An evaluation of fiber orientation and organization in nonwoven fabrics by tensile, air permeability and compression measurements

Three indirect techniques—tensile, compression, and air permeability measurements—have been used to investigate the fiber network organization inside a highly porous nonwoven. They are standard material property measurements that require relatively simple equipment and are hence an interesting alternative to more costly direct analysis methods such as image analysis or X-ray tomography. The tensile measurement provides information on in-plane anisotropy of the nonwoven, through the use of an experimental parameter obtained from the tensile moduli measured in two perpendicular directions. The air permeability and compression analyses are based on existing models that describe the 2D or 3D isotropy. It is also possible to obtain two characteristic lengths that describe the fiber network: the hydrodynamic diameter and the mean distance between fiber junctions. Another important parameter is the fraction of fibers oriented in the thickness direction that could be determined from the permeability data. Our study shows that the observations and results from all three independent techniques are very well correlated for the range of nonwovens studied, and thus provide coherent description and insight of their internal structure. The nonwovens were found to exhibit in-plane anisotropy, while fitting 3D isotropic models in compression and permeability behavior.