Radiation effects, in polymers

In respect of radiation effects in polymers, the primary application of NMR spectroscopy is in chemical analysis to determine the changes in chemical structure which may occur on exposure. 

The study of the very fast processes that follow on the absorption of radiation in organic systems is a very active field with pulse radiolysis with picosecond time resolution being one of the major tools. This technique, the latest version of which employs twin linear accelerators(69), has time resolution of about 20 ps. These methods are being used to investigate the fast recombination of charges, the formation of excited states and free radicals, mainly in hydrocarbon media, but have also recently been applied to the study of radiation effects in polymers(70). 

A good understanding of the mechanisms of radiation effects in polymers is required for operating another large scale radiation technology the sterilization of plastic medical supplies which cannot be sterilized by heat (see ref. 25). 

Radiation-induced Degradation.—There have been several reports on radiation effects in polymers,288 including single crystals,287 fluoropolymers,288 polyamides,289 polysiloxanes,270 polyethylene and its copolymers,271 polypropylene,272 polyolefins,273 polystyrene and its copolymers,274 poly(vinyl chloride) and related polymers,275 rubbers,278 polysulphones and other sulphur-containing polymers,277 polycarbonate,278 nylon,279 poly(vinylpyridines),280 and wool.281... 

Simha, R., Wall, L. A., Mechanism of high energy radiation effects in polymers. Journal of Physical Chemistry, 61(4), pp. 425-430 (1957). 

Cross-linking and degradation are well known radiation effects in polymers. The molecular weight increases and gels are formed for the cross-linked type poiymers... 

The following conclusions were made by Battelle workers in 1979 on sterilizing radiation effects in polymers that might be used in adhesive ... 

A. Charlesby, Radiation Effects in Polymers in Polymer Science Vol. 1, Chapter 23,... 

In this brief section, we have not touched the vast field of radiation-induced polymerization and radiation effects on polymers. Fortunately, the field has been surveyed very well in international conference proceedings published in Radiation Chemistry and Physics referred in the beginning of this section. The earlier books by Charlesby (1960) and by Dole (1973) provide adequate background information. 

Research studies of radiation effects on polymer materials are normally carried out on samples in powder, granule, film or sheet form in a completely unstressed condition. 

Much research into radiation effects on polymers is done with samples sealed under vacuum. However, polymer materials may, in practical applications, be subjected to irradiation in air. The effect of irradiation is usually substantially different in air, with increased scission at the expense of crosslinking, and the formation of peroxides and other oxygen-containing structures. Diffusion rates control the access of oxygen to radicals produced by the radiation, and at high dose rates, as in electron beams, and with thick samples, the behaviour may be similar to irradiation in vacuum. Surface changes may be quite different from bulk due to the relative availability of oxygen. 

Charlesby, A. Atomic Radiation and Polymers International Series of Monographs on Radiation Effects in Materials, Vol.l Charlesby, A., Ed. Pergamon Oxford, 1960. 

The species present in polymers that can be studied by ESR are often highly reactive, short-lived and are present in low concentrations. However, developments in instrumentation have offered improvements in sensitivity and,combined with more reliable interpretation of data (1), the increasing application of this method of polymer characterization in studying radiation effects on polymers can be expected. 

RADIATION-INDUCED REACTIONS IN POLYMERS 3.1. Fundamentals of Radiation Effects on Polymers... 

Classical investigations of radiation effects on polymers have been summarized in some books or review articles in the 1970s to the 1990s [29,62-64]. Many of the works were focused... 

Radiation effects on polymers are more subtle than normal radiation chemistry, in that small chemical changes may have pronounced effects on the physical properties. Because of the sensitivity of these physical properties, the radiation chemistry of Polyox is best discussed in two parts—the chemical reactions occurring and the effects of these reactions on the physical properties. 

Some radiation effects in long chain polymers. Plastics Institute Trans. 23, 133-138 (1955). 

A number of investigations on radiation effects of polymers at ambient temperature have been carried out and summarized in some recent publications [38-40]. However, there are very few experimental results on cryogenic temperature irradiation of conventional polymers. Figure 5 shows the summary of early experiments on irradiation of polymers at 77 K up to y-ray dose of 2 x 106 Gy [41,42]. As is evident from Fig. 5, the candidate polymers that can be used at cryogenic temperatures are only aromatic based epoxy resins, poly-imides, and polystyrene. This means that the choice of polymers for superconducting magnets to be operated in a radiation environment is rather limited. Therefore, the intention of this chapter is to give information on the radiation tolerance of recently developed polymers. 

Charlesby A (1960) Atomic radiation and polymers radiation effects in materials. Pergamon Press, Oxford... 

G. J. Dienes, G. H. Vineyard, Radiation Effects in Solids, Interscience, London, 1957 A. J. Swallow, Radiation Chemistry of Organic Compounds, Pergamon, Oxford, 1960 A. Charlesby, Atomic Radiation and Polymers, Pergamon, Oxford, 1960... 

The meeting on radiation effects on polymers was held at the Radiation Laboratory at the University of Notre Dame to review and discuss advances in the radiation processing of polymers. The trends in the basic research, R D and industrial applications were reported. 

GINSBERGEN J., OVERBERGH N., Radiation effects on polymer blends, in Radiation processing of polymers (eds SINGH A., SILVERMAN J.) Hanser - Oxford Univ.Press, Munich - New York, 1992. 

Generally, the spectrum of sunlight is predominantly visible and infrared. Only about 6% of UV light cases fading and other photodegradation effects in polymers and WPCs, and only wavelengths between 100 and 290 nm are the most destructive. In fact, UV radiation with these wavelengths is filtered out with the earth s ozone layer. 

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