Search results for "IRRADIATION"

Thermal, Pressure and Light Induced Spin Transition in the Two-Dimensional Coordination Polymer [Fe(pmd)2[Cu(CN)2]2]

2008

[EN] A complete structural, calorimetric, and magnetic characterisation of the 2D coordination spin crossover polymer {Fe(pmd)(2)[Cu(CN)(2)](2)} is reported. The crystal structure has been investigated below room temperature at 180 K and 90 K, and at 30 K after irradiating the sample at low temperature with green light ( lambda = 532 nm). The volume cell contraction through the thermal spin transition is only 18 angstrom(3) which is lower than the usually observed value of around 25-30 angstrom(3) while the average Fe-N bond distances decrease by the typical value of about 0.19 angstrom. The structural data of the irradiated state indicate that the high spin state is well induced since the …

Irradiation of low density and high density polyethylenes in presence of carbon dioxide in subcritical and supercritical conditions

1998

Abstract The grafting of carboxylated and oxygenated functions on low density and high density polyethylenes is carried out by gamma irradiation in the presence of carbon dioxide. Both crosslinking and grafting of oxidised groups occur. The extent of these molecular modifications depends on the physical conditions of the gas phase and on the nature of the polymer matrix.

1975

The formation and the behaviour of radiation induced free radicals in poly[1-(tert-butoxy carbonylthio)ethylene] (2) and in a statistical copolymer 4 from O-tert-butyl S-vinyl thiocarbonate (1) with N-vinylpyrrolidone (1:1) was studied, using ESR spectroscopy. After γ-irradiation at 77 K, tert-butyl radicals and other species were detected in the polymers. The yield for the homopolymer was evaluated to be Gtert-butyl = 0.18. Investigations on the behaviour of radicals with an annealing procedure revealed, that at first the tert-butyl radicals disappear with increasing temperature and that a further warming up leads to a concentration rise of this radical species. A radical cation localized …

Thermal properties of e-beam cured epoxy/thermoplastic matrices for advanced composite materials

2007

The aim of this work is to investigate the possibility to improve the thermal behaviour of epoxy based systems, cured by ionizing radiation, in order to produce matrices for advanced carbon fibres composites. Blends of two epoxy monomers, difunctional and trifunctional, have been polymerized by e-beam irradiation and the dynamic mechanical thermal properties have been investigated. The increase of the concentration of the trifunctional epoxy monomer in the blend causes a marked increase of the Tg, but strongly decreases the reactivity. Subsequently, blends of the same epoxy monomers with a high Tg thermoplastic toughening agent have been considered and their reactivity and the thermal prope…

Characterization of ultra-high-molecular-weight polyethylene (UHMWPE) modified by ion implantation

2004

Abstract Surface modification of ultra high molecular weight polyethylene (UHMWPE) is induced by ion implantation of different ions at 300 keV energy. The aim of this work was the chemical, physical and mechanical characterization of the modified material in order to know deep inside about the effect of the ion beam upon the polymer. The irradiated surfaces are investigated by Raman spectroscopy, infrared absorption and micro-hardness analysis, scanning electron microscopy. Pin on disc measurements valuated the wear of the UHMWPE against a stainless steel probe; wear resistance increases of about 76% after the ion implantation. This result can be attributed to the ion bombardment inducing a…

Studies on electron-beam irradiation and plastic deformation of medical-grade ultra-high molecular weight polyethylene

2011

Abstract Separated and combined electron-beam irradiation and plastic deformation effects on the structures of ultra-high molecular weight polyethylene (UHMWPE) were studied. It was found that the concentration of carbonyl (ketones, esters and peresters), hydroxyl and vinyl groups increases with the growing dose of adsorbed electrons. It also tends to exhibit a slight increase in the melting point and crystallinity of the samples. A mechanical stress in the polymer was found to accelerate radiation-induced degradation. It was concluded that each of the factors studied (i.e. electron beam sterilization and plastic deformation) had a different impact on the polymer structure. The change in th…

Effects of gamma-irradiation on the alpha-tocopherol and fatty acids content of raw unpeeled almond kernels (Prunus dulcis)

2014

Abstract The present study evaluated fatty acid composition and α-tocopherol content of almond as a function of irradiation dose in order to determine dose levels causing minimal undesirable changes to almonds. Raw unpeeled almonds variety Tuono ( Prunus dulcis (Mill.) D. A. Webb) were irradiated using 60 Co source at dose of 0.5, 1.5, 3, 6, 8 and 10 kGy. Both control and irradiated samples were kept frozen and immediately analyzed. The data obtained showed no change in fatty acid compositions up to a dose of 10 kGy; on the contrary, a general trend observed is that increasing the dose of irradiation resulted in the decrease of α-tocopherol content. The study has shown that irradiation is a…

A new equipment to measure the combined effect of humidity, temperature, mechanical stress and UV exposure on the creep behaviour of polymers

2008

To be able to study and predict the physical properties of a polymeric material under different environmental conditions is very important. Moisture, UV irradiation, thermal and mechanical stresses can dramatically change the characteristics of the material and hinder some specific applications. In this work, a new equipment able to perform creep tests under different environmental conditions (temperature, humidity, stress) is presented. Some preliminary results are also presented using a sample of polyamide 6. As this polymer is sensitive to all these variables, it is appropriate to verify the effectiveness of the new instrument.

Photoinduced molecular rearrangements. Some comments on the ring-photoisomerization of 1,2,4-oxadiazoles into 1,3,4-oxadiazoles

2001

The ring-photoisomerization of 3-amino- and 3-methylamino-5-phenyl-1,2,4-oxadiazoles into the corresponding 2-amino- and 2-methylamino-5-phenyl-1,3,4-oxadiazoles has been reinvestigated by examining the effect of a base on the photoreaction. On irradiating at λ = 254 nm in methanol, yields of the ring-photoisomers were found to be significantly enhanced by the addition of triethylamine (TEA) in the photoreaction medium. By contrast, irradiation of the 3-amino-5-phenyloxadiazole in acetonitrile containing TEA gave an almost complete photoreduction into benzoylguanidine, while few percent of the ring photoisomer were detected. Furthermore, the pyrene-sensitized photolysis of 3-amino-5-phenylo…

ChemInform Abstract: Photoinduced Molecular Rearrangements. Some Comments on the Ring-Photoisomerization of 1,2,4-Oxadiazoles into 1,3,4-Oxadiazoles.

2010

The ring-photoisomerization of 3-amino- and 3-methylamino-5-phenyl-1,2,4-oxadiazoles into the corresponding 2-amino- and 2-methylamino-5-phenyl-1,3,4-oxadiazoles has been reinvestigated by examining the effect of a base on the photoreaction. On irradiating at λ = 254 nm in methanol, yields of the ring-photoisomers were found to be significantly enhanced by the addition of triethylamine (TEA) in the photoreaction medium. By contrast, irradiation of the 3-amino-5-phenyloxadiazole in acetonitrile containing TEA gave an almost complete photoreduction into benzoylguanidine, while few percent of the ring photoisomer were detected. Furthermore, the pyrene-sensitized photolysis of 3-amino-5-phenylo…