Task 4: REFINING

"Refining" is an intense mechanical treatment performed on pulp fibers to make them more suitable for papermaking. After pulping and possibly bleaching, the fibers are hollow, tub-like structures (similar to drinking straws). To expose the most surface area for fiber-to-fiber bonding, these tubes must be collapsed into flat ribbons. Refining is the action that does this. Refining also makes the outer layer of the fibers hairy instead of smooth (scratches up the surface), which subjects more surface area of the fibers to hydrogen bonding.

Strong paper cannot be made without the use of refining. Without refining, sheets of paper feel like felt, fluffy and weak. In the pulp and paper industry, refining is carried out by passing the pulp between grooved plates rotating at high speed less than 1 mm apart. Some bad effects that happen to the pulp during refining include the water draining more slowly from it and some of the fibers are damaged severely in the process. However, papermakers need the strength of refining so much that they are willing to put up with these negative effects.

In the laboratory, refining can be carried out in a kitchen blender. The shearing action of the blender blade causes the collapse of the fibers into flat ribbons. The amount of refining required for an optimum strength depends on the nature of the fiber itself. For this activity, a standard refining time of 5 minutes will be used.

Describe the importance of refining in the papermaking process.

Are all the results of the refining process positive? Explain.

How will you refine fibers in the laboratory?

Determine the mass of wet pulp after bleaching and filtering: _________ g wet bleached fiber. Add this fiber to the blender.

The bleaching process alters the original OD grams. The percent yield of new grams of OD fibers you have can be determined by the following formula:

%yield = new grams OD fiber (bleached)

original grams OD fiber

For this lab we will assume a 90% yield. Calculate the new grams of OD fiber based on this % yield and the original grams OD fiber from Step 1a of Bleaching lab.

 

 

 

The basic recipe for a batch of pulp to be refined is grams OD fiber at a 1% consistency.

1% slurry = g new OD fiber

grams total mixture

Solve this equation for grams total mixture: grams total mixture = ___________________

grams total mixture = ( g wet bleached fiber) + (grams water)

Calculate the mass of water needed to add to your grams of wet fiber to equal mass of total mixture.

Convert the mass of water calculated in Step 4 to milliliters.

 

 

Add the volume of water calculated in Step 5 to the blender containing the massed wet fiber.

Energize the blender for 5 minutes. Use the "Blend" setting or similar mid-range speed.

The slurry is now ready for measuring out for handsheets.