Search results for "Gradation"
showing 10 items of 1275 documents
Enhanced operational stability through interfacial modification by active encapsulation of perovskite solar cells
2020
Encapsulates are, in general, the passive components of any photovoltaic device that provides the required shielding from the externally stimulated degradation. Here we provide comprehensive physical insight depicting a rather non-trivial active nature, in contrast to the supposedly passive, atomic layer deposition (ALD) grown Al2O3 encapsulate layer on the hybrid perovskite [(FA0.83MA0.17)0.95Cs0.05PbI2.5Br0.5] photovoltaic device having the configuration: glass/FTO/SnO2/perovskite/spiro-OMeTAD/Au/(±) Al2O3. By combining various electrical characterization techniques, our experimental observations indicate that the ALD chemistry produces considerable enhancement of the electronic conductiv…
Pickering Emulsions of Fluorinated TiO2: A New Route for Intensification of Photocatalytic Degradation of Nitrobenzene
2020
International audience; Fluorination of the TiO2 surface has been often reported as a tool to increase the photocatalytic efficiency due to the beneficial effects in terms of production of oxidizing radicals. Moreover, it is shown that the unique amphiphilic properties of the fluorinated TiO2 (TiO2-F) surface allow one to use this material as a stabilizer for the formulation of Pickering emulsions of poorly soluble pollutants such as nitrobenzene (NB) in water. The emulsions have been characterized in terms of size of the droplets, type of emulsion, possibility of phase inversion, contact angle measurements, and optical microscopy. The emulsified system presents micrometer-sized droplets of…
Thermomechanical properties and thermal degradation kinetics of poly(methyl methacrylate) (PMMA) and polycarbonate (PC) filled with cerium-doped yttr…
2016
This paper reports on the thermomechanical properties and thermal degradation kinetics of poly(methyl methacrylate) (PMMA) and polycarbonate (PC) composites filled with cerium-doped yttrium aluminium garnet (Ce:YAG) at different contents ranging between 0.1 and 5 wt%, and prepared by melt compounding. The interaction between PMMA and the filler was much stronger than that between PC and the filler, and this resulted in a significant improvement in the dynamic mechanical properties of the PMMA composites. The presence of filler did not significantly increase the thermal stability of the PC, while an observable increase in the thermal stability was only observed at higher filler loadings for …
Advanced ultra-high molecular weight polyethylene/antioxidant-functionalized carbon nanotubes nanocomposites with improved thermo-oxidative resistance
2015
Multiwalled carbon nanotubes (CNTs) functionalized with hindered phenol moieties are dispersed in ultra-high molecular weight polyethylene (UHMWPE), and the stabilizing action of the antioxidant (AO) functionalized CNTs (AO-f-CNTs) is studied through a combination of rheological and spectroscopic (FT-IR) analyses. The effectiveness of two alternative compounding methods, namely hot compaction (HC) and melt mixing (MM), is compared. The combination of high temperature and mechanical stress experienced during MM brings about noticeable degradation phenomena of the matrix already in the course of the compounding step. Differently, the milder conditions of the HC process preserve the stability …
Influence of small amounts of polyvinylchloride on the recycling of polyethyleneterephthalate
1999
Abstract Polyethylene terephthalate (PET), and polyvinyl chloride (PVC), are commonly encountered in plastics stream coming from separate collections of plastic bottles. The presence of PVC in the recycled PET is very dangerous because of the chain scission provoked by the hydrogen chloride evolved from the macromolecules during degradation of PVC. Recycled PET must be free of PVC; contents of PVC as little as 100 ppm can induce degradation and discoloration of the polyester. PET, in its turn, is degraded when the processing is carried out in the presence of water. In previous work, however, the degradation of PET was eliminated and rather an increase of the molecular weight has been measur…
Testing of a kinetics equation of mechanical degradation
1987
A modification of the kinetics equation of mechanical degradation of Harrington and Zimm is proposed to fit experimental data taken on a molten polystyrene. This equation is applied to each molecular weight of the discretized molecular weight distribution curve, and the limiting molecular weight is determined for each molecular weight. With this modification the theoretical curves fit both Mw and Mn curves well.
Long-term ISO 23936-2 sweet oil ageing of HNBR
2021
Abstract A hydrogenated nitrile butadiene rubber (HNBR) compound is subjected to ageing in a simulated oil and gas environment in accordance with ISO 23936-2 standard at two elevated temperatures (130 °C and 150 °C) for a period of up to 9 months. Shore D hardness, thermal expansion, dynamic mechanical analysis (DMA), Fourier transform infrared (FTIR) spectroscopy, compression and compression set (CS) measurements are made before and after the chemical exposure. The hardness, modulus at short times, degree of relaxation and CS increases while the coefficient of thermal expansion in HNBR tends to decrease with ageing time and temperature. Temperature is shown to impose a greater effect on th…
Reprocessing of PLA/graphene nanoplatelets nanocomposites
2017
This work reports a study on the effect of multiple reprocessing on the properties of poly(lactic acid) (PLA) filled with graphene nanoplatelets (GnP) compared to the melt reprocessed neat polymeric matrix. In particular, morphological, X-Ray Diffraction and Micro-Raman analyses, intrinsic viscosity measurements, thermal, rheological and mechanical tests were carried out on materials reprocessed up five times by means of a single screw extruder. The results indicated that the presence of GnP decreased the degradation rate as a function of the reprocessing cycles in comparison with the neat PLA that, on the contrary, showed a more drastic reduction of the molecular weight. Moreover, the repr…
Long-term thermomechanical degradation of molten polystyrene
1985
Abstract Rheological data on polystyrene samples processed for long periods under various mechanical stresses are presented. The data indicate that thermomechanical degradation occurs and that the rate of thermal degradation is increased by the applied stress. Moreover degradation does not reach a limiting value even at high processing times.
Material valorisation of amorphous polylactide. Influence of thermo-mechanical degradation on the morphology, segmental dynamics, thermal and mechani…
2012
[EN] This paper reports the effects of multiple mechanical recycling on the structure and properties of amorphous polylactide (PLA). The influence of the thermo-mechanical degradation induced by means of five successive injection cycles was initially addressed in terms of macroscopic mechanical properties and surface modification. A deeper inspection on the structure and morphology of PLA was associated to the thermal properties and viscoelastic behaviour. Although FT-IR analysis did not show significant changes in functional groups, a remarkable reduction in molar mass was found by viscometry. PLA remained amorphous throughout the reprocessing cycles, but the occurrence of a cold-crystalli…