Abstract
The role of fiber morphology in a thermal point bonding operation was investigated. Primary objectives were to understand the changes taking place in fiber structure due to applied heat and pressure, and the role of fiber morphology in determining optimum process conditions and properties of the webs. To study fibers with varying morphology, i.e., from partially drawn as in spunbonding to fully drawn as in staple fiber nonwovens, fibers with a wide range of crystallinity and orientation were spun and characterized, from two polypropylene resins. Thermally bonded carded webs were produced, using these fibers, and characterized in order to understand thermal bonding behavior of fibers with different morphology. The fibers with different morphology differed significantly in their bonding behavior. The fibers with higher molecular orientation and crystallinity tended to form a weak and brittle bond due to lack of polymer flow and fibrillation of the fibers in the bonded regions. In general, fibers with lower molecular orientation and lower crystallinity yielded stronger and tougher webs. Fibers with relatively less developed morphology also exhibited lower optimum bonding temperature. Morphological changes in fibers were observed during the thermal bonding process, in bonded as well as unbonded regions of the web. As a final step to see how the observations from staple-fiber study translate to one of the relevant processes during scale-up, spunbond studies were also conducted in a similar way.