1,721,234 research outputs found
Radiation Engineering of Multifunctional Nanogels
No full textNanogels combine the favourable properties of hydrogels with those of colloids. They can be soft and conformable, stimuli-responsive and highly permeable, and can expose a large surface with functional groups for conjugation to small and large molecules, and even macromolecules. They are among the very few systems that can be generated and used as aqueous dispersions. Nanogels are emerging materials for targeted drug delivery and bio-imaging, but they have also shown potential for water purification and in catalysis. The possibility of manufacturing nanogels with a simple process and at relatively low cost is a key criterion for their continued development and successful application. This paper highlights the most important structural features of nanogels related to their distinctive properties, and briefly presents the most common manufacturing strategies. It then focuses on synthetic approaches that are based on the irradiation of dilute aqueous polymer solutions using high-energy photons or electron beams. The reactions constituting the basis for nanogel formation and the approaches for controlling particle size and functionality are discussed in the context of a qualitative analysis of the kinetics of the various reactions
Influence of polymer electrospun nanofibers on thermal properties of epoxy resins
No full textElectrospinning of polymers has gained surging interest in the last decades due to its wide range of applications in different fields, such as sensors, electronic devices, separation systems, biomedical materials. Still there are only few reports on the use of these nanofibers as reinforcement in polymer composites. In this paper, solution electrospinning was employed to produce nanofibrous mats impregnating two epoxy resins to form “monolayer“systems, with the aim to study the influence of the nanofibers on both the curing behaviour and the morphology of the resin systems. Three polymers were chosen for producing electrospun mats, a polysulfone (PSF), a polyamide Nylon 6,6 (Ny66) and a polyacrilonitrile (PAN). The nanofibrous mats were employed to produce mat/epoxy monolayers by soaking the mat in two different epoxy resin systems, one in lab-synthesized-high performance, and the other commercial-low performance. The results show a different extent of swelling of the electronspun mats, as derived by morphological analysis. The observation of the fractured surfaces also indicates the formation of several fracture planes or phase separation phenomena, suggesting the possibility of dissipation of fracture energy by the epoxy/mat nanocomposites. Additionally, for all resin/mat arrangements, thermal analysis indicates no significant interference of the mat with the cure reactions of the resins and only slight changes of the glass transition temperatures
Control of end-of-life oxygen-containing groups accumulation in biopolyesters through introduction of crosslinked polysaccharide particles
Full text linkThe formulation of bio-based materials with good performance in service and controlled end-of-life is imperative for an effective circular economy. In this work, an innovative approach to induce and control the end-of-life of biodegradable polyesters through introduction of crosslinked polysaccharide particles is proposed. Chitosan (Ch) has been subjected to ionotropically crosslinking and then added to polylactic acid (PLA) at different amounts (1.0–4.0%w) by melt mixing. All obtained results suggest that the addition of crosslinked Ch (cCh) particles does not modify significantly the investigated biopolyester properties. Specifically, the thermal analysis of the composites reveals that the addition of unmodified Ch alters the PLA thermal behavior, while the addition of cCh particles does not change the PLA glass transition, cold crystallization and fusion phenomena. The infrared and UV–visible spectroscopic analyses suggest no significant changes in PLA structure. PLA/cCh films show a good optical transparency, which is a desirable property for food packaging applications. In addition, thin PLA-based films have been subjected to UVB exposure and the accumulation of oxygen-containing groups has been monitored in time through spectroscopic analysis. Interestingly, at low exposure time, the presence of chitosan slows down the accumulation of these groups, while at long exposure time, chitosan induces accelerated oxygen-groups formation, supporting its beneficial effect as end-of-life accelerant
Synthesis, characterisation and properties of α,β-poly(N-2-hydroxyethyl)-dl-aspartamide-graft-maleic anhydride precursors and their stimuli-responsive hydrogels
Full text linkA 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 a,b-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 (1H NMR), Fourier-Transformed Infrared Spectroscopy (FTIR)
and Size Exclusion Chromatography (SEC) for structural and molecular determination. Aqueous solutions
of selected PHEA–MA precursors were subjected to gamma-irradiation at different irradiation doses and
polymer to water concentrations in order to induce chemical crosslinking without the addition of crosslinking
agents. The yield of crosslinking reactions was evaluated by solubility tests as well as the effect of
ammonium persulphate, as assistant radical initiator for gamma crosslinking. Selected hydrogels were
tested through swelling measurements to prove their pH and electric field responsiveness. Structural features
of the different variants produced were related to the swelling behaviour
Far infrared radiofrequency generated a new non invasive method for the treatment of head and neck pathologies
No full textThe role of water in radiation-induced fragmentation of cellulosic backbone polysaccharides
Full text linkXyloglucan (XG) is a cellulosic backbone polysaccharide commercially used for food applications, but also widely investigated in biomedical applications, for its gelling properties and specific biological activity. In this study, the possibility of using gamma radiation to cleave XG and generate lower molecular weight variants was explored. The impact of absorbed dose and irradiation conditions on the XG molecular weight distribution was investigated. Two other cellulosic polysaccharides, hydroxypropyl cellulose (HPC) and an oxidized variant of XG (CXG), were also studied for comparison. Before irradiation, the polymers were characterized with thermal gravimetric analysis and, after irradiation, with gel permeation chromatography. The results showed that for XG irradiated in dilute aqueous solution, a dose of 10 Gy is sufficient to significantly reduce the polymer molecular weight, while HPC is less affected by irradiation under identical conditions. When the polymers were irradiated in the solid form, either dry or humid, the reduction in average molecular weight is much less pronounced. Interestingly, for HPC the cleavage of the chains is more pronounced for the dry than for the humid powder. A similar behavior, but less pronounced, was observed for XG and CXG. Arguably, when water was present in the system as bound water it had a protective effect. This is probably due to energy transfer from the polymer to the bound water preventing chain scission. Indeed, humid HPC has more bound water than XG and CXG. Conversely, when water was present as solvent, water radiolysis products were able to efficiently induce depolymerization
Electrospun rubber/thermoplastic hybrid nanofibers for localized toughening effects in epoxy resins
No full textSynthetic rubber/thermoplastic blends were electrospun from their solutions. The rubber was a solid acrylonitrile/butadiene/acrylic acid copolymer and the thermoplastic was polyacrylonitrile. The aims of this study were to identify suitable systems and processing conditions for obtaining rubber-based electrospun nanofibers, to investigate the ability of an epoxy resin system to impregnate and swell selected hybrid rubber/thermoplastic mats, and to assess the impact of the nanofibers on the resin morphology and curing behavior. In particular, electrospinning trials were carried out varying the composition of the feed solution and process parameters, such as the applied voltage, the flow rate, and tip-to-collector distance. The morphology of the hybrid mats was characterized by scanning electron microscopy and their thermal properties by thermogravimetry. An epoxy resin-mat monolayer was also prepared and its fracture surface inspected; both rubber nanoparticles and PAN nanofibers were evident. The highly corrugated fracture surfaces suggest activation of local epoxy-resin toughening mechanisms. Altogether, the results encouraged the application of hybrid mats as interleaves in high-performance carbon/epoxy composites to contrast delamination
Numerical Simulations of Nanogel Synthesis Using Pulsed Electron Beam
No full textIn this work, a new method for numerical simulation of the radiation chemistry of aqueous polymer solutions exposed to a sequence of electron pulses is presented. The numerical simulations are based on a deterministic approach encompassing the conventional homogeneous radiation chemistry of water as well as the chemistry of polymer radicals. The multitude of possible reactions in the macromolecular system is handled by allowing for a large number of macromolecular species. The speciation of macromolecular species is done to account for variations in molecular weight, number of alkyl radicals per chain, number of peroxyl radicals per chain, number of oxyl radicals per chain, and number of internal loops. As benchmarking, previously published results from a series of experiments on pulsed irradiation of aqueous poly(N-vinylpyrrolidone) (PVP) solutions are used. The numerical simulations clearly show that the pulsed nature of the radiation must be accounted for. The simulations qualitatively reproduce the experimentally observed impact of initial gas saturation (air and N2O) and polymer concentration on the molecular chain length upon irradiation. The formation of double bonds as a function of dose as well as the impact of effective dose rate on the final chain length are also qualitatively reproduced in the simulations
Numerical Simulation of the Kinetics of Radical Decay in Single-Pulse High-Energy Electron-Irradiated Polymer Aqueous Solutions
Full text linkA new method for the numerical simulation of the radiation chemistry of aqueous polymer solutions is introduced. The method makes use of a deterministic approach combining the conventional homogeneous radiation chemistry of water with the chemistry of polymer radicals and other macromolecular species. The method is applied on single-pulse irradiations of aqueous polymer solutions. The speciation of macromolecular species accounts for the variations in the number of alkyl radicals per chain, molecular weight, and number of internal loops (as a consequence of an intramolecular radical-radical combination). In the simulations, the initial polymer molecular weight, polymer concentration, and dose per pulse (function of pulse length and dose rate during the pulse) were systematically varied. In total, 54 different conditions were simulated. The results are well in line with the available experimental data for similar systems. At a low polymer concentration and a high dose per pulse, the kinetics of radical decay is quite complex for the competition between intra- and intermolecular radical-radical reactions, whereas at a low dose per pulse the kinetics is purely second-order. The simulations demonstrate the limitations of the polymer in scavenging all the radicals generated by water radiolysis when irradiated at a low polymer concentration and a high dose per pulse. They also show that the radical decay of lower-molecular-weight chains is faster and to a larger extent dominated by intermolecular radical-radical reactions, thus explaining the mechanism behind the experimentally observed narrowing of molecular weight distributions
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