Surface-modified microcrystalline cellulose for reinforcement of chitosan film.

We here report an inexpensive active filler of surface-modified microcrystalline cellulose (MCC) particle for reinforcement of polymer material. A commercial MCC powder with particle size of about 50 μm was mixed with urea and was then irradiated under microwave for the modification. The obtained urea-modified MCC (u-MCC) was able to be dispersed in a chitosan solution without precipitation for over 48 h, which provided a time window for its processing. After the mixture slurry was cast onto glass substrate and then coagulated in a NaOH aqueous solution, a full natural polymer composite film has been prepared. The mechanical properties of the obtained composite films have been carefully measured and discussed. Our results indicate that the mechanical properties reach the highest when the urea-modified MCC is 7 wt% in the composite film: the tensile strength, the breaking elongation, the Young's modulus and the fracture energy are respectively about 2.0, 2.1, 2.4 and 6.0 times those of the pure chitosan film. The reinforcement of the composite material with the u-MCC particles was studied through scanning electron microscopy, Fourier transform infrared spectroscopy and X-ray diffraction analyses, and has been attributed to the strong interaction between the surface-modified MCC particles and the neighboring chitosan chains in the film matrix. Moreover, the water vapor permeability and the transparency of the composite films have been determined to evaluate the potential applications such as gas impervious material and packaging material.