Pulping process of kraft paper bags

The pulping process of kraft paper bags starts with the selection of suitable raw materials. Usually, the main raw material of kraft paper is wood fiber, and the choice of wood directly affects the strength, flexibility and durability of kraft paper.
Coniferous trees: Coniferous trees such as pine, fir and spruce are usually selected for kraft paper production. These tree species have longer fibers, and the fiber length is usually 2.5-4 mm. The characteristic of long fibers is that they can form a more compact and strong paper structure, and improve the tear resistance and compression resistance of paper.
Broadleaved trees: Sometimes some broadleaved trees are also used for pulping. The fibers of these trees are shorter, about 0.5-1.5 mm in length. The addition of short fibers helps to improve the surface smoothness of the paper, but its strength is relatively low. Therefore, in the production of kraft paper bags, coniferous and broadleaved tree fibers are usually mixed to take into account both strength and surface quality.
In addition, with the improvement of environmental awareness, more and more pulp mills have begun to use waste paper recycled fibers and renewable plant fibers, such as hemp fiber and bagasse, to reduce dependence on natural wood resources.
Wood pretreatment is the first step in the pulping process. The main purpose is to cut, chip and remove the bark of the wood. The bark contains a lot of resin and impurities, which is not suitable for pulping and will affect the quality of the finished paper. Therefore, before entering the pulping process, the wood is usually debarked and sliced ​​to ensure the purity of the fiber.
Slicing process: The wood is cut into small pieces or chips suitable for processing, usually 1-3 cm long. These chips will then enter the next step of chemical treatment.
Kraft pulping is the core process of kraft pulping and widely used chemical pulping methods in the world. Compared with the traditional acid pulping method, the main advantage of the Kraft method is that it can better retain the cellulose chains in the wood, thereby producing tougher paper.