From wood to pulp, to pulp, paper, and paper products

Two, pulp

Pulp is a fibrous substance made from plant fibers by different processing methods. It can be divided into many subdivisions according to the source of raw materials, processing methods, processing degrees, etc., and can be widely used in papermaking, artificial fibers, plastics, chemical and other fields.

Pulp is mainly divided into wood pulp, waste pulp and non-wood pulp according to the source of raw materials. Wood pulp is divided into two categories, are coniferous pulp (including masson pine, larch, red pine, spruce and other species of wood pulp) and broad-leaf pulp (including birch, poplar, linwood, eucalyptus, maple and other species of wood pulp), generally coniferous pulp has stronger toughness and stretchability than broad-leaf pulp, Therefore, in the use of wood pulp is usually mixed with a certain proportion of coniferous pulp to enhance the toughness of paper; Waste pulp is the paper pulp which is sorted and screened after the waste paper is recycled, soaked with warm water, and then repulped for reuse. There are three main types of non-wood pulp: grass fiber pulp (such as straw, wheatgrass, reed, bamboo, bagasse, etc.), bast fiber pulp (such as hemp, kenaf, flax, mulberry bark, cotton stalk bark, etc.) and seed wool fiber pulp (such as cotton fiber, etc.).

Pulp according to the processing technology is divided into mechanical pulping, chemical pulping, semi-chemical pulping. Mechanical pulping refers to the method of making pulp from fiber raw materials (mainly wood) by simply using mechanical grinding, and its products are collectively referred to as mechanical pulp; Chemical pulping refers to the method of making pulp by treating raw materials with chemical agents, and its products are collectively referred to as chemical pulp; Semi-chemical pulping (also known as chemical mechanical pulping) refers to the pulping method using chemical pretreatment and mechanical grinding after treatment, and its products are collectively referred to as chemical pulp (CMP).

In addition, pulp according to the degree of processing is divided into refined pulp, bleached pulp, semi-bleached pulp and this color paste, such a classification standard is mainly the degree of bleaching of pulp, different whiteness of pulp is also used in different paper industry because of its different nature, such as bleached sulfate wood pulp can be used to manufacture advanced printing paper, painting newspaper, offset paper and writing paper. This color paste is mainly used for making medium printing paper, thin wrapping paper, translucent paper and greaseproof paper.

1. Classification of bleached coniferous pulp

There are two major categories of bleached coniferous wood sulfate pulp: Northern bleached coniferous wood sulfate pulp (NBSK) and Southern bleached coniferous wood sulfate pulp (SBSK) :

(1) Northern bleached coniferous wood sulfate pulp (NBSK) :

Scandinavia: The Scandinavian countries produce only two main conifers, pine and spruce. Generally, the total length of the fiber is 3.1-3.3mm, and the diameter is only 30-32μm, which is shorter and thinner than the domestic similar varieties such as Canada. These fibers are uniformly distributed in the pulp and have roughly the same size and similar cell walls. This NBSK does not have particularly high tensile or folding resistance, has a much lower tear than any southern coniferous pulp, but has a higher rupture resistance, and has a higher fiber number per unit weight (fiber number/gram) due to the longer fiber length and smaller diameter. Therefore, it is suitable for the manufacture of low weight coated offset paper, double-sided coated paper, single-side coated paper, gravure printing paper, pressure resistant paper and so on.

Russia: The main species of NBSK in Russia are red, white pine and larch. Red and white pine are similar to spruce and fir in Canada, with low late wood rate and thin cell wall, and can produce better synergistic effect with larch, so mixed pulping is generally adopted. The NBSK of the Russian Far East is roughly in the same category as that of Scandinavia.

Canada: Canada has a vast territory, the production of NBSK because of different materials, the fiber itself has a great inconsistency, and China imports NBSK from Canada is also the most. Canadian forests can be roughly divided into six areas, and pulp mills are generally close to forest areas.

(2) Southern bleached softwood sulfate Pulp (SBSK) :

Although there are seven major different tree species in this category, they all belong to the pine family. The four dominant species are thick-walled pine, long-leaved pine, thin-walled loblolly Pine and short-leaved pine, collectively known as Southern Pine. The first two (wet pine and longleaf pine) are mostly grown in the southeastern United States and are well suited for fluff absorbent products, silky wool (deep caustic soda treatment) products, infiltrated latex products, and chemical fiber derivatives. The end use of this type of pulp makes it more expensive than loblolly pine and shortleaf pine. Thin-walled loblolly pine has better beating performance than thick-walled pine. The remarkable property of SBSK is that its tearing (which decreases with beating) is much better than NBSK. The bleached pulp of Phoenix Paper Company and paper company in Guangxi is made of Masson pine, and the bleached pulp of Yunjinglin Paper Company in Yunnan is made of Simao pine, both of which belong to SBSK.