Microstructural characterization of nanocellulose foams prepared in the presence of cationic surfactants. (1st September 2018) - Mariano, Marcos
Graphical abstract: Highlights: The presence of cationic surfactants can lead fibers to aggregate in aqueous suspension. Aggregation modifies porosity and mechanical properties of final materials. True structure of foams is revealed through microtomography characterizations. n -Decane absorption is used to obtain available surface area and discuss surface properties. Abstract: In this work, we explore the architecture of highly porous foams based on cellulose nanofibers (CNFs) prepared by using cationic surfactants (e.g., C12 TAB, C14 TAB, and C16 TAB) 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 m 2 g −1, obtained by n -decane adsorption, are reported.