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Image Analysis and the Characterization of Cellular Plastics

An evaluation of sprayed polyurethane foams manufactured with alternative blowing agents is being performed under a joint research program be tween the Society of the Plastics Industry of Canada and the Institute for Research in Construction. Image analysis, or the computer-aided quantification of the cell structure of the foams is a part of this evaluation. Samples of foams prepared using the same polymer with different blowing agents were examined under a low-power microscope. The blowing agents used in prepar ing the foam samples were: CFC-11, CFC-11 + 1% water, HCFC-123, HCFC- 141b, and a blend of the two HCFCs with 0.5% water. With the aid of a computer, histograms were obtained of the distribution of areas and of aspect ratios for win dows undamaged in the sectioning process as well as for cells that were opened during the sectioning of the foams. A comparison of these histograms allows one to differentiate the foams. In addition, reasonable estimates of average cell size can be made from measurements of cross-sectional areas of cell windows and of opened cells. Thickness of struts, i.e., the edges where two cell windows intersect, were esti mated by the use of a thinning technique on strut images, and estimates of cell wall thickness were made using an optical interference technique.