What are the effects of mechanical and chemical papermaking on paper durability?
Mechanical papermaking (machine-made paper) generally goes through the following processes. First, the raw materials are prepared, and then the pulp is made. According to the method of making pulp, it can be divided into mechanical and chemical methods.
Mechanical method is to use mechanical method to dissociate fibers to make mechanical wood pulp. The lignin of this kind of wood pulp can not be removed, and its fiber is short and thick, and contains more non-cellulose. Therefore, the paper made of this kind of wood pulp is loose, easy to break, and easy to oxidize and turn yellow in sunlight and air, which is one of the factors of poor durability.
Chemical method is to use an appropriate amount of chemical agents to remove lignin and other non-cellulose in the process of cooking raw materials, so that the fiber can be dissociated into a pulp. According to the different chemicals used, chemical methods can be divided into sulfite method, alkali method and chlorination method, etc.
1. Sulfite process: The mixed solution of calcium bisulfite and sulfuric acid is used to cook fibers to make sulfite chemical pulp. This pulp contains a certain amount of hemicellulose, cooking liquor and acid lignosulfonic acid residues in the pulp. Therefore, the durability of the paper is greatly affected.
2. Alkali method: sodium hydroxide is used as cooking liquid to cook with raw materials at high temperature. As the alkalinity is too large, it will cause great damage to the fiber, reduce the strength of the paper, and increase the cost, it is rarely used now.
3. Chlorination method: the raw material is cooked with sodium hydroxide, treated with chlorination and lye to remove lignin, and then bleached. In this process, sometimes alkali, sometimes bleaching powder, and sometimes chlorine are used to treat , will damage the cellulose to varying degrees.
It can be seen from the pulp manufacturing method that the quality of pulp is directly related to the durability of paper.
