Find in Library

Complementary structural characterization methods are useful for studying the hierarchical cellular morphology of polymer foams. In this study, we employed scanning electron microscopy (SEM) and X-ray micro-computed tomography (micro-CT) to characterize the hierarchical cellular morphology of poly(methyl methacrylate) (PMMA) and polystyrene (PS) foams. The polymer foams were prepared using pure CO2 gas and CO2–chlorodifluoromethane (HCFC-22) gas mixtures as blowing agents. Depending on the type of polymer and HCFC-22 concentration, hierarchical cellular structures consisting of nanocells, microcells, and macrocells were obtained. The size distribution of the nanocells was determined by high-magnification SEM, while the size, shape, and spatial distribution of the microcells and macrocells in three dimensions were determined by micro-CT. Moreover, a well-designed micro-CT experiment enabled a brightness comparison between the foams and relative local density mapping of the foams based on the brightness. The results clearly showed the formation of a dense skin layer at the air interface of both PMMA and PS foams and dense matrix around the large macrocells in the PMMA foams. Thus, combining SEM and micro-CT provides a deeper understanding of the formation mechanism of the hierarchical cellular structure of polymer foams.