Degradation by High-energy Radiation

Low dose (0-60 kGy) irradiation is used both for the improvement of long-term properties (crosslinking of PE pipes, cables, and so on) and for medical applications. For the sterilisation of medical items, a dose of 25 kGy of Co y-rays can be nsed to destroy bacteria, fungi, and spores. 

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Polytetrafluorethylene (p.t.f.e.) This polymer does not absorb water, has no solvents and is almost completely inert to chemical attack molten alkali metals and sodium in liquid ammonia are the rare exceptions. Furthermore it does not soften below 320°C, is electrically inert and has a very low coefficient of friction. It is more expensive than general purpose plastics, requires special fabrication techniques, is degraded by high energy radiation, and has a low creep resistance. 

Some polymers like PE and NR get cross-linked on exposure to radiation while others like those based on vinylidene polymers, e.g., polymethylmethacrylate (PMMA), polyisobutylene, degrade. Certain other types of polymer stmctures (high aromatic content or thermoset) resist degradation by high-energy radiation. Coating polymers usually contain acrylic, methacryUc, or fumaric vinyl unsaturation along or attached to the backbone. 

Fundamental Aspects of Polymer Degradation By High-Energy Radiation... 

Section 7.2.2). This feature makes it unique among vinylidene polymers, which typically are degraded by high-energy radiation.74... 

Alternatively, clean and unfilled PTFE can be degraded by high energy radiation such as X-ray, gamma ray, or electron beam [3,89]. The degradation of high molecular scrap PTFE by electron beam irradiation is commercially widely used, and in practice continuous processes are used to improve the economics. After irradiation, the material is milled to the desired smaller particles sizes. 

We have studied the degradation by high-energy radiation of a number of families of polymers by using a variety of techniques, including ESR spectroscopy [10,11]. In this paper we show the similarities and differences in the role of free radicals in the radiolysis of polyfmethyl methacrylate), polystyrene, and random copolymers of methyl methacrylate and styrene. 

Schnabel, W. (1978) Degradation by high energy radiation, in Aspects of Degradation and Stabilization of Polymers (ed. H.H.G. Jellinek), Elsevier Scientific, Amsterdam, Ch. 4. 

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