Anionic and cationic nanocomposite hydrogels reinforced with cellulose and chitin nanowhiskers: effect of electrolyte concentration on mechanical properties and swelling behaviors

Various nanocomposite gels were prepared using cellulose nanowhiskers (CNWs) or chitin nanowhiskers (ChNWs) as reinforcing fillers and hydroxypropyl cellulose (HPC), carboxymethyl cellulose (CMC), or chitosan as network polymers. The use of CNWs with low surface charge induced significant CNWs aggregations, which were well explained by depletion effect. Young's modulus E and swelling ratio Q of CNWs/HPC · CMC gels were highest at zero electrolyte concentration and decreased above 0.01 M electrolyte, whereas stress at break σ of the gels showed its minimum at zero electrolytes and increased with an addition of electrolytes. In the case of ChNWs/chitosan gels, maximum of E and Q was located at 0.01 M electrolyte concentration, and σ did not indicate clear tendency with electrolyte concentration. Although all gels indicated an increase in E and a decrease in Q with an increase in whisker content, the most remarkable changes were observed under an absence of electrolytes, whereas the changes under the presence of electrolytes were somewhat negligible. Copyright © 2014 John Wiley & Sons, Ltd.