Influence of processing and sterilisation on properties of poly-ε-caprolactone

Poly-epsilon-caprolactone (PCL) is a significant member of a group of polymers regarded as bioabsorbable, having been the focus of extensive research for use as a diffusion controlled drug delivery system. Degradation of PCL proceeds through hydrolysis of the ester bonds in the polymer chains and is influenced significantly by the polymer's initial molecular weight and crystallinity. To evaluate the effects of processing and sterilisation on these properties, PCL pellets (CAPA 6400) were either injection moulded or extruded and sterilised by ethylene oxide gas (EtO). Procedures were used to evaluate mechanical properties, molecular weight and crystallinity. Upon processing and sterilisation the molecular weights of the injection moulded and extruded materials did not differ significantly from that of the PCL pellets, suggesting processing and sterilisation did not initiate chain scission of the polymer's ester bonds. However, the crystallinity of PCL proved to be sensitive to injection moulding with an increase of approximately 5% observed after processing, with sterilisation by EtO gas causing annealing of the PCL pellets, injection moulded and extruded material. After sterilisation the crystallinity of the PCL pellets and extruded material increased by approximately 10% with a 4% increase observed for the injection moulded material. The mechanical properties of both the injection moulded and extruded material where not influenced by sterilisation. The results from this investigation suggest that PCL's molecular weight is insensitive to processing and sterilisation. However, sterilisation by EtO gas in the temperature range of 38-48degreesC used in this study does result in annealing of the polymer.