Analysis and Modeling of the Influence of the Size and Fraction of Bonding Points onto the Mechanical Behavior of Polypropylene Spunbond Nonwovens

While the influence of fiber strength and calendering parameters on the mechanical strength of polypropylene spunbond nonwovens are investigated extensively, only a few nonsystematic studies are available on the influence of bonding point size and bonding point fraction. Therefore, systematic investigations of the influence of bonding point fraction, bonding point size, and spacing on the tensile properties of nonwovens are conducted. In addition, the influence of fiber orientation and cloudiness on the strength is evaluated. It is demonstrated that an increase in the bonding fraction leads to an increase in stiffness and strength, although this effect is weakened due to fiber damage at the edges of bonding points, when many small bonding points are used. An increase in bonding point size and distance between the points with a constant bonding fraction initially leads to an increase in strength. Only when the distance between the points exceeds, the size of the local nonuniformities the strength decreases again, whereas the stiffness decreases continuously with increasing distance between the bonding points. In addition, it is shown that the stress–strain behavior of nonwovens can be described using a Maxwell model and that the strengths can be modeled using statistical modeling with optically accessible parameters.