Thermal and crystallization studies of short flax fibre reinforced polypropylene matrix composites: Effect of treatments

The effect of fibre treatments on thermal stability of flax fibre and crystallization of flax fibre/polypropylene composites was investigated. For thermal stability study, flax fibres have been treated using maleic anhydride, maleic anhydride polypropylene copolymer, vinyltrimethoxy silane and alkalization. In order to compare thermal stability of flax fibres thermogravimetry (TG) analysis has been used. Kinetic parameters have been determined by Kissinger method. Results showed that all treatments improved thermal stability of flax fibres. For crystallinity analysis, three different techniques have been used, differential scanning calorimetry analysis (DSC), pressure–volume–temperature (PVT) measurements for analysis of volume shrinkage and polarized optical microscopy (POM). All techniques results showed that addition of flax fibre increased crystallization rate. Besides, depending on fibre surface treatment and crystallization temperature, flax fibre/PP composites can show transcrystallinity.     

The effect of water immersion and fibre content on properties of corn husk fibres reinforced thermoset polyester composite

This work presents an experimental investigation into the effect of cornhusk fibre (CHF) content upon the mechanical properties, water absorption behaviour, and swellability of CHF/polyester (PE) composites used in water environments. The CHF/PE was prepared at different volume fractions using hot compression (~175 °C). To investigate the rate of water absorption and swellability behaviours, composites were immersed in water for varying durations. The mechanical properties of composites (i.e. tensile, bending and compression strengths) immersed in water were carefully evaluated. The results indicate that the composites with an increased CHF content and a longer immersion time are prone to lower mechanical properties. The large amount of water absorbed by the composite reduces the bonding interface between CHF and PE, which is responsible for the damage. Moreover, the amount of water absorbed and the swellability increase with a corresponding increase in the CHF content. The lowest water absorption (2.39%) was detected in 20% CHF and 80% PE composite immersed for 6 days. The findings gathered in this research endorse CHF/polyester thermoset composites as a viable alternative for construction applications.     

Evaluation of interlaminar fracture toughness and dynamic mechanical properties of nano TiO2 coated flax fibre epoxy composites

In this study, fibre modification technique is performed by coating nano titanium dioxide (TiO₂) particles on flax fibres. The fibre surface is treated with silane coupling agents and coated with nanoparticles at weight percentage 0.2, 0.4, 0.6 and 0.8% to develop chemical bonding at the fibre matrix interface. The improved interface is evaluated by performing Mode I, Mode II interlaminar fracture toughness (ILFT), and Dynamic mechanical analysis (DMA). The results indicate that the fibre modified composites with 0.4 wt % and 0.6 wt % coating shows 37% and 24% improvement in Mode I and Mode II ILFT values respectively. The storage modulus from the DMA analysis also exhibits improvement for the fibre modified composites. SEM analysis explains the changes in the fracture mechanism. FTIR analysis provides the details on the fibre coating by nanoparticles.     

Recycled PP/EPDM/talc reinforced with bamboo fiber: Assessment of fiber and compatibilizer content on properties using factorial design

Thermoplastic composites reinforced with natural fibers have attracted the attention of many researchers, not only for environmental concerns, but also for economic reasons, recyclability, ease of processing, etc. One promising application is in the automotive industry due to their low cost and weight. This industry is increasingly pressured to produce vehicles that consume less fuel and are less polluting. Therefore, plastics reinforced with fibers are required to produce lighter parts to replace the much more abrasive glass fiber and mineral filled composites. One of the most widely used polymers in the automotive sector for manufacturing interior and exterior vehicle components is talc filled EPDM (ethylene-propylene-diene monomer) toughened polypropylene (PP). In this context, the aim of this study was to assess mechanical and thermal properties of bamboo fiber reinforced recycled talc filled PP/EPDM composites compatibilized with maleic anhydride grafted polypropylene (PP-g-MAH). Composites were prepared, according to a 2² factorial design with center point, in a Haake twin screw extruder with subsequent injection molding. Injected specimens were subjected to tensile, flexural, impact and fatigue testing. Morphological analyses were performed by scanning electron microscopy (SEM), and thermal analyses by thermogravimetry (TGA) and differential scanning calorimetry (DSC). Addition of bamboo fiber significantly increased tensile and bending strength, modulus and fatigue life, and decreased elongation at break and impact strength. On the other hand, addition of the compatibilizer had a positive effect only on tensile and flexural strength, and fatigue life whereas the effect was negative on elongation at break and impact strength. The addition of fiber and compatibilizer did not appreciably affect the matrix melting temperature, but slightly increased crystallization temperature and in some cases the degree of crystallinity.     

Determination of soluble phosphates in water samples using ytterbium(III) and dynamic measurements of light scattering intensity at long wavelength

A selective and fast method has been developed for the determination of phosphates by measuring the formation of ytterbium(III) phosphate through the variation of the light scattering intensity with time. The low solubility of this compound causes an efficient dispersion of the radiation at 490 nm, which is measured at 980 nm using the second-order grating effect. This approach minimizes potential background signals from the sample matrix. The initial rate of the system is automatically obtained in only 0.5 s by stopped-flow mixing technique. The variable optimization study has been carried out using univariate and multivariate methods. The dynamic range of the calibration graph is 0.09–7.9 mmol L⁻¹ (Pearson's correlation coefficient = 0.9999) and the detection limit is 0.03 mmol L⁻¹. The precision of the method, expressed as relative standard deviation, is 2.3%. The study of the potential interference of different inorganic anions showed that arsenate is the main interferent, although it is tolerated in a molar ratio of 5.5. The method has been satisfactorily applied to the determination of soluble phosphates in tap, ground and river water using a previous preconcentration step with a Dowex 1 (1 × 4–400) anionic resin. A 500-fold concentration has been achieved, which has allowed to decrease the detection limit up to 60 mmol L⁻¹. The recovery range is 97.5–102.5%. The results obtained are consistent with those obtained with the standard molybdenum blue method.