Microcrystalline Cellulose Surface-Modified with Acrylamide for Reinforcement of Hydrogels

In this work, microcrystalline cellulose particles (MCC, 25 μm) were modified with acrylamide under microwave irradiation. The functional groups or polyacrylamide (PAM) chains modified on the surface of the particles facilitated their even dispersion in water. So, the acrylamide-modified MCC (AM-MCC) particles were then dispersed in aqueous solution of monomer of N,N-dimethylacrylamide (DMAA), which was later polymerized to prepare a poly(N,N-dimethylacrylamide) (PDMAA)-based composite hydrogel. The microstructure of the composite hydrogel was carefully studied with Fourier transform infrared spectroscopy and scanning electron microscopy. The mechanical properties of the composite hydrogel were investigated through compressive and tensile tests. Our results indicate great improvement in the mechanical properties upon addition of the AM-MCC particles for the composite hydrogel. The analyses suggest that the evenly distributed AM-MCC particles can act as a physical cross-linker to connect the neighboring polymer chains to strengthen the composite hydrogel, on the basis of their strong interactions, including hydrogen bonding and chain entanglements. However, over-loading (more than 5.6 wt%) of the AM-MCC would lead to aggregation of the AM-MCC particles to destroy the uniform microstructure of the composite hydrogel, resulting in a reduction of the reinforcement effect. The reinforcement effect of the AM-MCC has also been evidenced by PAM-based composite hydrogels, which were prepared in a similar way. Moreover, the recoverability, cyclic, and swelling behaviors have been measured to indicate potential applications of the composite hydrogels. Therefore, our work provides an inexpensive but active filler of AM-MCC, which can be well-dispersed in water media and is suitable to reinforce hydrogels.