paper
, matted or felted sheet, usually made of
cellulose
fibres, formed on a wire screen from water
suspension
.
A brief treatment of paper follows. For full treatment,
see
papermaking
.
More From Britannica
art conservation and restoration: Paintings on paper
Paper has been traced to
China
in about
ad
105. It reached
Central Asia
by 751 and Baghdad by 793, and by the 14th century there were paper mills in several parts of Europe. The invention of the
printing press
in about 1450 greatly increased the demand for paper, and at the beginning of the 19th century
wood
and other vegetable pulps began to replace rags as the principal source of
fibre
for papermaking.
Before 1798,
Nicholas-Louis Robert
constructed the first paper-making machine. Using a moving screen belt, paper was made one sheet at a time by dipping a frame or
mold
with a screen bottom into a vat of pulp. A few years later the brothers Henry and Sealy Fourdrinier improved Robert’s machine, and in 1809 John Dickinson invented the first
cylinder machine
.
Although almost all steps in papermaking have become highly mechanized, the basic process has remained essentially unchanged. First, the fibres are separated and wetted to produce the paper
pulp
, or stock. The pulp is then filtered on a
woven
screen to form a sheet of fibre, which is pressed and compacted to squeeze out most of the water. The remaining water is removed by evaporation, and the dry sheet is further compressed and, depending upon the intended use, coated or impregnated with other substances.
Differences among the grades and types of paper are determined by several factors: the type of fibre used; the preparation of the pulp, either by mechanical (groundwood) or chemical (primarily sulfite, soda, or sulfate) methods, or by a combination of the two; by the addition of other materials to the pulp, among the most common being bleach or colouring and
sizing
, the latter to retard penetration by ink; by conditions under which the sheet is formed, including its weight; and by the physical or chemical treatments applied to the finished sheet.
Get a Britannica Premium subscription and gain access to exclusive content.
Subscribe Now
Although wood has become the major source of fibre for papermaking, rag fibres are still used for paper of maximum strength, durability, and permanence.
Recycled
wastepaper (including newsprint) and paperboard are also important sources. Other fibres used include
straw
,
bagasse
(residue from crushed
sugarcane
),
esparto
,
bamboo
,
flax
,
hemp
,
jute
, and
kenaf. Some paper, particularly specialty items, is made from
synthetic
fibres.
Weight or substance per unit area, called basis weight, is measured in reams (now commonly 500 sheets). Paper is also measured by caliper (thickness) and
density
. The strength and durability of paper is determined by factors such as the strength and length of the fibres, as well as their bonding ability, and the formation and structure of the sheet. The optical properties of paper include its brightness, colour, opacity, and gloss. Among the most important paper grades are bond,
book
,
bristol
,
groundwood
and
newsprint
,
kraft
,
paperboard
, and
sanitary
.