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Preparation technology of plant fiber pulp slurry
Release time：2020-09-08
1. The type, nature and composition of the slurry
1. Type of slurry
The commonly used papermaking raw materials in my country are wood pulp and straw pulp. Due to the lack of wood pulp resources in our country and the relatively abundant straw pulp resources, most of our country's papermaking raw materials, especially pulp molded products, use annual straw pulp fiber raw materials. As for how many acres of forest the paper mould industry consumes a year, it is completely misunderstood.
Wood pulp fibers are divided into softwood pulp fibers (such as masson pine, larch, red pine, spruce
Etc.) and hardwood pulp fibers (such as birch, poplar, basswood, eucalyptus, maple, etc.). Pulp molded products need to have a certain strength and can withstand stretching. Generally, there are
15-20% softwood pulp.
straw pulp fiber is divided into:
(1) Grass fiber 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) kinds of wool fiber raw materials (such as cotton fiber, etc.).
2. The difference between the physical and chemical properties of wood pulp and straw pulp
(1) Their fiber shape and physical condition are different. Softwood fibers are longer, generally between 2.56 mm and 4.08 mm in length, 40.9-54.9 microns in width, and their aspect ratios are often less than 70 times; hardwood fibers are short, generally in length At about 1 mm, the aspect ratio is often less than 60 times; among the grass fibers, the bagasse raw material fiber is longer, about 1.01 to 2.34 mm, and the width is between 16.7 and 30.4 microns. Its length-to-width ratio is mostly about 77 times; the length of reed raw material fiber is about 0.60 to 1.60 mm, the width is about 5.9 to 13.4 microns, and its aspect ratio is mostly about 115 times; The length of the raw material fiber is about 0.81~2.58 mm, the width is between 13.2~19.6 microns, and the aspect ratio is about 100 times.
(2) The composition of fibers is different. The main components of plant fiber raw materials include cellulose, semi-
Three kinds of cellulose and lignin. Minor components include pectin, starch, tannin, pigment, resin, fat, wax, ash, etc. Cellulose exists in the cell walls of all plants and is the main component of plant fibers, accounting for about 40 to 98%. It is the part that should be kept as much as possible during the pulping process.
Hemicellulose is a non-cellulose carbohydrate, the structure of hemicellulose is loose and amorphous,
It is easy to absorb water and swell and dissolve in dilute lye. The content of hemicellulose in grass materials accounts for about 30%, and its chemical properties are similar to cellulose, but the reaction is faster and easier than cellulose. Hemicellulose is also the part that should be retained as much as possible during the pulping process.
Lignin is an aromatic natural polymer compound composed of phenylpropane structural units, not
A single substance is the general term for this type of substance with similar properties, and it is a substance with an amorphous structure. Grass raw materials generally contain about 20% lignin. The more lignin in the raw materials, the more difficult it is to make pulp because lignin makes the fibers stick to each other. Chemical pulping is the use of chemicals to dissolve the lignin in the fiber raw materials to separate the fibers into pulp.
(3) Their chemical composition is different. Softwood has a tight tissue structure and low content of miscellaneous cells. The miscellaneous cells in the chemical slurry are mostly lost during washing. Therefore, the quality of the slurry is good, the lignin content is high, between 25 and 35%, and the polypentose content is low. It is mostly between 9-12%, the fiber is not easy to absorb water and swell, and beating is more difficult; hardwood tissue structure is more compact, and contains more miscellaneous cells, lignin content is lower than coniferous wood, generally between 20-24% , And the polypentose content is high, generally between 21-24%, so it is easy to beat; the characteristic of grass pulp is the high polypentose content, generally about 20% or more, the fiber is easy to hydrate, and the lignin content Low, all below 15%, ash content is higher than wood. Grass pulp contains more anionic impurities than wood pulp. The accumulation of such harmful anionic impurities in the wet part will make some cationic additives less effective, and may even completely invalidate the cationic additives. Its high cathodicity also affects the flocculation of fine fibers in the pulp and reduces the hydrogen bonding between the fibers, thereby affecting the retention and drainage of pulp fibers, and in severe cases, it will cause sticking of the net and block the mold holes.
(4) Their fiber surface potential is different. Fiber, fine fiber, soluble
Organic substances or colloidal substances (soluble organic substances and colloidal substances are collectively referred to as anionic impurities) and fillers generally have a certain amount of negative charge. Due to differences in raw materials and preparation processes, they vary widely. Their surface charge properties and The potential value is also different.
Due to the above differences between wood pulp and straw pulp, the choice of chemical additives must be considered
Applicable pulp types, filler types, their ionic characteristics, molecular weight, addition location, and the amount of chemical additives. The ideal additive amount is the amount when the potential value of the slurry system is zero (isoelectric point).
2. Process design of beating system
The process flow of the beating system is usually: selecting ingredients-pulping-dissolving-adding aid
Agent-forming on the Internet. The equipment of the system usually includes: hydraulic pulper, sulfur dust removal machine, agitator, etc. In order to produce high-quality paper tableware, some companies also install a washing drum after the pulper to wash the pulp.
1. Hydraulic pulper. The hydraulic pulper is mainly used to process crushed pulp, it has
Dispersion, without cutting off.
Hydraulic pulpers are divided into three types: low consistency, medium consistency, and high consistency pulp. Pulp molding pulping machine one
Generally use medium consistency pulper. Experience has proved that medium consistency pulping can shorten the beating time, reduce energy consumption, improve equipment utilization, reduce production costs, and can also improve the quality of the slurry, which is beneficial to the copy-making of the forming machine.
2, dual function deconstructing machine. Although it takes only a few seconds for the paper to pass through the decomposer,
The pulverized pulp crushed by the pulper is cut, divided into filaments, and fibrillated by the decomposer, which can make the paper products evenly distributed, improve the uniformity of chemical additives, and increase the strength of the finished product. Another function can remove dust.
3. Stirrer. The agitator of each slurry tank mainly plays a role of dispersing and homogenizing, but its stirring
Speed plays an important role in chemical additives. Some high-molecular-weight polymerization aids are subjected to the high-speed shearing action of the stirrer, which destroys its long molecular chain, which destroys the function of chemical additives and hydrolyzes. The stirring speed of the stirrer should generally be about 30 to 60 revolutions per minute.
Three, beating principle and function
The principle of pulp molding and beating is: using physical (mechanical) methods to treat suspended in water
The pulp fibers in the paper make it suitable for the production requirements of the pulp molded product forming machine, and enable the produced paper molded products to meet the expected quality requirements. This operation is called beating.
1. The principle of beating
After the pulp fiber is mechanically treated by the beating equipment, it becomes soft and plastic. Its principle is
It is through the action of the beating equipment on the fiber that the fiber is cut, crushed, swelled by water and fine fiber
Dimensionalization increases the surface area of the fiber, thereby increasing the bonding force between the fiber and the fiber. As the beating progresses, the binding force of the fibers continues to rise, but the average fiber length decreases. Practice has proved that some physical properties of paper products, such as folding resistance, bursting resistance, water absorption, air permeability, etc., are closely related to the beating method. Therefore, when determining the beating method, a reasonable choice should be made according to the different requirements of pulp raw materials and paper products.
2. The effect of beating on fiber
The effect of beating on the fiber is mainly to cause physical and chemical changes, no matter what
Various types of beating equipment can cut, crush, swell and refine the fibers. When the fiber is subjected to the above effects, the main changes occur in the cell wall of the fiber. The changes of the fiber cell wall have the following forms:
(1) Beating causes displacement and deformation of the fiber cell wall. Displacement and deformation of the cell wall
The reason is that after the fibers are subjected to mechanical force during the beating process, the microfibers at a certain position in the middle layer of the secondary wall are bent and deformed, which increases the gap between the microfibers, which creates more water for the fibers to absorb. Under the condition, the fiber becomes soft after absorbing water, which plays an important role in removing the outer layer of primary wall and secondary wall.
(2) Beating makes the fiber primary wall and secondary wall broken. The fiber of the primary wall is not removed
It appears smooth, stiff, and not easy to absorb water and swell. Therefore, the mechanical force of the beating equipment and the mutual friction between the fibers must be used to break the outer layer of the primary wall and the secondary wall to separate the fine fibers in the middle layer of the secondary wall. Only when it comes out can the purpose of full swelling and fine fiberization of the fiber be achieved. Under normal circumstances, the difficulty of removing the outer layer of the primary wall and the secondary wall of different types of fiber materials is different, so the degree of difficulty of fibrillation is also different during beating. For example, straw pulp is more difficult to remove than wood pulp. More difficult, the removal of kraft pulp is more difficult than kraft pulp.
(3) After beating, the pulp fiber absorbs water and swells. Before the fiber primary wall is broken, the degree of water swelling of the fiber is slow. After the beating treatment, the outer layer of the fiber primary wall and the secondary wall is continuously broken, which increases the water swelling of the fiber and makes the fiber soft and plastic. , The external surface area is increased, the internal tissue structure is relaxed, and the intermolecular cohesion is reduced, which is beneficial to the progress of fibrillation. Because there are amorphous regions and a large number of hydroxyl groups in the molecular structure of cellulose and non-cellulose, they are polar attracted to water molecules, and water molecules enter the amorphous region, which increases the distance between cellulose molecular chains and increases the outer surface area of fibers. Large, causing water swelling.
(4) After the physical (mechanical) action of the beating equipment, the fiber is fibrillated.
In the process of beating, the pulp fiber is subjected to the mechanical action of the beating to produce longitudinal splitting, and the surface of the fine fiber is separated, and the two ends of the fiber are broomed and fluffed, which is called fibrillation. Due to the occurrence of fibrillation, the interweaving ability between fibers is enhanced, so that the physical strength of paper products is greatly improved.
(5) Due to the shearing action of the beating equipment, the fiber is cut transversely. During the beating process, the fibers are cut due to the shearing action of the beating equipment. At the same time, when the beating pressure is high and the concentration is high, the friction between the fibers will also cause the transverse cutting of the fibers. Properly cutting long fibers can improve the uniformity and smoothness of the paper molded product. But if the cut is too short, the strength of the paper product will decrease. Under normal circumstances, the cutting of fibers is related to the degree of swelling. Under the same beating condition, it absorbs water and swells well, and the fiber has good softness and plasticity, so it is not easy to be cut, and it is easy to split into filaments. On the contrary, if it absorbs water and swells badly, the fiber is hard and it is easy to be cut.
(6) The relationship between beating and the properties and strength of paper products. The quality of beating directly affects
It affects the strength of paper products and the binding force of fibers. Good beating quality can produce paper molded products with higher strength. If the strength of the paper molded product is insufficient, it cannot be simply attributed to the insufficient strength of a single fiber, but should consider whether the fiber binding force is insufficient. The strength of paper molded products is determined by various factors, which depend on the mutual bonding ability between fibers, fiber length, fiber strength, fiber surface condition and fiber arrangement. In short, the strength of the paper molded product is mainly derived from the binding force of the fibers, which is determined by the degree of hydrogen bonding.
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