Reinforcement of Self-Healing Polyacrylic Acid Hydrogel with Acrylamide Modified Microcrystalline Cellulose†

Summary of main observation and conclusion Self-healing hydrogel such as polyacrylic acid (PAA) hydrogel has attracted increasing attention based on its promising potential applications. However, it usually suffers from low strength especially as mechanical device. Herein, a commercial microcrystalline cellulose (MCC) was modified with acrylamide to graft polyacrylamide (PAM) chains on the particle surface. The acrylamide-modified MCC (AM-MCC) was then dispersed in monomer solution of acrylic acid to prepare composite hydrogel. The mechanical properties of the obtained composite hydrogels and the self-healed hydrogels were carefully measured by compressive and tensile tests, and by dynamic mechanical analysis. Our results demonstrate that introduction of a small amount of AM-MCC such as 3 wt% can not only reinforce the original hydrogel and the healed hydrogel markedly, but also improve self-healing efficiency obviously. The analyses indicate that in addition to the reversible multi-interactions such as hydrogen bonding and ionic interactions, the entanglements between the PAA chains of the hydrogel matrix and the PAM chains grafted on the MCC particles have also played an important role on the improvement in mechanical performances and the healing ability of the hydrogel. Moreover, the responsiveness to exterior ion has been tested to indicate potential application of the composite hydrogel as self-healable sensor.