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Abstract
In this work, a series of multi-constituent nonwovens possessing multi-modal fiber diameter distribution was prepared and the air permeability of such nonwoven structures was measured. This approach was extended to bi-constituent nonwovens consisting of fibers with bi-modal diameter distribution and mono-constituent nonwovens composed of fibers with mono-modal diameter distribution. The multi-constituent nonwovens exhibited highest air permeability, followed by the bi- and mono-constituent nonwovens for the same mean fiber diameter. This was explained in terms of the mean pore diameter of the multi-, bi-, and mono-constituent nonwoven structures. An analytical expression of mean fiber diameter of multi-constituent nonwoven structures was derived. The square of the mean fiber diameter in the multi-constituent nonwovens was found to be the harmonic mean of the volume-weighted square of the mean fiber diameter of the individual constituents. The mean fiber diameter coupled with Kozeny–Carman equation was found to predict the air permeability of the multi-, bi-, and mono-constituent nonwovens very well. It was observed that the mono-constituent nonwoven displayed the highest value of Kozeny–Carman coefficient, followed by the bi- and multi-constituent nonwovens.