Morphology distributions in thermally point bonded nonwovens

Nonwoven fabrics make up one of the fastest growing segments of the textile industry. Critical parameters for the properties and performance of thermally point bonded nonwovens are the fiber type (morphology and properties), overall fiber orientation in the nonwovens, the process time, temperature and pressure as well as the bond size, shape and bond density. Although much knowledge has been gained about how the structure of a nonwoven affects its properties, it is not clear how the morphology (structure) and properties of the original fibers are transformed in the nonwoven via the bonding process as a result of the process variables of time and temperature. Crossing this major hurdle is complicated by the lack of good analytical techniques to determine what structural changes occur during processing. Due to the complex structures of nonwoven fabrics and difficulty of extracting fibers from nonwovens, traditional methods for measuring the morphologies are inadequate for nonwovens.; In this work, a technique, polarized laser Raman microspectroscopy, combined with routine measures, is found to be capable of determining the morphology of individual fibers, individual bonds and small critical regions at the bond edge for nonwovens. This provides detailed information about the process/morphology/property relationships on the size scale necessary to understand how the morphology and the properties of the original fibers are transformed in nonwovens via the bonding process variables. The results obtained in this work include: (1) Developed effective methods to give detailed morphological information about fibers within nonwovens, (2) Developed iPP morphology/Raman spectra correlations, (3) Determined morphology distributions in isotactic Polypropylene (iPP) thermally point-bonded nonwovens, (4) Determined morphology distributions in Polyethylene terephathalate) (PET) thermally point-bonded nonwovens using existing PET correlations, (5) Based on existing theoretical models of “polymer-polymer adhesion”, how bonding conditions affect strength of bond has been attempted to understand. Major factors in forming a strong thermal point bond in a short time are the molecular weight of the surface polymer and the fraction of this polymer that resides in the non-crystalline region at the interface between the fibers being bonded. This is in turn controlled by the temperature at the interface.