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Abstract
The use of dense CO2 in polymer processing can provide a response to the need for more environmentally-friendly industrial processes. Products with high-purity, sterility, and porosity can be achieved using dense gas technology (DGT). Currently, DGT has been used in different aspects of polymer processing including polymerization, micronization, and impregnation. Due to its solubility in polymers, CO2 can penetrate and plasticize polymers, while impregnating them with low-molecular weight CO2 -soluble compounds. Biodegradable polymers and other medical-grade polymers have benefited from the application of DGT. Dense CO2 processing properties of inertness, non-toxicity, and affinity for various therapeutic compounds are specifically advantageous to the medical and biomedical industries. In this work, the different applications of DGT in polymer processing are revised, then implemented.
The polymerization of polycarbonate (PC) and polycaprolactone (PCL) in dense CO2 are presented. The syntheses of both polymers were successful and were aided by the use of dense CO2 . A multi-stage approach using dense CO2 as a sweep fluid to extract the PC polymerization by-product phenol is reported. Polycaprolactone was synthesized with varying temperatures and dense CO pressures, then impregnated with a CO2 -soluble therapeutic agent. The impregnated PCL acted as a drug reservoir with a drug-loading of 27wt% and a sustained drug release profile was observed for all samples over several days.
Polymer blends of PC/PCL have potential industrial and biomedical applications both in vivo and in vitro. The applicability of PCL can be extended by enhancing its mechanical properties by creating a bio-blend with a stronger polymer such as PC. In this work, PC/PCL nonporous and porous blends were produced. Three novel dense CO2 blending techniques were used. The macroporous PC/PCL blend was impregnated with a therapeutic agent using CO2 as the carrier. A drug loading of 20wt% was achieved and sustained drug release was observed over 3 days.
The applicability of dense CO2 in polymer processing was further demonstrated by sterilizing macroporous PC/PCL blends and soft hydrogels with dense CO2 . The PC/PCL blends and hydrogels were inoculated with vegetative bacteria and bacterial endospores. Industrial standard sterilization levels were achieved.