Degradation radiation effects

Radiation Effects. Polytetrafluoroethylene is attacked by radiation. In the absence of oxygen, stable secondary radicals are produced. An increase in stiffness in material irradiated in vacuum indicates cross-linking (84). Degradation is due to random scission of the chain the relative stabiUty of the radicals in vacuum protects the materials from rapid deterioration. Reactions take place in air or oxygen and accelerated scission and rapid degradation occur. 

Radiation Effects. The primary effect of radiation is the degradation of large molecules to small molecules. Molecular weight reduction can be... 

Like other perfluoropolymers. Teflon PFA is not highly resistant to radiation (30). Radiation resistance is improved in vacuum, and strength and elongation ate increased more after low dosages (up to 30 kGy or 3 Mrad) than with FEP or PTEE. Teflon PEA approaches the performance of PTEE between 30 and 100 kGy (3—10 Mrad) and embrittles above 100 kGy (10 Mtads). At 500 kGy (50 Mrad) PTFE, FEP, and PFA ate degraded. The effect of radiation on tensile strength and elongation is shown in Table 7. 

Temperature dependence (related to the temperature dependence of the conformational structure and the morphology of polymers) of the radiation effect on various fluoropolymers e.g., poly (tetrafluoroethylene-co-hexafluoropropylene), poly(tetrafluoroethylene-co-perfluoroalkylvinylether), and poly(tetrafluoroethylene-co-ethylene) copolymers has been reported by Tabata [419]. Hill et al. [420] have investigated the effect of environment and temperature on the radiolysis of FEP. While the irradiation is carried out at temperatures above the glass transition temperature of FEP, cross-linking reactions predominate over chain scission or degradation. Forsythe et al. [421]... 

Pheromones in urine will suffer degradation, hydrolysis, oxidation, and ultraviolet radiation effects. For example, the (Z)-7-12-acetyl derivative in elephant urine will gradually hydrolyze (Rasmussen, 1988). In this case, the lipoprotein carriers of the elephant acetate may also determine the life time of the signal besides serving to filter and select odorants, confer specificity, and play a critical role in the transport and transfer of an active ligand to the vomeronasal organ (Rasmussen and Schulte, 1998). 

Methods by which cellulose can be degraded have been reviewed. These include microbiological degradation, - the effect of ionizing radiation, - and the effect of alkali. Interest in both the pyrolysis and the flameproofing - of cotton continues. 

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... 

The foregoing discussion indicates that the primary processes which initiate degradation in alcohols and water may find close parallels in the carbohydrate field. Generally, the photochemistry of carbohydrates has not been considered in relation to these fields, and, consequently, for the radiation effects observed, several primary processes may operate simultaneously. Although little published information is as yet available, investigations known to the author which provide indications about the nature of the primary processes in photo-degradation of carbohydrates will now be considered. 

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... 

Zainuddin Razzak, M. T., Yoshii, E, Makuuchi, K., Radiation effect on the mechanical stability and biodegradability of CPP/Bionolle blend. Polymer Degradation and Stability 1999,63,311-320. 

---