Sorption and diffusion of compressed carbon dioxide in polycaprolactone for the development of porous scaffolds

Abstract

In this work different phenomena related to sorption of carbon dioxide in polycaprolactone (PCL) have been investigated systematically. The use of compressed carbon dioxide is discussed for obtaining porous scaffolds from this biocompatible polymer. In order to determine the plasticization effect of carbon dioxide on the degree of foaming it is necessary to discuss sorption data with respect to morphological features of the polymer at conditions nearby the melting point. The amount of carbon dioxide dissolved and the kinetics of the sorption process are found to depend strongly on temperature and pressure. The solubility takes values of up to 25 wt.% being favoured by a melting and glass transition temperature depression which can be observed along with an enhanced mass transfer rate. In general, CO2 sorption in PCL increases linearly with pressure. When decompressing, microfoaming occurs which enhances the rate of gas release. Changes in morphology and crystallinity occur as a consequence of the pressure treatment. Compared to the melting temperature at atmospheric pressure there is a dramatic reduction observed under pressure where melting occurs already at a temperature below 40 °C. Even after pressure-treatment, there is a remaining change in melting temperature and crystallinity observed. Optimum conditions for obtaining adequate porous scaffolds of PCL are a relatively slow decompression after treatment at 17 MPa and 35 °C.