ABSTRACT
Electrically insulating and thermally conductive polymer matrix composites are desirable for industry applications as they improve the reliability of high-performance electronic devices, particularly via heat dissipation in devices loaded with several electronic components. In this study, an aggregated ß-Si3N4 filler with randomly oriented grains was produced via combustion synthesis to improve the thermal conductivity of epoxy composites. The thermal conductivities of the prepared composites were investigated as a function of the filler content, and the values were compared to those of composites loaded with commercial ß-Si3N4 (non-aggregated). Negligible difference was observed in the thermal conductivities of both types of composites when the Si3N4 content was below 40 vol%; however, above 40 vol%, the aggregated ß-Si3N4 filler-loaded composites showed higher thermal conductivities than the commercial ß-Si3N4-loaded composites. The aggregated ß-Si3N4 filler-loaded composites exhibited isotropic thermal conductivities with a maximum value of 4.7 W m-1 K-1 at 53 vol% filler content, which is approximately 2.4 times higher than that of the commercial ß-Si3N4-loaded composites, thereby suggesting that the morphology of the aggregated filler would be more efficient than that of the commonly used non-aggregated filler in enhancing the thermal conductivity of a polymer matrix composite.
ABSTRACT
Eggshells have high bioavailability and can be used as a source of calcium. The main component is CaCO3, which, when heated, is converted to CaO. Seashells are also mainly composed of CaCO3 and were previously found to exhibit antimicrobial activity after being heated. In this study, heated eggshell powder (HESP) was found to have antimicrobial activity against bacterial vegetative cells, fungi and bacterial spores. Parameters, such as the minimum inhibitory concentration, were determined with kinetic analysis using an indirect conductimetric assay. Moreover, HESP was able to kill the Bacillus subtilis spores. There were no significant differences in the activity between HESP, heated scallop-shell powder and pure CaO. The MIC values for HESP against bacteria and fungi were 0.29-0.43 and 1.3-1.5 mg/mL, respectively. Against B. subtilis spores, a reduction of two orders of magnitude of viability was confirmed following 20 min of treatment at 10 mg/mL at 60 â. The active oxygen generated from the HESP slurry was examined with chemiluminescence. The intensity of this increased with increasing concentrations of the HESP slurry. This suggests that HESP could be used as a natural antimicrobial agent. Although a high pH is the main contributor to this antimicrobial activity, active oxygen species generated from HESP are likely to be the main antimicrobial agents..
