Biomedical polyurethanes are rubbery copolymers currently used in many medical devices ranging from pacemakers to synthetic heart valves. However, the scope of application of these biomaterials is currently restricted due to either a lack of biostability (degradation resistance in the body) or properties such as creep resistance, tear resistance or compressive strength. Researchers have demonstrated that the mechanical properties can be enhanced by incorporating less than 3wt% of organically modified layered silicate into polyurethane.
Layered silicate/polyurethane nanocomposites were prepared via twin screw extrusion and solvent casting. The layered silicate was organically modified with two surfactants, alkylammonium and choline chloride. The ratio of these surfactants was varied systematically to examine the effect of adjusting the silicate surface energy. Tensile testing was carried out on both solvent cast and melt compounded materials. Solvent casting was found to be the preferred processing route due to the avoidance of polyurethane and surfactant degradation associated with melt processing. Addition of nanoparticles did not improve the tensile strength of the melt compounded material. Significant improvement was shown in the solvent cast material with a mixture of alkylammonium and choline chloride organosilicate. A composition ratio of 75% choline chloride and 25% alkylammonium increases the tensile strength by 20% as compared to pure polyurethane. The modulus of this formation was increased by 30%.