Search results for "IRRADIATION"
showing 10 items of 1012 documents
Synthesis, characterisation and properties of α,β-poly(N-2-hydroxyethyl)-dl-aspartamide-graft-maleic anhydride precursors and their stimuli-responsiv…
2009
Abstract A family of poly(amino acid)-maleic anhydride hydrogels were designed and synthesized. Water soluble polymeric precursors were prepared by partially substituting the hydroxyl groups of the α,β-poly( N -2-hydroxyethyl)- dl -aspartamide backbone with maleic anhydride, so as to provide double bonds for crosslinking and carboxylic acid groups for pH and electric field responsiveness. Reaction conditions (reactive mixture composition and catalysis) were systematically varied in order to obtain PHEA–MA precursors with different and reliable graft-maleic anhydride levels. PHEA–MA precursors were characterised by titration, Nuclear Magnetic Resonance ( 1 H NMR), Fourier-Transformed Infrare…
Gamma-radiation ageing of a low density polyethylene. Effects of irradiation temperature and dose rate
1993
Abstract Ageing due to gamma radiation of a low density polyethylene at various dose rates and temperatures is studied; the effect of thermal treatment only is also considered. The modifications induced in the molecular and crystallinity behaviour of the polymer are investigated by means of gel extraction, measurements of intrinsic viscosity and thermal analysis. Results indicate the occurrence of both crosslinking and oxidative degradation; the extent of the latter increases on decreasing the irradiation dose rate and on increasing the irradiation temperature. Some exceptions are found because of the increase in the mobility of free radicals at high temperature. These effects modify also t…
Influence of morphology and chemical structure on the inverse response of polypropylene to gamma radiation under vacuum
1999
Abstract In this work the influence of the chemical structure and of the morphology on the gamma-radiation effects on polypropylene based polymers is studied on the basis of a previously discussed kinetic model [1] . For this aim an isotactic polypropylene and a random ethylene–propylene copolymer were irradiated under vacuum at one dose rate and several absorbed doses after well defined solidification conditions. We show that the model is reliable varying both the chemical structure and the morphology of the polypropylene based polymer. An inversion of the response of the material to gamma radiation under vacuum is always observed, and the inversion conditions depend on the irradiation par…
Swift heavy ion induced modifications of luminescence and mechanical properties of polypropylene/ZnO nanocomposites
2014
Abstract The effect of irradiation with 150 MeV Kr ions at fluencies 10 11 and 10 12 ions/cm 2 on luminescence of PP/ZnO nanocomposites and PP matrix has been studied. In unirradiated composite the luminescence is comparatively weak and is contributed mainly by the excitonic luminescence of ZnO. Irradiation of nanocomposite and PP matrix leads to a strong increase of luminescence intensity in a wide spectral range of 360–600 nm. It follows from the obtained results that the enhancement of luminescence originates mainly from the broken bonds in PP matrix. Ion-induced scission of polymer bonds and fragmentation of polymer chains is deduced also from the nanoindentation tests which show a rem…
Influence of gamma-irradiation on thermally-induced mesoscopic gelation of degalactosylated xyloglucans
2014
Thermoresponsive degalactosylated xyloglucans have been already proposed as in situ gelling scaffolds for tissue engineering, due to their reversible macroscopic thermal gelation at body temperature and biodegradability. The highly branched, hydroxyl group-rich molecular structure renders xyloglucans interesting raw materials also in the form of micro/nanoparticles for application as nanoscalar drug delivery devices in cosmetic and pharmaceutical formulations. Owing to their natural source, xyloglucans show high average molecular weight, broad molecular weight distribution and poor water solubility, as large and compact aggregates usually form via inter-molecular hydrogen bonding. Co-60 gam…
High energy radiation cure of resin systems for structural adhesives and composite applications
2002
Abstract Radiation cure polymerisation of a commercial diglycidyl ether of bisphenol F epoxy resin has been achieved using a 60Co irradiation source, compounding the monomer with few percentage of an onium salt catalyst. The cure process has been monitored by a gamma-calorimetric technique and systems irradiated at doses corresponding to different positions in the gamma-calorimetric curve have been characterised via solubility tests and dynamic mechanical torsion analysis. Changes in both the measured gel fractions and tan δ values were associated with the progress of polymerisation and crosslinking reactions and these were dose dependent. Furthermore, systems irradiated at lower doses exhi…
Studies of network organization and dynamics of e-beam crosslinked PVPs: From macro to nano
2012
Abstract In this work the influence of poly(N-vinyl pyrrolidone) (PVP) concentration in water on the organization and dynamics of the corresponding macro-/nanogel networks has been systematically investigated. Irradiation has been performed at the same irradiation dose (within the sterilization dose range) and dose rate. In the selected irradiation conditions, the transition between macroscopic gelation and micro-/nanogels formation is observed just below the critical overlap concentration (∼1 wt%), whereas the net prevalence of intra-molecular over inter-molecular crosslinking occurs at a lower polymer concentration (below 0.25 wt%). Dynamic–mechanical spectroscopy has been applied as a cl…
Physical and structural characterization of blends made with polyamide 6 and gamma-irradiated polyethylenes
1996
Abstract Morphological, calorimetric and rheological results of blends made with polyamide 6 and polyethylene gamma irradiated in air are presented. The polar oxidized groups grafted in the poliolefin chains through gamma-radiation induce “compatibilization” effects in the blends with a more uniform and finer distribution of the polyethylene “phase” in the polyamide matrix, with respect to blends made with the unirradiated polymer. This effect, observed with polyethylenes of different molecular structure, i.e. low density, linear low density and high density, was attributed to the presence of interactions among the functional oxidized groups of the polyethylene chains and the polyamide. Tes…
E-beam curing of epoxy based blends in order to produce high performance composites
2007
In this work, blends of a difunctional epoxy monomer and a thermoplastic toughening agent are E-beam irradiated at two different dose rates and two different total absorbed doses. The influence of the processing conditions on the thermal properties and on the morphology of the obtained matrices has been investigated. In particular, it is shown how the increase of the dose rate causes an increase of the temperature during irradiation, thus inducing a simultaneous thermal and radiation curing. On the contrary, at low-dose rate the system mainly undergoes to radiation curing, thus making the cured material very sensible to a post-irradiation thermal treatment with a significant improvement of …
Structural induced modifications in blends of polyamide with gamma irradiated low density polyethylene
1992
Abstract Blends of gamma irradiated and unirradiated low density polyethylene and polyamide 6 were made in order to study possible modifications induced by this irradiation. Results indicate that blends with gamma irradiated polyethylene have structure and properties significantly different with respect to blends made with the unirradiated one. This difference has been ascribed to the formation of functionalized groups in the polyethylene chains, which interact with polyamide.