4 way stretch spandex fabric

1.Spandex (PU fiber)
Spandex fiber (referred to as PU fiber), belongs to the 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, softening temperature of about 200℃ or more. Spandex is resistant to sweat, seawater, and various dry washes and most sunscreens. Long-term exposure to sunlight or chlorine bleach will also fade, but the degree of fading varies greatly depending on the type of spandex. The clothing made with spandex fabric has good shape preservation, stable size, no pressure and comfortable wearing. Usually, as long as 2% to 10% of spandex is added, the underwear can be soft, comfortable and beautiful, so that the sportswear is soft and flexible, so that the fashion and casual wear has good drappability, shape preservation and fashion. Therefore, spandex is an essential fiber for the development of high elastic textiles.

2, polyethylene terephthalate propylene glycol ester fiber
Polyethylene terephthalate propylene glycol ester fiber (PTT fiber) is a new product in the polyester family, belongs to polyester fiber, is commonly used polyester PET family products. PTT fiber has the characteristics of both polyester and nylon, soft feel, good resilience, easy to dye under atmospheric pressure, bright color, good dimensional stability of fabric, very suitable for the field of clothing. PTT fiber can be blended, twisted and interwoven with natural or synthetic fibers such as wool and cotton, and can be used in woven fabrics and knitwear. In addition, PTT fiber can also be used in industrial fabrics and other fields, such as the manufacture of carpets, ornaments, webbing and so on. PTT fiber has the advantages of spandex elastic fabric, but the price is lower than spandex elastic fabric, which is a new kind of fiber with great development prospect.
3, elastic fiber T400
T-400 fiber is a new type of elastic fiber product developed by DuPont for the limited application of spandex fiber in textiles. T-400 does not belong to the spandex family, and is made of two polymers with different shrinkage rates, PTT and PET, and is a parallel composite fiber. It solves many problems such as not easy dyeing, excess elasticity, complex weaving, unstable fabric size and aging of spandex during use.
The fabric made of it has the following characteristics:

(1) The elasticity is easy, comfortable and durable;

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

(3) Flat cloth, good wrinkle resistance;

(4) Moisture absorption and quick drying, feel smooth;

(5) Good dimensional stability, easy to arrange.

T-400 can be blended with natural fibers and man-made fibers to improve strength and softness, the appearance of the blended fabric is clean and smooth, the outline of the clothing is clear, the clothing can still maintain a good shape after repeated washing, the fabric has good color fastness, is not easy to fade, and is still worn as new clothes for a long time. At present, T-400 because of its excellent performance, is widely used in pants, denim, sportswear, high-end women's wear and other fields.

Identification methods of three kinds of fibers

1、Combustion method

Combustion method is to use the chemical composition of various fibers, resulting in the difference of combustion characteristics to identify the types of fibers. The method is to take a small bundle of fiber samples to burn, carefully observe the fiber burning characteristics and the shape, color, hardness and hardness of the residue, and sniff the odor produced by it.

From the combustion characteristics of the above three kinds of elastic fibers, we can easily distinguish PU from the other two kinds of fibers according to the situation after the three kinds of fibers leave the flame. In addition, the smell and residue characteristics produced by the combustion of these three fibers are significantly different, which can be identified.

2. Microscopy

Microscope method is the use of microscope to observe the fiber longitudinal and transverse cross section morphology, according to the fiber morphological characteristics compared with standard microscope photos and standard data to identify the fiber.

3, chlorine and nitrogen color reaction method

Chlorine and nitrogen color reaction method is based on the fiber containing chlorine and nitrogen with flame, acid-base method will show a specific color reaction to identify whether the fiber contains chlorine and nitrogen two elements. During the test, take a clean copper wire, remove the oxide layer on the surface with fine sandpaper, contact the specimen immediately after the copper wire is burned red in the flame, and then move the copper wire to the flame, if the flame is green, it indicates that the fiber contains chlorine; Put a small amount of chopped fiber on the test tube, and cover it with an appropriate amount of sodium carbonate, heat the test tube on an alcohol lamp, and put a red litmus paper at the mouth of the test tube. If the litmus paper turns blue, it indicates that the fiber contains nitrogen.

As can be seen from Table 3, PU fiber can be easily identified by chlorine and nitrogen color method, but PTT and T-400 fibers cannot be distinguished.

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

4. Dissolution method

The dissolution method is based on the different chemical composition of various fibers, and the difference in solubility in different chemical reagents to identify fibers. During the test, it is advisable to put a small amount of fiber into the test tube, inject a certain reagent (the ratio of the sample to the reagent is 1:50), and observe its solubility under certain conditions. Three kinds of chemical reagents were used to dissolve these elastic fibers, and the results were shown in the table.

                                                                                                      Solubility of three kinds of elastic fibers

As can be seen from the table, PU and PTT, T-400 chemical properties are more obvious differences, but PTT and T-400 are polyester fibers, their chemical properties are very similar, so the simple use of dissolution method is more difficult to identify, only combined with microscope observation, combustion method can be identified.

Sum up

The three kinds of elastic fibers PU, PTT and T-400 were identified by combustion method, microscope method, chlorine-nitrogen color method and dissolution method. The identification of the three elastic fibers is as follows:

(1) PU fiber identification: through the combustion method can be preliminarily determined as PU fiber; The longitudinal morphological characteristics can be quickly distinguished from PTT and T-400 fibers by microscopy. Through the chlorine-nitrogen color reaction method or the use of 75% sulfuric acid as the solvent, it can be further distinguished from the other two kinds of elastic fibers and further verified as PU fiber.

(2) PTT and T-400 fiber identification: through the combustion method to identify their polyester fibers; PTT and T-400 fibers can be quickly distinguished by observing the longitudinal and transverse morphological characteristics of the fibers. The longitudinal shape of PTT fiber is a single strip shape, and the cross section is circular or approximately circular. The longitudinal shape of T-400 fiber is double parallel shape, and the cross section is dumbbell type.