Effects of Erucamide on Fiber "Softness": Linking Single-Fiber Crystal Structure and Mechanical Properties.

Erucamide is known to play a critical role in modifying polymer fiber surface chemistry and morphology. However, its effects on fiber crystallinity and mechanical properties remain to be understood. Here, synchrotron nanofocused X-ray Diffraction (nXRD) revealed a bimodal orientation of the constituent polymer chains aligned along the fiber axis and cross-section, respectively. Erucamide promoted crystallinity in the fiber, leading to larger and more numerous lamellae crystallites. The nXRD nanostructual characterization is complemented by single-fiber uniaxial tensile tests, which showed that erucamide significantly affected fiber mechanical properties, decreasing fiber tensile strength and stiffness but enhancing fiber toughness, fracture strain, and ductility. To correlate these single-fiber nXRD and mechanical test results, we propose that erucamide mediated slip at the interfaces between crystallites and amorphous domains during stress-induced single-fiber crystallization, also decreasing the stress arising from the shear displacement of microfibrils and deformation of the macromolecular network. Linking the single-fiber crystal structure with the single-fiber mechanical properties, these findings provide the direct evidence on a single-fiber level for the role of erucamide in enhancing fiber "softness".