Mechanism of Abrasion in Nonwovens and Strategies for Abrasion Resilient Nonwovens

Abstract

Fabric abrasion, especially pilling is a problem in textile industry. Pills on the fabric surface are the result of damage to the garment, which cause unappealing appearance. One of the requirements for the use of fabric in many applications is high abrasion resistance. In order to study the evolution of damage process during usage, and further investigate the relation between macro and micro mechanisms of abrasion, we performed in-situ experiments on nonwoven fabric. At macroscopic scale, different morphology of fabric have been identified when fabric rubs against a non-fiber abradant as well as against a fiber abradant. At the microscopic scale, four abrasion mechanisms at the individual fiber level have been identified. In addition, the correlation between two types of pills and six types of precursors have been found. To evaluate abrasion of nonwoven fabrics with minimal human interpretation, we apply two-dimensional, discrete-wavelet transforms to the images of nonwoven fabrics. We describe the degree of damage in terms of a gray-value ratio that is extracted from the details of the wavelet characterization, and show that this parameter correlates well with an independent qualitative assessment of the damage. In order to propose the next-generation design of fabric with better damage resistance, a fiber-level model is established using Rayleigh-Ritz and Finite-Element method based on Kirchhoff-rod theory. We have investigated the generation and evolution of perversions (an inversion of chirality) between helical segments of a fiber with uniform intrinsic curvature when the ends are restrained against rotation. The twist function k3 changes sign in passing through a perversion and this provides a convenient way to identify and approximate the morphology in more complex situations. The shape of an isolated perversion is well approximated by a simple Rayleigh-Ritz trial function. The lowest energy state is one in which perversions occur only when they are geometrically necessary because of the end restraint against rotation. However, the energy differential is small when the fiber is almost straight, so additional perversions may be introduced by noise in the early stages of unloading when the fiber is almost straight. If the fiber is further unloaded, perversion pairs may approach and annihilate each other, but if the perversions are too far from each other or from the fiber ends, an effective energy barrier exists so that they may persist well below the loading conditions where the energy differential is significant. A sufficiently rapid unloading resulted in a higher density of perversions being frozen into the fiber, than that obtained by slower rates of unloading, suggesting an analogy to the retention of defects in solids after thermal quenching.