Sergio Bocchini

Polylactic acid and polylactic acid-based nanocomposite photooxidation.

The importance of photooxidation in promoting formation of anhydride functional groups and thus promoting hydrolysis/biodegradation of polylactic acid and PLA nanocomposites were elucidated. PLA-based nanocomposites were prepared by adding 5% wt filler content of sodium montmorillonite (ClNa), sodium montmorillonite partially exchanged with Fe(III) (ClFe), organically modified montmorillonite (Cl20A), unmodified sepiolite (SEP), and fumed silica (SiO2). The pure PLA and nanocomposites were UV-light irradiated in artificial accelerated conditions representative of solar irradiation (λ > 300 nm) at 60 °C in air. The chemical modifications resulting from photooxidation were followed by IR and UV-visible spectroscopies. The infrared analyses of PLA photooxidation show the formation of a band at 1845 cm(-1) due to the formation of anhydrides. A photooxidation mechanism based on hydroperoxide decomposition is proposed. The mechanism proposed is confirmed by an increase in anhydride formation rate: the main responsible for this acceleration was identified as transition metals contained in the nanofillers as impurities and involved in the catalytic hydroperoxide decomposition.

Green and low-cost synthesis of PANI–TiO2 nanocomposite mesoporous films for photoelectrochemical water splitting

Among conductive polymers, polyaniline (PANI) has been widely used to improve electronic conductivity, solar energy transfer and photocatalytic activity of TiO2, due to its ease preparation and excellent environmental stability. In this study, a green and low-cost synthesis procedure was developed for the preparation of PANI–TiO2 nanocomposite films. A non-toxic and low-cost polymerization route, starting from aniline dimer and polystyrene sulphonate as emulsioning/doping agent in water, was employed to synthesize the conductive form of PANI (emeraldine salt, ES). Anatase TiO2 nanocrystalline mesoporous films were prepared by a novel and green sol–gel spin coating method, which employs titanium tetraisopropoxide, acetic acid and a nonionic surfactant (Tween 20) in excess of water, avoiding the use of flammable solvents. Uniform PANI–TiO2 composite films, containing PANI in either ES or pernigraniline base (PB) forms, i.e. PANI/TiO2 and PANIox/TiO2, respectively, were then prepared by a simple impregnation method. The films were characterized by means of XRD, ATR, FESEM and TEM techniques and their photocatalytic activity was assessed using them as photoelectrochemical water splitting photoanodes. Both PANI/TiO2 and PANIox/TiO2 showed an enhanced water oxidation efficiency under AM 1.5G simulated sunlight irradiation, reaching about 2 and 1.6 fold higher photocurrent densities, respectively, than a pure TiO2 nanoparticles film. They also demonstrated good stability after several hours of operation. UV-Vis spectrophotometry and IPCE analysis reveal the main role of PANI, in the system PANI/TiO2 for the PEC water oxidation, is as sensitizer of TiO2 in the UV light by significantly increasing charges separation, electrons transport and collected photoelectrons, indirectly contributing to the generation of O2. Indeed, PANI-ES photogenerated e− are transferred to the TiO2 conduction band while its h+ can react with OH− to produce OH radicals that generate H2O2, which can subsequently be photooxidized on the TiO2 NPs surface generating more O2 than such produced by the direct water oxidation on the TiO2 holes.

Silver nanoparticle ink technology: state of the art

Printed electronics will bring to the consumer level great breakthroughs and unique products in the near future, shifting the usual paradigm of electronic devices and circuit boards from hard boxes and rigid sheets into flexible thin layers and bringing disposable electronics, smart tags, and so on. The most promising tool to achieve the target depends upon the availability of nanotechnology-based functional inks. A certain delay in the innovation-transfer process to the market is now being observed. Nevertheless, the most widely diffused product, settled technology, and the highest sales volumes are related to the silver nanoparticle-based ink market, representing the best example of commercial nanotechnology today. This is a compact review on synthesis routes, main properties, and practical applications.

Synthesis of polyaniline-based inks for inkjet printed devices: Electrical characterization highlighting the effect of primary and secondary doping

Engineering applications for printed electronics demand solution processable electrically conductive materials, in the form of inks, to realize interconnections, piezoresistive pressure sensors, thermoresistive temperature sensors, and many other devices. Polyaniline is an intrinsically conductive polymer with modest electrical properties but clear advantages in terms of solubility and stability with temperature and in time. A comprehensive study, starting from its synthesis, primary doping, inkjet printing and secondary doping is presented, with the aim of elucidating the doping agent effects on its morphology, printability and electronic performance.

Ultraviolet mem-sensors: flexible anisotropic composites featuring giant photocurrent enhancement

By using two separate components, mem-sensing devices can be fabricated combining the sensitivity of a transducer with non-volatile memory. Here, we discuss how a mem-sensor can be fabricated using a single material with built-in sensing andmemory capabilities, based on ZnO microwires (MWs) embedded in a photocurable resin and processed from liquid by vertically aligning the MWs across the polymeric matrix using dielectrophoresis. This results in an ultraviolet (UV) photodetector, a device that is widely applied in fields such as telecommunication, health, and defense, and has so far implemented using bulk inorganic semiconductors. However, inorganic detectors suffer from very high production costs, brittleness, huge equipment requirements, and low responsivity. Here, we propose for the first time aneasy processable, reproducible, and low-cost hybrid UV mem-sensor. Composites with aligned ZnO MWs produce giant photocurrentscompared to the same composites with randomly distributed MWs. In particular, we efficiently exploit a mem-response where the photocurrent carries memory of the last electronic state experienced by the device when under testing. Furthermore, we demonstrate the non-equivalence of different wave profiles used during thedielectrophoresis: a pulsed wave is able to induce order in both the axis and the orientation of the MWs, whereas a sine wave only affects the orientation.

Isosorbide, a green plasticizer for thermoplastic starch that does not retrogradate.

Isosorbide is a non-toxic biodegradable diol derived from bio-based feedstock. It can be used for preparing thermoplastic starch through a semi-industrial process of extrusion. Isosorbide allows some technological advantages with respect to classical plasticizers: namely, direct mixing with starch, energy savings for the low processing temperature required and lower water uptake. Indeed, maize starch was directly mixed with the solid plasticizer and direct fed in the main hopper of a co-rotating twin screw extruder. Starch plasticization was assessed by X-ray diffraction (XRD) and dynamic-mechanical analysis (DMTA). Oxygen permeability, water uptake and mechanical properties were measured at different relative humidity (R.H.) values. These three properties turned out to be highly depending on the R.H. No retrogradation and changing of the material properties were occurred from XRD and DMTA after 9 months.

Rice husk as bio-source of silica: preparation and characterization of PLA–silica bio-composites

Silica powder has been extracted from rice husk employing a simple extraction procedure for preparing poly(lactic acid) bio-composites with differing filler contents (namely, 5, 10, 20 and 30 wt%). These materials have been obtained through a semi-industrial process of extrusion. The thermal, mechanical and morphological properties have been investigated. Despite a broad distribution of silica particle size, the prepared bio-composites have exhibited improved storage modulus and reduced oxygen permeabilities. The collected values at 10 and 30 wt% have been compared with those of homologous samples prepared using a commercial silica. Two micro-mechanical models (Voigt and Halpin–Tsai) have been used to also fit the mechanical data. Finally, an economic analysis of material and energetic costs has been performed on samples containing silica from rice husk in order to establish if the proposed process is sustainable or advantageous.

Ionic liquid-enhanced soft resistive switching devices

Resistive switching phenomena are of paramount importance in the area of memory devices. In the present study, we have fabricated a simple resistive switching device using a solution processable nanocomposite based on silver nitrate and poly(vinylidene fluoride-hexafluoropropylene). The change in resistance is ascribed to an initial ionic conduction, followed by a non-continuous field induced filament formation. The switching device fabricated with the above-mentioned active matrix displayed a volatile switching behavior. The addition of room temperature ionic liquid plays a fundamental role in triggering permanent memory and reducing the set voltage range up to ten-fold. The change in switching behavior with respect to the applied voltage bias and compliance level set during electrical characterization was studied thoroughly. The present work also gives a glimpse into the importance of device architecture on resistive switching phenomena.

MWNT Surface Self-Assembling in Fire Retardant Polyethylene-Carbon nanotubes nanocomposites

Abstract Multiwall carbon nanotubes (MWNT) were melt blended at different concentration with linear low density polyethylene (LLDPE). The nanotubes impart the fire-retardant characteristics to the polymer by formation of a thin protective film of MWNT/carbon char generated on the surface of the nanocomposites. The film formation mechanism is discussed

Polymeric materials as artificial muscles: an overview

Purpose The accurate selection of materials and the fine tuning of their properties represent a fundamental aspect in the realization of new active systems able to produce actuating forces, such as artificial muscles. In this regard, exciting opportunities for the design of new advanced systems are offered by materials belonging to the emerging class of functional polymers: exploiting their actuation response, specific devices can be realized. Along this direction, materials showing either shape-memory effect (SME) or shape-change effect (SCE) have been the subject of extensive studies aimed at designing of actuators as artificial muscles. Here, we concisely review active polymers in terms of properties and main applications in artificial muscle design. Structure The main aspects related to material properties in both shape-memory polymers (SMPs) and electroactive polymers (EAPs) are reviewed, based on recent scientific literature. SME in thermally activated SMPs is presented by preliminarily providing a definition that encompasses the new theories regarding their fundamental properties. EAPs are briefly presented, describing the working mechanisms and highlighting the main properties and drawbacks, in view of their application as actuators. For both classes of materials, some key examples of effective application in artificial muscles are offered. Outlook The potential in polymer architecture design for the fabrication of actively moving systems is described to give a perspective on the main achievements and new research activities.