Regardless of the molding equipment used, the production process flow of pulp molding products is roughly as follows: stock preparation - beating - add chemical additives - molding. They intertwined, interacted, and interacted with each other. In particular, preparations (slurry, fillers) and beating processes were the basis for pulp molding production. According to the requirements of the product, selecting the appropriate raw materials (including pulp type, filler and chemical additives) and scientifically designing the pulping process are important links for ensuring product quality and reducing product cost. Therefore, pulp molding companies must improve the quality of pulp molded products and reduce the cost of products. First of all, it is necessary to make clear the preparation materials, the mechanism of pulping process, and related knowledge in the pulp molding production process. Each process must be handled by professional and technical personnel. This is often overlooked by some companies.
The articles on adding fillers and using retention aids in the paper mold production process that I introduced in the China Packaging News last year have attracted the attention of relevant companies and have come to inquire. Because these problems are closely related to the preparation of slurry and the selection of the pulping process, I hereby give an introduction of the relevant knowledge of pulp preparation in eight parts, hoping to help some paper mold companies.
First, the kind of slurry, nature and composition of the 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 and 4.08 mm in length, between 40.9 and 54.9 microns in width, and have a length-to-width ratio of less than 70 times; hardwood fibers are short, generally length About 1 millimeter, the aspect ratio is mostly below 60 times; in the grass fiber, the raw material of bagasse fiber is longer, about 1.01 to 2.34 mm, and the width is between 16.7 to 30.4 microns. The length-width ratio is 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 the aspect ratio is about 115 times more; The raw material fiber length is about 0.81 to 2.58 millimeters, the width is between 13.2 to 19.6 microns, and its length to width ratio is 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).
Second, the process of pulping system design The process flow of the pulping system is usually: selection of ingredients - pulping - desorption - add additives - online forming. The equipment of this system usually includes: hydraulic pulper, sulfur de-dusting machine, agitator and the like. In order to produce high-quality paper cutlery, some companies also install washing drums for pulp washing after the pulper.
1, hydraulic pulper. The hydraulic pulper is mainly used to treat the smashed pulp. It has a dispersing effect on the pulp without cutting off.
Hydraulic pulper is divided into low concentration, medium concentration, high concentration pulp, pulp pulping machinery generally choose medium pulper. Experience has shown that medium and heavy pulp can shorten beating time, reduce energy consumption, increase equipment utilization, and reduce production costs. It can also improve the quality of the slurry and facilitate the manufacture of the forming machine.
2, dual function sparser. Although the time for the paper material to pass through the disintegration machine is only a few seconds, the pulverization of the pulp by the pulper can be cut off by the disintegrator, and the filaments can be evenly distributed to improve the chemical additives. Evenness can also increase the strength of the finished product. Another feature can dust.
3, stirrer. The agitators in each pool mainly function as dispersing and homogenizing, but its agitation speed plays an important role in chemical additives. Some high-molecular-weight polymerization aids are subjected to high-speed shearing by a stirrer, destroying its long molecular chains, and destroying and hydrolyzing the action of chemical aids. Stirrer stirring speed should generally be around 30 to 60 rpm.
Third, the principle and role of pulping Pulp pulping pulping principle is: the use of physical (mechanical) method, processing pulp fibers suspended in water, so that it has to adapt to the characteristics of the production of pulp molding products, and make the production of the Paper molded products can achieve the desired quality requirements. This operation is called pulping.
1. The principle of beating Pulp fibers become soft and plastic after being mechanically processed by the pulping equipment. Its principle is that through the action of the pulping equipment on the fibers, the fibers are cut, crushed, absorbed, swelled, and fibrillated, so that the surface area of ​​the fibers is increased, thereby increasing the binding force between fibers and fibers. As the beating progresses, the binding force of the fibers continues to increase, but the average fiber length decreases. Practice has proved that some of the physical properties of paper products, such as folding degree, bursting degree, water absorption, air permeability, etc., have a close relationship with the beating method. Therefore, when determining the beating method, reasonable choices should be made according to the different requirements of pulp raw materials and paper products.
2. The effect of beating on fibers The effect of beating on the fibers is mainly to cause physical and chemical changes. No matter which type of beating equipment is used, the fibers are cut, crushed, absorbed and swelled and the fibers are refined. When the fiber is subjected to the above-mentioned effects, its major changes occur on the cell wall of the fiber. The changes of the fiber cell wall are as follows:
(1) Beating causes displacement and deformation of the fiber cell wall. The reason for the displacement and deformation of the cell wall is that after the fibers are subjected to mechanical forces during the beating process, the microfibers in the middle layer of the secondary wall are bent and deformed, so that the gap between the microfibers is increased, which is the absorption of the fibers. More moisture creates the conditions, the fiber becomes flexible after absorbing water, and plays an important role in removing the primary wall and the outer layer of the secondary wall.
(2) Beating causes the primary and secondary walls of the fiber to break. The fibers that have not been removed from the primary wall appear smooth, stiff and difficult to absorb and swell. Therefore, the mechanical forces of the pulping equipment and the mutual friction between the fibers must be used to break the outer layers of the primary and secondary walls to make secondary fibers. The thin fibers in the middle layer of the wall are separated to achieve the purpose of full swelling and fine fiberization of the fiber. Under normal circumstances, the difficulty of removing the primary wall and the secondary wall outer layer of different types of fiber raw materials is also not the same, so the degree of difficulty in fibrillation during beating is also not the same, such as the removal of pulp from wood pulp. To be difficult, the removal of sulphate wood pulp and sulphate wood pulp is difficult.
(3) After the pulping, the pulp fiber absorbs moisture and swells. Before the fiber initial wall is not broken, the degree of water absorption and swelling of the fiber is relatively slow. After the beating treatment, the primary wall of the fiber and the outer wall of the secondary wall are continuously broken, which increases the water absorption swelling of the fiber and makes the fiber soft and plastic. The increase of the external surface area, the relaxation of the internal structure, and the decrease of intermolecular cohesion are conducive to the progress of fibrillation. Due to the presence of amorphous regions and a large number of hydroxyl groups in the cellulose and non-cellulose molecular structures, polar attraction occurs with water molecules, and water molecules enter amorphous regions, increasing the distance between cellulose molecules and increasing the surface area of ​​fibers. Large, causing swelling and swelling.
(4) After the physical (mechanical) action of the pulping equipment, the fibers are fibrillated. Pulp fibers are subjected to mechanical action of beating in the process of beating to cause longitudinal splitting, the separation of fine fibers on the surface, and the phenomenon of fluffing at both ends of the fiber, known as fibrillation. Due to the occurrence of fibrillation, the interweaving ability between the fibers and the fibers is enhanced, so that the physical strength of the paper products is greatly improved.
(5) The fibers are cut transversely due to the shearing action of the beating device. During the beating process, the fibers are cut due to the shearing action of the pulping apparatus. At the same time, in the case of high beating pressure and high concentration, the mutual friction between the fibers can also cause the transverse cut of the fibers. Long cut fibers can be appropriately cut to improve the uniformity and smoothness of the paper molded articles. However, when cut too short, the strength of paper products will be reduced. In the usual case, the cut off of the fibers is related to the degree of swelling. Under the same beating condition, the water swelling and swelling are good, and the fiber has good softness and plasticity, and it is not easy to be cut, and it is easy to split the silk. Conversely, water swelling is not good and fibers are hard and they are easily cut.
(6) The relationship between beating and paper product properties and strength. The quality of beating directly affects the strength of paper products and the binding force of fibers. A good beating quality can produce higher strength paper products. If the strength of the paper-based molded article is not enough, it cannot be simply attributed to the fact that the strength of the single fiber is insufficient, and it should be considered whether the fiber-binding force is insufficient. The strength of a paper moulding product is determined by various reasons. It depends on the mutual binding ability between the fibres, the length of the fibres, the strength of the fibres themselves, the condition of the fibre surface and the arrangement of the fibres. In short, the strength of paper molded products mainly comes from the binding force of fibers, which is determined by the degree of hydrogen bond formation.
The articles on adding fillers and using retention aids in the paper mold production process that I introduced in the China Packaging News last year have attracted the attention of relevant companies and have come to inquire. Because these problems are closely related to the preparation of slurry and the selection of the pulping process, I hereby give an introduction of the relevant knowledge of pulp preparation in eight parts, hoping to help some paper mold companies.
First, the kind of slurry, nature and composition of the 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 and 4.08 mm in length, between 40.9 and 54.9 microns in width, and have a length-to-width ratio of less than 70 times; hardwood fibers are short, generally length About 1 millimeter, the aspect ratio is mostly below 60 times; in the grass fiber, the raw material of bagasse fiber is longer, about 1.01 to 2.34 mm, and the width is between 16.7 to 30.4 microns. The length-width ratio is 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 the aspect ratio is about 115 times more; The raw material fiber length is about 0.81 to 2.58 millimeters, the width is between 13.2 to 19.6 microns, and its length to width ratio is 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).
Second, the process of pulping system design The process flow of the pulping system is usually: selection of ingredients - pulping - desorption - add additives - online forming. The equipment of this system usually includes: hydraulic pulper, sulfur de-dusting machine, agitator and the like. In order to produce high-quality paper cutlery, some companies also install washing drums for pulp washing after the pulper.
1, hydraulic pulper. The hydraulic pulper is mainly used to treat the smashed pulp. It has a dispersing effect on the pulp without cutting off.
Hydraulic pulper is divided into low concentration, medium concentration, high concentration pulp, pulp pulping machinery generally choose medium pulper. Experience has shown that medium and heavy pulp can shorten beating time, reduce energy consumption, increase equipment utilization, and reduce production costs. It can also improve the quality of the slurry and facilitate the manufacture of the forming machine.
2, dual function sparser. Although the time for the paper material to pass through the disintegration machine is only a few seconds, the pulverization of the pulp by the pulper can be cut off by the disintegrator, and the filaments can be evenly distributed to improve the chemical additives. Evenness can also increase the strength of the finished product. Another feature can dust.
3, stirrer. The agitators in each pool mainly function as dispersing and homogenizing, but its agitation speed plays an important role in chemical additives. Some high-molecular-weight polymerization aids are subjected to high-speed shearing by a stirrer, destroying its long molecular chains, and destroying and hydrolyzing the action of chemical aids. Stirrer stirring speed should generally be around 30 to 60 rpm.
Third, the principle and role of pulping Pulp pulping pulping principle is: the use of physical (mechanical) method, processing pulp fibers suspended in water, so that it has to adapt to the characteristics of the production of pulp molding products, and make the production of the Paper molded products can achieve the desired quality requirements. This operation is called pulping.
1. The principle of beating Pulp fibers become soft and plastic after being mechanically processed by the pulping equipment. Its principle is that through the action of the pulping equipment on the fibers, the fibers are cut, crushed, absorbed, swelled, and fibrillated, so that the surface area of ​​the fibers is increased, thereby increasing the binding force between fibers and fibers. As the beating progresses, the binding force of the fibers continues to increase, but the average fiber length decreases. Practice has proved that some of the physical properties of paper products, such as folding degree, bursting degree, water absorption, air permeability, etc., have a close relationship with the beating method. Therefore, when determining the beating method, reasonable choices should be made according to the different requirements of pulp raw materials and paper products.
2. The effect of beating on fibers The effect of beating on the fibers is mainly to cause physical and chemical changes. No matter which type of beating equipment is used, the fibers are cut, crushed, absorbed and swelled and the fibers are refined. When the fiber is subjected to the above-mentioned effects, its major changes occur on the cell wall of the fiber. The changes of the fiber cell wall are as follows:
(1) Beating causes displacement and deformation of the fiber cell wall. The reason for the displacement and deformation of the cell wall is that after the fibers are subjected to mechanical forces during the beating process, the microfibers in the middle layer of the secondary wall are bent and deformed, so that the gap between the microfibers is increased, which is the absorption of the fibers. More moisture creates the conditions, the fiber becomes flexible after absorbing water, and plays an important role in removing the primary wall and the outer layer of the secondary wall.
(2) Beating causes the primary and secondary walls of the fiber to break. The fibers that have not been removed from the primary wall appear smooth, stiff and difficult to absorb and swell. Therefore, the mechanical forces of the pulping equipment and the mutual friction between the fibers must be used to break the outer layers of the primary and secondary walls to make secondary fibers. The thin fibers in the middle layer of the wall are separated to achieve the purpose of full swelling and fine fiberization of the fiber. Under normal circumstances, the difficulty of removing the primary wall and the secondary wall outer layer of different types of fiber raw materials is also not the same, so the degree of difficulty in fibrillation during beating is also not the same, such as the removal of pulp from wood pulp. To be difficult, the removal of sulphate wood pulp and sulphate wood pulp is difficult.
(3) After the pulping, the pulp fiber absorbs moisture and swells. Before the fiber initial wall is not broken, the degree of water absorption and swelling of the fiber is relatively slow. After the beating treatment, the primary wall of the fiber and the outer wall of the secondary wall are continuously broken, which increases the water absorption swelling of the fiber and makes the fiber soft and plastic. The increase of the external surface area, the relaxation of the internal structure, and the decrease of intermolecular cohesion are conducive to the progress of fibrillation. Due to the presence of amorphous regions and a large number of hydroxyl groups in the cellulose and non-cellulose molecular structures, polar attraction occurs with water molecules, and water molecules enter amorphous regions, increasing the distance between cellulose molecules and increasing the surface area of ​​fibers. Large, causing swelling and swelling.
(4) After the physical (mechanical) action of the pulping equipment, the fibers are fibrillated. Pulp fibers are subjected to mechanical action of beating in the process of beating to cause longitudinal splitting, the separation of fine fibers on the surface, and the phenomenon of fluffing at both ends of the fiber, known as fibrillation. Due to the occurrence of fibrillation, the interweaving ability between the fibers and the fibers is enhanced, so that the physical strength of the paper products is greatly improved.
(5) The fibers are cut transversely due to the shearing action of the beating device. During the beating process, the fibers are cut due to the shearing action of the pulping apparatus. At the same time, in the case of high beating pressure and high concentration, the mutual friction between the fibers can also cause the transverse cut of the fibers. Long cut fibers can be appropriately cut to improve the uniformity and smoothness of the paper molded articles. However, when cut too short, the strength of paper products will be reduced. In the usual case, the cut off of the fibers is related to the degree of swelling. Under the same beating condition, the water swelling and swelling are good, and the fiber has good softness and plasticity, and it is not easy to be cut, and it is easy to split the silk. Conversely, water swelling is not good and fibers are hard and they are easily cut.
(6) The relationship between beating and paper product properties and strength. The quality of beating directly affects the strength of paper products and the binding force of fibers. A good beating quality can produce higher strength paper products. If the strength of the paper-based molded article is not enough, it cannot be simply attributed to the fact that the strength of the single fiber is insufficient, and it should be considered whether the fiber-binding force is insufficient. The strength of a paper moulding product is determined by various reasons. It depends on the mutual binding ability between the fibres, the length of the fibres, the strength of the fibres themselves, the condition of the fibre surface and the arrangement of the fibres. In short, the strength of paper molded products mainly comes from the binding force of fibers, which is determined by the degree of hydrogen bond formation.
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