Hydrophobically modified pullulan adsorption onto rod-like cellulose nanocrystals

Interactions between polysaccharides have attracted great interests as a key to improving wood-fiber /thermoplastic composites. This study probes interactions between hydrophobically modified pullulans (HMPs) and rod-like cellulose nanoparticles (CNCs) in dilute solutions as a potential model system for the modification of wood fibers. A combination of UV–Vis spectroscopy, zeta-potential measurements, and light scattering techniques reveals the adsorption of pullulan derivatives onto cellulose nanocrystals even though hydrogen bonds are weakened. In UV–Vis spectroscopy and light scattering, aggregates were readily observed when UV cross-linking reactions occurred without cellulose nanocrystals and the system was relatively unaffected by the addition of cellulose nanocrystals after UV cross-linking. Otherwise, aggregates were not observed for long UV exposure time when both HMPs and CNCs existed in the ternary system. Large aggregates immediately precipitated when they were observed. Zeta-potential measurements also showed hydrophobically modified pullulan adsorption onto cellulose nanocrystal. Adsorbed hydrophobically modified pullulans screen the surface hydroxyl and sulfate groups of the cellulose nanocrystals. It could be demonstrated HMP/CNC/water ternary systems are effective model system of polysaccharide colloidal solutions having weak interactions. Graphic abstract