As the most abundant natural polymer, cellulose has attracted wide attention in sustainable materials due to its renewable and biodegradable properties. Cellulose can be made into nanocellulose through mechanical and chemical treatments, and further made into cellulose film, which has important applications in packaging materials, electronic devices and other fields. However, the common methods use various chemical reagents and complicated processing procedures, which increase the preparation time and pollution. As a simple, fast, green technology, ball milling has the potential to solve these problems. In this study, bleached bamboo pulp was used as raw material to prepare nanocellulose without adding any harsh chemicals. The differences in structure and morphology of cellulose before and after ball milling were characterized by XRD, FTIR, AFM and other methods. Compared with the raw bamboo cellulose fibers with several micrometers in diameter and millimeters in length, the nanocellulose, which contained nanofibrils with tens of nanometers in diameter and serval micrometers in length, and nanosheets with about hundred nanometers in thickness, had undergone significant nanofibrillation under the ball milling. The crystallinity and chemical structure of cellulose did not change significantly after ball milling. Subsequently, by vacuum filtration and dehydration the nanocellulose, a flexible, high strength and translucent cellulose film was prepared and its mechanical and optical properties were studied. The cellulose film had a significant improvement in mechanical properties. Ball milling for 60 minutes made the tensile strength and Young's modulus of the cellulose film reach 124 MPa and 6.5 GPa, which compared with the sample without ball milling increased by 786% and 333%, respectively. Further tests had revealed that the improvement in mechanical properties could be attributed to the different entanglement of fibers and fracture modes in the film. The refinement of the cellulose fibers diameter also increased specific surface area and exposed more hydrogen bonds, making the ball milled sample have a high Young's modulus. In addition, this film had high transmittance up to 80% in visible light region, which was also due to the refinement of cellulose fibers. This green and high efficiency method to prepare the cellulose films is promising for large-scale preparation of degradable packaging materials.
 

Nanocellulose,Cellulose film,Ball milling