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Graphite–aluminium (Gr–Al) composites are being used for diverse engineering applications because of their light weight, good electrical conductivity and thermal properties. However, their applications are limited by high coefficient of thermal expansion and low microhardness values which can be enhanced by adding cheap and efficient fillers. This paper reports the effect of addition of eggshell (ES) particles on the properties of sintered Gr–Al-based composites. Five different composites (Gr–Al, Gr–Al + 20 wt.%Si, Gr–Al + 20 wt.%SiC, Gr–Al + 20Si wt.% + 20 wt.%ES and Gr–Al + 20SiC wt.% + 20 wt.%ES) were sintered at a temperature of 540 ℃, holding time of 10 min, heating rate of 52 ℃/min and pressure of 50 MPa using spark plasma sintering system. The sintered samples were characterized based on morphology, microhardness, relative density, coefficient of thermal expansion and electrical conductivity. Based on SEM images, graphite particles of flake-like structure were largely undeformed while Al particles were smaller, round and irregular in shape and fairly uniformly distributed in the composites. The microhardness value of sintered Gr–Al + 20 wt.%SiC + 20 wt.%ES composite was 39.55 HV compared to 30.46 HV for Gr–Al, the least of the samples. The Gr–Al + 20 wt.%SiC + 20 wt.%ES composite also has a very low thermal expansion coefficient (0.98 × 10−5/K) but lowest electrical conductivity at temperature beyond 150 ℃. Highest densification and minimum relative density (94%) were obtained in Gr–Al + 20 wt.%Si + 20 wt.%ES composite. These enhanced performances are largely due to the incorporation of ES particles. This study therefore demonstrated that ESs particles enhanced microhardness and lowered thermal expansion of Gr–Al-based composites which have promising applications in industries especially for thermal management. [ABSTRACT FROM AUTHOR]

For the first time, Silicon Carbide-Zinc Oxide-Graphite reinforced hypereutectic Aluminium–Silicon composites were fabricated by two-step stir casting. The mechanical properties and abrasive wear performance of the composites were experimentally tested. A multilevel factorial design of experiment was conducted to develop a numerical model for predicting the wear rate of composites and optimization of their wear performance as a function of reinforcement characteristics. The results indicated that high content of silicon carbide in the composites superlatively enhanced hardness, tensile strength and fracture toughness by 69.04%, 163.22% and 77.42%, respectively. Correspondingly, high content of graphite indicated superlative wear resistance of 95.87% reduction in wear index while high zinc oxide content revealed enhanced fracture toughness highly comparable with that observed for high silicon carbide content. Nevertheless, in comparison with the monolithic alloy, the trade-offs in the strains-to-fracture of the composites were more pronounced with high silicon carbide content. The developed 2-factor-interaction effects model strongly agrees with the experimental results after passing various model validity tests available in Design Expert Software. It revealed that the composition of reinforcing constituents influenced the model more than the volume fraction, and the interaction between the composition of reinforcement constituents and volume fraction. [ABSTRACT FROM AUTHOR]

Thermal and rheological properties of polyamide 6/layered double hydroxide (PA6/LDH) composites were studied. Pristine (U-LDH) and organically modified (M-LDH) clays were used in this study. Some evidence of intercalation was observed on the microstructure of PA6/M-LDH samples, while PA6/U-LDH was characterised by microcomposite morphology as shown by the transmission electron microscopy results. The scanning electron microscopy results showed a complete delamination of the M-LDH in the PA6 matrix while U-LDH was evenly dispersed as immiscible tactoids. In the melt state, the M-LDH had a significant influence on the melt microstructure of PA6 matrix when compared to U-LDH. Differential scanning calorimetry results, both dynamic and isothermal experiments, showed that LDH had a heterogeneous nucleating effect on the PA6 matrix, with the U-LDH showing better nucleating effect when compared to M-LDH. The thermogravimetric analysis results showed that M-LDH had a negative influence on the thermal stability of the composites, while U-LDH improved their thermal stability. The X-ray diffraction and dynamic mechanical analysis results showed that the presence of M-LDH promoted the formation of γ -crystallites in the PA6 matrix, while U-LDH composites were dominated by the α -crystallites. This phenomenon had a positive correlation with increasing content of both LDH clays. An overall improved dynamic mechanical properties were observed for PA6/U-LDH when compared to PA6/M-LDH composites. [ABSTRACT FROM AUTHOR]

Kenaf and sisal fibres were selected for the development of natural fibre-reinforced thermoplastic composites because they are in abundance in South Africa. These materials can be used in the building industry, where good mechanical and fire resistance properties are required for structural and non-structural applications. High load bearing, moisture and fire can negatively affect the properties of these composites and decrease their performance. The effect of water glass, maleic anhydride-grafted-polypropylene (MAPP) treatment and fibre loadings on mechanical and thermal properties as well as fire resistance of kenaf and sisal fibre-reinforced polypropylene composites were investigated. The fibre-reinforced polypropylene composites were produced by injection and compression moulding processes. A significant improvement of the tensile strength and modulus of kenaf fibre composites was more pronounced when compared to sisal fibre composites. However, the water glass has a slight negative influence on mechanical properties of fibre/polypropylene matrix composites but showed better fire resistance and thermal properties when compared to the untreated fibre/polypropylene composites. Generally, the impact strength of fibre/polypropylene composites decreased with the addition of MAPP. The low impact strength could be the results of weak interfacial bond strength between the fibre and the matrix. The total heat release was reduced by water glass treatment due to the non-flammable polysilicate coating, while the average mass loss rate was slightly reduced by MAPP. [ABSTRACT FROM AUTHOR]