Effect of composition of polyurethane foam template on the morphology of silicalite foam

Two different types of polyurethane foam, namely, polyether polyol-based polyurethane (Ether–PUF) and polyester polyol-based polyurethane (Ester–PUF) were tested as the templates for the synthesis of silicalite foams. Both types of polyurethane foam readily produced corresponding silicalite foams (Ether–SLFs and Ester–SLFs) upon reaction with synthesis gel. However, the morphologies of the produced SLFs were entirely different depending on the type of PUF. Thus, while the cell-forming membranes of Ether–SLFs are comprised of two parallel sheets of thin silicalite films, those of Ester–SLFs are thicker and single bodied. While the struts of Ether–SLFs are hollow, the interiors of the struts of Ester–SLFs are stuffed with loosely packed, yet interconnected silicalite crystals. As a result, the mechanical strengths of the SLFs produced from Ester–SLFs increased by ∼2-times over those of Ether–SLFs. The surfaces of the Ester–SLFs are rougher and spikier than those of Ether–SLFs. The fundamental difference between the two different types of PUFs that give rise to the above different results lies on the fact that the rate of hydrolysis of Ester–PUF is higher than that of Ether–PUF. This paper thus demonstrates that the PUF-based morphosynthesis is sensitively governed by the chemical composition of PUF.