Paper and papermaking
Last updated: November 16, 2009.
If you weren't glued to your
computer screen right now, you might be reading this
article on paper from a book; for about 2000 years until the
appearance of the World Wide Web, virtually all written information
was distributed in printed form. The idea of getting information from
inked-up sheets of paper is starting to seem a little bit
old-fashioned, but that doesn't mean we're going to ditch paper
anytime soon. People have been predicting the arrival of the
"paperless society" for decades and it still seems no nearer; if
anything, we use more paper now than ever before—and not just for
printing. Huge amounts of paper and card are still for product
packaging, in towels and diapers, and in a wide variety of building
materials. It's probably no exaggeration to say that paper is the
world's favorite material. Let's take a closer look and what it is
and how it's made!
Photo: Even in the computer age, we still use vast quantities of paper. This is 100 percent recycled Evolve paper made by M-real.
What is paper?
Paper is a dried, compressed mat of plant fibers—nothing more, nothing less. It's a bit
like clothing you can write on. No, really! Clothes are made
by weaving together yarns such as cotton and wool spun from natural
fibers. Paper is more like the fabric we call felt, made without the
weaving stage by pressing together cellulose fibers extracted from
plants and trees so they knit and fuse to form a strong, solid, but
still very flexible mat.
Photo: Look really closely at almost any ordinary paper and you'll see just how fibrous
it is! The photo on the right is a closeup of the one on the left. It might look like a pile of folded
fluffy bathroom towels, but really it's sheets of paper!
How is paper made?
Most paper pulp is made from trees (mainly fast-growing, evergreen conifers), though it
can also be made from bamboo, cotton, hemp, jute, and a wide range of
other plant materials. Smooth papers used for magazines or packaging
often have materials such as china clay added so they print with a
more colorful, glossy finish.
Here's the basic idea: you take a plant, bash it
about to release the fibers, and mix it with water to get a soggy
suspension of fibers called pulp (or stock). Then spread the
pulp out on a wire mesh so the fibers knit and bond together, squeeze
the water away, dry out your pulp, and what you've got is paper!
Paper is really easy to make by hand (try it for yourself) but people use so much of it that most is now
made by giant machines. Whichever method is used, there are
essentially two stages: getting the pulp ready and then forming it
and drying it into finished sheets or rolls.
Photo: Paper can be made from lots of different materials. Left: Trees felled in Anderson, California destined for papermaking. Photo by Warren Gretz. Right: Stacks of hay waiting to be made into low-grade
paper in Hebei Province, China. China and the United States are the world's leading paper makers, each producing close to 80 million tons of paper per year. Photo by Simon Tsuo. Both photos by courtesy of US DOE/NREL (US Department of Energy/National Renewable Energy Laboratory).
Papermaking by hand
The raw plant material is placed in a large vessel filled with water and literally
beaten to a pulp to make a thick suspension of fibers called
half-stuff. This is formed into sheets of paper using a very
basic frame made of two parts: a metal mesh called a mold that
sits inside a wooden frame known as a deckle (a bit like a
picture frame). The mold and deckle are dipped into the half stuff
and gently agitated so an even coating forms on top, with most of the
water (and some of the pulp) draining through. The deckle is then
removed from the mold and the soggy mat of paper is placed on a sheet
of felt. This process is repeated to make a number of interleaved
sheets of paper and felt, which are then placed inside a
screw-operated press and squeezed under immense pressure to squash
out virtually all the remaining water. After that, the sheets of paper
are taken out and hung up to dry.
Papermaking by machine
Although some expensive papers are still crafted by hand, most are churned out
quickly, efficiently, and automatically by gigantic machines. Pulp is prepared
for papermaking machines either mechanically or chemically. The
mechanical method (generally used to make lower-grades of paper) is
called the groundwood process, because the pulp
was originally made by using huge stones to grind up logs. Nowadays, pulp is
prepared by giant machines that cut, wash, chop, beat, and blend
wood, rags, or other raw materials into a soggy mass of fibers. In
the chemical method, known as the Kraft process (from the
German word for "strength," because it produces strong paper),
plant materials are boiled up in strong alkalis such as sodium sulfide or
sodium hydroxide to produce fibers. At this point,
loading materials (surface coatings such as clays), dyes (to make
colored paper), and sizes (to strengthen and waterproof and prevent
inks from spreading) can be added to the mixture to change the
properties of the finished paper (sometimes they're added later).
Once the pulp has been prepared, it's turned into paper by an enormous roller machine.
The best known type of papermaking machine is called a Fourdrinier
machine (named for the two English brothers who invented it at
the start of the 19th century), though there are alternatives (including the
cylinder machine developed a few years afterward by John Dickinson).
Wet pulp enters the machine from a trough called a headbox at
one end and is spread over a moving, wire-mesh conveyor belt. The
belt is shaken, sucked, and blown to remove water from the matt of
fibers, before a watermark, texture, or other finish is pressed into
it by a patterned roller called the dandy roll. The paper is
then pressed further and fully dried, looping again and again around a series of rollers, before getting its final, very
smooth pressing by large, heavy, steel rollers called calenders.
The finished paper emerges as webs (very large sheets) or rolls (for
printing things like newspapers and magazines). The biggest
Fourdrinier machines produce paper at an astonishing rate of over 60km/h (40 mph)!
Photo: A small papermaking machine from the early 20th century. Photo by
courtesy of National Institute of Standards and Technology (NIST) Photographic Collection.
Who invented paper and papermaking?
- 105 CE: Chinaman Ts'ai Lun (c.50–121 CE; also written Cai Lun) invents paper based on tree bark for the Emperor of China. Papermaking technology gradually spreads throughout Asia
and, by about the 12th century, reaches Europe.
- 1450s: German Johannes Gutenberg (c.1400–1468) invents movable metal type and the
modern printing press, and prints around 180 copies of his famous Gutenberg Bible. This
invention greatly increases the demand for paper.
- 1790s: Papermaking machines are invented by Frenchman Nicholas Louis Robert (1761–1829), then improved by British brothers
Henry Fourdrinier (1766–1854) and Sealy Fourdrinier
(1774–1847) around 1803. (The National Portrait Gallery has
a painting of the Fourdrinier family.)
- 1809: Several years after the Fourdiniers, Englishman John Dickinson (1782–1869) invents and patents an alternative papermaking apparatus called the cylinder machine.
- 1840: The Groundwood method of making wood pulp is developed in Germany.
- 1883: German inventor Karl Dahl develops a chemical method for making strong paper pulp called the Kraft ("strength") process.
Further reading
Books
Websites
- Paper Chase: Sam Martin considers the huge environmental impact of paper for ecology.com.
- Paper related statistics: An interesting collection of paper facts and figures from Environmental Paper Network (though some of the numbers are a little dated).
