Anisotropy in the Mechanical Properties of Thermally Spot-Bonded Nonwovens: Experimental Observations

Anisotropy is evaluated for in-plane mechanical properties, such as tensile modulus, maximum stress in tension, elongation at maximum stress, shear modulus, and bending rigidity, of three designed sets of spot-bonded nonwoven fabrics. Image analysis is used to quantify the fiber orientation distribution and identify failure mechanisms. The non-woven fabrics in this study have been produced specifically to explore the effects of different processing conditions (temperature, pressure, and bond area) on mechanical performance. The results show that, within a typical window of processing conditions, bond area and bonding temperature have a significant influence on all the mechanical properties. The data also suggest that failure of thermally bonded nonwoven structures is likely to be governed by critical stress-based criteria. An important inference from this work is the recognition that the mechanical properties of thermally spot-bonded nonwoven structures can be described quantitatively through a simple composite model. The results also suggest that the azimuthal properties of the bonded and nonbonded regions, and thus the nonwoven, are likely to be amenable to continuum models of materials with ortho-tropic symmetry.