Discriminating Structural Characteristics of Starch Extrudates through X-ray Micro-tomography using a 3-D Watershed Algorithm

X-ray micro-tomography (XMT) was used to characterise the pore structure of two open-cell biopolymer foams (starch extrudates). A three-dimensional watershed algorithm was applied to XMT images to segment pore structure. Distributions of pore sizes and interconnecting pore aperture sizes were determined and pore geometry was visualised. The technique was used to analyse samples having an inhomogeneous porosity distribution. Results were not sensitive to threshold values set during image analysis. Pore size and pore aperture distributions were extracted. Pore size was based on volume fraction, aperture size was based on area fraction and both on number frequency. Volume fraction of porosity was calculated from image analysis and compared with that deduced from density measurements. The value from image analysis was sensitive to the set threshold contrast. Average cell wall thickness was calculated from two-dimensional image analysis. This shows that XMT, with appropriate data processing, is a powerful method for structural characterisation of starch extrudates.