Papermaking
Chemical pulping To make pulp from wood, a chemical pulping process separates lignin from cellulose fibers. This is accomplished by dissolving lignin in a cooking liquor, so that it may be washed from the cellulose; this preserves the length of the cellulose fibers. 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 the 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 fibers 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 method extent before the second world war. The kraft pro...