Quantifying The Softness of Wool via Structure-Property Relationships

State-of-the-art evaluation of textile touch sensation (e..g., scratchiness) follows broadly-adopted qualitative and time-intensive procedures that rely on consumer-based studies. This is due to the lack of understanding of how material properties and fiber morphology affect the surface interaction of the fabric with human skin. Wool, in particular, is an animal-derived fiber that can range from extremely soft to uncomfortably scratchy, due to the broad range of fiber properties depending on the source. Here, the morphological, compositional, and mechanical properties of a variety of natural wool fibers of reported consumer-based haptic feel are investigated. Using scanning electron microscopy (SEM) and a custom image analysis framework, we assessed the evolution of fiber morphology (e.g., diameter and surface roughness) across a large variety of animal sources. We also analyzed how fiber composition varies between sheep breeds through Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), and x-ray diffraction (XRD). Last, we characterized the mechanical properties of the fibers such as tensile strength and viscoelastic moduli through dynamic mechanical analysis (DMA) and uniaxial tensile testing. This comprehensive study of wool fibers is essential in establishing structure-property relationships and quantifying how composition, microstructure, and mechanical properties impact fiber interaction with human skin and haptic feel. This will in turn enable the development of standardized human-subject-free test methods for fiber scratchiness and will guide the design of new fibers and textiles for the apparel and medical industries.