Ultrasonic Welding of Fiber-based Paperboard: Experimental Investigation and Optimization

Abstract

A comprehensive understanding of the influences of joining parameters and material-related factors on the ultrasonic joining process for fiber-based materials is essential to optimize the process parameters in a targeted manner. Previous studies have been limited to commercially available materials with unknown compositions, leaving fundamental influencing factors largely unexplored. In this study, paper made from cellulose-rich natural fibers was used to systematically analyze the effects of amplitude, joining force, moistening, and joining energy. Effects of fiber type and fiber length were systematically analyzed. The joining force had the greatest influence on the joint strength across all materials analyzed, followed by humidification and joining energy. In contrast, amplitude only had a minor influence on the joint strength. The fiber type and fiber length also had a significant influence on the strength of the joint, with joints made from softwood fibers tending to have higher strength values. In addition, the bleaching process improves the joint strength because of the lignin reduction, as it promotes fiber cross-linking. Mechanically digested fibers (CTMP), on the other hand, proved to be less suitable for the ultrasonic joining process, as their increased stiffness made it more difficult to form a stable joint, compared to fibers obtained by purely chemical delignification.