Performance of polyvinyl alcohol hydrogel reinforced with lignin-containing cellulose nanocrystals

Abstract

Lignin-containing cellulose nanocrystals (LCNCs) were produced from old newspapers using the sulfuric acid hydrolysis process, and the product was used in reinforcing polyvinyl alcohol (PVA) based hydrogel. The lignin content of LCNCs was quantitatively analyzed by X-ray photoelectron spectroscopy (XPS), and LCNCs had 8–19 wt% lignin located on their surfaces. The transmission electron microscopy (TEM) confirmed the presence of lignin on LCNCs as small globular-like particles/patches. The increase in the lignin content of LCNCs increased the thermal stability and hydrophobicity while decreasing the crystallinity of LCNCs. Moreover, the effect of LCNC loading (0.1–1 wt%) on the mechanical strength, rheological properties, swelling behavior, morphology, and thermal stability of PVA-based hydrogel was further elucidated. The incorporation of LCNCs in hydrogel at a low dosage improved the swelling behavior of hydrogel. The lignin present on the surface of LCNCs led to enhanced viscoelasticity, increased compressive strength, and improved thermal stability of hydrogel. In addition, the pore size of the hydrogel dropped more significantly (4.26–1.52 μm) with the use of LCNCs containing more lignin. At a low dosage of 0.1 wt%, all studied properties of hydrogels were improved using the LCNC with high lignin content. This study provides a new prospect for the use of lignin-containing CNCs for the production of a high-performance hydrogel.