In situ Raman Spectroscopic Study of Microstructure–Tensile Properties Relationship of Plant Fibers

Plant fibers represent a class of natural composite materials that exhibit an exceptional balance between strength and toughness, a characteristic derived from their sophisticated hierarchical architecture. Through comprehensive X-ray diffraction (XRD) analysis and single fiber tensile testing, we systematically investigated key structural parameters, including crystalline cellulose content and microfibril angle (MFA), along with their corresponding mechanical properties in three representative plant fibers: hemp, sisal, and coir. Furthermore, the fracture morphologies of them were examined using scanning electron microscope (SEM). Specifically, the inherent variations in mechanical properties of plant fibers were quantitatively characterized using a two-parameter Weibull statistical analysis. In addition, the failure mechanism of plant fibers was investigated by combining single fiber tensile test with in situ Raman spectroscopic measurement. The results showed that the high cellulose content and low MFA were associated with the elastic behavior and brittle fracture of plant fibers. The fracture of element fibers was the main failure mechanism of the hemp and sisal fibers with high cellulose content and low MFA. In contrast, the final breakage of the coir fiber with lower cellulose content and higher MFA was attributed to the accumulation of interface sliding including debonding of element fibers and cellulose microfibers.