Zhiqiao introduction: detailed explanation of basic performance indexes of paper is worth collecting.
Used pulp and paper machine network forwarding
1) fracture length
Fracture length is a method of expressing the tensile strength of paper, which is mainly determined by the fiber binding force, the average length of the fiber, the interweaving arrangement of the fiber and the strength of the fiber itself.
Usually, the crack length rises quickly at the initial stage of beating, then gradually slows down, and rises to a certain value, the crack length will drop, and there will be a turning point. The reason for the transition is mainly affected by the changes of fiber binding force and average fiber length.
At the initial stage of beating, the fiber binding force mainly affects the breaking length of paper; With the extension of beating time, although the fiber binding force is still improved, the breaking length can be continuously improved, however, as the average length of the fiber continues to decline, the broken length of the paper decreases. As the influence of the decrease of the average length of the fiber exceeds the influence of the increase of the fiber binding force, the turning point of the broken length occurs.
In addition, the strength of the fiber itself and the interweaving arrangement of the fiber in the paper forming process will also directly affect the breaking length of the paper to a certain extent.
2) Folding endurance
Folding endurance refers to the folding times that paper can withstand 180 ° reciprocating under certain tension.
The factors that affect the folding resistance include the average length of the fiber, the binding force of the fiber, the interweaving and arrangement of the fiber, the strength of the fiber itself and the proportion of the length.
The folding endurance of paper increases with the increase of beating degree.
Similar to the fracture length, that is, a turning point occurs after reaching the highest value. The influence of fiber binding force on fracture resistance is not as great as that on fracture length. On the contrary, the average fiber length has a great influence on fracture resistance. Therefore, the turning point of fracture resistance curve is earlier than that of fracture length, when the beating degree is not very high, the folding endurance begins to decline.
3) tear degree
The degree of tear is the ability of the paper to resist tearing. The tear degree is different from the fracture length, which is mainly determined by the average length of the fiber.
At the initial stage of beating, due to the improvement of beating degree, the specific surface area of the fiber is greatly increased, which is conducive to improving the binding force of the fiber, but at the same time, the average length of the fiber decreases. At this stage, as the effect of fiber binding force is greater than that of average fiber length, the tear degree is on the rise.
After rising a certain value, due to the sharp decline in the average length of the fiber, the tear degree decreases rapidly. Since the tear degree depends more on the average length of the fiber, the turning point of the tear degree curve appears earliest.
4) breaking resistance
Burst resistance indicates the maximum pressure that a paper sheet can withstand. The main factors that affect the breaking resistance are the fiber binding force, followed by the average length of the fiber, the strength and interweaving of the fiber itself.
Therefore, the rupture resistance curve is very similar to the fracture length curve, only because the paper is not only affected by tensile force but also by tearing force when it breaks, when the beating degree is relatively high, because the average length of the fiber is low, the degree of breakage resistance is lower than that of the fracture length.
5) absorbency
Absorbency is the ability of paper to absorb water or other liquids. The main factor affecting the absorbency of paper is the degree of beating, which decreases with the increase of the degree of beating of the slurry. There is no turning point and it is in the shape of a decreasing curve.
However, this absorption curve is exactly symmetrical with the growth curve of binding force in beating. This symmetrical relationship shows that there is a connection between each other. This is because the beating process increases the specific surface area of the fiber, reduces the number of pores and capillaries, and as a result, the absorption properties decrease.
At the same time, the absorbency is related to the purity of the fiber and the content of hemicellulose. The slurry with high hemicellulose content is easy to split silk and fine fibrosis in the process of beating, and the paper is tightly combined, which affects the absorption.
6) air permeability
The air permeability is the degree of ventilation of the paper, which can reflect the size of the gap in the middle of the paper layer. The main factors affecting the air permeability are similar to the absorption, but also the degree of beating and the chemical composition of the fiber.
The air permeability decreases with the increase of beating degree. Due to the small resistance of air through the paper, the air permeability curve is larger than the slope of the absorption curve.
7) opacity
Opacity refers to the degree to which a paper sheet is opaque. The opacity of paper mainly depends on the binding force of fibers, which decreases with the increase of beating degree. There is no turning point. If the binding of fibers in the paper relaxes, there will be air between the fibers, light is refracted through air, improving the opacity of the paper.
It can be seen from this that the higher the beating degree is, the more tightly the fiber is combined, the less air between the fibers is, the smaller the refraction surface is, the more transparent the paper is, and the lower the opacity is. For the production of paper with large opacity, it is advisable to use pulp with less semi-fiber, low beating degree, and at the same time select fillers with large refractive index.
8) tightness
Tightness refers to the degree of tightness of the paper. The main factors that affect the tightness of paper are beating degree, pulp type, hemicellulose content, squeezing and calendering in paper machine copying, etc. The higher the pulp beating degree, the more hemicellulose content, the greater the tightness of the paper.
9) Scalability
Scalability refers to the relative change in size when paper is immersed in water or humidified or dehumidified at different humidity. The scalability of paper is closely related to beating method, hemicellulose content, fiber strength and elasticity.
There are many hemicellulose, high beating degree and large fiber binding force, so the paper shrinks due to surface tension during drying.
When it is wet, it is easy to expand, which makes the paper deformed and the scalability increased. Cut short fibers in a short time during the beating process to prevent the fibers from being excessively moistened and swollen, avoid the excessive hydration of the fibers, and reduce the scalability of the paper.
10) Sizing degree
One of the main effects of beating is to increase the specific surface area of the fiber, and the split wire of the fiber is broom, which increases the binding force between the fibers and the fibers and the added materials, and improves the rubber, filler, keep the fine fibers.
The fine fiber has a stronger affinity for the rubber, so the sizing effect is improved.
11) brittleness
At the initial stage of beating, the beating degree increases and the brittleness decreases. With the further improvement of beating degree, the brittleness of paper increases again.
The reason is that the length of the fiber has a great influence on the brittleness. With the increase of beating degree, the length of the fiber decreases and the brittleness of the paper will continue to increase.
In addition, the fine fibrosis of the fiber also has a great influence on the brittleness. The fine fibrosis of the fiber is conducive to the dispersion of the stress of the paper sheet and can reduce the brittleness of the paper sheet, such as further improving the fine fibrosis of the fiber, the tightness of the paper will rise and the brittleness of the paper will increase.
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