Formation of two-dimensional mixed monolayers of integrated-cellulose nanofibers and starch nanoparticles using cellulose acetate and soluble starch

Abstract

In this study, mixed monolayers comprising starch and cellulose nanofibers are prepared on the water surface and effectively controlled their surface morphologies. Through the spreading of cellulose acetate on the water surface, we achieve the preparation of integrated films with the spontaneous formation of nanocellulose. It is confirmed that starch, which is insoluble in the spreading solvent, is solubilized through a soluble treatment and spreads into a monolayer on the water surface. Upon mixing the nanocellulose integrated layer and starch particle layer, the morphology changes based on the mixed ratio of these components. In the monolayer film of a 1:1 mixture of cellulose acetate and soluble starch, the morphology predominantly consists of fibers, with particulate aggregates incorporated here and there. Furthermore, when the ratio changes to 1:5, the mixed monolayer transforms into a single particle layer, while the mixed monolayer evolves into a fibrous integrated film at a ratio of 5:1. Meanwhile, from the evaluation of the surface pressure-area isotherms, it is predicted that both components constitute an ideal mesoscopic miscible system. In addition, in the subphase temperature dependence of the cellulose acetate:soluble starch = 1:1 mixed monolayer, fibers are promoted under low-temperature conditions, and substantial domains are formed under high-temperature conditions. Notably, the mixed film remains amorphous at all ratios and exhibits low surface free energy, simultaneously suggesting hydrophobic and oil-repellent properties.