Strong, transparent, and thermochromic composite hydrogel from wood derived highly mesoporous cellulose network and PNIPAM

Abstract

Composite polymer hydrogels are of significant interests for high optical transparency and mechanical performance. In this work, a strong and transparent composite hydrogel is developed from a highly mesoporous cellulose network prepared from wood via top-down delignification followed by TEMPO-mediated oxidation and in situ polymerization of PNIPAM. Individualization of cellulose microfibrils inside the wood cell wall is critical for the fabrication of free-standing composite hydrogel with high water content of 94.9 wt% and high optical transmittance of 85.8% with anisotropic light scattering behavior. The composite hydrogel also showed anisotropic mechanical properties with a tensile strength, Young’s modulus and toughness of 317 kPa, 5.4 MPa, and 39.2 kJ m−3 in axial direction, and 152 kPa, 0.31 MPa and 57.1 kJ m−3 in the transverse direction, respectively. It also showed thermochromic behavior, i.e., reversibly changing between transparent and brightly white by a temperature change between 25 and 40 °C, demonstrating great potential for optical applications.