Desirable Mechanical Strength Research Articles

Influence of Tricalcium Aluminate Phase on In Vitro Biocompatibility and Bioactivity of Calcium Aluminate Bone Cement

The influence of tricalcium aluminate (3CaO·Al2O3) phase doping on in vitro biocompatibility and bioactivity of calcium aluminate (CaO·Al2O3) based bone cement has been investigated. It is demonstrated that the presence of approximately 25% tricalcium aluminate in the bone cement remarkably improves the bioactivity, yet still retains desirable mechanical strength and biocompatibility. An intermediary compound layer such as Ca3Al2(OH)12 was formed on the surface of the doped sample onto which hydroxyapatite (HAp) began to form soon, after only 2 days of immersion in a simulated body fluid solution. This is about seven-fold acceleration in the HAp formation over undoped calcium aluminate cement on which it took approximately15 days to nucleate the HAp phase. The depth of the HAp-containing layer after60 days of soaking was as much as 85 μm, about an order of magnitude more than the undoped calcium aluminate cement. The dramatically accelerated nucleation and growth of hydroxyapatite caused by the presence of tricalcium aluminate is attributed to the occurrence of intermediate layer materials such as Ca3Al2(OH)12, which most likely acts as the nuclei for HAp formation. This doped bone cement can be useful for injectable orthopedic applications, as the setting time for hardening has also been significantly reduced (by a factor of at least 4) to a practical regime of tens of minutes.

The Influence of Surface Energetics of Calcium Carbonate Minerals on Mineral-Polymer Interaction in Polyolefin Composites

Surface energetics of ground calcium carbonates (GCC), with or without stearic acid treatment, were determined by Inverse Gas Chromatography (IGC). The surface energy data were utilized as a predictive tool to explain the optimum coating level often needed on calcium carbonate minerals to obtain the desirable mechanical strength in filled polypropylene composites. The dispersive components of the surface energies for the uncoated carbonates were also correlated with the corresponding impact resistance data. The surface with the highest energy was found to be the least resistant while the least energetic mineral, on a comparative scale, was the most resistant to impact. It is suggested that understanding the surface energetics of finely-divided solids may be a key for the development of future mineral-filled polymer composites.

Heat Transfer and Property Development in Liquid Silicone Rubber Molding

Abstract This study has used a heat transfer model to describe the cure of liquid silicone rubbers. The model shows that cure always starts from the wall and will continue during cooling. Thick parts may not be totally cured upon demolding, although the material near the wall has reached a desirable mechanical strength. Since silicone rubbers gel fast at high temperature, mold filling problems may occur for the thin and long molds, especially at high mold temperatures.