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Evaluation of Mechanical and Interfacial Properties of Individual Lignin Carbon Fiber and Composites



Use of lignin as a precursor, instead of PAN, for manufacturing carbon fiber shows promise in developing renewable and low-cost carbon fiber composites. The lignin used in this research was a highly pure form based on the extraction process that was implemented. Suitable procedures were developed to melt spun lignin fibers which were subsequently stabilized and carbonized. The resulting carbon fibers were characterized to determine mechanical and interfacial properties of single carbon fibers with future scale-up to fiber reinforced epoxy composite testing. Using VARTM, initial lignin carbon fiber composites were manufactured by the authors. Mechanical testing of single carbon fibers was performed using a highly precise nanouniversal testing machine and the results were interpreted using a Weibull statistical distribution. The tensile testing on single fibers resulted in a Weibull shape parameter of 3.66 and scale parameter of 630 MPa respectively. The interfacial properties were determined using a Single Fiber Fragmentation Testing and a custom testing apparatus. Average interfacial shear strength values on the order of 31 MPa were obtained with an average size of 100 μm delamination zone. X-Ray Diffraction (XRD) was used to determine the structural characteristics. The structure of the lignin carbon fiber developed to date had little to no crystalline regions with minimal alignment. Initial trials associated with the mechanical testing of these lignin-based carbon fiber composites prepared using VARTM were considered and are in development. Mechanical testing will integrate digital image correlation (DIC) for highly accurate strain mapping on specimen for future testing. This top-to-bottom approach will evaluate lignin at every step of the process in realizing a dream to make a lignin and bio-epoxy based renewable carbon fiber composite.

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