The 3D structure of fabric and its relationship to liquid and vapor transport

Polymeric carrier fabrics are commonly used in many industrial processes including manufacture of paper and board. Apart from acting as a carrier for the compressible porous material during the manufacturing process, the synthetic woven fabrics comprising mainly of poly ethylene terypthalate (PET) yarns, impart valuable product attributes, i.e. softness, bulk, absorbency, etc. in consumer products. The three-dimensional structure of the fabrics plays a critical role in deciding the manufacturing and energy efficiency as well as product end-use properties. X-ray micro computed tomography (X-μCT) provides a non-intrusive technique to visualize and analyze the three-dimensional structure of porous materials such as paper [The 3 Dimensional Structure of Paper and Its Relationship to Liquid and Vapor Transport, The Science of Papermaking, p. 1289; Tappi J 84 (2001) 1; APPITA 55 (2002) 230]. In this paper, we use this technique to visualize the three-dimensional structure of polymeric fabrics commonly used in paper manufacture [The 3 Dimensional Structure of Paper and Its Relationship to Liquid and Vapor Transport, The Science of Papermaking, p. 1289; Tappi J. 84 (2001) 1; APPITA 55 (2002) 230]. Digital image analysis techniques based on mathematical morphology and stereology were used to determine traditional pore descriptors such as porosity, yarn-void interfacial area, tortuosity and hydraulic radii distribution in the two principal orthogonal directions [The 3 Dimensional Structure of Paper and Its Relationship to Liquid and Vapor Transport, The Science of Papermaking, p. 1289; APPITA 55 (2002) 230]. Comparison of the average yarn diameter by X-μCT and image analysis and physical measurement using light microscopy agreed to within 3% indicating the good accuracy of the X-ray technique. The differences in fabric pore structural characteristics between the in-plane and transverse directions reported here help explain the differences in liquid and vapor transport in the two principal directions. Lattice-Boltzmann simulations of fluid flow and Monte-Carlo simulations of vapor diffusion through actual 3D structures of fabric provide a direct method to predict the permeability and diffusivity characteristics of these complex media. Comparison of structural characteristics between image analysis and simulations show reasonable agreement.