Filament Rheology
Extensional rheometrical measurement quantifies fluid filament thinning rates under liquid surface tension forces to evaluate liquid behavior during high-speed coating and adhesive application. Industrial laboratories run caber testing to predict whether high-speed converting adhesives or paper coatings will form persistent liquid threads during high-speed jetting or roll transfer. The physical measurement tracks the mid-filament minimum diameter over time as a liquid bridge narrows until filament rupture.
Necking Dynamics
Polymeric fluid elasticity resists capillary thinning and prolongs the liquid bridge lifespan well beyond Newtonian predictions. During caber testing, fluid response transitions from a visco-capillary balance to an elastocapillary balance where the characteristic relaxation time of the polymer chain controls the rate of diameter decay. Extensional viscosity values extracted from filament thinning curves indicate how a formulation responds to sudden tensile stretching in nozzle application.
Severe strain hardening within the thinning filament delays final droplet separation, generating persistent filament threads on high-speed packaging machinery. Measuring this decay rate establishes precise numerical thresholds for polymer concentration adjustments in water-based adhesive formulations.
Transfer Limit
Formulation boundaries emerge when fluid elasticity prevents clean necking at converting line speeds. Excessive relaxation times recorded during caber testing correlate directly with misting on roll coaters and trailing tails on jet applicators. Measurement accuracy fails when low-viscosity fluids break up before the top plate reaches its full step-strain displacement.
