How Is Paper Made?

If you really want to know about paper and papermaking, you've got to get to know trees and the wood they contain.

A tree is a complete unit: bark, roots, trunk, stems, leaves, whatever. Wood is the trunk and main stems of trees, suitable for building, paper making, and other uses.

Fiber is the building block of all trees and other plant material. Wood is comprised of fibers, the tiny cellulose strands stuck together with a natural adhesive material called lignin. It is by separating and reorganizing those fibers that we make paper.

Some paper is made brand-new from trees — either small trees harvested just for that purpose, or from sawmill scraps left over when larger trees are made into lumber. A second source of papermaking material is recycled fiber. Each year, more and more paper is recycled — its fibers used a second, third or fourth time. Every year, about 50% of the paper Americans use is recovered for recycling and other uses.

Almost all of the paper you use today is made of wood fibers. Some specialty papers, like stationery and money, are made from linen, cotton, or other plants. Other papers contain a combination of cellulose fibers and synthetics such as latex. Still others are made completely from synthetic materials such as polyolefine. You might find latex in a waterproof mariner's chart, or polyolefine in a rugged courier envelope. But you'll find natural fiber paper almost everywhere!

First, workers harvest trees, mostly from special tree-growing areas called tree farms. After the trees are removed, more trees are planted in their place. While they are growing, the young trees produce lots of oxygen, and provide great habitat for deer, quail, turkeys and other wildlife.

The logs are transported to the paper company where they get a bath to rinse away dirt and other impurities before being turned into small chips of wood. The chips are then sorted according to size, and moved to the pulping operation, where they will be turned into pulp for making paper.

In the pulping stage, the individual wood fibers in the chips must be separated from one another. This can be accomplished using one or more pulping techniques. The type of paper that's being made determines the pulping process that is used. The finished pulp looks like a mushy, watery solution. But if you look at it under a microscope, you will see that the individual wood fibers have all been separated.

Now it's time to make paper out of our pulp. That mainly means getting the water out of the wood-fiber soup, since this papermaking stock is about 99% water. The first area in which this takes place is called the wet end of the papermaking machine.

In the dry end, huge metal cylinders are heated by filling them with steam. The wet paper, which can be up to 30 feet wide, passes through these hot rollers — sometimes dozens of them, and often in three to five groups. Heating and drying the wet sheet seals the fibers closer and closer together, turning them gradually from pulp into paper.

When you look at a piece of paper, can you find any difference in thickness in that single sheet? Probably not, thanks to a part of the paper machine called the calender — big, heavy cast iron rollers that press the drying paper smooth and uniform in thickness.

Some paper has a coating added, often with fine clay. This serves as a "primer" to allow for a smoother, finer surface and enables more detailed ink holdout. This coating can be glossy or can be produced in various levels of matte/dull/satin.

A bit more drying, then rolled onto a big spool or reel, the pulp — a miraculous mat of fibers from trees - has become paper, ready for a thousand uses.

Source: sappi.org