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Wei P.,Shanghai JiaoTong University | Bocchini S.,Center for Space Human Robotics Polito | Camino G.,Polytechnic University of Turin
European Polymer Journal

This paper addresses the combustion behaviour of polylactide (PLA) nanocomposites based on organomodified montmorillonite clays. It is shown that PLA nanocomposites burn in a very different way compared to virgin PLA. Indeed, nanocomposites burning rate is usually lower respect to PLA, with a rate decrease depending on clay type and concentration. However, an easier ignition is shown by PLA nanocomposites as compared to PLA which is due to a catalytic effect of the clays. It is shown that these peculiar features of nanocomposites burning behaviour may prevent reliable comparison between polymers and nanocomposites based only on a single parameter such as UL 94 test ranking or the Limiting Oxygen Index value (LOI). It is also shown that by an extended use of data provided by the LOI apparatus, the peculiarities of nanocomposites combustion process are easily detected. © 2012 Elsevier Ltd. All rights reserved. Source

Bocchini S.,Center for Space Human Robotics Polito | Frache A.,Polytechnic University of Turin
Express Polymer Letters

Polylactide (PLA) based nanocomposites of organically modified montmorillonite and micro-talc based microcomposites were prepared with different compositions and were UV-light irradiated under artificial accelerated conditions representative of solar irradiation. The chemical modifications resulting from photo-oxidation were followed by infrared (IR) and ultraviolet (UV)-visible spectroscopies. The infrared analysis of PLA photooxidation shows the formation of a band at 1847 cm-1 due to the formation of anhydrides. The filler addition provokes an increase of anhydride formation rate dependent on filler nature, amount and dispersion degree on the matrix. The main factors that influence oxidation rate are the total extension of polymer/filler interfacial area and the presence of transition metal impurities of clays. © BME-PT. Source

Griffini G.,Polytechnic of Milan | Bella F.,Polytechnic University of Turin | Bella F.,Center for Space Human Robotics Polito | Nisic F.,University of Milan | And 5 more authors.
Advanced Energy Materials

A new multifunctional coating for photovoltaic cells incorporating light-management, UV-protection, and easy-cleaning capabilities is presented. Such coating consists of a new photocurable fluorinated polymer embedding a luminescent europium complex that acts as luminescent down-shifting (LDS) material converting UV photons into visible light. The combination of this system with ruthenium-free organic dye-sensitized solar cells (DSSCs) gives a 70% relative increase in power conversion efficiency as compared with control uncoated devices, which is the highest efficiency enhancement reported to date on organic DSSC systems by means of a polymeric LDS layer. Long-term (>2000 h) weathering tests in real outdoor conditions reveal the excellent stabilizing effect of the new coating on DSSC devices, which fully preserve their initial performance. This excellent outdoor stability is attributed to the combined action of the luminescent material that acts as UV-screen and the highly photostable, hydrophobic fluoropolymeric carrier that further prevents photochemical and physical degradation of the solar cell components. The straightforward approach presented to simultaneously improve performance and outdoor stability of DSSC devices may be readily extended to a large variety of sensitizer/luminophore combinations, thus enabling the fabrication of highly efficient and extremely stable DSSCs in an easy and versatile fashion. A new multifunctional coating system based on a photocurable fluoropolymer that incorporates luminescent-down shifting, UV-screening, and easy-cleaning functionalities is presented. The use of such coating in organic dye-sensitized solar cell (DSSC) devices allows for significant improvement of the power conversion efficiency of uncoated devices and imparts outstanding long-term device stability in real outdoor operating conditions. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

Battezzato A.,Center for Space Human Robotics Polito
Mechanism and Machine Theory

The current paper deals with the kinetostatic analysis and consequent optimization of an underactuated mechanism, whose aim is to constitute an exoskeleton device, designed to enhance the force of the human finger with whom it is coupled. Given an exoskeleton architecture, optimal from the point of view of the simplicity, the geometric parameters are further optimized, to let the transmitted forces be as similar as possible to the specific force profile, set as a reference for the device. In particular, extra-vehicular activity (EVA) for astronauts is recognized as a possible field for hand exoskeletons, since EVA gloves are very demanding in terms of strength and fatigue. Thus, the force profile for a specific EVA glove is provided as an example, and different optimized devices are obtained from the stochastic optimization process. Their kinetostatic performances are hence analyzed and discussed, thanks to a properly defined performance index. Finally, a verification of the actual encumbrance of the synthesized structure is performed, with respect to EVA-specific constraints. © 2014 Elsevier Ltd. Source

Bella F.,Center for Space Human Robotics Polito | Bella F.,Polytechnic University of Turin | Bongiovanni R.,Polytechnic University of Turin
Journal of Photochemistry and Photobiology C: Photochemistry Reviews

Dye-sensitized solar cells (DSSCs) have attracted large attention due to their easy fabrication, low cost and high conversion efficiency. One of the major problems limiting the long-term stability of these devices is the volatilization of the liquid electrolytes traditionally used. To solve this problem and improve technological perspectives of DSSCs, many recent studies have been addressed to the preparation of quasi-solid electrolytes, in which a polymer network is able to effectively retain the redox mediator and its additives. In this context, photoinduced polymerization is increasingly proving to be the most effective method of preparation of these polymer electrolytes, since it is a rapid, economic, functional and environmentally friendly process, besides being easily transferable to the industrial scale. This review focuses on the techniques adopted for the preparation of UV-cured quasi-solid electrolytes, on the expedients designed to overcome the inhibition phenomena typical of some photoinitiated mechanisms, and on the evaluation of photoelectric performance obtained in presence of these photopolymer electrolytes. © 2013 Elsevier B.V. Source

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