Preparation Technology of Pulp Molding Slurry

Regardless of the molding equipment used, the production process of molded pulp products is roughly as follows:

PreparationMaterial-pulping-add chemical additives-molding. They are related to each other, interact and influence each other, especially the preparation material (slurry, filler) and beating process are the basis of pulp molding production.

According to the requirements of the product, select the appropriate raw materials (including pulp, fillers and chemical additives).Learning to design pulping process is an important link to ensure product quality and reduce product cost. Therefore, paperPulp molding enterprises to improve the quality of pulp molding products, reduce the cost of products, first of all, the pulp mold.The mechanism and related knowledge of the preparation and pulping process in the plastic production process should be clear, and each process must beResponsible by professional and technical personnel, this is often ignored by some enterprises.The author introduced in the China Packaging News about the paper mold production process to add filler,The use of retention aids has attracted the attention of the relevant enterprises, have to inquire. Because of these problemsIt is closely related to the preparation of slurry and the choice of pulping process. Here I put the relevant knowledge of slurry preparationIt is divided into three parts to make an introduction, hoping to help some paper mold enterprises.

 　　Types, Properties and Composition of 1. Slurry

1, the type of slurry.

China's commonly used papermaking raw materials are wood pulp and straw pulp two categories. Due to the lack of wood pulp resources in China,The straw pulp resources are relatively rich, so China's papermaking raw materials, especially pulp molded products are mostlyAnnual straw pulp fiber raw material is used. As for the paper mold industry to consume how many acres of forest a year to sayThe law is a complete misunderstanding.

Wood pulp fibers are divided into coniferous wood pulp fibers (such as masson pine, larch, red pine, spruceetc.) and hardwood pulp fibers (such as birch, poplar, basswood, eucalyptus, maple, etc.). PulpMolded products because of the need to have a certain strength and can withstand stretching, the slurry is generally added.15 ~ 20% of the conifer pulp.

Grass pulp fiber and points:

(1) Poaceae fiber raw materials (such as straw, wheat straw, reed, bamboo, bagasse, etc.);

(2) Bast fiber raw materials (such as hemp, kenaf, flax, mulberry skin, cotton stalk skin, etc.);

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

The difference between the physical and chemical properties of wood pulp and grass pulp.

(1) They differ in fiber morphology and physical condition. Coniferous wood fiber is longer, generally longThe degree is between 2.56 and 4.08mm, the width is between 40.9 and 54.9 microns, and the width ratio isMore than 70 times; Hardwood fiber is short, generally about 1mm in length, and its length and width are mostlyUnder 60 times; in grass fiber, bagasse raw material fiber is longer, in 1.01~2.34mm leftRight, the width is between 16.7 and 30.4 microns, and its length-to-width ratio is about 77 times that of reed raw materials.The fiber length is about 0.60~1.60mm, the width is 5.9~13.4 microns right, and its lengthThe width ratio is about 115 times more. The length and width of the raw material fiber of awn stalk are about 0.81~2.58mm.Between 13.2 and 19.6 microns, its aspect ratio is more than 100 times.

(2) The composition of the fiber is different. The main components of plant fiber raw materials include cellulose, semiCellulose and lignin three. Secondary ingredients include pectin, starch, tannins, pigments, resins, fats, waxes, ash, and the like.

Cellulose exists in the cell wall of all plants, is the main component of plant fiber, accounting for about40 ~ 98%, it is the part that should be retained in the pulping process.

Hemicellulose is a non-cellulosic carbohydrate, and the structure of hemicellulose is loose and amorphous,Easy to absorb water swelling, soluble in dilute lye. The content of hemicellulose in grass raw materials is about 30%,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 during the pulping process.

Lignin is an aromatic natural polymer composed of phenylpropane structural units, not aA 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 raw materials, the more difficult pulping, because lignin makes the fibers stick to each other. Chemical pulping is the use of chemicals to dissolve the lignin in the fiber raw material, so that the fibers are separated into pulp.

(3) Their chemical composition is different. The tissue structure of coniferous wood is tight, the content of miscellaneous cells is small,The hybrid cells in the chemical slurry are mostly lost during washing, so the quality of the slurry is good and 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,Beating is more difficult; hardwood tissue structure is more compact, and contains more hybrid cells, lignin content is moreConiferous wood is low, generally between 20 ~ 24%, and the content of pentose is high, generally between 21 ~ 24%Therefore, pulping is easy. Grass pulp is characterized by high pentose content, generally around 20% or more,The fiber is easy to hydrate, the lignin content is low, all below 15%, and the ash content is higher than that of wood. GrassPulp contains more anionic impurities than wood pulp, and the accumulation of such harmful anionic impurities in the wet end willThe effect of some cationic additives is deteriorated, and it is even possible to completely fail the cationic additives. its high yinThe electric property also affects the flocculation of fine fibers in pulp and reduces the hydrogen bonding between fibers, thus affecting the retention and filtration of pulp fibers, which will cause sticking to the mesh and blocking the holes of the mold in serious cases.

(4) Their fiber surface potentials are different. Fibers, fines, soluble in pulporganic substances or colloidal substances (soluble organic substances and colloidal substances are collectively referred to as anionic impurities),Fillers generally have a certain amount of negative charge, due to differences in raw materials, preparation processes, etc., a wide range of variation, 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 be considered.The appropriate pulp species, filler species and their ion characteristics, molecular weight size, addition location and the amount of chemical additives. The addition amount of the auxiliary agent is preferably such that the potential value of the slurry system is zero (isoelectric point).

 Process Design of 2. Pulping System

The process of the pulping system is usually: select the ingredients-pulp-dredge-add help.Agent-online forming. The equipment of the system usually includes: hydraulic pulper, sulfur removal dust removal machine, stirring.

Mixer, etc. Some enterprises in order to produce high quality paper tableware, in the pulper also installed after the drum, used to wash pulp.

1, hydraulic pulper. The hydraulic pulper is mainly used to deal with the crushing pulp, it has a pulp.Dispersion without cutting off.

Hydraulic pulper is divided into low consistency, medium consistency, high consistency pulping three kinds, pulp molding pulping machinery one.General selection of medium-thick pulper. Experience has shown that medium-thick pulping can shorten pulping time, reduce energy consumption,Improve the utilization of equipment, reduce production costs, but also improve the quality of the slurry, conduciveThe copying of the shape machine.

2, dual-function dredging machine. Although the time for the paper material to pass through the dredging machine is only a few seconds,The pulp crushed by the pulper is cut, divided and fine-fiberized by the pulper, which can make the paper finished cloth.The slurry is uniform, improving the uniformity of chemical additives, and at the same time increasing the strength of the finished product. Another function can beto dust.

3, mixer. The mixer of each slurry tank mainly plays the role of dispersion and homogenization, but its stirring speed plays an important role in chemical additives. Some high molecular weight polymerization additives through the high-speed shearing of the mixer, the destruction of its long molecular chain, so that the role of chemical additives was destroyed, hydrolysis. The stirring speed of the stirrer should generally be about 30 to 60 r/min bells.

 Principle and Function of 3. Pulping

The principle of pulp molding is: the use of physical (mechanical) methods to deal with suspended in water.In the pulp fiber, so that it has the characteristics to adapt to the production requirements of the pulp molding machine, and make.The production of paper molded products can meet the expected quality requirements, this operation process is called beating.

1, the principle of beating

The pulp fiber becomes soft and plastic after mechanical treatment by the beating equipment. Its principle isIt is through the action of the pulping equipment on the fiber, so that the fiber cut, crushing, water absorption swelling and fine fiber.The surface area of the fiber increases, thereby increasing the binding force between the fiber and the fiber. With beatingThe binding force of the fiber is increasing, but the average length of the fiber is shortened. practice has proved that,Some physical properties of paper products, such as folding resistance, breaking resistance, water absorption, breathability, etc., are all related to pulping.type has a close relationship. Therefore, when determining the beating method, according to the pulp raw materials and paper productsDifferent requirements, reasonable choice.

2. The effect of beating on fiber

The effect of the beating on the fiber is mainly to make it undergo physical and chemical changes, regardless of the use.All types of beating equipment make fibers cut, crush, absorb water and swell and refine fibers. WhenAfter the fiber is affected by the above effects, the main changes occur in the cell wall of the fiber, and the cell wall of the fiberThe changes take the following forms:

(1) beat the fiber cell wall to produce displacement and deformation. Cell wall displacement and deformationThe reason is that after the fiber is subjected to mechanical force in the beating process, the middle layer of the secondary wall is certain.The microfibers in the position produce bending deformation, so that the gap between the microfibers has increased, which is the fiber.Absorbing more moisture creates conditions for the fiber to become soft after absorbing water and deformation, which is very important for removing the primary wall andThe outer layer of the secondary wall plays an important role.

Beating (2) breaks down the primary and secondary walls of the fiber. Fibers from the primary wall not removedIt is smooth, hard, and not easy to absorb water and swell, so it is necessary to use the mechanical force of the beating equipment andThe mutual friction between the fibers breaks the outer layer of the primary wall and the secondary wall, making the middle layer of the secondary wall.Fine fiber separation, in order to achieve the purpose of fiber full swelling and fine fiber. In the usual situationUnder the circumstances, the degree of difficulty in removing the outer layer of the primary wall and secondary wall of different types of fiber raw materials is also different.The same, so the difficulty of fine fibrosis in beating is also different, for example, straw pulp is more difficult to remove than wood pulp.It is difficult to remove kraft wood pulp than kraft wood pulp.

(3) After beating, the pulp fiber absorbs water and swells. Before the fiber primary wall is broken,The degree of water absorption and swelling of the fiber is slow. After beating, the outer layer of the primary wall and secondary wall of the fiber is notThe break is broken, which increases the water absorption and swelling of the fiber, making the fiber soft and plastic, and the outer surface area is large,The internal tissue structure is relaxed and the intermolecular cohesion is decreased, which is conducive to the fine fibrosis. Due to the fiberThere are amorphous regions and a large number of hydroxyl groups in the molecular structure of Vasin and non-cellulose, and water molecules.Polar attraction, water molecules into the amorphous region, so that the distance between the cellulose molecular chains increases, the surface area of the fiber increases, resulting in water absorption swelling.

(4) After the physical (mechanical) action of the beating equipment, the fibers are finely fibrillated.Pulp fibers are subjected to the mechanical action of beating in the process of beating, resulting in longitudinal splitting and surface separation.The phenomenon of fine fibers and fluffing at both ends of the fibers is called fine fibrosis. Due to the occurrence of fibrillation, the interlacing ability between fibers is enhanced, resulting in a greater improvement in the physical strength of the paper product.

(5) The fibers are cut transversely due to the shearing action of the beating equipment. In the beating process,Due to the shearing action of the beating equipment, the fibers are cut off. At the same time, in the beating pressure is larger, the concentrationIn the higher case, the fibers rub against each other, which also causes transverse cutting of the fibers. long fiberThe tissue uniformity and smoothness of the paper molded product can be improved by proper cutting. But cut too short, paperThe strength of the product will be reduced. In general, the cutting of the fibers is related to the degree of swelling. InUnder the same beating conditions, the water absorption and swelling are good, and the fiber has good softness and plasticity.Easy to be cut off, and easy to split broom. On the contrary, the water absorption and swelling is not good, the fiber is hard, it is easy to beCut off.

(6) The relationship between beating and the nature and strength of paper products. The quality of beating is directly affected.Sound to the strength of paper products and fiber binding force. Good beating quality can produce higher strengthof paper molded products. If the strength of the paper molded product is not enough, it cannot be simply attributed to the strength of a single fiber.Not enough, but should consider whether the fiber binding force is insufficient. The strength of paper molded products is high and low by manyIt depends on the ability of the fibers to bond to each other, the length of the fibers, the length of the fibers themselves.factors such as strength, fiber surface condition and fiber arrangement. In short, the strength of the paper molding products to obtain the main.It is determined by the binding force of the fibers, that is, the degree of hydrogen bonding.