Absorption properties

Question 1

Which measurements are there to measure sizing?

Answer 1

Cobb
Hercules size test (aggressive green)
Contact angle
PDA (penetration dynamic analyser)

Question 2

What is the principle of cobb testing

Answer 2

You weigh the paper before and after exposing it to water for a set amount of time. Depending on the absorption properties the paper will absorb more or less

Question 3

What is the principle if the Hercules size test

Answer 3

Calibration completed using a black cover to 0% reflectance then one side of the paper is covered with an aggressive green ink the reflectance is constantly measured it will increase as ink begins to penetrate through the paper. The time taken to reach a certain reflectance% is recorded

Question 4

What is the principle of the dynamic penetration analyser (PDA)?

Answer 4

Measures absorption within the first milliseconds.
In dry paper the ultrasound passes through easily
When the paper becomes wet the fibres begin to swell and absorb the ultrasound.

Question 5

What does a penetration dynamic analyser (PDA) graph look like?

Answer 5

The signal will begin to increase at the begining - this shows the displacement of air within the sample. This is the wetting phase.
Once the air is out we move to the penetration phase - the signal will be decreasing due to the fibres swelling and absorbing ultrasound
The graph is Time vs transmission

Question 6

What is the advantage of PDA over Cobb

Answer 6

It gives you dynamic behavior not just one end value.
Also gives data about the very initial stages within milliseconds

Question 7

How do you calculate cobb?

Answer 7

Final weight - initial weight. Then x100 this multiplication is to convert to grams per square meter assuming we have used the standard 100cmsquared sample size