Popular Science | Can you sort out these three types of elastic fibers: spandex, PTT and T-400?

Spandex (PU) fiber

Spandex fiber (PU fiber for short) is a polyurethane structure with high extensibility, low elastic modulus and high elastic recovery rate , In addition, spandex also has excellent chemical stability and thermal stability. It is more resistant to chemical degradation than latex silk, and its softening temperature is approximately above 200°C. Spandex fiber is resistant to sweat, sea water, various dry cleaning agents and most sunscreen oils. It can also fade with long-term exposure to sunlight or chlorine bleach, but the degree of fading varies greatly depending on the type of spandex. Clothes made of spandex-containing fabrics have good shape retention, stable dimensions, no sense of oppression, and are comfortable to wear. Usually, as long as 2% to 10% spandex is added, the underwear can be soft and close-fitting, comfortable and beautiful, the sportswear can be soft and move freely, and the fashion and casual wear can have good drape, shape retention and fashionability. Therefore, spandex is an essential fiber for the development of highly elastic textiles.

Polytrimethylene terephthalate (PTT) fiber

Polytrimethylene terephthalate fiber ( PTT fiber (referred to as PTT fiber) is a new product in the polyester family. It belongs to polyester fiber and is a similar product to the commonly used polyester PET. PTT fiber has the characteristics of both polyester and nylon. It has a soft hand, good elastic recovery, is easy to dye under normal pressure, has bright colors, and good dimensional stability of the fabric, making it very suitable for the field of clothing. PTT fiber can be blended, twisted, and interwoven with natural fibers such as wool and cotton or synthetic fibers, and can be applied to woven fabrics and knitwear. In addition, PTT fiber can also be used in industrial cloth and other fields, such as manufacturing carpets, decorations, webbing, etc. PTT fiber has the advantages of spandex elastic fabric, but its price is lower than spandex elastic fabric. It is a promising new fiber.

Elastane T-400

T-400 fiber is DuPont’s spandex fiber that has certain limitations in textile applications , a new type of elastic fiber product developed. T-400 does not belong to the spandex family. It is made of two polymers, PTT and PET, with different shrinkage rates, spun side by side. It is a side-by-side composite fiber. It solves many problems of spandex, such as difficulty in dyeing, excess elasticity, complex weaving, unstable fabric dimensions, and aging of spandex during use.

The fabric made of it has the following characteristics:

(1) Elastic, comfortable and durable;

(2) The fabric is soft, crisp and has good drape;

(3) The cloth surface is smooth and wrinkle-resistant;

(4) Moisture absorption Quick-drying and smooth to the touch;

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(5) Good dimensional stability and easy to handle.

T-400 can be combined with natural fibers and The blended fabric is blended with man-made fibers to increase strength and softness. The blended fabric has a clean and smooth appearance, and the clothing has clear outlines. The clothing can still maintain a good shape after repeated washing. The fabric has good color fastness and is not easy to fade. It will still look like new clothes after being worn for a long time. At present, T-400 is widely used in pants, jeans, sportswear, high-end women’s clothing and other fields due to its excellent wearing performance.

PU, PTT and T-400 fiber identification methods

Burning method

The combustion method uses various fibers Different chemical compositions produce differences in combustion characteristics to identify fiber types. The method is to take��A small bundle of fiber samples is ignited and burned. Carefully observe the fiber burning characteristics and the shape, color, softness and hardness of the residue, and smell the odor it produces.

Burning characteristics of three elastic fibers

Fiber type	Close to the flame	Contact with flame	Leave the flame	Burning smell	Residue features
PU	Collapse	Melting combustion	Self-destruction	Special smell	White gel
PTT	Condensation	Melting combustion	Molten burning liquid falls and emits black smoke	Pungent smell	Brown wax flake
T-400	Collapse	Melting combustion	Molten burning liquid emits black smoke	Sweetness	Hard and black bead-like

From the combustion characteristics of the above three elastic fibers, we can easily distinguish PU from the other two fibers based on the conditions of the three fibers after leaving the flame. In addition, the odors and residue characteristics produced by these three fibers when burned are obviously different, so they can be identified.

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Microscopy

Microscopy is to use a microscope to observe the longitudinal and transverse cross-sectional shapes of fibers, and identify fibers based on their morphological characteristics by comparing them with standard microscope photos and standard data

Chlorine-containing nitrogen color reaction method

The chlorine- and nitrogen-containing color reaction method is based on the fact that fibers containing chlorine and nitrogen elements will show specific color reactions using flame and acid-base methods to identify whether the fiber contains…Two elements: chlorine and nitrogen. During the test, take a clean copper wire and use fine sandpaper to remove the oxide layer on the surface. Burn the copper wire in a flame and immediately contact it with the sample. Then move the copper wire to the flame. If the flame is green, it means that the fiber Contains chlorine; put a small amount of chopped fiber into a test tube, cover it with an appropriate amount of sodium carbonate, heat the test tube on an alcohol lamp, and place a piece of red litmus paper at the mouth of the test tube. If the litmus paper turns blue, it means that the fiber contains nitrogen. . As can be seen from Table 3, we can easily identify PU fiber through the chlorine-nitrogen colorimetric method, but we cannot distinguish between PTT and T-400 fibers.

Color reaction of three types of elastic fibers containing chlorine and nitrogen

Fiber type

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