Estimation of Tensile Strength and Young’s Modulus of Nonwovens Containing Adhesive Polyvinyl Butyral Polymer

Estimation of the tensile strength and Young’s modulus of nonwovens is difficult owing to complex internal fiber entanglement. In the present study, we developed a property estimation model whereby a polyethylene terephthalate (PET) fiber web mixed with sheath–core fibers containing a polyvinyl butyral (PVB) polymer adhesive is heated. We found that increasing the sheath–core fiber mixing ratio steepened the stress–strain curve and increased the strength. When plotted against the square of the mixing ratio, which represents the fiber contact probability or “entanglement point density,” the tensile strength exhibited a linear relationship, whereas the Young’s modulus became saturated at approximately 64%. Specifically, the strength is linearly dependent on the entanglement point density, whereas the Young’s modulus increased exponentially. Similar tendencies were observed for needle-punched nonwovens with various needle densities. However, the increase in the Young’s modulus was delayed in these nonwovens, and some samples demonstrated a decreasing tendency in strength in addition to a linear increase. We attributed these differences to a reliance on fiber friction rather than chemical adhesion for entanglement and physical fiber damage caused by excessive needle punching. Our model successfully quantifies the mechanical behavior of nonwovens based on the probability of fiber contact.