Paper is a necessary thing in our daily life. Generally, it is made from plant fibers or waste paper. Paper can be generally classified into cultural paper, industrial paper, household paper, and special paper according to the use, and cultural paper can be simply classified into uncoated paper and coated paper. Uncoated paper includes newsprint, offset paper, xerographic paper, and writing paper. The coated paper includes calendar paper, and Asian, glossy paper, glass cardboard, etc.
What is paper and pulp making? The paper and pulp making can be divided into two stages including pulping and paper making. Paper pulping refers to the processing of making paper virgin or bleached pulp from plant fibers by chemical, mechanical or chemi-mechanical process. Papermaking is the combination of pulp fibers suspended in water and processed fibers into various types of papers.
How to make paper from fibers?
Paper mills generally need to store enough raw materials for 4 to 6 months, allow the raw materials to be naturally fermented during storage to facilitate pulping and ensure continuous production of paper mill. Raw materials such as reed, wheat straw, and wood are cut into pieces (for chemical pulp) or wood chips (for production of ground wood pulp) through the preparation section. And then put small pieces into the digester and add chemical liquid, use steam to heat digester. After that, the pulp is washed with pulp washing equipment like vacuum drum washer, and the coarse pieces, knots, stones, sand, and the like in the pulp are removed by screening and purification. According to the requirements of different paper, the pulp is bleached to the desired whiteness by pulp bleaching equipment like disc filter, twin roll press, and etc. Then, to improve the performance of the paper, add fillers, rubbers, sizing agents, or various additives to the pulp, after further purification and screening, and pulp is finally sent to the paper machine for water filtration, press dewatering, drying of the dryer, and calendering. Cut and rewind to produce roll and flat paper.
In addition to the above basic processes, it also includes some auxiliary processes, such as the pulp cooking, the pulp bleaching, the tanning of rubber compounds, and etc.
Materials for paper and pulp making
The raw materials for modern papermaking include plant fibers (wood, bamboo, grass, etc.), mineral fibers (asbestos, glass filaments, etc.), other fibers (nylon, metal wire, etc.), as well as polymer materials obtained by cracking petroleum. Currently writing, printing, and packaging paper is still mainly made of plant fiber. As the main raw materials of paper and pulp making, plant fibers can be divided into two types: wood fiber and non-wood fibers.
- Wood fiber: directly obtained from wood.
- Non-wood fiber: obtained from straw fiber, bast fiber or seed hair fiber. such as reed pulp, straw pulp, bamboo pulp, bagasse pulp, jute pulp and cotton pulp.
Paper pulping process
Paper pulping process can be classified into three types, such as chemical pulping, mechanical pulping and chemi-mechanical pulping.
Chemical pulping
Chemical pulping means that use chemical liquid to treat plant fiber materials at a certain temperature and pressure. Dissolving lignin and non-fibrous carbohydrates or oils, resins of raw materials, and retaining cellulose and hemicellulose as much as possible, separate the raw material fibers into pulp.
Mechanical pulping
As name suggested mechanical pulping use mechanical treatment to make pulp from fiber materials. The most popular types of mechanical pulp in the paper and pulp industry is mechanical wood pulp, also known as ground wood pulp. The mechanical pulp retains a large amount of lignin of raw material, and the pulp yield is higher than that of the chemical pulp.
About pulp bleaching
Why the bleaching process is needed? The paper pulp made by chemical pulping and mechanical pulping is called virgin pulp, and it is usually yellow or brown. For meeting different requirements of paper uses, sometimes, the virgin pulp should be bleached, so that paper can have high-degreed whiteness. To be specific, bleaching process refers to Bleaching is the dissolution of residual lignin in the pulp by oxidation, reduction or decomposition with a suitable bleaching agent, or discoloration of the colored material while retaining lignin.
About beating
After pulp cooking or mechanically grinding, pulp washing, pulp screening and pulp bleaching, paper pulp cannot be directly used for papermaking. Since the fibers of the pulp are lack of flexibility, the connection between the fibers is not good. If pulp is directly used for papermaking, the paper will be loose, porous, rough, and low in strength, and cannot meet the requirements for use. Beating means treat the fibers of pulp with mechanical method, so that it is deuterated and moderately cut. More importantly, the fibers absorb and swell during beating, it has higher elasticity and plasticity, meeting the requirements of paper machine production, so that The paper can reach the expected quality indicators.
Paper making
There are two classification of paper making including dry- type and wet-type. Dry-type paper making process uses air as the medium, and is mainly used for synthetic fiber making; wet –type papermaking uses water as medium. Mainly apply for plant fiber papermaking. At present, most of the paper is made by wet method.
