What is the pulping process?

Pulping is the process of separating plant fibers from raw materials of and obtaining pulps. The pulping process can be mainly divided into mechanical method, chemical method and chemical-mechanical method to obtain mechanical pulp, chemical pulp and chemical-mechanical pulp respectively.

 

pulping mill
pulping mills

Pulping purpose

The lignin is eluted in raw material, and the material is separated into single fibers, and the specific surface area (surface area per unit weight of the fiber) of the fiber is increased.

Pulping requirements

Under the premise that the fiber is not damaged or less, the plant fiber is separated into monomer fibers, and the pulp has a certain specific surface area and interlacing performance, which creates conditions for recombination between the fibers.

Pulping process development

The pulping and paper-making industry is an important industry in the development of national economy. It has experienced several development stages and still holds an important position in national economy. Throughout the development of the pulping process, we have seen that there are many ways to make pulp. But the alkaline pulping method is influential. Conventional alkaline pulping method includes lime process, caustic soda process, sulfate process, sulfite process, and pre-hydrolysis process. Among them, caustic soda method and sulfate method are mainly used, and two methods can be widely used for cooking various raw materials, and can also be used for producing semi-chemical pulp and chemical-mechanical pulp. In recent years, in order to accelerate the release of lignin, to protect cellulose and hemi-cellulose from degradation, thereby increasing the yield of pulp, improving the quality of pulp, or in order to reduce environmental pollution, the alkaline pulping develops very fast with various additives. At present, the production of wood pulp is mainly based on the sulfate method in China and abroad. The production of straw pulp is still based on the alkaline method (including the sulfate method), while the caustic soda method and the alkaline sulfate method improves very quickly. Its pulping yield is high, the whiteness is good, and pulp strength is high. It is easy to wash, bleach and has less foam, etc. It has obvious advantages, and the development prospects are optimistic.

Pulp is a lignocellulosic fibrous material prepared by chemically or mechanically separating cellulose fibres from wood, fiber crops, waste paper, or rags. Many kinds of paper are made from wood with nothing else mixed into them. This includes newspapers, magazines and even toilet paper. Pulp is one of the most abundant raw materials.

A pulp mill is a manufacturing facility that converts wood chips or other plant fibre source into a thick fibre board which can be shipped to a paper mill for further processing. Pulp can be manufactured using mechanical, semi-chemical or fully chemical methods (kraft and sulfite processes). The finished product may be either bleached or non-bleached, depending on the customer requirements.

A paper machine (or paper-making machine) is an industrial machine which is used in the pulp and paper industry to create paper in large quantities at high speed. Modern paper-making machines are based on the principles of the Fourdrinier Machine, which uses a moving woven mesh to create a continuous paper web by filtering out the fibres held in a paper stock and producing a continuously moving wet mat of fibre. This is dried in the machine to produce a strong paper web.

The pulp produced up to this point in the process can be bleached to produce a white paper product. The chemicals used to bleach pulp have been a source of environmental concern, and recently the pulp industry has been using alternatives to chlorine, such as chlorine dioxide, oxygen, ozone and hydrogen peroxide.

Chemical pulp is produced by combining wood chips and chemicals in large vessels called digesters. There, heat and chemicals break down lignin, which binds cellulose fibres together, without seriously degrading the cellulose fibres. Chemical pulp is used for materials that need to be stronger or combined with mechanical pulps to give a product different characteristics. The kraft process is the dominant chemical pulping method, with the sulfite process second. Historically soda pulping was the first successful chemical pulping method.