In addition to cellulose, hemicellulose, and lignin, pulp also contains a small number of substances that are insoluble in water but soluble in neutral organic solvents (such as acetone, ether, and benzyl alcohol). These compounds are called organic solvent extracts, which represent resins in plants.
The resin of coniferous wood is mainly composed of free resin acids, free fatty acids, triglycerides, and unsaponifiable. Although the content of these substances in the pulp is small, it has a great influence on the quality of pulp, paper, and products. In the process of pulping and papermaking, the resin in the pulp will deposit on the surface of the equipment in many ways, resulting in a series of resin problems. For a paper mill with a daily output of several hundred tons (for example, for a newsprint mill), the total amount of resin passing through the pulping and papermaking equipment is about several tons per day. If several hundred grams of these resins are deposited on the surface of the key papermaking equipment, a very serious resin problem will occur. The loss of a softwood kraft bleached pulp with a daily output of 800 tons is as high as several million US dollars per year due to resin problems. Therefore, it is necessary for pulp and paper workers to deepen the understanding and understanding of the resin in pulp and its deposition and control.
There are two main effects of resin deposition on Pulping and papermaking. One is that resin deposition can lead to the decline of product quality; Second, the deposition of resin can affect the pulping and papermaking process and reduce the output of products. Specifically, resins and their deposits in the paper industry have the following hazards:
(1) In the pulp washing and bleaching section, the resin in the pulp is deposited on the sieve plate of the screen, the lower lip of the thickener, the inner wall of the pipe and the surface of the pulp pool, the screw of the pulper and the pulp concentration regulator. The most serious problem is that these sediments may fall off from the deposited surface and block the sieve plate and cone-shaped slag remover, thus greatly reducing the screening and purification efficiency. In addition, these resin deposits fall off and form spots and dust in the pulpboard, thus reducing the quality of the paperboard.
(2) In the paper-making section, the resin is easy to deposit in the blanket and water suction tank, as well as in the pulp tank, sieve plate, headbox, papermaking net, couch roll, press roll, and calendar roll of the dryer. These deposits will reduce the dehydration efficiency and the evenness and strength of the paper, or form resin spots and holes, thus reducing the quality of the finished product. In addition, the deposition of resin can cause web breakage, increase the cleaning and maintenance time of equipment, resulting in a decline in output.
(3) Resin in pulp and paper wastewater is the main source of nonbleaching wastewater toxicity. The existence of resin in the pulp can reduce the binding force between fibers, thereby reducing the strength of the pulp and affecting the water absorption of the pulp (especially fluff pulp).