Determination of fiber volume fraction of carbon fiber-reinforced polymer using thermogravimetric methods

In a composite, the fiber volume fraction is one of the most important factors affecting its mechanical and physical properties. This study proposes thermogravimetric analysis as a potential method for determining fiber volume fraction. The analysis method was developed using a systematic approach in which heating rate, analysis atmosphere, and sample size were considered. Using a unidirectional carbon fiber-reinforced epoxy composite as the test material, the new method was benchmarked against the standard wet chemical analysis method. The optimum thermogravimetric testing process is a two-stage procedure in which ground composite samples were first subjected to matrix decomposition under nitrogen, followed by the elimination of remaining char under technical air. A mass-rate-controlled heating program was found to be most suitable to distinguish char degradation from carbon fiber degradation. The new thermogravimetric method and the traditional wet chemical method produced comparable results.