Preparation of the hottest paper pulp molding slur

2022-10-22
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Preparation of pulp molding slurry

no matter what kind of molding equipment is used, the production process of pulp molding products is roughly as follows: material preparation - beating - adding chemical additives - molding. They are implicated, interacted and influenced by each other. The annual average growth of China's new material industry remains at about 25%, especially the preparation (pulp, filler) and beating process are the basis of pulp molding production. According to the requirements of products, selecting appropriate raw materials (including pulp species, fillers and chemical additives) and scientifically designing the beating process are important links to ensure product quality and reduce product costs. Therefore, in order to improve the quality of pulp molding products and reduce the cost of products, pulp molding enterprises should first be clear about the mechanism and relevant knowledge of material preparation and beating process in the process of pulp molding production. Each post symbol process must be in the charge of professional technicians, which has always been ignored by some enterprises

the article about adding fillers and using retention aids in the production process of paper mold that I introduced in China Packaging News last year attracted the attention of relevant enterprises and called for consultation. Because these problems are closely related to the preparation of pulp and the selection of beating process, here I will introduce the relevant knowledge of pulp preparation in eight parts, hoping to be helpful to some paper mold enterprises

I. types, properties and tissue components of pulp

1. Types of pulp

the commonly used papermaking raw materials in China include wood pulp and straw pulp. Due to the lack of wood pulp resources and the relatively rich straw pulp resources in China, annual straw pulp fiber raw materials are mostly used for papermaking raw materials, especially for pulp molding products. As for the statement about how many acres of forest the paper mold industry consumes a year, it is completely a misunderstanding

wood pulp fibers are divided into coniferous wood pulp fibers (such as masson pine, larch, Korean pine, spruce, etc.) and broad-leaved wood pulp fibers (such as birch, poplar, basswood, eucalyptus, maple, etc.). Because pulp molded products need to have a certain strength and can withstand tension, 15 ~ 20% coniferous pulp is generally added to the pulp

straw pulp fiber is divided into:

(1) cereal 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 bark, etc.)

(3) wool fiber raw materials (such as cotton fiber, etc.)

2. Differences in physical and chemical properties between wood pulp and straw pulp

(1) their fiber morphology and physical condition are different. Coniferous wood fiber is long, generally between 2.56 ~ 4.08 mm in length and 40.9 ~ 54.9 microns in width, and its length width ratio is more than 70 times; Hardwood fiber is short, generally about 1 mm in length, and its length width ratio is more than 60 times; Among grass fibers, bagasse raw fiber is longer, about 1.01 ~ 2.34 mm, with a width of 16.7 ~ 30.4 microns, and its length width ratio is about 77 times; The length of reed raw fiber is about 0.60 ~ 1.60 mm, the width is about 5.9 ~ 13.4 microns, and its length width ratio is about 115 times; Awn stalk raw fiber is about 0.81 ~ 2.58 mm long, 13.2 ~ 19.6 microns wide, and its length width ratio is about 100 times

(2) the composition of fibers is different. The main components of plant fiber raw materials include cellulose, hemicellulose and lignin. The secondary components include pectin, starch, tannin, pigment, resin, fat, wax, ash, etc

cellulose exists in the cell wall of all plants and is the main component of plant fiber, accounting for about 40 ~ 98%. It is the part that should be tried to be retained in the pulping process

hemicellulose is a non cellulosic carbohydrate. Its structure is loose and amorphous, easy to absorb water and swell, and easy to dissolve in dilute lye. Hemicellulose accounts for about 30% of grass raw materials. Its chemical properties are similar to cellulose, but the reaction is faster and easier than cellulose. Hemicellulose is also a part that should be strongly retained in the pulping process

lignin is an aromatic natural macromolecular compound composed of phenylpropane structural units. It is not a single substance. It is the general name of this kind of substances with similar properties. It is a substance with amorphous structure. Grass raw materials generally contain about 20% lignin. The more lignin the raw materials contain, the more difficult it is to pulping, because lignin makes the fibers stick together. Chemical pulping is to use chemicals to dissolve the lignin in the fiber raw materials, so that the fibers can be separated into pulp with environmental media

(3) their chemical compositions are different. The tissue structure of coniferous wood is tight, the content of heterogenous cells is small, and most of the heterogenous cells in the chemical pulp are lost during washing, so the pulp quality is good, the lignin content is high, between 25 ~ 35%, and the content of pentose is low, mostly between 9 ~ 12%, the fiber is not easy to absorb water and moisten, and it is difficult to beat; The tissue structure of hardwood is more compact, and it contains more miscellaneous cells. The lignin content is lower than that of coniferous wood, generally between 20 ~ 24%, and the content of pentosan is high, generally between 21 ~ 24%, so it is easy to beating; Straw pulp is characterized by high content of pentose, generally about 20% or more, easy hydration of fiber, low lignin content, all below 15%, and higher ash content than wood. Straw pulp contains more anionic impurities than wood pulp. The accumulation of such harmful anionic impurities in the wet end will make some cationic additives worse, and may even make cationic additives completely ineffective. Its high electronegativity also affects the flocculation of fine fibers in pulp and reduces the hydrogen bond bonding between fibers, thus affecting the retention and drainage of pulp fibers, which will cause stickiness and blockage of mold holes in serious cases

(4) their fiber surface potentials are different. Fibers, fine fibers, soluble organic substances or colloidal substances (soluble organic substances and colloidal substances are collectively referred to as anionic impurities) and fillers in the slurry generally carry a certain amount of negative charge. Due to the differences in raw materials and preparation processes, the range of changes is large, and 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 species, filler varieties, their ionic properties, molecular weight, adding position and the dosage of chemical additives. The ideal additive amount is when the potential value of the slurry system is zero (isoelectric point)

II. Process design of the beating system

the process flow of the beating system is usually: selecting ingredients - pulping - Dredging - adding additives - upper forming. The equipment of the system usually includes: hydraulic pulper, sulfur decomposition dust remover, agitator, etc. In order to produce high-quality paper tableware, some enterprises also install washing drums after the pulper to wash pulp

1. Hydraulic pulper. Hydraulic pulper is mainly used to deal with crushed pulp. It has dispersing effect on pulp without cutting effect

hydraulic pulpers are divided into low consistency, medium consistency and high consistency pulps. Medium consistency pulpers are generally selected as pulp molding pulping machines. Experience has proved that medium consistency pulping can shorten the beating time, reduce energy consumption, improve the utilization of equipment, reduce production costs, and improve the quality of slurry, which is conducive to the copying of forming machines

2. Dual function relieving machine. Although it takes only a few seconds for the paper to pass through the disintegrator, the shredded pulp crushed by the pulper can be cut, separated and fine fibrosed by the disintegrator, which can make the pulp distribution of the finished paper products uniform, improve the uniformity of chemical additives, and increase the strength of the finished products at the same time. Another function can remove dust

3. Agitator. The agitator of each slurry tank mainly plays the role of dispersion and homogenization, but its mixing speed plays an important role in chemical additives. Some high molecular weight polymerization additives are destroyed by the high-speed shear action of the agitator, which destroys and hydrolyzes the role of chemical additives. Generally, the mixing speed of the mixer should be about 30 ~ 60 rpm

III. beating principle and function

the principle of pulp molding beating is to use physical (Mechanical) methods to treat the pulp fiber suspended in water, so that it has the characteristics to meet the production requirements of the pulp molding product forming machine, and make the produced paper molding products meet the expected quality requirements. This operation process is called beating

1. Beating principle

pulp fibers become soft and plastic after mechanical treatment by beating equipment. Its principle is that through the action of beating equipment on the fiber, the fiber will be cut, crushed, water absorption and swelling, and fine fibrosis, so as to increase the surface area of the fiber, thereby increasing the binding force between the fiber and the fiber. With the progress of beating, the binding force of the fiber continues to rise, but the average length of the fiber is shortened. Practice has proved that some physical properties of paper products, such as folding resistance, bursting resistance, water absorption and air permeability, are closely related to beating methods. Therefore, when determining the beating method, it should be reasonably selected according to the different requirements of pulp raw materials and paper products

2. The effect of beating on fiber

the effect of beating on fiber is mainly to make it undergo physical and chemical changes. No matter what type of beating equipment is used, the fiber will be cut, crushed, bloated and refined. When the fiber is subjected to the above effects, its main changes occur on the cell wall of the fiber. The changes of the fiber cell wall have the following forms:

(1) beating makes the fiber cell wall displacement and deformation. The reason for the displacement and deformation of the cell wall is that the microfiber at a certain position in the middle layer of the secondary wall is bent and deformed after the fiber is subjected to mechanical force in the beating process, which increases the gap between the microfibers, which creates conditions for the fiber to absorb more water. The fiber becomes soft after water absorption and deformation, which plays an important role in removing the outer layer of the primary wall and the secondary wall

(2) beating breaks the primary and secondary walls of fibers. The fibers without removing the primary wall appear smooth, stiff and not easy to absorb water and swell. Therefore, the outer layers of the primary wall and the secondary wall must be broken by using the mechanical force of the beating equipment and the mutual friction between the fibers, so that the fine fibers in the middle layer of the secondary wall can be separated, so as to achieve the purpose of full swelling and fine fibrosis of the fibers. Under normal circumstances, the difficulty of removing the outer layers of primary and secondary walls of different kinds of fiber raw materials is also different, so the difficulty of fine fibrosis during beating is also different. For example, straw pulp is more difficult to remove than wood pulp, and sulfate wood pulp is more difficult to remove than sulfite wood pulp

(3) after beating, the pulp fiber absorbs water and swells. Before the primary wall of the fiber is broken, the degree of water absorption and swelling of the fiber is slow. After beating, the outer layers of the primary wall and secondary wall of the fiber are constantly broken, which increases the water absorption and swelling of the fiber, making the fiber soft and plastic, the external area increases, the internal tissue structure is loose, and the intermolecular cohesion decreases, which is conducive to the progress of fine fibrosis. Because there are amorphous regions and a large number of hydroxyl groups in the molecular structure of cellulose and non cellulose, polar attraction occurs with water molecules, and water molecules enter the amorphous region, which increases the distance between cellulose molecular chains and the surface area of fiber, resulting in water absorption and swelling

(4) through the physical (Mechanical) action of beating equipment, the fiber produces fine fibrosis. Pulp fiber in the beating process

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