High cellulose nanowhisker content composites through cellosize bonding

Abstract

Flexible composite films with a high cellulose nanowhisker (CNW) content of up to 75% by weight were produced by casting from aqueous solution with water soluble cellosize (CS). The surface topography of the films displayed an aggregated morphology influencing the surface roughness and light transparency properties of the blends. Using fluorescently labelled CS, we were able to determine the extent of aggregation in the composites which indicated that up to 13% of CNWs can be homogeneously blended with CS, above which larger CNW aggregates occur. However, even in a somewhat aggregated form, the CNWs still form a percolated network and appear to be homogeneously dispersed as larger aggregated entities. The composite CNW–CS films further exhibited improved thermal stability compared to both the CNWs and CS alone with decomposition temperatures shifting from 261 °C for CNWs and 313 °C for CS to 361 °C for blends containing 75% CNWs. Surface induced crystallisation of CS by CNWs was also found with higher crystallinity for the composite films than for the individual constituents. Due to the reinforcing effect of CNWs within the matrix, an increase in the tensile strength (294%) and modulus (2004%) was observed for the blend containing 75% CNWs compared to the pure CS film (tensile strength ∼12.23 MPa and modulus ∼0.39 GPa). The storage modulus of all the flexible blends/films investigated also revealed an increasing trend with the CNW content across the temperature region explored. The swelling kinetics of the CNW–CS blends in phosphate buffered saline (PBS) media at 37 °C were also investigated and CNWs were shown to have a strong influence on reducing the equilibrium swelling capacity and initial swelling rate of the blends.