Degradation model of starch-EVOH+HA composites

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Abstract
Composites of starch based blends (starch-EVOH) reinforced with bioactive bone-like hydroxyapatite (HA) have been recently proposed for temporary biomedical implants. Very promising mechanical results were obtained so far, both by the introduction of coupling agents (titanates, zirconates and silanes) or by optimizing the respective processing route. In this study coupled and non-coupled composites were aged up to 30 days in two types of simulated physiological solutions (with and without added proteins/enzymes) and the respective property variation was evaluated by means of: weight loss, water-uptake and mechanical performance (strength, stiffness and ductility). The interfacial attack generated by the solutions was observed by scanning electron microscopy (SEM) and quantified (calcium and phosphorous amounts in the solution) by atomic emission spectrometry (ICP). The in-vitro degradation process of starch-EVOH+HA composites consists apparently of three main stages: i) for short periods (0–6 days) it is characterized by a high degradation rate due to the leaching of plasticizers, low molecular weight polymeric chains and some dissolution of HA; ii) for longer periods (7–15 days), the major extraction of the plasticizers occurs and the material becomes brittle and; iii) from the 15th immersion day on, the degradation rate is lower and, eventually chemical attack on the polymer structure takes place, mainly in the presence of enzymes/proteins. The confirmation of this type of behavior will support the potential use of these composites, already tested for their non-cytotoxic character, in temporary applications where the retention of mechanical properties for 3 to 6 weeks is required