An enhanced cross-sectional analysis to evaluate tensile properties of silk waste fibers

To promote sustainability and circular economy, silk waste could be recycled and upscaled into nonwoven fabrics for composite production. With such goal in mind, a thorough characterization of the tensile properties of silk waste fibers was conducted. Silk is a natural protein fiber, appreciated and widely used in the textile industry. It is composed of fibroin and sericin, the latter being removed during the degumming process. A major challenge in characterizing silk fibers is their non-circular cross-section, which leads to significant errors in the evaluation of tensile properties when a cylindrical model is assumed. Both raw and degummed silk waste fibers were investigated, using SEM, optical microscopy, FT-IR spectroscopy and single fiber tensile tests. A novel method was proposed to refine the analysis of the cross-section, correcting the error introduced by the cylindrical approximation. Tensile strength, strain at break and Young’s modulus were described by gage length dependent two-parameter Weibull distributions. The experimental campaign indicated that degumming effectively removed sericin and resulted in higher strength and modulus. The proposed correction method for the cross-section significantly affected Weibull parameters, particularly for raw fibers, resulting in larger values of strength and modulus scale parameters. An equivalent fibroin cross-section model was proposed as well, finding a good agreement with the experimental results obtained from degummed fibers, thus confirming the limited load-carrying capability of sericin. This study provides a foundation for refined analysis of the properties of silk waste fibers to be used for composite materials.