Microstructural characterization of nanocellulose foams prepared in the presence of cationic surfactants

In this work, we explore the architecture of highly porous foams based on cellulose nanofibers (CNFs) prepared by using cationic surfactants (e.g., C₁₂TAB, C₁₄TAB, and C₁₆TAB) as modifying agents. The addition of surfactants to CNF suspensions led the nanoparticles surface to be covered by these molecules, reducing the ζ-potential from -35 to -8 mV, which, together with hydrophobic interactions of adsorbed surfactants, causes CNF flocculation. After freeze-casting and lyophilization, mechanical properties and pores structure of the low-density foams obtained (15.6-30.9 mg cm^-3) proved to be strongly dependent on nanofibers agglomeration degree. The primary causes of such dependence could not be observable by scanning electron microscopy but were found to be very significant on X-ray microtomography analysis. Total porosity, pore-size, and wall thickness of the foams were calculated and related to the surfactant chain size. Surface areas from 4.7 to 48.6 m² g^-1, obtained by n-decane adsorption, are reported.