Pullulan Foams Prepared Using Only Subcritical Water

ABSTRACT A new foaming method applicable to polysaccharides has been established. Using this method, pullulan foams have been successfully obtained as molded products after a few minutes of heating under subcritical water conditions. Because the raw material is just a mixture of pullulan and water, nothing other than water vapor is emitted throughout the process. The transmission observation using X‐ray CT has revealed that the pullulan foams have the so‐called open cell structures. The cell diameter decreases with the increasing preparation temperature and with the decreasing water content of the mixture. The mechanical behavior of the pullulan foams against compression deformation can be explained in the framework of a simple model for elastic–plastic foams with open cell structures proposed by Gibson and Ashby. The rigid mechanical properties are maintained even at high temperatures, indicating the high heat resistance of the pullulan foams.