Paper Research

632 Words Mar 21st, 2013 3 Pages
History

Main article: History of paper

Hemp wrapping paper, China, circa 100 BCE.
The oldest known archaeological fragments of the immediate precursor to modern paper date to 2nd century BC in China. The pulp papermaking process is ascribed to Cai Lun, a 2nd century AD Han court eunuch.[1] With paper an effective substitute for silk in many applications, China could export silk in greater quantity, contributing to a Golden Age.

Paper spread from China through the Middle East to medieval Europe in the 13th century, where the first water-powered paper mills were built.[2] In the 19th century, industrial manufacture greatly lowered its cost, enabling mass exchange of information and contributing to significant cultural shifts. In
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Paper made from chemical pulps are also known as wood-free papers–not to be confused with tree-free paper. This is because they do not contain lignin, which deteriorates over time. The pulp can also be bleached to produce white paper, but this consumes 5% of the fibers. Chemical pulping processes are not used to make paper made from cotton, which is already 90% cellulose.

The microscopic structure of paper: Micrograph of paper autofluorescing under ultraviolet illumination. The individual fibres in this sample are around 10 µm in diameter.
There are three main chemical pulping processes. The sulfite process dates back to the 1840s, and it was the dominant process before the second world war. The kraft process, invented in the 1870s and first used in the 1890s, is now the most commonly practiced strategy. One advantage is a chemical reaction with lignin produces heat, which can be used to run a generator. Most pulping operations using the kraft process are net contributors to the electricity grid or use the electricity to run an adjacent paper-mill. Another advantage is the process recovers and reuses all inorganic chemical reagents. Soda pulping is a specialty process used to pulp straws, bagasse, and hardwoods with high silicate content.

Mechanical pulping
There are two major mechanical pulps, thermo mechanical pulp (TMP) and groundwood pulp (GW). In the TMP process, wood is chipped and then fed into large steam-heated refiners where

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