The effect of the composition of spruce and pine tannin-based foams on their physical, morphological and compression properties

Tannin-based foams were successfully prepared, using Norway spruce and maritime pine tannins. Various parameters, including the amount of procyanidins, were varied in order to observe the effect of changes in the density of the foam, on the structure its pores, and on the homogeneity, compressive strength, and compressive modulus of the foams. It was found that an optimum amount of spruce tannin exists, which results in a foam with the lowest density whereas the amount of cross-linker affects homogeneity, and the foam morphology is defined by the surfactant. A partial replacement of pine tannin with spruce tannin decreased the foaming temperature and led to decreased compressive strength and a decreased compressive modulus of the foams. The main attribute affecting the reaction was the amount of polyphenols, or the amount of impurities (cellulosic sugars) present in the tannin extract.