E. Adem

Changes in poly-vinylidene fluoride produced by electron irradiation

Abstract A study was made of the effects of electron irradiation of poly-vinylidene fluoride, using the DSC, FTIR, and X-ray techniques, as well as determining the percent cross-linking. Changes in crystallinity and melting point of the sample as a function of dose were found, the latter due to competition between cross-linking and crystallinity. The cross-linking was observed to increase with radiation dose. Chemical changes observed include the formation of carbonyl groups and double bonding, associated with the loss of HF.

Compatibilization of recycled and virgin PET with radiation-oxidized HDPE

Abstract Blends of high-density polyethylene (HDPE), which cross-links on radiation, and both, recycled and pristine polyethylene terephtalate (PET), one of the most radiation-stable polymers, that contain aromatic groups, which are effective at dissipation of the energy of the ionizing radiation, were irradiated with gamma rays, in order to form a copolymer capable of improving the compatibility of the blend HDPE/PET. Due to the low content of the PET in the resulting copolymer, blends PET and radiation-oxidized HDPE, were also studied. The tensile and flexural properties were improved when the PET content was increased and when the HDPE was pre-irradiated; the largest increase in the mechanical properties was observed for PET contents between 10% and 20% (w/w). The improvement in the properties is believed to occur because of a percolation effect of the PET in the HDPE matrix and the radiation-improved compatibility by means of polar groups formed in the polyethylene. However, impact properties were observed to decrease when the PET content increased in spite of the irradiation.

ESR and optical absorption studies of gamma- and electron-irradiated sugar crystals

Electron spin resonance (ESR) studies of the free radicals induced in gamma- or electron-irradiated sugar crystals were performed. The number of radicals increases linearly, pointing out that this material can be used as a dosimeter. The optical absorption studies show the presence of several distinctive bands in the infrared and UV region, whose intensity changes with the irradiation dose. An interpretation of these results in terms of the formation of free radicals and possible crosslinking along the sugar molecular chains is presented.

Crosslinking of recycled polyethylene by gamma and electron beam irradiation

Recycling of polymeric materials is usually accompanied by degradation and deleterious properties. Irradiation crosslinking of recycling low density polyethylene by electron beam and gamma rays could be the solution to improve their properties. This paper presents a comparison on the effects of gamma and electron irradiation on virgin and recycled polyethylene. Their mechanical, thermal and chemical properties were analyzed. VPE samples shown higher crosslinking percentages than RPE samples in all range of doses studied, unirradiated RPE samples had higher values on their tensile properties than VPE. Percentage crystallinity was similar in all range of doses studied.

Effect of irradiation dose, storage time and temperature on the ESR signal in irradiated oat, and corn and wheat

Results obtained for electron-irradiated oat, corn and wheat kernels are discussed. The applied irradiation doses were up to 160 kGy. For doses up to approx. 50 kGy the number of free radicals produced by the irradiation is linear with the absorbed dose; moreover, the decay at room temperature in the dark or in the presence of light is quite similar. These facts point to the possible use of these kernels as dosimeters. An analysis of the free radical decay as a function of time and temperature shows the contribution of at least three types of radicals, whose half-lifes, radiochemical yields and activation energies are given.

Electron and proton irradiation of poly(vinylidene fluoride): characterization by electron paramagnetic resonance

Films of poly(vinylidene fluoride) (PVDF) were exposed to proton and electron beam irradiation at high doses, from 50 to 5000 kGy. Modifications induced in the samples were determined by electron paramagnetic resonance (EPR). Samples irradiated with electrons and protons showed similar behaviours, with the presence of several types of radicals. The number of radicals produced as a function of dose in the proton case is slightly below that of the electron case, indicating non-linear effects. The evolution of radical density and its decay in the dark and in normal light conditions at room temperature was studied, as well as its decay with increase in temperature. When kept in the dark for up to 180 days, no decay of radicals was observed.

Electron paramagnetic resonance studies of γ-irradiated corn

Gamma-irradiated corn samples in the range 0.1-2.0 kGy dose range were studied by the EPR technique. The signal consists of one structureless line with a width of 0.82 +/- 0.02 mT and a g-factor of 2.004 +/- 0.002. The intensity of this line shows a linear dependence in this dose range. The corn samples were ground prior to irradiation. Before grinding the samples did not show any EPR signal. After grinding they present a free radical EPR line with the same characteristics as that produced by the gamma rays. The stability of these centers as a function of the temperature and time after irradiation was investigated. Analysis of these results suggest the presence of only one type of radical produced by both the mechanical and irradiation processes.

Comparison of60Co gamma radiation and accelerated electrons for suppressing emergence of Sitophilus spp. in stored maize

Abstract A pilot plant developed for the irradiation of maize with accelerated electrons was compared with a 60 Co gamma radiation source for suppressing the emergence of Sitophilus spp. in supplies of commercial maize. 60 Co radiation was more effective than accelerated electrons against pupae and adults. At doses of 15 and 25 krad both radiation sources were equally effective in preventing the development and emergence of adults from maize infested with eggs and larvae. There was evidence that 60 Co doses of 1 to 5 krad stimulated adult emergence from maize 1 to 3 weeks after irradiation.

EFFECT OF ELECTRONIC IRRADIATION IN THE PRODUCTION OF NbSe2 NANOTUBES

In this work, we report the production of NbSe2 (niobium diselenide) nanotubes formed by irradiating NbSe2 with high doses of electron irradiation. The apparatus used for the irradiation was a 2 MeV Van de Graaff accelerator at the following conditions: voltage 1.3 MeV, current 5 μA, dose rate 25 kGy/min, and total dosage 1000 kGy. These conditions were maintained fixed while irradiation dosage was changed between 100, 250 and 500 Mrad. We observed enormous and very well defined nanotubes with a length of several nm and width of a few nm, which are hollow and capped at one end. As the level of irradiation is increased to 500 Mrad, onion-like structures were observed.

Crosslinking of recycled polyethylene by gamma irradiation in the presence of sensitizers

Abstract Recycled and pristine low-density polyethylene samples were crosslinked by 60 Co gamma rays in the presence of two commercial sensitizers : trimethylolpropanetriacrylate (TMPTA) and trimethylolpropanetrimethacrylate (TMPTMA), and another laboratory-synthesized sensitizer, hexakisalylaminocyclotriphosphazatrine (HAAP). The gel per cent and radiochemical yields for crosslinking and degradation were determined for both recycled and pristine polyethylene. TMPTA was found to be the most efficient sensitizer. The gel dose did not change significantly with different sensitizers.