Filament breaking length - Experimental and numerical investigations

The tendency of liquid adhesives to draw threads or stretch filaments during manufacturing, a consequence of the visco-elastic properties of all polymer liquids, is a serious issue in industrial bond bonding processes. Description of that phenomenon and identification of influencing parameters have not yet matured enough to allow practitioners adjusting adhesives such to minimize filament breaking lengths. Existing approaches are either too general-by focusing on global rheological properties or too complex-thus impossible to implement in industrial processes. The present paper presents and validates an approach that mitigates between simplicity and complexity, and offers practitioners an estimate for filament breaking length. The methodology requires, besides geometrical (dimensions) and process parameters (displacement rates) only basic rheological parameters (density, viscosity, surface tension, flow-index, and phase shift) that can be determined using standard equipment. The approach was first validated on Newtonian resins, extended to non-Newtonian ones, and complemented by validated Computer Fluid Dynamics calculations to extend the range of rheological parameters considered. Finally, a relatively simple estimate for filament breaking length was proposed, which proved accurate if compared to experimental evidence, as differences between predicted and measured values ranged between 1 and 10 %.