Characterization and mechanical studies on laminated bacterial cellulose / kevlar composite

Cellulose is a well-known eco-friendly and sustainable biopolymer. It attracts many research works on the use of plant based cellulose fibers as a mechanical reinforcing agent in composite. This is mainly due to its high strength, high stiffness, low weight and biodegradability properties. Plant based cellulose extraction however, involves chemical processes that led to high cost and environmental risks. This study focuses on the structural characterization of Nata de Coco bacterial cellulose sheet and its mechanical property as reinforcing agent in Kevlar. Bacterial cellulose sheet and bacterial cellulose powder from Nata de Coco were successfully prepared using three different methods which were oven drying, chemical and mechanical treatment. BC sheet has dimension of 300 mm x 150 mm while BC powder as average grain size of 100 µm and 125 µm. BC sheet has high crystallinity percentage, Xe of 81.76% and also, high thermal stability at Td of 343°C. FESEM image of BC sheet show web-like morphology that consist of cellulose nanofibrils and the functional groups appeared in BC sheet's vibrational spectra confirmed the cellulose produced from Nata de Coco is a pure cellulosic material. Composite Kevlar possessed high mechanical strength as bulletproof material in military applications. BC/Kevlar composite was prepared using hand lay-up technique equipped with vacuum bagging system. BC sheets and Kevlar layers were laminated into several layered structures. Mechanical studies were done using tensile test, low velocity-impact test and dynamic mechanical analysis. Tensile test applied on BC sheet gave tensile strength of 167.64 MPa, Young modulus of 12.78 GPa and elongation at break of 5.2%. Epoxy was applied as the binder in the BC/Kevlar composite. It was found that rigidity in epoxy resin increased the stiffness of BC/Kevlar composite, as a result the composite cannot endure tensor stress. Interestingly, the impact force increased as much as 43% to 197% during the impact test by replacing 1 Kevlar layer with 3 alternating BC sheets to 6 consecutive BC sheets. It was found that the storage modulus, E' and Tan 8 are significantly dependent on the number of BC sheets and its layering structures. The highest storage modulus value of 1120 :MPa was observed when BC sheets arranged alternately with Kevlar layers. Different damage mechanisms associated to the number of BC sheets and its layered-structures suggested that BC sheet is functioning as impact energy absorber, as well as strengthening fibers in composite Kevlar applications.