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

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.