Electron beam-initiated irradiation

For all three diallyl phthalate isomers, gelation occurs at nearly the same conversion DAP prepolymer contains fewer reactive allyl groups than the other isomeric prepolymers (36). More double bonds are lost by cyclisation in DAP polymerisation, but this does not affect gelation. The heat-distortion temperature of cross-linked DAP polymer is influenced by the initiator chosen and its concentration (37). Heat resistance is increased by electron beam irradiation. 

Silicone acrylates (Fig. 5) are again lower molecular weight base polymers that contain multiple functional groups. As in epoxy systems, the ratio of PDMS to functional material governs properties of release, anchorage, transfer, cure speed, etc. Radiation induced radical cure can be initiated with either exposure of photo initiators and sensitizers to UV light [22,46,71 ] or by electron beam irradiation of the sample. 

The influence of the gel content in polyisoprene-tackifier blends on creep resistance and peel behaviour have been recently studied [62]. The gel content was achieved by cross-linking the adhesives with electron beam irradiation. The molecular weight of the soluble fraction in the blend was always dominated by that of the initial elastomer. Creep resistance was achieved either through molecular weight increases or gel content increases. However, the peel strength is strongly... 

An analogous mechanism should also produce polymers on irradiation of epoxies. Crivello s recent mechanistic suggestions [29] are consistent with the mechanisms given above. One can conclude that radiation-induced polymerization of epoxies can proceed via several mechanisms. However, further work is needed to determine the relative contributions of the different mechanisms, which might vary from one epoxy to another. As part of the Interfacial Properties of Electron Beam Cured Composites CRADA [37], an in-depth study of the curing mechanism for the cationic-initiated epoxy polymerization is being undertaken. 

The increase in the modulus for Bis A PSF and Hq/Bp PSF with irradiation indicated that crosslinking predominated for both polymers and that the crosslink structures were probably basically similar. Hq/Bp(50) PSF was considerably more radiation resistant than Bis-A PSF, as shown by the rate of decrease in the elongation at failure. For both polymers, there was an initial rapid decrease in the elongation at failure followed by a slower decrease. This effect was also demonstrated by the variation in the fracture toughness (KI(.) with irradiation for Bis-A PSF. This work with cobalt-60 gamma radiation complements earlier studies of these materials using high dose rate electron beam irradiation (6). 

The energy, or power, of electron beam induced in the flue gas is divided and absorbed by their gas components roughly depending on their electron fraction. Therefore almost all the energy is absorbed by the main components of the flue gas, namely, N2, O2, CO2, and H2O. Table 2 shows a typical concentration of the components in coal-fired flue gas in Japan. The ratio of the total number of electrons in each gas components is also listed in the same table. The energy absorbed directly by the toxic components (SO2 and NO) is negligibly small. For electron beam treatment of flue gas, ammonia gas is added to the flue gas before the irradiation. The amount of ammonia is usually set as stoichiometrically, i.e., 2A[S02] + A[NO], where A[S02] and A[NO] are the concentrations of SO2 and NO intended to be treated, respectively. The concentration of ammonia is usually higher than the initial concentration of SO2 and NO however, it is still far lower than that of the main components. 

To avoid this problem, Wills and Boyd have applied a semi-empirical method [18]. They used relative cross sections for 100 eV electrons and calculated the yields for the various processes based on the ff -values. This method is rather simple and contains many assumptions nevertheless, the results are a good indication for radiation chemists to provide a specific amount of initial species. The following equations [19] show the amounts of initial species from the main components of flue gas with electron beam irradiation based on the data listed in Ref. 18. 

Therefore one pair of ions produces one OH and one HO2 radicals. The total amount of radicals, which are produced in flue gas by electron beam irradiation, is possible to calculate using reported G-values. The main radicals produced initially through direct and ionic decomposition processes are OH, N, HO2, O, and H. 

The amount and uniformity of the solid state reaction of halogen with TTF was probed by the electron microprobe technique. In this analytical method, low energy electron irradiation of a sample provides X-ray core level emissions, characteristic of the element and its relative concentration. Our initial analyses indicated a dramatic dependence of the halogen concentration with the energy of the electron beam. To probe this phenomenon further,... 

In view of the above, the initiation of polymerization and cross-linking reactions in polymeric systems is different from events induced by photons. Most of the events initiated by UV irradiation occur near the surface, because the absorption is governed by the Beer-Lambert Law, whereas the reactive species produced by electron beam are dispersed randomly throughout the entire thickness of the material (see Figure 5.1). 

Systems in which a multilayer structure is formed from molecules containing one or more double bonds and in which polymerisation is subsequently initiated by irradiation by y-rays, ultraviolet light or an electron beam. 

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