Degradation high-energy radiation

Films, coatings, adhesives, laminates outstanding in heat resistance, flame resistance, abrasion resistance, electrical iruulation resistance. resistance to oxidative degradation, high energy radiation and most chemicals (except strong bases) used in specialist applications. e.g.,Kapton, Vespel. 

Like almost all synthetic polymers, styrene plastics ate susceptible to degradation by heat, oxidation, uv radiation, high energy radiation, and shear, although... 

Ejfects of Thermal, Photochemical and High-energy Radiation 97 Table 5.9 Thermal degradation of selected polymers (Ref, 7)... 

The polymers also have excellent resistance to oxidative degradation, most chemicals other than strong bases and high-energy radiation. Exposure for 1500 hours to a radiation of about 10 rads at 175°C led to embrittlement but the sample retained form stability. 

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. 

The primary product which arises from the degradation of PVC, whether induced thermally, photochemically or by high energy radiation, is a distribution of conjugated polyene sequences of various lengths produced by a dehydrochlorination process which may be written -... 

Changes in the properties of polymer materials caused by absorption of high-energy radiation result from a variety of chemical reactions subsequent to the initial ionization and excitation. A number of experimental procedures may be used to measure, directly or indirectly, the radiation chemical yields for these reactions. The chemical structure of the polymer molecule is the main determinant of the nature and extent of the radiation degradation, but there are many other parameters which influence the behaviour of any polymer material when subjected to high-energy radiation. 

PTFE, FEP and PEA are sensitive to high-energy radiation. Exposure to 1 Mrad can lead to a measurable degradation. 

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

There is evidence that both ionic and free radical species are involved in the degradation and depolymerization of poly (olefin sulfone) s by high energy radiation (70). Thus, the yields of olefins from poly (1-butene sulfone) at 30 °C (the sample was heated to 70 °C during removal of the gaseous products) are shown in Table II. The butene is not solely 1-butene, but comprises significant proportions of all three isomers, 1-butene, 2-butene and isobutene. 

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