Processing and in vitro Degradation of Starch/EVOH Thermoplastic Blends

This paper describes the processing dependence of the mechanical properties of three blends of starch/ethylene vinyl alcohol (EVOH) with potential uses as biomaterials. These blends exhibit a distinct rheological behaviour and mechanical performance. Using shear controlled orientation in injection moulding (Scorim) it was possible to induce anisotropy into the mouldings and to simultaneously enhance sti†ness and ductility. Degradation was studied in simulated physiological solutions (HankÏs balanced salt solution) with and without added bovine serum. Both the dry weight loss and the changes in mechanical properties were determined for ageing periods up to 80 days. The degradation behaviour proved to be strongly dependent on the formulation of the material studied, and on the addition of proteins. The susceptibility of the starch/EVOH blends to degradation when sterilised with ethylene oxide (EtO) was also studied, and showed that the polymers could stand one EtO sterilisation cycle. However, two consecutive cycles severely degraded the polymer structure and properties.