Filament stretching of high viscous industrial adhesives

The tendency of liquid adhesives to draw threads or stretch filaments during manufacturing is a serious issue in industrial bond bonding processes. Formation of adhesive filaments is a consequence of the visco-elastic properties of all polymer liquids. Description of that phenomenon, and identification of influencing parameters, have both not yet matured enough to allow practitioners adjusting adhesives such to minimize filament breaking lengths. Previous work [1] has not been able to accurately predict the filament tendency of industrial adhesives. To increase the knowledge regarding this problem with high relevancy for industry, five industrial adhesives were examined with regard to their filament tendency. Previous experiments have shown that the filament tendency cannot be determined solely by oscillation measurements using rotational rheometers. It has been shown that filament tendency is linked to several rheological parameters, as viscosity, flow index, surface tension and density, and elastic properties of the adhesives [2]. To quantify the filament tendency the maximum filament breaking length and the resulting maximum Hencky strain were determined by an elongation flow test with four different elongation rates (5, 15, 30 40 mm/s), as illustrated by Fig 1.Fig 1. Filament stretching test With the aid of the numerical flow simulation Polyflow® (typical results displayed inFig.2), and an implemented filament failure criterion, filament stretching test could be simulated, and breaking lengths estimated based on aforementioned rheological parameters. Numerical modelling allowed to isolate the individual influence of each of the individual parameters (viscosity, flow index) and material parameters (surface ension and density) on the filament breaking length. From the findings of the rheological tests obtained and the numerical simulations a mathematical model was derived to predict the filament tendency on viscous adhesives. The validity of the model was then assessed experimentally on a wide range of commercially available adhesives, and a good agreement was found.