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Microstructure Of Cotton Fiber And Its Relationship With Fiber Properties

2010/7/17 14:51:00 46

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Cotton fiber

The physical properties are determined by the internal structure of the fiber, and its physical properties determine its spinnability and use value. The physical properties of cotton fibers are naturally formed. They are closely related to the growth and development of fiber and the formation process of the main components.

It can be said that the growth and development of cotton fiber is not only the formation process of fiber material, but also the formation process of fiber physical properties. The physical properties of fibers are external manifestations of growth, development and structural characteristics.

To grasp the characteristics of moisture absorption, mechanical properties, thermal properties, optical properties and usability of cotton fabrics, we must understand and grasp the growth and development process, forming characteristics, material composition, morphological characteristics and structural characteristics of cotton fibers.

The following physical and mechanical properties of fibers are analyzed from the cotton fiber growth and development process, mainly the formation process of fiber microstructure.

1 the formation process of cotton fiber microstructure

Cotton fiber

It is formed by the single cell differentiation of the cotton ovule epidermis. According to its formation and development process, the differentiation and development of cotton fiber can be divided into four periods: the differentiation and protuberance stage of fiber, the elongation period of fiber, the thickening stage of fiber secondary layer and the maturity stage of fiber dehydration.

The differentiation of fibrous primary cells is the process of the differentiation of ovule epidermal cells into fibrous primordial cells. The time to start differentiation of fibroblasts is usually difficult to determine in morphology. Because before the morphogenesis of cells, a series of changes have taken place inside the cell. Generally, in the three day before flowering, the fiber primordial cells have been differentiated and formed, and fibroblasts continue to develop under the stimulation of pollination.

The original cells of differentiated growth fibers expand into spherical or hemispherical protuberances. The differentiation of fiber cells sooner or later directly affects the length of the mature fibers on the ovule, and the early differentiation of fibrous growth fibers. After three days, the differentiated fibers become cotton lint, and the fiber cells begin to elongate on the day of flower opening. It usually takes 24 days to 32 days, and the fiber elongation is fastest in 10 days after flowering.

Fiber elongation can be divided into two stages: non-polar expansion and polar elongation. During non-polar expansion, the fiber cells expand nonpolar until the final diameter of the fiber is formed.

This developmental stage determines the fineness of the fiber and the deposition of secondary fibrous cells to the 40 day to 50 days after flowering. The deposition and thickening of cellulose in the cell wall are controlled by two different systems of the primary layer thickening, but they are not completely separate. When the fiber is stretched, the cellulose begins to uniformly deposit along the whole fiber.

Cellulose is deposited in the cell wall normally under a normal layer, so that the fiber cross section is stacked in a circle, called the daily ring.

The main component of cotton fiber is cellulose, and the rest is cellulose and living things.

The content of cellulose and its companion organisms in cotton fiber depends on the maturity of cotton fibers.

The cellulose content of normal mature cotton fiber accounts for about 94% of the total weight of cotton fiber and less biological content.

The primary layer of cotton fiber consists of 30% cellulose and neutral, acidic polysaccharides and so on, which is closely related to the surface properties of cotton fiber.

The secondary component of cotton fiber cells is cellulose, whose content is about 90% to 95%, which determines the main physical and mechanical properties of cotton fibers.

Cellulose is a natural polymer compound. It is a polysaccharide substance, and each cellulose macromolecule is formed by N glucose residual base chain.

There are two states in the arrangement of cellulose macromolecules, that is, some local regions are crystalline regions, some of which are amorphous crystalline regions.

In the crystalline region, the macromolecules of the fibers are arranged regularly and neatly and densely, and the pores and pores of the pores are few.

Similarly, macromolecules in fibers are not crystallized. The regions with regular and orderly arrangement are called amorphous regions. Macromolecules are arranged in disorder, and are stacked loosely. There are many gaps and holes, low density, little contact strength, and no saturation.

In a fiber, there are both crystalline and amorphous regions. The percentage of crystalline part of the whole fiber is called crystallinity, and the crystallinity of cotton fiber is about 70%.

When the crystallinity is high, the moisture absorption of the fiber is more difficult, the strength is higher, the deformation is smaller, and when the crystallinity is low, it is easy to absorb moisture, easy to dye, and shows low intensity and large deformation.

In the later stage of cotton fiber growth and development, the cotton bolls split and the fibers lose moisture after wadding.

fibre

Natural twisting and natural twisting are the unique longitudinal features of cotton fibers.

The twist of each cotton fiber is different from the size of the helix angle and the thickness of the secondary layer. The better the fiber is, the thicker the cell wall is, the more distorted it is.

Because the main component of cotton fiber is cellulose, the deposition of cellulose in the tubular cell wall gradually stops with the growth period and finally forms the middle cavity.

At the same time, when the cell walls of cotton fibers are deposited, cellulose is distributed in layers of spiral fibrils, and when the spiral direction is left and right, so when the fibers are drying and shrinking, the cell wall occurs when the left and right spiral twist occurs, forming irregular natural distortion.

Therefore, the special natural structure of cotton fiber determines its unique physical characteristics.

Relationship between microstructure and moisture absorption properties of 2 cotton fibers

Cotton fiber is a porous substance from microscopic structure. At the same time, there are many free hydrophilic groups on cellulose macromolecules, which can absorb moisture from moist air and release moisture into dry air. This phenomenon becomes the hygroscopicity of cotton fibers.

The hygroscopicity of cotton fibers is a complex physical characteristic, mainly determined by four factors.

(1) hydrophilic group

The main component of cotton fiber is cellulose.

Cellulose macromolecules have a large number of hydrophilic groups, and have a considerable affinity for water molecules. Therefore, the more hydrophilic groups in the molecular structure, the greater the moisture absorption capacity of cotton fibers.

(2) molecular alignment

The cellulose chains in cotton fibers are not evenly distributed, and there are crystalline and amorphous regions. In the crystalline region, cellulose chains are arranged orderly, and water molecules are not easy to enter.

In the amorphous region, cellulose chains are arranged in disorder, which is a relaxed network structure. Most hydrophilic groups are open to water molecules and water molecules are easy to enter, so the moisture absorption of cotton fibers mainly occurs in the amorphous region.

Therefore, the lower the crystallinity of cotton fiber, the stronger the moisture absorption ability.

(3) surface adsorption

When exposed to the atmosphere, cotton fibers adsorb a certain amount of water vapor and other gases on the surface of the fiber. This phenomenon is called surface adsorption.

The surface adsorption capacity is related to the specific volume of cotton fiber.

The surface volume of cotton fiber per unit volume is called the specific volume of cotton fiber.

The thinner the cotton fiber, the more the pores in the cotton fibers are, the larger the specific volume and the greater the hygroscopicity.

(4)

cellulose

Companion organism

In addition to cellulose, the main components of cotton fiber include a small amount of pectin, protein, pentosan, fat and wax, and some inorganic salts and other accompanying organisms.

Fat and wax are hydrophobic substances, which protect cotton fibers from moisture.

Pectin, protein, pentosan, and inorganic salts are all hydrophilic substances that enhance the hygroscopicity of cotton fibers.

After the moisture absorption, the weight of cotton fibers will increase, the density will increase first and then decrease, the strength and elongation will increase, the electrical conductivity will increase, and the fiber volume will expand.

Compared with the mature cotton fiber, the proportion of amorphous region is larger, the free hydrophilic group is more, the fiber is finer, and the volume of the meter is larger. These are conducive to the moisture absorption of the fiber. Under the same conditions, the immature low grade cotton has stronger hygroscopicity.

Therefore, the rational use and adjustment of hygroscopicity of cotton fibers plays an important role in seed cotton processing, fiber performance testing and textile production.