Band 35, Heft 4

Sansevieria trifasciata fibre has low costs, wide availability, high specific strength, renewability and low density and can be used as reinforcement in polymer composites. This review aims to evaluate the recent developments in Sansevieria trifasciata fibre and its application in polymer composites. This was done to evaluate the progress of research, identify knowledge gaps and predict interesting areas for future work. Extraction of Sansevieria trifasciata fibre is mainly by decortication and water retting. The composites are prepared mostly by hand lay-up and cured by either compression molding (cold or hot press) or casting. The surface treatment of S. trifasciata fibre can enhance the fibre-matrix interfacial adhesion and improve the mechanical properties of the composites. S. trifasciata fibre-reinforced composites have relatively good mechanical properties, which depend on processing methods, fibre loading, fibre length and fibre orientation. Future work is suggested in the area of detailed chemical compositions, novel preparation techniques, evaluation of electrical properties, lifecycle analysis and techno-economic analysis.

This work reports the preparation and characterization of poly(lactic) acid/acrylonitrile butadiene styrene/graphene nanoplatelets/Cloisite C20A montmorillonite (PLA/ABS/GnP/C20A) nanocomposites via melt blending. The clay is hybridized with graphene to increase its dispersion in the polymer matrix. The melt processing temperatures play a vital role in the properties of the resulting nanocomposites in dictating the extent of thermal stability and dispersion of the fillers. The hybrid nanocomposites were characterized for stress-strain, thermal, chemical, and morphological properties. The findings were that there was an increase in the mechanical properties in terms of tensile strength and Young's modulus with the PLA/ABS/GnP/C20A at the high-temperature profile having the highest values of 43.1 MPa and 2533 MPa. The elongation at break increases slightly, due to the brittle properties of GnP. It was found that the dispersion of the fillers increased with increasing temperature profiles, as revealed by the morphological analysis by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The void size was also observed to be smaller and more homogenous with increasing temperature. However, in terms of thermal degradation analysis, the addition of fillers increases its thermal stability as the decomposition onset temperature increases by 22.5°C.

The effects of nanosilica (NS) and nanoclay (NC) particle inclusions on mode II delamination and thermal properties as well as water absorption capability of carbon/aramid fiber reinforced hybrid composites (CAFRE) were experimentally investigated at different nanoparticle contents. NS and NC particles modified CAFRE samples were reinforced with intraply woven and twill weave of carbon and aramid fibers, and were manufactured by using hot mold press assisted with hand-layup method. Various thermal properties such as thermal conductivity, thermal diffusivity, and specific heat capacity were experimentally measured with respect to NS and NC particle weight contents according to ISO-22007 standard. In addition, the water absorption test was performed according to ASTM D570-98 standard. Results from this study showed that addition of NS and NC particles improved mode II delamination toughness of CAFRE composites at 1.5 wt% and 2 wt% of NS and NC particle contents, respectively. Water absorption capacity of the CAFRE samples was increased as increasing NS and NC weigh contents while thermal tests showed that thermal diffusivity values increased, and specific heat decreased with increasing both NC and NS particle weight contents.

Hygroscopic polymers absorb and bind water. If not dried properly, the residual moisture can cause major problems for converting and affect the product quality significantly. Therefore, an effective drying down to an acceptable moisture level is essential for a successful production. Though data sheets give recommendations for drying parameters, these do not consider the actual current moisture up-take of the plastic pellets or the current ambient conditions. This paper investigates the interdependencies of polymer characteristics, like thermal properties and molecular structure, and the drying kinetics of the respective polymers. Tests are carried out with five different polymers on a State-of-the-Art desiccant dryer. The results show that distinctive drying behaviors can be attributed to the molecular structure of the respective plastic. This is reflected by the activation energy according to Arrhenius, the diffusion coefficient and the Flory-Huggins-Parameter, all showing a positive correlation with drying speed and therefore can be used as indicators to estimate drying times. Also, an industrial scale prototype of a microwave enhanced drying system was used to investigate the effect of microwave application on the drying kinetics. Experimental results show potential for reducing the drying times needed, especially for lower temperatures of the drying air and highly hydrophilic plastics. For higher temperatures, however, the prototype could not compete with the state-of-the-art desiccant dryer, due to heat losses and inefficient tubing of the prototype. Considering this, the benefits of microwave application could be shown representatively for polyamide 6 also at higher temperatures.

This paper presents a case study of simulation-based design and experimental validation of the insert-injection molding process of a complex polyurethane part. The part under consideration is a dowel holder which is a machine element used in the concrete railway sleepers production. A simulation study was carried out to define the relevant mold design options and optimal molding parameters as well as to evaluate their influence on the part's quality indexes. Simulation was performed using the software Moldex3D. The mold was constructed according to the optimization analysis and a batch of pieces was manufactured under the optimized conditions. A mechanical testing experiment – representing the actual service loading conditions – was designed and performed to validate the mold and process designs and the part performance. Simulation and statistical analysis results allowed determining those conditions that lead to a better assembly between the part and the metallic insert and to its structural integrity. The mechanical performance evaluation demonstrated that the part meets all its functional and structural requirements, validating simulation predictions.

Graphene oxide (GO) sheets were obtained via an improved Hummer's method, and the Poly(vinylidene fluoride) (PVDF)/GO membranes employing GO as nucleating agent were prepared by solution casting. The crystalline behaviors and the crystallization kinetics of PVDF/GO membranes with varying GO concentration were investigated after isothermal crystallization at different temperatures. The results showed that the addition of GO induced the β-phase formation of PVDF. The spherulite diameter reached the peak value when the content of GO was 0.1 wt%, then reduced to the minimum value at 1 wt% GO within the tested temperature range of isothermal crystallization. It is worth mentioning that the relative fraction of β phase F(β) was dramatically improved to 0.85 for the PVDF/GO membrane with 0.5 wt% GO at 155°C. Furthermore, an enhancement of the crystallization rate was observed as the contents of GO increased in the system.