Polyethylene radiation damage

Figure 7. Energy loss spectra of polystyrene (PS), poly (2-vinylpyridine) (PVP), and polyethylene (PE), oi q 0 before and after significant radiation damage (a) dose < 4 C/mt (b) dose 175 C/m for PS, 88 C/m for PE, and 51 C/m7...

TRM images for two orientations of their solutlon-grow n folded-chain crystals. PPS appears to be at least an order of magnitude more stable than polyethylene against radiation damage. 

Recently Cartier and Pfluger [27] reported that hot electrons with a threshold energy of about 4 e " induce a radiation damage in a polyethylene model substance. This means that there exists a coupling of local electronic states with quasi mobile states, as supposed by Zakrevskii and Pakhotin. 

Fig. 3.15 Sequence of electron diffraction patterns from a polyethylene crystal at 100 kV, showing how the sharp spots fade and spread so the final result is a ring pattern. The crystals have become completely amorphous because of radiation damage. The doses are (A) 35-27 C m (B) 53-55.5 C m" (C) 70.5-74 C m" ...

An important staining technique was developed by Kanig [114] for the enhanced contrast of polyethylene, a material which has been a model compound for fundamental polymer studies. PE crystals cannot be sectioned, nor are they stable in the electron beam, due to radiation damage. The chlorosulfonation procedure crosslinks. 

In many cases, plastics degrade in the presence of oxygen at irradiation doses that are without influence or result in crosslinking in vacuum. Because of oxidation, ultimate tensile strength and strain at break in polyethylene, polypropylene, polyvinyl chloride, polystyrene and in styrene-copolymers decrease faster with increasing doses when irradiated in air than when irradiated in a vacuum, whereas this is not the case for polyethylene terephthalate, polyvinyl alcohol, and acetyl cellulose. Oxidative degradation is also the reason for radiation damage doses that are notably smaller when irradiated in air than when irradiated in a vacuum [711],... 

An important staining technique was developed by Kanig [246] for the enhanced contrast of PE, a material that has been a model compound for fundamental polymer studies. Polyethylene crystals cannot be sectioned, nor are they stable in the electron beam, due to radiation damage. The chlorosulfonation procedure cross links, stabilizes, and stains the amorphous material in crystalline polyolefins, permitting ultrathin sectioning and stable EM observation. Chlorosulfonic acid diffuses selectively into the amorphous material in the semicrystalline polymer, increasing the density of the amorphous zone compared with the crystalline material. The treatment stains the surfaces of the... 

For process water, steel pipes are used unless iron pickup is to be minimized. Plastic pipes (polyethylene and polyvinylchloride) are used but they sometimes need external protection from solvents present in industrial atmospheres, ultraviolet radiation (including sunlight), freezing and mechanical damage. 

Early work in this field was conducted prior to the availability of powerful radiation sources. In 1929, E. B. Newton "vulcanized" rubber sheets with cathode-rays (16). Several studies were carried out during and immediately after world war II in order to determine the damage caused by radiation to insulators and other plastic materials intended for use in radiation fields (17, 18, 19). M. Dole reported research carried out by Rose on the effect of reactor radiation on thin films of polyethylene irradiated either in air or under vacuum (20). However, worldwide interest in the radiation chemistry of polymers arose after Arthur Charlesby showed in 1952 that polyethylene was converted by irradiation into a non-soluble and non-melting cross-linked material (21). It should be emphasized, that in 1952, the only cross-linking process practiced in industry was the "vulcanization" of rubber. The fact that polyethylene, a paraffinic (and therefore by definition a chemically "inert") polymer could react under simple irradiation and become converted into a new material with improved properties looked like a "miracle" to many outsiders and even to experts in the art. More miracles were therefore expected from radiation sources which were hastily acquired by industry in the 1950 s. 

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