Improved mechanical properties of poly(styreneblock-isobutylene-block-styrene) due to nanoclay Reinforcement

The effect of nanoclay reinforcement on the ultimate tensile strength and elongation at break of a biocompatible copolymer was studied and quantified. The styrene-isobutylene-styrene block (SIBS) copolymer is used for certain load-bearing medical applications due to its excellent biocompatibility. Relatively low tensile strength may preclude the use of this otherwise suitable polymer in many applications for which biocompatibility is the primary requirement. Samples of 0.25, 0.5, and 1 percent Cloisite® 15 organoclay by weight were prepared by solution casting with toluene as the solvent. Adequate nanoclay dispersion was achieved via a simple highshear mechanical mixing step, as verified by X-ray diffraction analysis. The fullymixed solutions were cast in thin films and the solvent was allowed to evaporate completely. The nanoclay-reinforced film was then mechanically pelletized for use in injection molding, which is a common method of fabrication of thermoplastic polymer implants. The injection-molded dumbbell tensile specimens were tested to failure in a bench-top elastomer testing machine. Neat samples exhibited an average ultimate strength of 12.3 MPa, while samples with 0.5 and 1 percent nanoclay content by weight had an improved ultimate strength of 14.9 MPa and 13.5 MPa respectively, with little variation for neat samples. These results are indicative of an optimal nanoclay-loading percentage within this range, with a minimum improvement of nearly 20%. Tested samples show a significant improvement of elongation at break due to the nanoclay content. Neat samples failed at an average elongation of 361%, while samples with 0.5 percent nanoclay withstood an elongation of 491% before failure. Based on these results, the addition of nanoclay up to 1% by weight is an effective reinforcement in SIBS for enhanced tensile properties.