1,721,089 research outputs found
Permeation of methanol/methyl-t-butyl ether mixtures through poly(ethylene-co-vinyl acetate) films
No full textThe permeation of methanol and methyl-t-butyl ether (MTBE) liquid mixtures through poly(ethylene-co-vinyl acetate) (EVAc) films of different compositions have been investigated. Experiments were performed by contacting the polymer film with a liquid mixture and removing the vapour on the other side with an inert gas flux, a set-up for a membrane process of pervaporation with sweeping gas. In the presence of the liquid mixture, the membranes swell to an extent that increases as the vinyl acetate content in the membrane or the MTBE in the liquid increase. This behaviour can be explained by two main factors: the crystalline content of the polymer and the distance between the polar solubility parameters of the liquid mixture and the centre point of the copolymer solubility sphere. The pervaporation results evidence a methanol higher permeability with low separation factors for all the membrane compositions and high fluxes, which increase with the membrane swelling. Very high flux values have been observed for the copolymer with the greatest vinyl acetate content at liquid composition close to the azeotropic one. In steady state conditions, the permeants showed a Fickian behaviour which allowed to evaluate the activation energy of the diffusion process through the membranes. © 2004 Elsevier B.V. All rights reserved
UV-curable coatings for energy harvesting applications: Current state-of-the-art and future perspectives
No full textGenerally speaking, energy harvesting is an up-to-date technology that describes the possibility of capturing small amounts of energy (thermal, solar, or mechanical) from the surroundings and storing them as electrical energy for later uses when needed. Among the energy harvesting systems, the use of piezoelectric thin films and coatings is gaining increasing interest from both the academic and industrial communities, as these systems allow for the design and development of micro- and nano-scale devices, thanks to the possibility of being micromachined and to the added functionality offered by the electromechanical coupling. These peculiarities justify their use for different applications, ranging from high energy density harvesters to high sensitivity sensors, and even low power consumption and large displacement actuators. Further, the current focus of the research on piezoelectric energy harvesting coatings is shifting from fully inorganic to hybrid organic-inorganic (i.e., composite) systems, as the latter can offer higher flexibility (i.e., lower stiffness), making them more sensitive to small vibrations and therefore suitable for these specific harvesting conditions. In this regard, photoinduced polymerization (the so-called "UV-curing") has become a suitable and reliable technique for the manufacturing of piezoelectric composite systems, as it is a solvent-free approach that allows for transforming a liquid mixture of monomers/oligomers into a solid 3D network in a few seconds, with a very limited energy consumption and a very high conversion. Besides, as the UV-curing process is very fast, the dispersed ceramic piezoelectric phase is not prone to settle down in the liquid resin, hence ensuring its homogeneous distribution within the polymer network after curing and better piezoelectric performance. The present review aims to provide the reader with an up-to-date overview of UV-curable coatings for piezoelectric energy harvesting purposes, highlighting their potential and piezoelectric features; further, some perspectives about possible future developments will be proposed
Recycling of polyurethanes: where we are and where we are going
Full text linkPolyurethanes (PUs) represent a family of useful synthetic polymers (thermoplastic or thermosetting) obtained from diisocyanates and diols/polyols via polycondensation reactions. Within the circular economy concept and also considering the current need for limiting the environmental impact of plastics, several methods have been designed, assessed, and exploited for the recovery at the end-of-life of polyurethanes and for their recycling. Indeed, the processing of polyurethane wastes can be significantly beneficial not only from an ecological but also from an economic point of view. At present, feedstock (namely, glycolysis) and mechanical recycling are the two most important strategies to recover and recycle polyurethanes; notwithstanding, “biological recycling”, an approach that exploits the biological degradation of the polymer, is gaining interest. This review aims to elucidate the recycling processes of both thermoplastic and thermosetting polyurethanes, providing the reader with some perspectives about their possible future developments
Insights into the effect of different macromolecular architectures on the charring ability of polyethylene
Full text linkThe induction period preceding the ignition is a fundamental stage in controlling the protection of polymeric materials from fire. In fact, at this stage, the formation of a non-pyrolyzable carbonaceous layer (char) onto the material surface could prevent the development of a sustained flame, hence delaying or preventing polymer burning. In this work, the charring ability of four samples of high- and low-density polyethylene was evaluated in different scenarios, namely isothermal oxidative conditions and cone calorimetry tests at different heat fluxes, aiming at assessing the possible influence of the polymer macromolecular architecture on their charring ability. First, the selected polymers were characterized from a thermal and rheological point of view; the obtained results allowed for disclosing the different microstructure of the materials, in terms of molecular weight and possible presence of short- or long-chain branching. Then, isothermal thermogravimetric analyses and cone calorimetry tests were performed, demonstrating a different charring ability of the investigated polyethylenes. Finally, the observed behaviours were correlated to the different chemical structure and to the specific macromolecular architecture of the polymers, allowing a systematic evaluation of the relationship between the molecular weight or the presence of branched structures and the mechanism and rate of char formation
New vistas in frontal polymerization
No full textFrontal Polymerization is a technique for the synthesis of polymers that, by exploiting the heat liberated by the self-same reaction. generates a hot front that can sustain and propagate itself from one end of the reactor to the other converting monomer into polymer. After the acivation and following formation of the front. it is not necessary, to provide any other form of energy in order to carry out polymerization. In this article we will summarize some of the recent results we have obtained in the application of Frontal Polymerization to the preparation of polyurethanes, unsaturated polyester resins, and polyacrylates
Synthesis and Characterization of a Polyester/Styrene Resin Obtained By Frontal Polymerization
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