Enhancement of the mechanical properties of polysaccharide composite films utilizing cellulose nanofibers

Abstract

We have demonstrated that free-standing films with thicknesses of several tens of micrometers made from chondroitin sulfate C (CS) and chitosan (CHI) are readily obtained by utilizing the hot press technique. To improve the mechanical properties of the polysaccharide composite films, especially in the wet state, we investigated the incorporation of cellulose nanofibers (CNFs) in the films as a nanofiller in the present study. CNFs were homogeneously incorporated into polyion complex (PIC) gels under optimized conditions. The CNF-incorporated films were evaluated morphologically and spectroscopically by optical and electron microscopy and infrared microscopy; the results indicated that there were micrometer-scale domains in the CNF-incorporated films. The mechanical properties of the CNF-incorporated films were also investigated in the dried and wet states. Especially in the wet state, the Young’s moduli were effectively enhanced with an increased weight fraction of CNFs in the films. The mechanism of the filler effects was determined in terms of the dependency of the CNF content on the mechanical properties of the films. The results indicated that the nonionic nanofillers were incorporated with minimum influences on polysaccharide PIC formation, which contributed to the effective enhancement of film strength. Cellulose nanofibers (CNFs) were utilized as nanofillers to improve mechanical properties of polysaccharide composite films made of polyion complexes (PICs) of chondroitin sulfate C (CS) and chitosan (CHI). Nonionic CNFs were homogeneously incorporated in the PIC gels, constructed by multiple electrostatic interactions, and the resulting free-standing films. The filler effects of CNFs were observed, especially in the Young’s modulus of the films in the wet state. Results indicated that CNFs in the films formed a rigid network structure with polysaccharides, contributing the reinforcement of the film strength.