The overarching objective of this work was to develop composite materials based on bacterial cellulose for military use using renewable, sustainable, and environmentally-friendly prudent processing and manufacturing techniques. Approaches to produce oriented crystalline structures to enable the formation of next-generation fibers whose properties will allow the synthesis of composites possessing improved strength and functionality were investigated. The bacterial cellulose fibers were produced from renewable non-food agricultural products via cultivation of bacterial species already used in food-production. This research will provide critical high-performance materials that are based on sustainable resources and green, renewable processing.
A process for cellulose biosynthesis by bacteria to yield unidirectionally-oriented nanofibers formed as fibrous sheets by application of external electrical fields was devised. Approaches to synthesize novel bacterial cellulose composite materials based on task-specific ionic liquids and graphene oxide were studied. Methods to optimize the carbon yield from bacterial cellulose were also investigated.
This limited scope project provides critical proof-of-concept for developing new composite materials based on bacterial cellulose. Electric field alignment studies showed that the choice of media formulation, the geometry of the apparatus, and the use of planktonic (free floating cell cultures) were all important issues for cellulose synthesis in electric fields. A novel approach of templated growth of the bacteria to allow the bacteria to be propagated from a fixed position in the electric field growth chamber provided unequivocal evidence for directional synthesis of cellulose during the application of an external electric field. Two different approaches for producing bacterial cellulose composite materials were investigated. The water in bacterial cellulose hydrogels was replaced with an ionic liquid ([emim][Tf2N]) and performed comparably to, and in some respects better than, state-of-the-art commercial porous polyethersulfone membranes in liquid membrane CO2/N2 separations. This novel approach married the functional properties of ionic liquids with the structural properties of bacterial cellulose for the development of a new class of membrane. Finally, by using a dehydrating agent it was possible to obtain a near theoretical yield of carbon after pyrolysis of bacterial cellulose, which has important implications for development of carbon-based composites and high-value carbon fibers from bacterial cellulose.
The knowledge gained in this work will be applied toward developing techniques to produce carbon fibers and other novel composite fibers with high structural strength and controlled properties. The processing methods use renewable, sustainable, and environmentally responsible methods. Several patents and publications are expected to result from this work. The next step will be to produce materials with properties superior to the current state-of-the-art petroleum-derived composite materials. Such materials will include carbon fibers and carbon cloths—militarily useful due to their low weight and high strength—as well as novel metal, ceramic, and polymer matrix composites.