Polymer (cationic polyacrylamides)
Flocculation, retention, and drainage is affected by the quality of the backwater as well as the polymer characteristics, these characteristics affect the electrokinetic energy between the fibers namely the charge density, size of the particles, the weight of the molecules etc.
A balance has to be made between the flocculation of stock and the drainage of the stock. This balance results in a need for fiber flocculation to be limited but the flocculation of fine particles and retention additives should be maximized. As the fibers and fillers flock together to form bonds the drainage on the wire decreases. The molecular weight of the polymer affects the drainage and flocculation. With higher weight flocks are better formed. To improve the drainage the weight of the molecule has to be reduced. It is very important to choose the right polymer to keep the balance.
The total branching of the polymer affects the flocculation. Branching is the term used to describe the polymers ability to bond with multiple chemicals, fibers, fines etc. with industrial water (Backwater system/ dirty water) it was found that polymer with a high degree of branching and a higher weight had more resistance against shear forces and held overall better bonds. This made a positive effect on the retention and drainage of the stock. The dosing point of the polymer is before the primary screen where it will experience high shear forces. Using a polymer with both of these qualities will benefit the formation/ retention.
Polymer used is a dry chemical mixed with dilution water and stored in a chemical tank before being dosed. The issue with the liquid polymer is that it can affect the chemical balance in the thick stock system (flocculation/ retention is reduced) a higher dosing rate is needed to achieve the same parameters as the dry polymer.
The Diluted polymer is added pre-Primary screen and used to create flocks of fibres by reducing the negative charge between the fibres. The polymer is made up of Nano particles and chains which bond together fillers and fines to create flocks. Polymer bonds between the individual fibres forming hydrogen bonds between them. The screen breaks these down into smaller flocks/ chains. This aids in the formation and will improve strength.
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