Paper pulp is made from some plants. It is the basic raw material for papermaking. Do you really know the paper pulp? As a manufacturer of paper pulp machine, CNBM has plenty of experience in manufacture paper pulp making machines. Today we will find secrete of paper pulp from two aspects including paper pulp processing and pulp application.
Paper pulp processing
The process of wood pulp can be broadly classified into mechanical pulping, chemical pulping or chemi-mechanical pulping. According to different processes, the obtained pulp is called mechanical pulp, chemical pulp, and chemi-mechanical pulp.
The mechanical pulping process presses the wood section from the length direction to a moist rough and uniform rotating stone, thereby separating the fibers from the wood section, and filtering and concentrating process to make pulp from fibers. The mechanical pulp has the characteristics of short fiber, low bursting strength, low whiteness, and high yield.
The chemical pulping immerses the wood chips in the aqueous solution with suitable content of chemical and cooks them at a high temperature and high pressure to dissolve the lignin of the wood chips, thereby obtaining complete cellulose. And then, the pulp is formed after the subsequent process, and the pulp is obtained by this process is called chemical pulp. The sulfate pulping and the sulfite pulping are two basic chemical pulping processes. In the 1930s, the sulfate pulping began to take advantage of various types of wood that were not suitable for sulfite pulping. Therefore, most of the paper pulp mill commonly use the sulfate pulping to produce pulp. The chemical pulp has a long fiber and a high breaking strength, so it has different applications.
The chemi-mechanical pulping process combines chemical and mechanical pulping. Firstly, the wood chips are softened or cooked with chemicals, and then the remaining pulping is done by the mechanical process. The chemi-mechanical pulp mainly mixes with chemical pulp, the mixed pulp is used for printing with paper-coated printing and writing paper, packaging paper and cardboard.
The bleached softwood KP pulp adopts the chemical pulping process, and its process mainly includes raw material preparation and shaving, pulp cooking, pulp washing, pulp screening, pulp bleaching, drying, slicing and packaging, and other processes. The specific process as follow:
- Firstly, get the long logs are ready, peeled and cut them into smaller pieces.
- Secondly, the selected qualified pieces are cooked in the digester with sodium hydroxide (NaOH) and sodium sulfide (Na2S) solution for 1 to 2 hours. The pulp cooking process removes lignin and separates the wood into cellulose fibers.
- After the pulp cooking process, the crude pulp is washed by a washer such as a vacuum drum washer, single screw press, twin roll press. The oversized pieces are removed by a sieve to obtain a fine pulp.
- Next, the fine pulp is bleached and concentrated in multiple stages, it is made into a wet pulp board and sent to a dryer for drying.
- Finally, after slicing and packaging, the obtained pulp can be delivered in the form of a pulp package.
The production process of wood pulp has the characteristics of a circular economy, in which the water resource recycling rate can exceed 90%. After the used cooking liquid is evaporated, burned, causticized, the alkali recovery rate can reach over 95%, and the remaining Organic matter of pulping process can be used to produce electricity by burning or achieve self-supply of energy.
For different types of wood pulp, bleaching softwood pulp and bleaching hardwood pulp have same pulp production, the main difference is that the bleaching softwood pulping has a recovering process of the turpentine compared with bleaching hardwood pulping, and the parameters (such as cooking time) is different. Therefore, a wood pulp production line can produce both bleaching softwood pulp and bleaching hardwood pulp. However, the two pulps cannot be produced at the same time, and the equipment must be thoroughly cleaned, and the relevant parameters and some processes must be changed before it can be used to produce another pulp.
Application of paper pulp
Because of the long fiber length, high breaking strength and good tensile strength of wood pulp, the paper made from wood pulp has the characteristics of folding resistance, breakage resistance and high tear strength. It is mostly used for the production of coated printing writing paper, uncoated printing writing paper, sanitary, special industrial paper and paperboard. Generally, the wood pulp are processed by a paper mill to produce paper products on the market, such as books, printing papers, napkins, and etc.
Non-wood pulp is more used for the production of sanitary paper, wrapping paper and handmade paper due to easy availability of raw materials, close to the production area, low price, etc. there are a varity of paper is made from non-wood pulp, such as natural bamboo pulp paper, rice paper and so on.
According to the quality of raw materials, the waste paper pulp can be used for the production of newsprint, wrapping paper and cardboard, corrugated paper, whiteboard and cardboard and etc.