Characterization of nonwoven structures by spatial partitioning of local thickness and mass density

In this investigation the distributions of local mass, thickness, and density for various nonwoven materials were mapped and analyzed. Non-contacting twin laser profilometry was used to map 10 mm square regions to a resolution of 25 μm. The areal distribution of mass was obtained using β-transmission radiographic imaging. Samples were selected from three common categories: nonwoven hybrids, polymer extruded nonwovens, and wet laid nonwovens. Several samples had embossed regions where the structure was compressed by melt bonding to impart strength. Structural maps were partitioned using binary masks to isolate the embossed features from the stochastic background structure. The joint distributions of thickness versus areal density were plotted and used to characterize the separated regions. Based on the structural distributions obtained from mapped regions, the background structure of most of the samples provided similar results to those observed for other stochastic fibrous web materials, such as paper. The wet laid samples and one spun-bonded extruded polymer nonwoven appeared stochastic with good correlation between local thickness and local areal mass density. In contrast samples with induced features such as embossing, melt bonding, and calendering show that thickness became independent of mass as a result. Examination of the thickness distributions within embossed regions for different samples showed different responses to compression that appeared dependent on material density and thickness.