Polyvinyl alcohol composite hydrogels containing mixtures of cellulose nanocrystals and chitin nanofibers*

Among bio-based polymers, cellulose and chitin are abundant and available in a variety of forms, including nanofibers. Due to their anticipated mechanical properties and anisotropic structure, nanofibers of cellulose and chitin are desirable reinforcing fillers in polymers. These nanofibers are also dispersible in water, making them desirable as reinforcing fillers in polymer hydrogels as well. In this work, we have examined how cellulose nanocrystals (CNCs) and chitin nanofibers (ChNFs) may be used separately and as mixtures to affect the properties of poly(vinyl alcohol) (PVA) hydrogels. CNCs and ChNFs have negative and positive surface charges, respectively, providing opportunities for bonding between the nanofibers when used as mixtures and modifying the hydrogel properties further. The results of this work suggested that the types of networks formed were different with different filler types and these differences were observed through swelling behavior of the hydrogels and mechanical properties. Overall, these results demonstrate that nanoparticle mixtures may be used as effective reinforcements for polymer nanocomposites when compatible surface interactions are present between all the components.