Chemical pulp is produced by combining wood chips and chemicals in large vessels known as digesters where heat and the chemicals break down the lignin, which binds the cellulose fibres together, without seriously degrading the cellulose fibres This fiber source is produced by chemical pulping mainly from softwood(e.g. spruce, pine) and hardwood(e.g. birch, beech, aspen, eucalyptus), but also with less portions from annual non- wood plants, e.g. rice and wheat straw, bagasse, esparto grass, reed, bamboo.During chemical pulping, the lignin is removed and therefore the pulp yield is only 45-55%.