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.

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Ethylene propylene diene monomer rubber (EPDM)-silica (SiO2) composites were pre- pared by means of an in situ sol–gel process with tetraethoxysilane (TEOS) as precursor and bis-[-3-(triethoxysilyl)-propyl]-tetrasulfide (TESPT) as coupling agent. Homogenous dispersion of the silica particles was observed in all cases, as well as good adhesion be- tween the filler and the matrix. The swelling and gel content results indicated that the number of crosslinks decreased, while the network was still extensive enough to maintain the high gel content. These results indicate that the coupling agent acted as a bridge be- tween the hydrophilic silica and the hydrophobic rubber and enhanced the rubber-silica interactions. This enhanced interaction gave rise to increased thermal stability of the EPDM. The values of the Nielsen model parameters, which gave rise to good agreement with the experimentally determined Young’s modulus values, indicate improved dispersion and reduced size of silica aggregates in the EPDM matrix. Good agreement was found between the storage modulus and Young’s modulus values. The filler effectiveness (Factor C) indicated a mechanical stiffening effect and a thermal stability contribution by the filler, while the damping reduction (DRNorm) values confirmed that the EPDM interacted strongly with the well dispersed silica particles, and the polymer chain mobility was restricted

This article is concerned with the preparation of a filled elastomer by means the nonconventional bottom-up approach to\ud polymer composites, alternatively with the conventional mechanical compounding of preformed filler particles with rubber. EPDM rubber was modified with in situ generated silica particles prepared by means of a sol–gel process adopting a solution process. The used synthetic procedure permitted the preparation of highly filled rubbers (up to 40 wt % of silica) with silica particle dimensions ranging from 0.2 to 2 um. Equilibrium swelling and extraction tests indicated a hindering effect of the presence of in situ generated silica on the vulcanization process which reduced the cross linking degree of the rubber matrix. Both tensile tests and dynamic–mechanical analysis showed a significant improvement in the mechanical properties due to the presence of the reinforcing filler, with an enhancement more significant than that expected from a simple hydrodynamic reinforcing mechanism

In this study, bio-based coatings were used for reducing water sorption of composites containing flame retardant treated natural fibres and phenolic resin. Two types of coatings; polyfurfuryl alcohol resin (PFA) and polyurethane (PU) were used on the composites and compared with a water resistant market product. Uncoated and coated samples were conditioned at 90 °C and relative humidity of 90% for three days and the relative moisture content and mechanical properties after conditioning were analysed. In addition, the changes in the weight loss of the conditioned samples were also investigated by thermogravimetric analysis. The moisture diffusion characteristics of coated laminates were also studied at room temperature under water immersion conditions. PFA coated samples showed better moisture resistance and mechanical performance than other bio-based coatings when subjected to long term environmental aging.

Silica nanoparticles were synthesized by means of a sol–gel method and generated in ethylene propylene diene monomer rubber (EPDM) by in situ synthesis. The properties were determined using scanning electron microscopy, attenuated total reflectance Fourier‐transform infrared spectroscopy, thermogravimetric analysis, tensile testing, dynamic mechanical analysis, swelling tests, and gel content determination. The silica particles were homogenously dispersed in the EPDM matrix, with the presence of agglomerates, especially for high silica contents. The swelling experiments showed a decrease in the crosslinking density of the vulcanized rubber due to the presence of the silica nanoparticles. The mechanical properties, however, were significantly improved by the presence of the stiff silica nanoparticles. The effect of the amount of silica on the thermomechanical properties and thermal degradation of EPDM was also investigated. The presence of silica showed an increase in the storage and loss moduli at high temperatures, probably due to the increasing filler content. The thermal degradation analysis showed that the presence of silica particles incorporated in the EPDM matrix had no significant influence on the thermal stability of the composites. POLYM. COMPOS., 36:825–833, 2015. © 2014 Society of Plastics Engineers

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Burning of plastics present a serious problem for both our health and safety when applied in advanced applications. Based on the above argument, there is need to enhance the flammability resistance of polymers in order to meet the required flammability standards. Various flame-retardant fillers are incorporated into polymers in order to provide a protection against heat into the system and inhibit the diffusion of volatile materials out of the polymer composite system. Different flame-retardant fillers including phosphorusbased materials, carbon-based flame retardants, and inorganic hydrated flameretardant fillers have been added into polymers in order to improve the flame retardancy of the plastics. Amongst the abovementioned flame-retardant fillers, inorganic hydrated fillers have gained popularity, especially magnesium hydroxide (Mg(OH) 2 ) due its high heat absorption capacity, less smoke release, and non-toxic, as a result environmentally friendly flame-retardant filler. However, an effective content of magnesium hydroxide for better flammability retardancy is approximately 60 wt%, which happens to deteriorate the mechanical properties of the magnesium hydroxide/polymer composites. In order to try and compensate for reduction in mechanical properties and improve the flame retardancy of the composites at the same time, magnesium hydroxide is incorporated with another flame-retardant fillers. This review article covers an in-depth discussion on the effect of magnesium hydroxide modification, synergistic effect with other fillers, particle size of the magnesium hydroxide, and the effect of compatibilizer(s) on both mechanical and flammability properties of magnesium hydroxide reinforced polymer composites.