Fabrication of a highly elastic nanocomposite hydrogel by surface modification of cellulose nanocrystals

Abstract

Cellulose nanocrystals (CNCs) pre-grafted with polymerizable groups have been used as nano crosslinking joints and nano reinforcements to synthesize highly-elastic hydrogels. However, the polymerizable CNCs usually have dispersion problems during hydrogel fabrication because of the hydrophobicity of the grafted polymerizable groups. In this study, TEMPO oxidation was successfully utilized to overcome this problem by introducing more hydrophilic groups on the CNCs surface, facilitating their homogeneous distribution in aqueous solution and hydrogels. Furthermore, AC and UC gels crosslinked by CNCs that were pre-grafted with acryloyl chloride (AC) and 10-undecylenoyl chloride (UC) on their surfaces were fabricated for finding out a more effective way to synthesize stronger nanocomposite hydrogels. The results showed that UC gels showed both higher tensile strength and higher elongation than the corresponding AC gels. It was shown that UC gels, which had longer grafted carbon chain lengths on CNC surfaces, possessed a better energy dissipation capacity under stretching than AC gels. The water swelling ratios of UC gels (13.0–36.7 g g⁻¹) were also much higher than those of the corresponding AC gels (11.2–21.0 g g⁻¹) as a result of larger spaces to hold water in the hydrogel network. This work gives an insight into the influence of carbon chain length on the properties of CNC crosslinked nanocomposite hydrogels, and provides an effective way to fabricate nanocomposite hydrogels with higher mechanical strength.