Cotton Pulp Making

cotton pulp making

The cotton pulp is generally made by soda process, and the raw materials of cotton pulp include waste cotton and linters of textile industry. The cotton pulp contains pure cellulose, it has long and thin fiber, good tenacity, elasticity, and absorptivity. The cotton pulp paper is fine and soft, usually has high opaqueness and also can be stored for a long time. Bleached cotton pulp applies for text paper manufacture, such as filter paper, drawing paper, security paper. The unbleached cotton pulp is used to manufacture vulcanized paper and baby paper. Besides, the cotton pulp can be used as the raw material of rayon, cellulose acetate.

About cotton fiber

As main raw material of cotton pulp, cotton linter refers to the short fiber that leaves on the cottonseed hull. The cotton linter is shorter than lint cotton, but they have similar maturity. Cotton linter has the higher content of cellulose, is the fiber materials for light industry, military industry, chemical industry and medical industry. According to the cotton ginning process, the cotton linter can be divided into three types and nine classes.

The cotton linter has high content of cellulose and low content of lignin, the cotton pulp is easy to bleach and hard to yellow. Chloride content of cotton pulp is low, and suitable pentosan content decides the good water absorption of cotton fiber, the ash content is high and can be removed by special methods. Maturity is a key indicator of cotton linter quality, it has close connection with other indicators. The higher is the maturity, the larger is the cellulose content, and the less is the non-cellulose impurities content.

Advantages of cotton fiber

Except for the high content of cellulose, low content of non-fibrous cell and long fibers, the cotton fiber has other advantages as follows.

  • The crystallinity of cotton fiber is about 70%.
  • The thinner is cotton fiber, the better is hygroscopicity.
  • The bendability of cotton fibers, it is hard to break.
  • The heat resisting property of cotton fiber is the best among all natural fibers.
  • Cotton fiber has high beating degree, and it is long and even.
  • The natural bending of cotton fibers decides it has some good mechanical properties like friction and cohesion.

Cotton pulp applications

Because the cotton pulp has different property with wood pulp, wheat straw pulp, it can be applied to manufacture various kinds of paper, such as security paper, vulcanized base paper, condenser paper, napkin, drafting paper, tracing paper and abrasion resistant paper, etc.

Security paper

Security paper is used to print paper money, bond, and credentials. Security paper is strong, durable and water-fast. Raw materials of security paper adopt chemical wood pulp or bleached rag pulp. The cotton pulp for security paper is soft and thin, the high cellulose content and lignin content of cotton pulp decide the high degree of whiteness and durability of cotton pulp.

Vulcanized base paper

Vulcanized base paper is a kind of industrial and technical paper that is used as the material of vulcanized fiber paper. The cotton pulp cellulose has high purity and low content of non-fibrous impurity. Based on the processing, the vulcanized base paper has high strength, evenness and absorptivity.

Cotton linter alkaline pulping process

Cotton linter alkaline pulping is the most common in the cotton pulp making. The main process of cotton linter alkaline pulping can be generally divided into 5 procedures, including material preparation, pulp cooking, pulp washing, pulp screening and degritting, pulp bleaching and beating.

Material preparation

The cotton linter is treated before entering into paper and pulp mills. Open and break up the treated cotton linter with cotton slitter, feed the cotton linter into carding machine and remove the cotton seed hull and stalk and other impurities. The impurity rate of treated cotton linter is between 1% and 3%, purifying rate is required above 85%.

Pulp cooking

The cotton linter was send into cyclone separator, white liquor is also added, and the cotton linter is evenly dipped and sent into pulp digester. To reduce the temperature of cellulose pulp and alkaline content, the cooked pulp should be sent into next step – pulp washing process. The cotton pulp cooking is mainly used to improve wettability of cotton fiber by removing the oil, fat, pectin, lignin and other impurities. As for the cotton pulping equipment, rotary digester is typical in China, the pulp mills of USA, Japan usually adopt continuous tubular digester.

Pulp washing

The cooked cotton pulp fiber is long, should be beated, or the pulp will affect the pulp screening, bleaching process. Excepting for cutting the fibers, beating also increase the hydration degree of cotton pulp fiber and wash the cotton pulp. Cotton pulp washing equipment includes vacuum drum washer, twin roll press, single screw press, etc.

Pulp screening and degritting

Pulp screening process uses the hole of screen to separate fine pulp and coarse screenings. For removing different impurities, the cotton pulp screening adopts various screening equipment in series.

The pulp degritting clear the sand, metal debris and other impurities that produced by cotton linter and pulp cooking process.

Pulp bleaching

After the pulp screening, cleaning, concentration, for improving the purity and whiteness of cotton pulp, the virgin pulp can be bleached according to specific requirement. Currently, most pulp mills adopt the hypochlorite bleaching, in order to prevent the cotton pulp from damage, the bleaching agent, pulp consistency, pH value, bleaching temperature and time should be strictly controlled.

CNBM is a paper pulping machine manufacturer that provides paper pulp solution and related pulp making equipment, such as pulp digester,  blow tank, twin roll press, vacuum drum washer, etc. We customize the pulp plants like wood pulp production line, bamboo pulp production line, bagasse pulp production line, wheat straw pulp production line, reed pulp production line, jute pulp production line, etc.

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