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RAW MATERIALS
• Paper is made from fibers of cellulose. The most common source of
cellulose is trees, but cellulose from cotton, hemp, and many other
materials can be used.
• Cellulose from trees contains lignin: "brown stuff"
that must be bleached and rinsed out to make printing and writing
papers.
• Bleaching can leave traces of acid, which is what
causes paper to turn yellow and crumble with age. "Acid free" papers
contain no acid residue and last much longer.
PULPING
• Cellulose fibers are separated from wood chips by washing, cooking,
and bleaching. The pulp stock (a.k.a. "furnish") that remains is 99
percent water.
"WET END"
• In the papermaking machine, the stock is sprayed onto a long, wide,
moving screen called a "wire." Water drains through the wire, and the
pulp fibers begin to bond together in a very thin mat on the top side
of the wire.
• The fiber mat is then squeezed between felt-covered
press rollers to absorb more of the water. At this point the "paper" on
top of the wire is still about 60 percent water.
"DRY END"
• The wet paper is heated and dried by passing through a series of
steam-filled metal cylinders. Heating and drying the wet sheet seals
the fibers together and turns them into finished paper.
"CALENDERING" and COATING
• The paper is run through a series of smooth-surfaced, chilled metal
cylinders known as the "calender." The calender presses the drying
paper smooth and uniform in thickness.
• "Supercalendering" the paper through an additional set of rollers
gives more smoothness and adds gloss.
• Sometimes the paper is coated with a fine clay (kaolin) to fill in
surface irregularities. This makes the paper brighter, more opaque, and
easier to print on.
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