Retention, dewatering and formation are important parameters governing sheet formation and the final paper properties. Formation affects a wide range of mechanical, structural and optical paper properties. A high retention allows the use of higher amounts of fillers and thereby a reduction of costs. Fast dewatering improves economy and runability of the paper machine. Retention, dewatering and formation are highly interrelated. Changing one of these three properties will most certainly affect the two others.
To achieve a better understanding of this interrelation, simultaneous measurement in a setup resembling the dewatering section of large scale production is necessary. A novel device was developed enabling the simultaneous measurement of retention, dewatering and formation under industry-oriented conditions in the lab scale.
In the project ScherZeit this setup resembling a fourdrinier former is complemented with a device to induce shear forces in the suspension after dosage of retention aids (single components or systems based on two components are possible). This device induces shear in a gap based on a Taylor-Couette flow profile between two cylinder walls (rotating outer cylinder). The induced shear forces are in the range relevant for industrial scale. Thereby the effect of different cationic polymers on retention, formation and dewatering under different shear loads is accessible.
The whole setup allows trials on different retention aids and dosage strategies and their effect on retention, dewatering and formation under industry oriented conditions. Thereby process optimization in this field can be prepared in the lab-scale with reasonable effort (one trial is based on 40 litres of suspension and lasts 45 seconds) to reduce the number of necessary costly industrial trials.