Studying Pore Structure of Nonwovens with 3D Imaging and Modeling Permeability

摘要

Nonwovens are classified as a porous material and pore structure is named as the most important and complex feature of them. Since pore structure is out of control during any nonwovens manufacturing processes, many attempts have been made to measure the major characteristics of a pore network including: pore size, pore volume, pore surface area and pore shape. Among all pore characteristics, pore size due to its significant influence on many nonwovens applications such as filtration is counted as the most significant one. Generally, experiment, theoretical modeling and image analysis are the most common methods to measure pore size of nonwovens. Normally, pores in nonwovens make many convergences and divergences along the length and for this reason, many pore diameters could be assigned for a media. Due to inefficiency of the aforementioned techniques to measure all these diameters, they are not precise enough to study pore structure.;The initial objective of this research is obtaining information of the pore structure, especially pore sizes, by applying image analysis techniques to a 3D image of nonwovens obtained through 3D imaging techniques such as DVI and micro CT. This 3D structure of the nonwoven media will be transformed to a graph, employing skeletonization through AvizoRTM software. The obtained graph exhibits topology, shape and connectivity of the pore structure for the utilized nonwoven. In this graph, each node and link would be a representative for pores intersection and body of pore, respectively. Saving the information of this graph results to some matrices/vectors including nodes coordinated, connectivity and nodes thickness, which exhibits the pore size. Therefore, all the pore sizes available in the structure will be extracted through this method.;As expected, the information obtained from pore network is very complex consisting many numbers, so analyse them would be very difficult. Therefore, it was tried to use the saved information to model permeability of the media. So, pore was assumed as a capillary and employing the similarity between Hagen-Poiseuille's and Ohm's laws results in simplifying a network of capillaries to a single number. For this purpose, the capillary network was considered as a resistor network and the equivalent resistance of this network was used to calculate permeability of the nonwoven, in conjunction with Darcy's law at the scale of imaged sample. Using several datasets (real and simulated) indicates that there is a decent agreement between the model and experiment.