Hydroentanglement of polymer nonwovens. 1: Experimental and theoretical/numerical framework

Hydroentanglement is a versatile and important process used to form highly entangled nonwoven materials comprised of polymer fibers. It is a key element of polymer processing in the world, with the nonwovens market worth of tens of billions of the US dollars. No fundamental theoretical models of hydroentanglement were available so far, even though such modeling is required to facilitate the entirely empirical efforts to optimize the process. No model experiments on hydroentanglement aiming at its underlying physics were conducted either. These challenging problems are in focus in the present work. A model experiment is conducted and a quasi-one-dimensional model of individual polymer fibers is proposed and implemented for a number of fibers subjected to water jets impacting as a curtain normally to the nonwoven surface and undergoing filtration motion in the inter-fiber pores. The nonwoven is assumed to be located on a moving substrate with water suction through it. The model allows for a number of two-dimensional water jets and a number of suction ports in the substrate. The quasi-one-dimensional model allows for the three-dimensional motion of individual viscoelastic polymer fibers and the fiber-fiber interaction, which makes them non-self-intersecting. Then, the governing quasi-one-dimensional equations of fiber motion are discretized and solved numerically by using a discrete element method with mesh refinement of the Lagrangian mesh during the time marching. Using the developed code, several basic model problems were solved. Specifically, the behavior of several viscoelastic polymer fibers under the action of water jets with and without fiber-fiber interaction is described. Accordingly, a quantitative measure of the fiber-fiber entanglement is introduced based on the observed morphologies in the accompanying second part of this work.