Epoxy composites loaded with different concentrations (5-50 wt%) of high abrasion furnace carbon black (HAF) with and without the addition of 10 wt% Mg(OH) 2 were prepared and subjected to electrical, mechanical, flammability, and thermal measurements. It was found that the permittivity " 0 and dielectric loss " 00 increased by increasing HAF content. This increase is slightly lowered by the addition of Mg(OH) 2 . The electrical conductivity of HAF-epoxy composites increased from the pure polymer towards that of pure carbon. A low frequency region with relaxation time 1 in the range 3.5-4.5 Â 10 À4 s is found to be unaffected by either filler content or the presence of Mg(OH) 2 . The higher frequency range with relaxation time 2 is nearly the same for lower concentrations of HAF up to 10 wt% (percolation threshold concentration). Above this concentration a dramatic increase was noticed.Incorporation of 10 wt% of HAF led to an increase in the compressive strength value. Further increase in HAF content resulted in a decrease in compressive strength values. The tensile strength values of the composite samples before and after the addition of 10 wt% Mg(OH) 2 are higher than that of the unloaded one.The addition of 10 wt% Mg(OH) 2 improved both the thermal stability and the fire retardant efficiency of HAF-epoxy composites.

ABSTRACT:The main objective of this study was to investigate the effect of different additives, namely, maleic anhydride, alumina trihydrate (ATH), and a mixture of both on wood flour/polyolefin (50/50) composite samples. The polyolefins used were polyethylene (PE), polypropylene (PP), and a mixture of both PE and PP (50/50 w/w). The effects were studied in terms of the percentage water absorption, volumetric swelling efficiency, and mechanical and electrical properties. We found that the absorption of water and volumetric swelling were greatly retarded after 3 weeks in all of the wood flour/polyolefin composite samples containing various additives. It is also clear from the results that the mechanical properties were enhanced. The presence of ATH improved the electrical properties and enhanced the thermal stability of the wood flour composites. Generally, the PE composite samples gave better results compared to the PP ones.

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Polypropylene fumarate (PPF) as unsaturated linear polyester crosslinked with three different monomers namely N-vinyl pyrrolidone (NVP), methyl methacrylate (MMA), and a mixture of NVP/MMA (1 : 1 weight ratio) were prepared. The chemical structure of the PPF was characterized by means of 1 H-NMR, FTIR, as well as GPC. The mixture of PPF resin with the crosslinking monomers filled with (60, 65, and 70 wt %) of gypsum were also prepared as bone cement composites. The dielectric measurements carried out on these prepared samples at frequency range from 100 Hz-100 kHz indicate that the permittivity e 0 and dielectric loss e 00 follow the order NVP > NVP/MMA > MMA. Both parameters were found to decrease by increasing the percentage of gypsum. According to Fröhlich and Havriliak Nagami functions, the relaxation times obtained could be attributed, respectively, to Maxwell-Wagner effect and to the relaxation process related to carboxyl, hydroxyl, and ester functions associated with main chain. The latter relaxation time was found to increase by increasing gypsum content, whereas the electrical conductivity was found to decrease. The mechanical data of the investigated samples containing 60 wt % gypsum is characterized by the best properties and the behavior of the composites follows the order found in the case of dielectric properties (NVP > NVP/MMA > MMA). Formation of carbonate apatite of composite samples loaded with 60 wt % gypsum after immersing the samples for 4 weeks in simulated body fluid (SBF) was confirmed by the dielectric measurements and FTIR spectroscopy. In addition, the weight loss and the mechanical properties for such systems were also studied.