[en] The biological action of vitamin K may involve mono electronic exchanges. Therefore, in this work we achieved a radiolytical study on one land, of mono electronic reduction of vitamin K hydroquinone symbolized by KHsubn pp. We also studied the vitamin K2 model of glutamic residue( B - Glu ) by radiolytic mean. The study of radical mechanisms of vitamin K1 reduction in ethanolic solution showed that vitamin K1 is a good sensor of free radicals alpha - hydroxyethyles ( R sup . ) issued from the radiolysis of vitamin K1 ethanolic solutions, saturated with N sub2 O. The final product is hydroquinone K sub 1 H sub 2. It has been demonstrated that mono electronic reduction can be also initiated by solvated electrons. The mono electronic oxidation of K H sub p has been studied in ethanolic solution.The results showed that K H sub p is a good sensor of peroxyl radicals model (RO sub2) sup . issues from ethanol. The oxidation leads to the formation a dimeric from of the quinone K. All these results showed that the free radicals R sup . centred on carbon are efficient reducing agents of vitamin K1, and that the peroxyl radicals R Osub2 centred on oxygen are possible oxidants of KH sub p. At the end and for modeling the eventual interaction of semi quinonic radical with glutamic acid. We have irradiated mixture of vitamin K1 and a compound having a glutamic residue, the concentration ratio (B-Glu) sub 0/ (K sub 1) sub 0 varying for 0,03 to 1. The obtained results showed that the yield of vitamin K sub 1 disappearance is superior to G (R sup .)/R for low concentration of B-Glu. 80 figs., 5 tabs., 105 refs. (F. M.)

[en] Fo0r recycling of waste polymers, degradation behavior of polypropylene (PP) and polyoxymethylene (POM) was studied by a combination of radiolysis and thermolysis methods. The results revealed that thermal degradation temperature of PP was significantly reduced when PP was irradiated in the presence of zeolite. Irradiation induced temperature reduction depended on zeolite structure and composition as well as on the morphology of the mixture. In the presence of zeolite, a series of oxidized products were formed. Initial temperature for the pyrolysis of POM was depressed by irradiation and the irradiated POM had lower final temperature of pyrolysis in the presence of zeolite

[en] Progress in radiation grafting and curing is briefly reviewed. The two processes are shown to be mechanistically related. The parameters influencing yields are examined particularly for grafting. For ionising radiation grafting systems (EB and gamma ray) these include solvents, substrate and monomer structure, dose and dose-rate, temperature and more recently role of additives. In addition, for UV grafting, the significance of photoinitiators is discussed. Current applications of radiation grafting and curing are outlined. The recent development of photoinitiator free grafting and curing is examined as well as the potential for the new excimer laser sources. The future application of both grafting and curing is considered, especially the significance of the occurrence of concurrent grafting during cure and its relevance in environmental considerations

No abstract available

[en] The irradiation effects of polymers was studied in the wide temperature range from very low temperature to high temperature under vacuum or oxygen free atmosphere.The chemical reactions for polymers showed a rather large difference depending on irradiation temperature in quality and/or quantity. The dependence is though to be the difference in molecular motion of polymers during irradiation. The clear difference on irradiation temperature was observed for polytetrafluoroethylene(PTFE) and polystyrene(PS). For other polymers, the irradiation temperature effects are observed, which may be expanding to develop new products. The newly developed technology in radiation application is the curing of polymer fiber as ceramic fiber precursor. The silicon carbide(SiC) fiber is synthesized from silicon containing polymer of polycarbosilane(PCS) fiber by the pyrolysis at high temperature of 1200 deg or more. As the melting temperature of PCS is about 230 deg, the fiber must be cured to not melt down during the pyrolysis. The purpose of this work was the radiation crosslinking of PCS fiber without oxygen contamination. The basic research was carried out using gamma-rays irradiation under vacuum, where the fundamental data were obtained such as the yield of active sites and the reactivity with oxygen and the decomposed gases. The SiC fiber obtained from the radiation cured PCS fiber has a high tensile strength of 3GPa and high heat-resistance up to 1700 deg. The heat resistance of SiC fiber obtained from ordinary processing is about 1200 deg. This technology was transferred to a company and the product is supplied to the market. The silicon nitride(Si₃N₄) fibre was also synthesized from radiation cured PCS fiber by the pyrolysis in ammonia gas atmosphere

[en] Full text: Aliphatic halides, with the exception of fluorides, are among the organic compounds most sensitive to radiation. In these compounds carbon halogen bonds are weaker and the main effect of radiation is to break this bond to give halogen radicals. Due to the differences in reactivities, the final products obtained from chloro and bromo compounds are different. For example, radiolysis products from chloro compounds tend to include hydrogen chloride whereas bromides give bromine as well as hydrogen bromide. Due to the above behaviour of low molecular weight alkyl halides when exposed to high energy radiation, it is interesting to see the behaviour of polymers which contain halogen atoms. While butyl rubber is known to undergo predominantly chain scission during exposure to high energy radiation, a drastically different response towards high energy radiation has been reported for the halogenated butyl rubbers. Rapid gelation occurs in these polymers at low doses. No detailed study has been reported on the radiation induced reactions in halogenated butyl rubbers. We have used ESR and NMR techniques to study these reactions. Information regarding the changes in structure during exposure of butyl, chlorinated butyl and brominated butyl rubbers, to high energy radiation will be presented. Butyl rubber is predominantly polyisobutylene with 1-2 % isoprene units incorporated. The isoprene units in the halogenated butyl rubbers are of exo structure. ESR spectra indicate that during high energy irradiation, most of the radicals are generated in halogenated isoprene units. A higher radiation yield for scission was observed in chlorinated butyl rubbers than brominated butyl rubbers

[en] Full text: Poly (2-hydroxy ethyl methacrylate) [PHEMA] and poly (2-ethoxy ethyl methacrylate) [PEEMA] are of biomedical and industrial interest due to their biocompatibility with living tissue. In this paper the effect of high energy radiation on these polymers is reported. PHEMA and PEEMA have similar molecular structures to poly (methyl methacrylate)[PMMA], and the γ irradiation of this polymer is well understood. Hence the radiation chemistry of PMMA is used as model system for the the analysis of the radiation chemistry of these polymers. The mechanism of the radiation induced chemistry of the polymers has been investigated using a range of techniques including electron spin resonance spectroscopy (ESR) to establish free radical pathways, GC to identify small molecule volatile products, NMR to identify small molecule radiation products and Gel Permeation Chromatography (GPC) to determine molecular weight changes. Whilst much of the major part of the radiation chemistry can be attributed to similar reactions which can be observed in PMMA, there are a number of new radicals which are present as a result of the influence of the side chain interactions which reduces the mobility of the polymer chain

[en] An emulsion polymerisation typically consists of two phases: the continuous aqueous phase, and the discreet organic phase, which comprises of monomer droplets and latex particles. This system is stabilised by some form of surfactant. While polymerisation mainly occurs in the latex particles, the events which initiate polymerisation usually occur in the aqueous phase. Therefore, the transfer of radical activity from the aqueous phase to the organic phase (otherwise known as entry) is important in the kinetics of polymerisation. Likewise, transfer of radicals from the latex particles to the aqueous phase (exit), is important as a means whereby polymerisation in the latex particle ceases. This study utilizes seeded emulsion polymerisations. Two electrostatically stabilised styrene lattices were grown, of 24 nm and 44 nm particle radius. Poly(acrylic acid), an electrosteric stabiliser, was absorbed onto the surface of the latex particles as a second stage procedure, forming electrosterically stabilised lattices. Dilatometry was used to measure the conversion rate: the steady rate with chemical initiator and relaxation from steady state in a system initiated by γ radiolysis has been used to obtain the exit rate coefficient

[en] Chlorinated organic substances such as polychlorinated biphenyls can be dechlorinated with advantage by a procedure during which oxygen is removed from their alkalinized isopropanol solution (e.g., by nitrogen purging) and the latter is exposed to electrons accelerated to 1-5 MeV (typically 4 MeV) at dose rates of 10^-2 to 10² kGy/s (typically 0.1-10 kGy/s), total dose 1-100 kGy. A flow-through apparatus has been designed for this procedure, consisting of an accelerator, an irradiation circuit, and a separation circuit. The irradiation circuit comprises a tank for the chlorinated substances, a pump, an irradiation cell, and a filtering device. The separation circuit encompasses a tank for the irradiated substrate, a distillation facility where the solvent and volatiles from the dechlorination reaction are removed, and a separation unit where the final dechlorination product is separated. A relatively high dechlorination degree can be achieved even at high dose rates and doses as compared with gamma irradiation. (P.A.)

[en] The effect of pH on the process of radiolysis of aqueous ribose-5-phosphate (R-5-P) solutions was investigated. Solutions at concentration 10^-2 M were irradiated in the γ⁶⁰Co source in the presence of N₂ over the range of doses from 0 to 1.4 Mrad. It has been found that pH of the solution affects the radiation yield of ribose-5-phosphate decomposition, G-values measured by loss in reducing power were 3.7 for a solution of pH=2.20 and 2.9 for neutral and alkaline solutions. Similarly, pH has been found to affect the radiation yield of the formation of inorganic phosphate, malondialdehyde and substances absorbing in ultraviolet region (lambdasub(max)=263 nm). (author)