitting, (3) line shape and (4) line width. These simulated spectra are then summed, corresponding to the percentages of individual radicals, to produce a spectrum similar to that obtained experimentally. The application of ESR to the study of radiation degradation of polymers is extremely valuable and the techniques described above have been used extensively in the present work. 

The CRP on The Stability and Stabilization of Polymers under Irradiation was organized from 1994 to 1997 (IAEA-TECDOC-1062). The participants began research into the production of polymers under preparation of blends, which should withstand irradiation through the course of their useful lifetimes. They concluded that much remains to be learned in terms of understanding degradation mechanisms and phenomena. The application of radiation for the preparation of polymers for biomedical applications was the subject of the CRP on Radiation Synthesis and Modification of Polymers for Biomedical Applications implemented from 1996 to 2000 (IAEA-TECDOC-1324). 

Realistic studies of bulk and Interfaclal degradation of polymers for outdoor applications must be concerned with the effects of UV radiation, temperature, temperature cycling, and... 

Polymers which undergo radiation degradation on exposure to radiation are also important commercially. The best-known example is the group of polymers used as positive resist materials in electron beam microlithography. These include aliphatic poly(sulfone)s and poly(methacrylate)s. Finally, an understanding of the radiation chemistry of polymers is essential for their application in environments where they are exposed to high doses of ionizing radiation, for example in the nuclear and space industries. 

Although most polymers are resistant to corrosion in indoor applications, radiation from indoor fluorescent lighting can cause yellowing in many plastics. Applications exposed to other types of artificial radiation, such as from high-intensity discharge lamps of gamma sterilization, can also subject various polymers to degradation. Prior to use the suitability of a particular resin should be checked. 

Moreover, these impurities are capable of absorbing the near-UV portion (290-400 nm) of the solar radiation that reaches the Earth, and may therefore jeopardize or curtail the stability of polymers in outdoor applications, hastening their degradation. 

Over the last few decades, the use of radiation sources for industrial applications has been widespread. The areas of radiation applications are as follows (i) Wires and cables (ii) heat shrinkable tubes and films (iii) polymeric foam (iv) coating on wooden panels (v) coating on thin film-video/audio tapes (vi) printing and lithography (vii) degradation of polymers (viii) irradiation of diamonds (ix) vulcanization of mbber and rubber latex (x) grain irradiation. 

Chlorine-containing polymers such as poly(vinyl chloride) PVC undergo an autocatalytic dehydrochlorination reaction under the influence of elevated temperature and UV radiation. Since the HCl originating from the dehydro chlorination of the PVC chains is believed to sustain this autocatalytic process, stabilizers that irreversibly bond HCl can thus inhibit the degradation. Heavy metal compounds such as cadmium stearate or lead stearate are currently used for this purpose. However, alternatives are required due to environmental problems associated with the use of heavy metals. Indeed, the largest current application of LDH materials is in the polymer industry, mainly to stabilize PVC [3,229-232]. 

Once radioactive decay starts, it continues until all the atoms have reached a stable state. The radioisotope can only be shielded to prevent exposure to the radiation. The most common applications of gamma rays are sterilization of single-use medical supplies, elimination of organisms from pharmaceuticals, microbial reduction in and on consumer products, cancer treatment, and processing of polymers (cross-linking, polymerization, degradation etc.). 

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