Chemical pulp

Pulp is a lignocellulosic fibrous material prepared by chemically or mechanically separating cellulose fibres from wood, fiber crops or waste paper. The wood fiber sources required for pulping are "45% sawmill residue, 21% logs and chips, and 34% recycled paper" (Canada, 2014). Many kinds of paper are made from wood with nothing else mixed into them. This includes newspaper, magazines and even toilet paper. Pulp is one of the most abundant raw materials worldwide.

Using wood to make paper is a fairly recent innovation. The ancient Egyptians were the first to make paper from reeds. Papermaking using cotton and linen fibers spread to Europe in the 13th century, and the increasing use of fabric brought more rag paper, which was a factor in the development of printing. By the 1800s, fibre crops such as flax, which provided linen fibres, were still the primary material source, and paper was a relatively expensive commodity. The use of wood to make pulp for paper began with the development of mechanical pulping in Germany by Friedrich Gottlob Keller in the 1840s, and by the Canadian inventor Charles Fenerty in Nova Scotia. Chemical processes quickly followed, first with J. Roth's use of sulfurous acid to treat wood, then by Benjamin Tilghman's U.S. patent on the use of calcium bisulfite, Ca(HSO₃)₂, to pulp wood in 1867. Almost a decade later, the first commercial sulfite pulp mill was built, in Sweden. It used magnesium as the counter ion and was based on work by Carl Daniel Ekman. By 1900, sulfite pulping had become the dominant means of producing wood pulp, surpassing mechanical pulping methods. The competing chemical pulping process, the sulfate, or kraft, process, was developed by Carl F. Dahl in 1879; the first kraft mill started, in Sweden, in 1890. The invention of the recovery boiler, by G.H. Tomlinson in the early 1930s, allowed kraft mills to recycle almost all of their pulping chemicals. This, along with the ability of the kraft process to accept a wider variety of types of wood and to produce stronger fibres, made the kraft process the dominant pulping process, starting in the 1940s.

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