Facile preparation of mouldable polyvinyl alcohol-borax hydrogels reinforced by well-dispersed cellulose nanoparticles: physical, viscoelastic and mechanical properties

Cellulose nanoparticle (CNP) reinforced polyvinyl alcohol-borax (PB) hydrogels were prepared through a facile approach in an aqueous medium. The effects of particle size, aspect ratio, crystal structure, and crystallinity of CNPs on the density, water content, optical transmittance and compression property of the hydrogels were investigated. The obtained stiff, high-water-capacity (~96 %), low-density (~1.1 g/cm³), translucent hydrogels exhibited birefringence behavior. The compression and dynamic oscillation measurements confirmed the incorporation of well-dispersed CNPs to PB system significantly enhanced the compressive strength and viscoelasticity of the hydrogels. The compression stress of cellulose I nanofiber reinforced PB hydrogel was 21-fold higher compared to the neat PB hydrogel. Highly-crystalline CNPs not only tangled with polyvinyl alcohol chains though numerous hydrogen bonds, but formed chemically crosslinked complexes with borate ions as well, thus acting as multifunctional crosslinking agents and nanofillers to physically and chemically bridge the 3D network of the hydrogels.