New application of crystalline cellulose in rubber composites

Graduation date: 2010Rubber without reinforcement has limited applications. The strength of reinforced rubber composites can be ten times stronger than that of unreinforced rubbers. Therefore, rubber composites are widely used in various applications ranging from automobile tires to seals, valves, and gaskets because of their excellent mechanical elastic properties. Silica and carbon black are the two most commonly used reinforcing materials in rubber tires. They are derived from non-renewable materials and are expensive. Silica also contributes to a large amount of ash when used tires are disposed of by incineration. There is a need for a new reinforcing filler that is inexpensive, renewable and easily disposable. Cellulose is the most abundant natural polymer. Native cellulose includes crystalline regions and amorphous regions. Crystalline cellulose can be obtained by removing the amorphous regions with the acid hydrolysis of cellulose because the amorphous cellulose can be hydrolyzed faster than crystalline cellulose. We recently discovered that the partial replacement of silica with microcrystalline cellulose (MCC) provided numerous benefits: 1) low energy consumption for compounding, 2) good processability, 3) strong tensile properties, 4) good heat resistance, and 5) potential for good fuel efficiency in the application of rubber tires. \ud \ud Strong bonding between fillers and a rubber matrix is essential for imparting rubber composites with the desired properties for many specific applications. The bonding between hydrophilic MCC and the hydrophobic rubber matrix is weak and can be improved by addition of a coupling agent or surface modifications of MCC. In this study, MCC was surface-modified with acryloyl chloride or alkenyl ketene dimer (AnKD) to form acrylated MCC (A-MCC) and AnKD-modified MCC (AnKD-MCC). The surface modifications of MCC did not change the integrity and mechanical properties of MCC, but provided functional groups that were able to form covalent linkages with the rubber matrix during the vulcanization. Both A-MCC and AnKD-MCC facilitated the process and production of rubber composites and improved tensile properties and heat resistance of the resulting rubber composites as MCC did when they were used for the partial replacement of silica in rubber composites. Furthermore, A-MCC and AnKD-MCC were superior to MCC in terms of improving tear properties of rubber composites. \ud \ud It has been well-established that the size and the geometrical features of reinforcing fillers play important roles in the mechanical properties of the reinforced composites. MCC was further hydrolyzed with acid to form nanocrystalline cellulose (NCC), i.e., cellulose crystals with their width of less than 100 nm. A novel differential centrifugation technique has been developed for separation of NCC mixtures into fractions with a narrow size distribution. The NCC was investigated as a filler in rubber composites through a dry blending process, but saw little success. NCC had to be dried before it could be blended with rubbers. However, NCC particles tended to aggregate after drying and could not be uniformly dispersed into the rubber matrix during the dry blending. As a result, NCC had poor reinforcing effect on rubbers. For future research, the mixing of aqueous suspension of NCC and rubber latex may improve the dispersion of NCC particles in rubbers, thus improving the reinforcing effects of NCC in rubbers