Air Permeability of Multilayer Needle Punched Nonwoven Fabrics: Theoretical Method

The theoretical permeability of multilayered nonwoven fabrics was studied using a modified Kozeny equation. The Kozeny equation is based on the concept of a hydraulic radius, i.e., a characteristic length parameter. It is limited to structures with porosities less than 0.94. The structures used in this research are intended for use as high temperature insulation and all had porosities of greater than 0.96. The Kozeny equation was therefore modified to extend its usefulness to fabrics with higher porosity. Fabric construction parameters, along with fabric and fiber properties were used as inputs to this model and theoretical air permeability was determined. The effect of number of barbs and layering structure on the determination of theoretical air permeability was also considered and discussed. Statistical analysis was performed showing that fabric thickness, number of needle barbs, mean pore size and fabric density are significant factors in predicting theoretical air permeability.