Paper made from wood starts usually starts as wood chips, bark or shavings left over from sawmill operations.
The Process
Paper made from wood usually starts as wood chips, bark or shavings left over from sawmill operations. The material is sorted according to size and moved to the pulping operation where it will be turned into pulp for making paper.
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In the pulping stage, the individual wood fibers must be separated from one another. This can be accomplished using one or more pulping techniques. The type of paper being made determines which pulping process 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.
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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.
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First, papermakers spray the stock onto a long, wide screen, called a wire. Immediately, water begins to drain out the bottom of the wire. This water is collected so that it can be reused over and over again. Eventually, this byproduct of the pulping process, known as pulping liquor, will be collected and recycled into energy.
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Meanwhile, the pulp fibers are caught on the top side of the wire, and begin to bond together in a very thin mat. The fiber mat remaining on the wire is then squeezed between felt-covered press rollers to absorb more of the water.
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Even when this wet end work is over, the pulpy stuff on the wire is still about 60% water. But now it’s time for the dry end.
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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.
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Then a part of the paper machine called the calender – big, heavy cast iron rollers – press the drying paper smooth and uniform in thickness. Sometimes the paper is coated, often with fine clay, to make it glossier and easier to print on.
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A bit more drying, then the paper is rolled onto a big spool or reel, ready for a thousand uses.
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Excerpted from www.tappi.org
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