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Abstract: Polyamide 6 (PA6)/clay nanocomposites, based on organo-modified and pristine (i.e. purified but non-modified) montmorillonite, were prepared using a water-assisted extrusion process based on the injection of water during extrusion. The formation of a single PA6/water phase during extrusion (shown by High Pressure Differential Scanning Calorimetry (HPDSC)) improves the clay dispersion, decreases the PA6 melting temperature by 66°C (so-called cryoscopic effect), and thus prevents the polymer matrix degradation during processing. This process enables the compounding of pristine clay-based nanocomposites whose dispersion state, thermal and mechanical performances are close to what is generally reported for organo-modified montmorillonite-based nanocomposites. Advantage was taken of water-assisted extrusion to optimize the clay dispersion by increasing shear rate and of the cryoscopic effect to limit the degradation by decreasing the processing temperature. Using these conditions PA6/pristine clay nanocomposites properties are similar to those of more conventional PA6/organomodified clay nanocomposites. [Copyright &y& Elsevier]

Abstract: Polypropylene (PP)/multi-wall carbon nanotubes (MWNTs) nanocomposites were prepared by diluting a PP/MWNT masterbatch by melt compounding with a twin screw extruder and prepared nanocomposites were characterized for their rheological, mechanical and morphological properties in terms of MWNT loading. The rheological results showed that the materials experience a fluid–solid transition at the composition of 2wt.%, beyond which a continuous MWNT network forms throughout the matrix and in turn promotes the reinforcement. The tensile modulus and yield stress of the nanocomposites are substantially increased relative to the neat polypropylene. Nanotube reinforcement thus enhanced the yield stress, while reducing the ductility. The same behavior is observed in flexural tests. Charpy impact resistance of the notched samples increases slightly by the addition of MWNT, while impact resistance for the un-notched samples decreases with the addition of MWNTs. Finally, optimum in mechanical properties was observed at 2wt.% MWNTs, which is near the rheological percolation threshold. From transmission electron microscopic (TEM) and scanning electron microscopy (SEM) images, it was observed that nanotubes are distributed reasonably uniformly indicating a good dispersion of nanotubes in the PP matrix. These results reveal that, preparation of nanocomposites from masterbatch dilution is an excellent method to obtain well-dispersed CNTs, while limiting the handling difficulties in plastics processing industrial workshops. [Copyright &y& Elsevier]

The aim of this paper is to understand the influence of plasticizer and plasticizer amount on the mechanical and deformation behaviors of plasticized starch. Glycerol, sorbitol and mannitol have been used as plasticizers. After extrusion of the various samples, dynamic mechanical analyses and video-controlled tensile tests have been performed. It was found that the nature of plasticizer, its amount as well as the aging of the material has an impact on the involved deformation mechanism. The variations of volume deformation could be explained by an antiplasticization effect (low plasticizer amount), a phase-separation phenomenon (excess of plasticizer) and/or by the retrogradation of starch. [ABSTRACT FROM AUTHOR]

Abstract: Novel bionanocomposites based on halloysite nanotubes as nanofillers and plasticized starch as polymeric matrix were successfully prepared by melt-extrusion for the first time. Both modified and non modified halloysites were added at different weight contents. The structural, morphological, thermal and mechanical properties of plasticized starch/halloysites nanocomposites were investigated. Melt-compounding appears to be a suitable process to uniformly disperse nanotubes in the plasticized starch matrix. Interactions between plasticized starch and halloysites in the nanocomposites and microstructure modifications were monitored using Fourier transfer infrared spectroscopy, X-ray diffraction and dynamic mechanical analysis. Addition of halloysite nanotubes slightly enhances the thermal stability of starch (onset temperature of degradation delayed to higher temperatures). The tensile mechanical properties of starch are also significantly improved (up to +144% for Young''s modulus and up to +29% for strength) upon addition of both modified and unmodified halloysites, interestingly without loss of ductility. Modified halloysites lead to significantly higher Young''s modulus than unmodified halloysites. [Copyright &y& Elsevier]

The relative importance of crosslinking and chain scissions reactions involved in the photothermal ageing of polycarbonates is shown to depend on the chemical structure of the polymer. The orientation of these reactions is linked to the modifications of the chemical structure resulting from photolysis, photooxidation and thermooxidation. In this paper, the effects of crosslinking and chain scission of tetramethyl bisphenol-A polycarbonate (TMPC) are determined by size exclusion chromatography (SEC) and gel fraction measurements. These evolutions are correlated to the modifications of the chemical structure observed by FTIR spectroscopy.The presence of the four ortho-methyl substituants on the aromatic rings accounts for the difference in the photothermal ageing of TMPC compared to bisphenol-A polycarbonate (PC). Tetramethyl substitution inhibits photo-Fries rearrangements in TMPC, but in contrast these methyl groups involve crosslinks under irradiation and are the source of a higher oxidizability of TMPC compared to PC. A proposal for the various routes accounting for the crosslinking and the formation of the oxidation products in TMPC is reported in this paper. [Copyright &y& Elsevier]

Starch was combined with plasticizers such as glycerol, sorbitol, glycerol/sorbitol and urea/ethanolamine blends by means of high shear extrusion process to prepare thermoplastic starch (TPS). Effect of storage time and plasticizers on the structural stability of melt processed TPS was investigated. Morphological observation, X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy reveal that melt extrusion process is efficient in transforming granular starch into a plasticized starch for all plasticizer compositions. XRD analysis highlights major changes in the microstructure of plasticized starch, and dependence of crystalline type and degree of crystallinity mainly on the plasticizer composition and storage time. Dynamical mechanical analysis (DMA) yields a decrease of the peak intensity of loss factor with aging time. The effect of ageing on tensile strength also appears to be highly dependent on the plasticizer composition. Thus, through different plasticizer combinations and ageing, starch-based materials with significant differences in tensile properties can be obtained, which may be tuned to meet the requirements of a wide range of applications. [ABSTRACT FROM AUTHOR]

The impact of organomodified montmorillonite on morphology, thermal and barrier properties of PHBV-based nanocomposites prepared by melt intercalation was investigated. XRD analyses and TEM observations have shown the presence of aggregated and intercalated structures with individual nanoclay platelets and a significant orientation of nanoclays into the nanocomposites. No nucleating effect induced by nanoclays was detected in DSC measurements, which indicates that the crystalline phase of the PHBV copolymer was not impacted. The improvement of barrier properties to gas and water was found to be dependent not only on the dispersion and orientation of nanoclays but also the nature of permeated molecules, the quality of the matrix/nanoclays interface and degradation effects induced during melting process. A competition between kinetic and thermodynamic contributions of the permeation process was highlighted. A dependence of the water diffusion coefficient with water concentration was observed as a result of water plasticization effect. [ABSTRACT FROM AUTHOR]

Abstract: Polymer based nanocomposites are a new broad class of materials widely used in a large range of applications as they generally exhibit improved properties compared with the neat polymer. These materials have been known for a few decades and they have been widely studied in academia and industries, regarding their preparation and properties characterization. More recently, environmental, health and public concerns related to air quality have imposed severe worldwide rules regarding the emissions of Volatile Organic Compounds (VOCs), odours and nanoparticles from such materials. Indeed some studies have shown that they may exhibit some risks to human health. In this study, measurements of VOCs, odours and nanoparticles emissions have been carried out on polyether-block-amide copolymer (PEBA) clay nanocomposites. Both the processing and the storage stages have been investigated. These measurements revealed that nanocomposites based on Cloisite™ 30B exhibit stronger odour than sodium montmorillonite (MMT) and that this may constitute a significant drawback for industrial applications despite their outstanding properties. This behaviour has been explained considering the nature of the emitted VOCs (Volatile Organic Compounds). Particularly it has been highlighted that potentially unhealthy compounds can be emitted during the storage of the material. Moreover, another processing route has been tested as an alternative to the use of organo-modified clays. This consists in injecting water during extrusion, with the aim of dispersing untreated MMT in order to get an exfoliated morphology. Measurements have revealed that in addition to substantial savings that can be achieved using this method, it also reduces emissions both during processing and further use, as compared with conventional processes. [Copyright &y& Elsevier]