A Note on the Effect of Fiber Diameter, Fiber Crimp and Fiber Orientation on Pore Size in thin Webs

erties on pore size and shape. A large series of simulated images are generated to study the effect of web density, fiber crimp and angular distribution on pore size and shape. Pore characteristics are analyzed for each of the series using object geometry. The results indicate that crimp and fiber orientation significantly influence the pore characteristics. Background It is well known that for a given fabric density and structure, smaller fibers result in smaller pores and better barrier properties, as well as higher flexibility and hand. It is not surprising that there is much effort underway to produce micro-denier and nano fibers in both meltblown and spunbonded fabrics. Similarly, there is significant interest in the use of bicomponent splittable fibers where the fibers are split to form smaller fibers during processing. What is equally important however, is that the pore size and shape characteristics are also influenced by fiber crimp and most importantly by the fiber orientation distribution function (ODF). The interactions between fiber diameter, crimp and ODF have received little or no attention. This situation is intensified by the fact that there are no reliable models available for predicting these characteristics as a function of the process and/or the material. Both meltblown and spunbonded fabrics are planar, with little or no order or orientation through the thickness. Therefore, the pores in lightweight webs may be idealized as two-dimensional entities. This allows the isolation and characterization of the pores easily. In an attempt to establish the interactions that exist between pore characteristics and fiber and structure properties, we employ a set of simulated images with varying properties. The simulation procedures have been previously discussed [1]. The simulated images reveal the degree to which fiber size and crimp and fabric structure affects the pore size and shape. Material and Methods A large set of “nonwoven” images were simulated. These were produced by using the m-randomness method described previously [1]. The set contains images varying in ODF, images employing the same ODF but varying in their crimp, and as images varying in their fiber diameter. The details are given in Table 1. Typical images are shown in Figures 1-4. When dealing with ODF anisotropy, an anisotropy parameter fp can be defined, with the help of the ODF y . The ODF y is a function of the angle q. The integral of the function y from an angle q1 to q2 is equal to the probability that a fiber will have an orientation between the angles q1 to q2. The function y must additionally satisfy the following conditions: fp can be defined as