Showing papers in "Express Polymer Letters in 2019"

Recent progress on natural fiber hybrid composites for advanced applications: A review

Abstract: Natural fibers, as replacement of engineered fibers, have been one of the most researched topics over the past years. This is due to their inherent properties, such as biodegradability, renewability and their abundant availability when compared to synthetic fibers. Synthetic fibers derived from finite resources (fossil fuels) and are thus, affected mainly by volatility oil prices and their accumulation in the environment and/or landfill sites as main drawbacks their mechanical properties and thermal properties surpass that of natural fibers. A combination of these fibers/fillers, as reinforcement of various polymeric materials, offers new opportunities to produce multifunctional materials and structures for advanced applications. This article intends to cover recent developments from 2013-up to date on hybrid composites, based on natural fibers with other fillers. Hybrid composites preparation and characterization towards their applicability in advanced applications and the current challenges are also presented.

Microwave treatment in waste rubber recycling – Recent advances and limitations

Abstract: Environmentally-friendly microwave heating is increasingly used in polymer chemistry and technology The selectivity and highly efficiency in the heat transfer present a huge advantage in systems based on recycling, improving their productivity and economic competitiveness In case of the industrial recycling of waste rubbers, especially end-of-life tires, microwave-induced devulcanization and pyrolysis are nowadays considered as promising approaches This work aims to report the recent progress in microwave treatments of vulcanized rubbers with different compositions Special attention is focused on the correlation between microwave processing parameters and devulcanization/pyrolysis efficiency, which have a significant impact on the structure-property relationships of the obtained products Moreover, the main challenges affecting the future of the industrial application of the microwave technology in rubber recycling are also discussed

Polylactic acid-lauryl functionalized nanocellulose nanocomposites: Microstructural, thermo-mechanical and gas transport properties

Abstract: Thermo-mechanical and gas transport properties of polylactic acid (PLA) matrix containing various amounts (from 1 to 20 wt%) of nanocellulose esterified with lauryl chains (LNC) were investigated on solvent cast film of about 50 micron. Scanning electron microscopy indicated that, up to a filler content of 6.5 wt%, LNC was well dispersed or formed small, sub-micrometric clusters. At higher filler contents, oval aggregates in the micrometric range were detected. The addition of LNC did not change the matrix glass transition temperature and melting temperature. Concurrently, as LNC content increased, both elastic and storage moduli at room temperature exhibited a sharp decrease up to 5 wt% of filler, and a lower reduction for LCN concentration of 10–20 wt.%. Nanocomposites with 3 and 5 wt% of LNC showed the highest strain at break and a large amount of plastic deformation due to a strong interfacial adhesion between the PLA and filler particles. For higher LNC fractions the presence of aggregates weakened the nanocomposite leading to lower values of maximum stress and strain at break. With the addition of LNC particles, gas barrier properties of the PLA film versus deuterium, nitrogen and carbon dioxide were improved up to a critical LNC concentration of 6.5 wt%, where the gas permeability of the nanocomposite resulted to be 70% lower than that of the PLA matrix. At higher filler contents, large LNC aggregates increased the gas permeability of the nanocomposites.

Barium titanate/epoxy resin composite nanodielectrics as compact capacitive energy storing systems

Abstract: Barium titanate/epoxy resin composite nanodielectrics were manufactured and their capability to store and harvest energy, upon request under DC conditions, was studied in this work. Morphological characterization in all nanocomposites was performed via scanning electron microscopy images and X-ray diffraction spectra, indicating the successful nanofiller’s integration and dispersion within the polymer matrix. Applied DC voltage level varied from 10 to 240 V and the measurements were performed in the temperature range from 30 to 160 °C. Filler content enhances the energy efficiency of the manufactured systems, reaching the highest value of 58.2% for the 7 phr BaTiO3 nanocomposite. Increase of temperature results in an ex- ponential decay of the coefficient of energy efficiency (neff), indicating leakage currents’ augment. DC and AC conductivity have been determined as a function of temperature for all nanodielectric systems. The temperature dependence of conductivity under DC and AC condition follows an Arrhenius form, which allowed the determination of activation energy in both cases.

Properties of biobased epoxy resins from epoxidized linseed oil (ELO) crosslinked with a mixture of cyclic anhydride and maleinized linseed oil

Abstract: This work has been supported by the Spanish Ministry of Economy and Competitiveness, PROMADEPCOL (MAT2017-84909-C2-2-R). MDS is recipient of a APOSTD2018 contract (APOSTD/2018/209) from Conselleria d'Educacio, Investigacio, Cultura y Esport de la Generalitat Valenciana.

Processing keratin from camel hair and cashmere with ionic liquids

Abstract: Keratin, a fibrous protein, that is available from a variety of animal sources as a constituent of hair, nails, horns, hoofs, wool and feathers, has applications in pharmaceutics, cosmetics and as a fertilizer. Like many naturally-derived biomaterials, the intrinsic biological activity and biocompatibility of keratin render this polymer a potential candidate for applications in medicine, and for the fabrication of scaffolds for tissue engineering. While several sources of keratin can be considered, the bioactivity of the keratins obtained can be quite different. In this study we discuss the processing and characterization of keratin from camel hair and goat cashmere. Specifically, the camel hair and cashmere were dissolved in an ionic liquid (1-butyl-3-methylimidazolium chloride), and the characteristics of the soluble and insoluble keratin were evaluated. The structure and properties of the raw material, soluble, and insoluble keratin were studied. Compared to the starting material, the soluble keratin showed chemical changes viz. decrease of cysteine, and minor structural changes. Preliminary in vitro biological properties performed by a lactate dehydrogenase (LDH) assay and scratch test showed good bioactivity in keratin from both sources. In particular, cell migration was observed to be faster when cells were cultured in the presence of soluble keratin extracted from camel hair and cashmere.

Electrospinning scale-up and formulation development of PVA nanofibers aiming oral delivery of biopharmaceuticals

Abstract: Electrospinning is a promising drying technology providing a rapid and gentle drying at ambient temperature, thus electrospinning of polyvinyl alcohol aqueous solutions was investigated for the solid formulation of biopharmaceuticals. The commonly used single-needle electrospinning does not have adequate productivity to satisfy the industrial requirements, therefore our aim was to study the scale-up of the technology by using high-speed electrospinning. High molecular weight polyethylene oxide as a secondary polymer was applied to enhance the fiber formation of polyvinyl alcohol. While polyvinyl alcohol-polyethylene oxide formulations resulted in adequate fiber formation it was not possible to process them further as the friability of the fibers was too low. In order to increase the friability, the effect of adding various sugars (mannitol, glucose, lactose, saccharose, and trehalose) was investigated. The results showed that mannitol was the best friability enhancing excipient because of its crystallinity and low moisture content in the fibrous sample. In contrast, glucose, lactose, saccharose, and trehalose were amorphous with higher moisture content and fibers containing these were grindable only after post-drying.

Light induced grafting-from strategies as powerfull tool for surface modification

Abstract: Chemical-induced grafting processes can be performed either by a grafting-to method, where preformed polymer chains are grafted on the surface previously activated, or alternatively, the polymer chains can be grown from the surface via a grafting-from method. The last one can be considered a bottom-up approach in which polymers are generated directly on the surface starting from their precursors. As a preliminary process, the substrate is functionalized with specific groups that can initiate a polymerization reaction. Although surface-initiated polymerizations are conventionally induced by a thermal initiator or directly by radicals formed by high energy treatment of the surface, they can be triggered by light. In this regard, light-induced grafting reactions have recently found increasing interest. With this review, by placing emphasis on the initiating system, we aim to show the significant feasibility of photografting-from method to properly functionalize any type of surface.