FAQs on P & P

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. How are pulp and paper made?
. Why is Paper Bleached?

How are Pulp and Paper Made?

Pulp is primarily made from trees, although alternative fibres like straw, hemp, and kenaf are used and should be incorporated wherever possible. The trees are usually either ground up by mechanical force or soaked in chemicals to get more purified fibres. The mix of pulp types is determined by the type of product the pulp will be made into at a later date. Pulp is sometimes bleached to make it whiter and brighter and then is either sent to the paper machine in the plant, or sold on the open market to the highest bidder.

Paper machines take wet pulp and spread it on a thin fabric known as a "wire". This thin pulp slurry is then sent through a high speed machine where it is dried and pressed and put onto giant rolls. Different additives are used depending on the type of end product desired.

Finally, the paper is sent to a converting or finishing plant where it becomes, 8 1/2" x 11" copy paper, cardboard boxes, envelopes, milk cartons, or any of the other hundreds of products made from paper.

For more detailed explorations of this question, see The Basics

Hardwood pulp is a natural tan, but custom dictates that it needs to be white.

If trees didn't contain lignin, we wouldn't need to bleach their pulp. The lignin in paper makes it darken when exposed to light. While chemical pulp contains less lignin than mechanical pulp, both need additional processing to produce pure white cellulose fibre.

After chemical pulp gets cooked and washed, some of the lignin remains in the fibre. The pulp is naturally brown, in a variety of shades.

After washing, the brown pulp is treated with chlorine gas to remove more lignin. The pulp is then bleached white in stages by chlorine and chlorine dioxide gas, or hypo-chlorite. This strong, white kraft pulp makes excellent paper for high speed, high quality printing.

Mechanical pulp, with its higher lignin content, is usually made brighter with hydrogen peroxide. This changes the lignin without removing it, and also lightens its colour.

Mechanical grinding breaks the cellulose fibres when it tears them apart,, and doesn't remove the lignin around them. This makes an opaque paper that's easy to read. Mechanical pulp's weak fibre is often reinforced with chemical pulp. It's used for newsprint and phone books.

Did you know that most of the world's pulp and paper mills don't use chlorine for bleaching? But until the discovery of dioxin in pulp mill effluent in the late 1980s, the use of chlorine was growing. Most papers are made from a mixture of pulps, with kraft pulp added for strength. Strong white paper can withstand the high speeds of modern printing presses, and makes advertising photos look superb.