Determination of fiber volume content in natural fiber reinforced polymers

Growing environmental awareness has intensified the demand for bio-based and eco-friendly materials. Natural fiber–reinforced composites have emerged as promising candidates for replacing traditional polymers and composites, provided that performance requirements are met. The fiber volume content in such composites significantly influences their thermomechanical and processability behavior. This study proposes a novel approach for quantifying natural fiber volume content in polymer composites using thermogravimetric Analysis. By applying a controlled thermal ramp followed by isothermal conditions at a temperature where fiber and matrix exhibit distinct degradation profiles, the fiber fraction can be mathematically derived. Experimental work was conducted on flax fiber–reinforced epoxy composites with fiber-to-matrix mass ratios between 20% and 50%. Results revealed that, within a specific time window of the TGA, calculated fiber contents closely matched nominal values for intermediate fiber loadings. However, at the lowest (20%) and highest (50%) fiber fractions, deviations were observed. Finally, this method was also applied to hemp/epoxy composites, demonstrating that, with the introduction of a modification factor, it can be extended to other types of natural fibers as well.