Paper Pulp Types and Properties and Their Composition

1, the type of slurry China's commonly used papermaking raw materials are wood pulp and straw two major categories. Due to the lack of wood pulp resources in China and the relatively rich grass pulp resources, most papermaking raw materials, especially pulp molded products in China, are made from strawwood fiber raw material of annual use. As for how many acres of paper forest industry consumes in one year, it is entirely a misunderstanding.
Pulp fibers are classified into coniferous wood pulp fibers (such as masson pine, larch, Korean pine, spruce, etc.) and hardwood pulp fibers (such as birch, poplar, beech, beech, maple, etc.) . Because the pulp molded products need to have a certain strength and can withstand stretching, 15 to 20% of the coniferous pulp is generally added to the pulp.
Grass pulp fiber is divided into:
(1) Fibre raw materials (such as straw, wheat straw, reed, bamboo, bagasse, etc.);
(2) Bast fiber raw materials (such as hemp, kenaf, flax, mulberry, cotton stalk, etc.);
(3) Kind of wool fiber raw materials (such as cotton fiber, etc.).
2. Differences between physical and chemical properties of wood pulp and straw pulp (1) Their fiber morphology and physical conditions are different. Softwood fibers are longer, generally between 2.56 to 4.08 mm in length, and between 40.9 to 54.9 microns in width, and their aspect ratio is mostly below 70 times; hardwood fibers are short, generally about 1 mm in length, and their length and breadth are More than 60 times more than in the grass fiber, bagasse fiber raw material is relatively long, in 1.01 ~ 2.34 mm, the width of 16.7 ~ 30.4 microns, the length-width ratio of about 77 times more; Reed raw material fiber length About 0.60 to 1.60 mm, with a width of about 5.9 to 13.4 μm, and an aspect ratio of about 115 times; mansard stalks, a raw material fiber length of about 0.81 to 2.58 mm, a width of 13.2 to 19.6 μm, and a large aspect ratio About 100 times.
(2) The composition of the fibers is different. The main components of plant fiber raw materials include cellulose, hemicellulose and lignin. Minor components include pectin, starch, tannins, pigments, resins, fats, waxes, ash, etc.
Cellulose is present in the cell walls of all plants and is the main component of plant fibers, accounting for approximately 40 to 98%. It is a part that should be tried to preserve during the pulping process.
Hemicellulose is a non-cellulosic carbohydrate, hemicellulose has a loose and amorphous structure and is easy to absorb and swell, and is easily soluble in dilute alkaline solutions. The content of hemicellulose in grass materials accounts for about 30%. Its chemical properties are similar to that of cellulose, but the reaction is faster and easier than cellulose. Hemicellulose is also a part that should be strongly retained during the pulping process.
Lignin is an aromatic natural polymer compound composed of phenylpropane structural units, not a single substance. It is a generic term for similar substances of this type and is an amorphous structure. Grass materials usually contain about 20% of lignin. The more lignin is contained in raw materials, the more difficult it is to pulp, because lignin sticks fibers together. Chemical pulping is the use of chemicals to dissolve the lignin in the fiber raw material and separate the fibers into a slurry.
(3) Their chemical composition is different. The structure of coniferous wood is tight, the content of heterocells is small, and the heterocells in chemical pulp are mostly lost during washing. Therefore, the quality of pulp is good, the content of lignin is high, between 25 and 35%, and the content of polypentose is low. Mostly between 9 and 12%, the fiber is not easy to absorb moisture, and it is difficult to be beaten. The hardwood structure is more compact and contains more heterocytic cells. The content of lignin is lower than that of coniferous wood, generally between 20 and 24%. , And multi-pentan sugar content is high, generally between 21 to 24%, so the pulping is easy; grass-like pulp is characterized by high content of multi-pentanose, generally about 20% or more, the fiber easily hydrated, lignin content Low, both below 15%, with higher ash content than wood. Grass pulp contains more anionic impurities than wood pulp. Accumulation of such harmful anionic impurities in the wet end will deteriorate the effectiveness of some cationic additives and may even completely disable cationic additives. Its high negative electrodepositivity also affects the flocculation of the fine fibers in the pulp and reduces the hydrogen bonding between the fibers, thereby affecting the retention of the pulp fibers and the filtering of the water. In severe cases, it will cause sticking and plugging of the die holes.
(4) Their fiber surface potential is different. Fibers, fine fibers, soluble organic substances or colloidal substances in the slurry (soluble organic substances and colloidal substances are collectively referred to as anion impurities), and fillers generally have a certain amount of negative charge, due to differences in raw materials, preparation processes, etc. Very large, their surface charge properties and potential values ​​are also different.
Due to the above differences between wood pulp and straw pulp, the selection of chemical additives must consider the pulp type, filler type, and their ion characteristics, molecular weight, addition position, and amount of chemical additives. The ideal addition amount of the additive is the addition amount when the potential value of the slurry system is zero (isoelectric point).