Multifunctionality of carboxyl groups carried by cellulose nanocrystals for mechanical and conductive properties of acrylic‑based hydrogels

Abstract

In this work, an integrated strategy was proposed for preparing hydrogel based on acrylic acid (AA) and sodium alginate (SA) by adding TEMPOoxidized cellulose nanocrystals (TOCNs) with different carboxylic groups (–COOH) contents. The addition of TOCNs and increase of its contents in poly(acrylic acid) (PAA)/SA hydrogel systems played a multifunctional role by which the mechanical properties and ionic conductivity of PAA/SA hydrogels were significantly affected and enhanced. TOCNs with their abundant –COOH groups disperses SA and AA in the hydrogel precursor solution for forming a uniform semi-interpenetrating network. It also provides more hydrogen bonds with SA and AA, and results in high modulus of the final hydrogel. Accordingly, the as-prepared hydrogels showed simultaneous good compressive (1.41 MPa at compressive strain of 70%) and tensile (365 kPa strength at fracture strain of 628%) stresses, excellent swelling rate (2509%), good transparency (86.3%) and conductivity (0.229 S m− 1). The work confirmed the important roles of – COOH in the TOCNs played in the construction and properties of the hydrogel, and the hydrogels may find great potential applications in the fields of flexible wearable sensors benefits by excellent natural biocompatibility from all the raw materials used.