Self-reinforced nanocomposite by partial dissolution of cellulose microfibrils in ionic liquid

All-cellulose nanocomposite films with different ratios of cellulose I and II were produced by partial dissolution of microfibrillated cellulose using ionic liquid and subsequent film casting. The films were isotropic, transparent to visible light, highly crystalline, and contained different amounts of undissolved cellulose I crystallites in a matrix of dissolved cellulose. X-ray diffraction confirmed that cellulose I, i.e., the major polymorphic modification of cellulose in these nanocomposites, is rearranged to cellulose II crystal packing after the partial dissolution. The all-cellulose nanocomposite showed enhanced thermal properties, with thermal degradation temperature increased by 22% compared with the dissolved cellulose. The SEM and AFM studies verified that the nano-sized cellulose crystallites were well dispersed in the matrix. Results from DMA showed that the storage modulus was increased from 270 MPa for the dissolved cellulose to 1104 MPa for the nanocomposite with lower dissolution grade. This indicates that the all-cellulose nanocomposite films contained undissolved cellulose fragments - possibly cellulose I crystallites or aggregates of crystallites in a matrix of regenerated cellulose.