is Paper Made?
If you really want
to know about paper and papermaking, you've got to get
to know trees.
Trees are all around you. But have you
ever really thought about how they're put together?
They're pretty cool.
Just look at a tree trunk. The bark
protects the inner wood from weather, insects and other
dangers. Just inside the bark is a thin layer called
the cambium, whose cells become both bark and
inner wood. Next is sapwood, which carries nourishing
sap throughout the tree the same way our blood flows
through our bodies to nourish us. Heartwood is
the innermost part of the trunk, and even though it
isn't alive, it provides the tree with strength and
All that wood material is formed of fibers,
tiny cellulose strands stuck together with a natural
adhesive material called lignin. It's by separating
and reorganizing those fibers that we make paper.
Consider the source
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
Wood is wood?
Yes, but it's not that simple. Each tree species grows
a certain way, and that affects the way its wood looks
and performs. Foresters divide trees into two categories:
hardwood and softwood species.
Hardwood trees such as oaks and maples
have wood with very short fibers. Paper made from these
species is weaker than that made from softwoods, but
its surface is smoother, and therefore better to write
and print on.
Softwood trees such as pine and spruce
have wood with long fibers, and paper made from this
type of wood is much stronger. This paper is ideal for
making products like shipping containers that require
superior strength. But the finish is rougher, and that's
not as good for writing, printing and many other uses.
Happily, we can blend fiber from hardwoods
and softwoods into a single paper, getting just the
combination of strength, whiteness, writing surface
and other characteristics that we want.
And that's just what we do! Most of the
paper you see today is made from both hardwoods and
softwoods, a special blend for each purpose.
We make newsprint to be opaque (that means
difficult to see through) - so you only see the newspaper's
comics, not the stock market report on the other side!
We make grocery bag paper strong, tissue
soft, fine writing paper smooth. Even within the same
category, there's quite a range. Among printing papers,
for example, compare the thin sheets of a Bible to the
thick, tough pages of a kid's picture book.
The basic recipe - wood, water and energy
- is adjusted to make just the paper that's needed.
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.
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. 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.
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.
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.
Sometimes the paper is coated, often with
fine clay, to make it glossier and easier to print on.
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