Nanoindentation study of individual cellulose nanowhisker-reinforced PVA electrospun fiber

Electrospun poly(vinyl alcohol) (PVA) fiber and its composites have been widely studied recently. However, most physical properties reported in literature are measured from a nanofiber web. In this study, for the first time, the mechanical properties of individual electrospun fiber, rather than fiber web, of cellulose nanowhisker-reinforced poly(vinyl alcohol) was studied using nanoindentation technique. The modulus is 2.1 GPa for a pure PVA electrospun fiber, and 7.6 GPa for 20.0 wt% cellulose nanowhisker-reinforced PVA electrospun fiber, respectively. The modulus of PVA/cellulose nanowhisker electrospun fibers increases linearly with increasing loading ratio of cellulose nanowhiskers up to 20.0 wt%. The experimental results were compared with that calculated using isotropic and longitudinal Halpin-Tsai models. The modules of the cellulose nanowhiskers are 60-80 % higher than the isotropic model predictions but lower than longitudinal model prediction, suggesting the nanowhiskers are partially aligned to the electrospun fiber direction.