Generation of biodegradable polycaprolactone foams in supercritical carbon dioxide

Generation of biodegradable polycaprolactone foams in supercritical carbon dioxide 

L YU and K DEAN, CSIRO - Manufacturing and Infrastructure Technology, Australia and Q XU, Zhenghou University, China 

Foamed polymeric materials are produced in a wide range of bulk densities that mainly determine their mechanical properties. A high-density foam that has an improved tensile strength and modulus can be used for load-bearing applications, such as structural parts, while a low-density foam can be used in thermal insulation and packaging applications. In addition to the foam density, the size and distribution of cells also affects the final properties of the foam. Conventional plastic foams have relatively poor mechanical properties because the cell size is typically larger than 100 /xm and the cell size distribution is very non-imiform. In general, foams with very fine cell size exhibit better mechanical properties. 

Carbon dioxide, a nontoxic fluid with a relatively low critical point (Tc = 31 C, Pc = 7.376 MPa) is the most widely used in the supercritical fluid field. Supercritical Uquid CO2 is found in the triangular region formed by the melting curve, the boiling curve and the Une that defines the critical pressure. Carbon dioxide is known to swell and significantly plasticize many amorphous polymers, such as poly(methyl methacrylate), polystyrene, polycarbonate and 

In this chapter, microcellular foaming of low-Tg biodegradable and biocompatible polycaprolactone (PCL) in supercritical CO2 will be described. The effects of a series of variable factors, such as saturation temperature, saturation pressure, saturation time and depressurization time on the foam structures and density were studied through measurement of density and SEM observation. The experimental results show that higher saturation temperatures lead to a reduction in bulk densities and that different saturation pressures result in different nucleation processes. In addition, saturation time has a profound effect on the structure of the product. Both X-ray diffraction (XRD) and differential scanning calorimetry (DSC) results show that the foaming treatment widi supercritical CO2 increased the crystallinity of PCL. 

---