3D Microstructure of supercritical fluid extrudates. II: Cell anisotropy and the mechanical properties

The mechanical properties of biopolymeric cellular foams are often governed by their microstructure. 2D and 3D microstructural data of supercritical fluid extrudates were obtained with X-ray microtomography and correlated with the mechanical properties determined using compression and three-point bending tests. Cell size from transverse cross-sections of SCFX extrudates decreased with radial distance from the center. In the longitudinal direction, the cell shapes were more elliptical than spherical and were aligned along the extrusion direction. These findings indicated the presence of a certain degree of anisotropy in SCFX extrudates in both directions. Both piece density and the ratio of cell wall thickness to cell diameter were observed to be good predictors of compressive and flexural mechanical properties, including jaggedness parameters. Compressive modulus data suggested that cell shape anisotropy due to cell elongation in the longitudinal direction actually affected the mechanical properties of SCFX extrudates. X-ray microtomography was found to be useful to investigate 2D and 3D morphology of SCFX extrudates, including cell shape and cell size anisotropy.