Effect of different processing techniques and presence of antioxidant on the chitosan film performance

In the last two decades, the naturally occurring polysaccharides have gained great attention because of their potential applications in different sectors, for example, from food to biomedical sectors. Chitosan is a cationic polysaccharide with good transparency, and currently, it has been considered also as suitable material for the formulation film and coating in cultural heritage protection. In this work, the chitosan films (Ch), with and without natural antioxidant such as citric acid (CA), are formulated considering two different processing techniques: (i) conventional solvent casting and (ii) compression molding, that is an unconventional method for this polysaccharide, giving the possibility to formulate films with extended surface and constant thickness. The effects of processing conditions and antioxidant presence on the properties and performance are evaluated by thermo-gravimetric analysis, FTIR and UV-visible spectroscopy, water contact angle measurements and tensile test. Besides, the durability of all investigated Ch and Ch/CA has been evaluated subjecting thin film to UVB exposure and monitoring their structural changes by FTIR analysis in time. All obtained results suggest that the chitosan films can be processed successfully by both solvent casting and compression molding techniques. Further, the CA presence in Ch films has a beneficial effect on the thermal resistance and durability and no negative effect on the transparency and optical properties

Flexible Perfluoropolyethers-Functionalized CNTs-Based UHMWPE Composites: A Study on Hydrogen Evolution, Conductivity and Thermal Stability

Flexible conductive composites based on ultra-high molecular weight polyethylene (UHMWPE) filled with multi-walled carbon nanotubes (CNTs) modified by perfluoropolyethers (PFPEs) were produced. The bonding of PFPE chains, added in 1:1 and 2:1 weight ratios, on CNTs influences the dispersion of nanotubes in the UHMWPE matrix due to the non-polar nature of the polymer, facilitating the formation of nanofillers-rich conductive pathways and improving composites' electrical conductivity (two to five orders of magnitude more) in comparison to UHMWPE-based nanocomposites obtained with pristine CNTs. Electrochemical atomic force microscopy (EC-AFM) was used to evaluate the morphological changes during cyclic voltammetry (CV). The decrease of the overpotential for hydrogen oxidation peaks in samples containing PFPE-functionalized CNTs and hydrogen production (approximately -1.0 V vs. SHE) suggests that these samples could find application in fuel cell technology as well as in hydrogen storage devices. Carbon black-containing composites were prepared for comparative study with CNTs containing nanocomposites

Hybrid supramolecular gels of Fmoc-F/halloysite nanotubes: systems for sustained release of camptothecin

Supramolecular gel hybrids obtained by self-assembly of Fmoc-L-phenylalanine (Fmoc-F) in the presence of functionalized halloysite nanotubes (f-HNT) were obtained in biocompatible solvents and employed as carriers for the delivery of camptothecin (CPT) molecules. The synthesis of the new f-HNT material as well as its characterization are described. The properties of the hybrid hydrogels and organogels were analyzed by several techniques. The presence of small amounts of f-HNT allows good dispersion of the tubes and the subsequent formation of homogeneous gels. The experimental results show that f-HNT functions only as an additive in the hybrid gels and does not demonstrate gelator behavior. The in vitro kinetic release from both f-HNT/CPT and Fmoc-F/f-HNT/CPT was studied in media that imitates physiological conditions, and the factors controlling the release process were determined and discussed. Furthermore, the antiproliferative in vitro activities of the gels were evaluated towards human cervical cancer HeLa cells. A comparison of data collected in both systems shows the synergistic action of f-HNT and the gel matrix in controlling the release of CPT in the media and maintaining the drug in its active form. Finally, a comparison with pristine HNT is also reported. This study suggests a suitable strategy to obtain two-component gel hybrids based on nanocarriers with controlled drug carrier capacity for biomedical applications

On the interlayer spacing collapse of Cloisite (R) 30B organoclay

When used as a nanofiller for the preparation of polymer/clay nanocomposites (PCNs), Cloisite (R) 30B (30B) often undergoes a d-spacing collapse, as demonstrated by a shift to wider angles of the XRD basal reflection. Such collapse has been variously attributed to organoclay contamination or, more often, to thermal degradation of the organic modifier with expulsion of the volatile products from the galleries. In this work, several PCNs loaded with 30B have been prepared by melt compounding, using different polymer matrices, and have subsequently been subjected to dissolution in appropriate solvents followed by precipitation in excess non-solvent and room temperature drying. An XRD analysis of the products has shown that this treatment makes the 30B basal plane reflection go back to the original angular position. These experiments indicate that, contrary to the situation prevailing when 30B is subjected to thermal treatments at temperatures well above the onset of degradation (similar to 180 degrees C), the d-spacing collapse observed after melt compounding 30B with polymer matrices at moderate temperatures is in fact a reversible phenomenon probably due to rearrangement of the alkyl chains of the clay modifier in a disposition intermediate between bilayer and monolayer. (C) 2011 Elsevier Ltd. All rights reserved

Effects of filler type and processing apparatus on the properties of the recycled "light fraction" from municipal post-consumer plastics RID E-1751-2011

Plastic waste or scraps are generated from two main sources: industrial wastes and post-consumer wastes. By using the flotation method, generally two fractions are obtained from municipal post-consumer wastes: a light fraction, floating on water, and a heavy fraction. The former is essentially made of low and high density polyethylene - LDPE, HDPE - and polypropylene - PP, the heavy fraction is formed by poly(vinyl chloride) PVC - and poly(ethylene terephthalate) - PET. In this work, the recycling of a light fraction from municipal post-consumer plastics has been studied, considering also the effect of filler type - glass fibres, calcium carbonate and wood fibres - and processing apparatus - discountinous mixer, single and twin screw extruder - on the properties. Although the similar chemical nature of the two main components, polyethylene and polypropylene of the light fraction, the mechanical properties of the recycled mixture are quite scarce, mainly because of the incompatibility and the possible presence of some heterogeneous particles. The recycling of the light fraction can significantly change the properties of the polymer system because of the thermomechanical stress and of the residence time during processing. The adding of the three fillers type leads to an increase of the thermomechanical and of some of the mechanical properties. The elastic modulus increases with the three fillers, in particular, glass fibres show the best results. The effect of the three fillers is quite similar for tensile strength, elongation at break and impact strength. The adding of inert filler strongly improves the rigidity of light fraction from municipal post-consumer plastics. Copyright (C) 2001 John Wiley & Sons, Ltd

Characterization and reprocessing of greenhouse films RID E-1751-2011

Films for greenhouses are an attractive source of post-consumer plastic materials because they are mainly made of polyethylene and can be easily collected in large amounts in small zones. The types of polymers for this application are, however, increasing and the films contain not only additives and stabilisers, but also fertiliser and pesticide residues. Finally, the extent of photooxidative degradation undergone during the use can strongly influence the recycling operations and the final properties of the secondary material. In this work, a complete characterisation of post-consumer films for greenhouses has been carried out and the properties of the recycled material have been correlated with the number of reprocessing steps and compared with those obtained by reprocessing virgin scraps of the same composition. The presence of small amounts of low molecular weight compounds (photooxidized species and pesticide residues) does not compromise the use of the recycled plastic in many applications. The mechanical properties decrease with the number of reprocessing steps and with increasing level of photooxidative degradation but are good enough for many applications. (C) 2001 Elsevier Science Ltd. All rights reserved