PULPSIL® 968 S, a medium-viscosity water-dispersible product, is a surfactant fluid based on a polyether-modified silicone. Its molecular structure has been optimized to make it less hydrophilic without compromising its pronounced hydrophobic or water-repellent properties. The resultant gain in water repellency, compared with other silicone surfactants, is what makes PULPSIL® 968 S such a particularly efficient dewatering agent.
The hydrophobic nature of the new product is reflected in its very low cloud point of 19 degrees Celsius, as determined in accordance with Method E of EN 1890. This value is far lower than that of other silicone surfactants in the product series. Above the cloud point, the silicone surfactant stops dispersing itself molecularly throughout the aqueous medium. Instead, it forms tiny fluid droplets which is a condition for triggering rapid dewatering.
Generally, in order for a surfactant to work as a dewatering agent, the temperature of the wash liquor must exceed the cloud point. The unusually low cloud point of PULPSIL® 968 S means that it will act with maximum efficiency even in relatively cold wash liquors. However, a corollary of the low cloud point is that products formulated with PULPSIL® 968 S need to be stabilized to prevent premature separation.
The pulp-washing process always involves a degree of air entrainment into the pulp slurry. Unless counter-measures are taken, most of the air would attach itself in the form of tiny bubbles to the cellulose fibers, and so retard drainage of the wash liquor. Processing auxiliaries such as PULPSIL® 968 S are therefore essential for efficient wash processes. In weakening the bond between the air and the fibers, they simultaneously promote coalescence of the tiny air bubbles to larger ones that will rise out of the slurry. This de-aeration creates channels that boost water drainage and greatly accelerate the washing process.
PULPSIL® 968 S is designed to serve as a raw material for service companies that develop ready-to-use auxiliaries for the pulp industry. With this new silicone surfactant, formulations can be tailored to the process of any given pulp mill. Like the dewatering agents PULPSIL® 955 S and PULPSIL® 960 S, PULPSIL® 968 S is generally used in combination with a silicone defoamer.