St Cuthberts Mill

Taking a look at the 'Chemical Charges of Pulp'

We were looking at the chemical charges of the pulp. Seeing how the addition of each chemical effects the charge of the pulp. We used samples of the pulps we use on the machine, both cotton and wood. The first step was to soak the pulp.

Then the pulp is beaten in the beater. A specific amount of pulp is weighed out and water is added. This gives us a similar consistency as is used on the machine. The pulp is added a strip at a time to the beater until it is all in. 

                       

Then the pulp is beaten to break up the fibres. We beat the pulp to 25 °SR, a measure of beating. We test this using the Schopper Reigler. Take a measured sample of the pulp from the beater. Make this up to 1litre and pour into the top of the Schopper Reigler. Release the lid. The water will drain through the mesh and come out of 2 funnels. The fibres will catch in  the mesh. The amount of water that comes out through the front spout gives us our reading. This test tells us how 'well beaten the fibres are.

Once we have beaten the stock to 25 °SR we take a sample and test the charge of the stock using the Zeta Potential machine. This measures whether the pulp is positively or negatively charged. (Cellulose fibres have a negative charge.)

We then return to the beater and add in the chemicals used in production, in the order they would be added during production. They are added one at a time, mixed in and the charge is tested.

The charge of the paper effects how the chemicals might perform, how well they are bonded to the fibres, etc.

Huge thanks to Nicola Dobson, our Quality Control Apprentice and Steve Carroll (Paper Chemist/Quality Control) for all the photos and info!