Observation of Poly{Vinyl Butyral}‐Dibutyl Phthalate Binder Capillary Migration

The movement of poly(vinyl butyral) (PVB) and dibutyl phthalate (DBP) plastic solution under the influence of capillary forces was observed directly by hot‐stage optical microscopy (T=160°C). Migration of a PVB‐DBP droplet within a tapered capillary was examined, allowing the surface tension of the binder system at elevated temperatures to be measured, while maintaining constant composition. Calculated surface tension values for PVB‐DBP plastic at T=160°C ranged from 8 × 10 −3 to 20× 10 −3 N/m (8 to 20 dyn/cm); the large error was attributable primarily to the difficulty in measuring the radii of curvature of the leading and trailing edges of the droplet.