Influence of Material Variables in Thermal Bonding of Nonwovens

The goal of this research was to understand the bonding behavior of different polymers in thermal bonding. Special attention was given to the interaction of the materials variables with processing characteristics of the polymers.

Initially, thermal bonding studies were done using films from different polymers. Polymer films of different morphology were produced from different grades of polypropylene. Thermal bonding of these films was carried out using the hot press. Effect of film structure, properties and bonding conditions on the bonding efficiency was studied. A range of bond temperatures covering poor, optimum and over bond- ing were studied to understand the changes taking place. Bonded film strength was analyzed using tensile testing. Change taking place to polymer in bond point and original surface were analyzed using SEM. Importance was given to material vari- ables of bonding and their influence on the bond strength are scrutinized in this work. Films bonded at lower sealing pressure and time gave better results. Films with lower orientation formed better bond.

Bonding studies on films were extended to fibers and webs. Polypropylene fibers manufactured with different processing conditions and with different cross-section, denier, and polymer melt-flow rate were bonded with different heat sealers. Bonding studies were also done with several sheath-core bi-component fibers.

Fiber bond strength results were similar to results observed in case of films with respect to bonding temperatures studied. Carded webs were prepared from polypro- pylene and other bi-component fibers. Effect of bonding temperature on property of calendered web was determined using tensile, tear and stiffness testing. Fiber web mechanical properties increased with the calendering temperature. At higher calen- dering temperature strength increased along with the stiffness. After certain optimum temperature, properties of the webs deteriorated.

Impact of spin finishes on the thermal bond strength was studied. Thermal bonding studies of polymer film, fibers and fiber webs with two different finishes at different concentration levels were carried out. In most of the cases, bond strength was lower compared to those without any finish, and the strength drop was higher with higher level of finish. Film, staple fiber and fiber web attained its optimum strength at slightly higher bonding temperature in the presence of finish.