The NO.1 in chemical fiber -- polyester.

The NO.1 in chemical fiber -- polyester.

polyester, scientific name Polyester, English name polyester, chemical formula (C10H8O4)n.

It is a synthetic fiber derived from the condensation of organic dibasic acid and dibasic alcohol "polyethylene terephthalate" by spinning, referred to as PET fiber. It is a polymer compound and is the first major variety of synthetic fibers.

The biggest advantage is that the wrinkle resistance and shape retention are very good, with high strength and elastic recovery ability. Firm and durable, wrinkle-resistant, non-ironing, non-sticky.

Development history

Polyester fiber is a synthetic fiber made of macromolecular chains connected by ester groups to form fiber polymers.

In China, the polyethylene terephthalate content of more than 85% of the fiber referred to as polyester.

There are many foreign product names, such as Dacron in the United States, Tetoron in Japan, Terlenka in the United Kingdom, and Lavsan in the former Soviet Union.

In 1894 Vorlander made a low molecular weight polyester with succinyl chloride and ethylene glycol.

In 1898, Einkorn synthesized polycarbonate.

In 1930, Carothers synthesized aliphatic polyester.

The polyester synthesized in the early years is mostly aliphatic compounds, its relative molecular weight and melting point are low, easily soluble in water, so it does not have the use value of textile fibers.

In 1941, Whinfield and Dickson in the United Kingdom synthesized polyethylene terephthalate (PET) with dimethyl terephthalate (DMT) and ethylene glycol (EG), which can be spun through the melt to produce fiber with excellent performance.

In 1953, the United States first built a plant to produce PET fiber.

PET fiber is the late development of the three synthetic fibers.

With the development of organic synthesis, polymer science and industry, a variety of practical polyester fibers with different characteristics have been developed in recent years. For example, polybutylene terephthalate (PBT) fiber and polypropylene terephthalate (PTT) fiber with high stretchability elasticity, and all-aromatic polyester fiber with ultra-high strength and high modulus.

Polyester fiber has a series of excellent properties, such as high breaking strength and elastic modulus, moderate resilience, excellent thermal setting effect, good heat and light resistance. The melting point of polyester fiber is about 255 ° C, the glass transition temperature is about 70 ° C, the shape is stable under a wide range of end-use conditions, and the fabric is washable.

In addition, it also has excellent impedance (such as resistance to organic solvents, soaps, detergents, bleaching solutions, oxidants) and good corrosion resistance, stable to weak acids, alkalis, etc., so it has a wide range of use and industrial uses.

The rapid development of the petroleum industry also provides more abundant and cheap raw materials for the production of polyester fiber, coupled with the development of chemical, machinery, electronic automatic control technology and other technologies in recent years, so that the raw material production, fiber forming and processing process gradually realize short-range, continuous, automation and high-speed, polyester fiber has become the fastest developing speed, the highest yield of synthetic fiber varieties.

In 2010, global polyester fiber production reached 37.3 million tons, accounting for 74% of the world's total synthetic fiber.

Performance and action

1. Physical properties

① Color. Polyester is generally milky white with mercerizing, matting agent TiO2 needs to be added before spinning to produce matting products, whitening agent needs to be added to produce pure white products, and pigment or dye needs to be added to spinning melt to produce colored silk.

② Surface and cross section shape. Conventional polyester has a smooth surface and a nearly circular cross-section. If the special-shaped spinneret is used, it can be made into fibers with special section shapes, such as triangular, Y-shaped, hollow and other special-shaped section wires.

③ Density. When fully amorphous, polyester has a density of 1.333g/cm3. When fully crystallized, 1.455g/cm3 Usually polyester has a higher crystallinity, with a density of 1.38 to 1.40g/cm3, similar to wool (1.32g/cm3).

④ moisture regain rate. Under the standard condition, the moisture regain rate of polyester is 0.4%, which is lower than that of acrylic fiber (1%~2%) and nylon fiber (4%). Polyester has low hygroscopic property, so its wet strength drops less and the fabric is washable and wearable. However, the phenomenon of static electricity is serious during processing and wearing, and the permeability and moisture absorption of the fabric are poor.

⑤ Thermal performance. The softening point T of polyester is 230-240℃, the melting point Tm is 255-265℃, and the decomposition point T is about 300℃. Polyester can burn in the fire, curl, and melt into beads, with black smoke and aroma.

⑥ Light resistance. Its light resistance is second only to acrylic fiber. The light resistance of polyester is related to its molecular structure, and polyester only has a strong absorption band in the 315nm light wave region, so its strength only loses 60% after 600h of sunlight irradiation, which is similar to cotton.

⑦ Electrical properties. Polyester is an excellent insulator because of its low hygroscopic property, so its conductivity is poor, and its dielectric constant is 3.0~3.8 in the range of -100 ~ +160 °C.

2. Mechanical properties

① High strength. The strength of the dry state is 4~7cN/dex, and the wet state decreases.

② The elongation is moderate, 20%~50%.

③ High modulus. Among the large varieties of synthetic fibers, the initial modulus of polyester is the highest, and its value can be as high as 14~17GPa, which makes the polyester fabric size stable, not deformed, not out of shape, and long-lasting pleats.

④ Good resilience. Its elasticity is close to wool, and when it is extended by 5%, it can be almost completely recovered after load removal. Therefore, the wrinkle resistance of polyester fabric exceeds that of other fiber fabrics.

⑤ Wear resistance. Its wear resistance is second only to nylon, and exceeds other synthetic fibers, and the wear resistance is almost the same.

3. Chemical stability. The chemical stability of polyester mainly depends on the molecular chain structure. In addition to poor alkaline resistance, polyester has good resistance to other reagents.

① Acid resistance. Polyester acid (especially organic acid) is very stable, at 100℃ in the mass fraction of 5% hydrochloric acid solution soaked for 24h, or at 40℃ in the mass fraction of 70% sulfuric acid solution soaked for 72h, its strength is not lost, but at room temperature can not resist the long-term effect of concentrated nitric acid or concentrated sulfuric acid.

② Alkaline resistance. The ester group on polyester macromolecule is easily hydrolyzed by alkali action. At room temperature and concentrated alkali, high temperature and dilute alkali interaction can cause fiber destruction, only at low temperature to dilute alkali or weak alkali is relatively stable.

③ Solvent resistance. Polyester has a strong resistance to general non-polar organic solvents, even polar organic solvents at room temperature also has a strong resistance. For example, at room temperature soaked in acetone, chloroform, toluene, trichloroethylene, carbon tetrachloride for 24h, the fiber strength does not decrease. Under heating condition, polyester can be dissolved in phenol, xylenol, o-dichlorophenol, benzyl alcohol, nitrobenzene, phenol - carbon tetrachloride, phenol - chloroform, phenol - toluene and other mixed solvents.

4. Microbial resistance. Polyester is resistant to microorganisms, not by moth, mold and other effects, collection of polyester clothing without moth, fabric preservation is easier.

Synthesis procedure

The production process of polyester includes two parts: polyester melt synthesis and melt spinning. The raw materials for the synthesis of polyester are polyterephthalic acid and ethylene glycol, which are mainly obtained from petroleum cracking, but also from coal and natural gas. Toluene, xylene and ethylene are obtained by pyrolysis of petroleum, and terephthalic acid or dimethyl terephthalate and ethylene glycol can be obtained by chemical processing. Dimethyl terephthalate and ethylene glycol were used as raw materials in the early polyester production because terephthalic acid was not easy to be refined. In 1965, the refining of terephthalic acid was successful, which reduced the production process and cost of polyester. The production of terephthalic acid and ethylene glycol as raw materials is increasing year by year. Polycondensation: dimethyl terephthalate and ethylene glycol are transesterification, the resulting diethylene terephthalate oligomer is polycondensation at 280 ~ 290℃ and under vacuum conditions to obtain polyethylene terephthalate; Or terephthalic acid is directly esterified with ethylene glycol, and then ethyl terephthalate is polycondensed to obtain polyester melt. The polyester melt can be used for preparing polyester slices and direct spinning of the melt. Polyester slicing is made by casting polyester melt and cutting it into pieces.

1、 Spinning. After drying and melting, polyester chips can be used for spinning, preparing polyester film, polyester bottles, etc. During the melting process, the water contained in the slice can hydrolyze the polyester and affect the spinning performance and fiber quality, so it must be dried before spinning to reduce the slice water content to less than 0.01%. The dried polyester slice is heated and melted in the screw, extruded into each spinning part of the spinning box, accurately measured and filtered by the metering pump, and sprayed out of the spinneret hole. The diameter of the spinneret hole is generally 0.15 ~ 0.30 mm. The ejected melt streams are cooled and solidified into filaments by cooling air. The cooled filament is divided into polyester filament and polyester staple fiber (or polyester filament) according to different processing processes.

2、polyester filament. When spinning staple fibers, a number of lines are gathered together and moistened with oil before falling into the silk bucket. Then through the bunching, stretching, crimping, heat setting, cutting and other processes to get the finished product. If the tensile heat is set at about 180 ° C after stretching, high strength and low elongation staple fibers with a strength of more than 6cN/dtex and a elongation of less than 30% can be obtained. Polyester staple fiber is divided into cotton type staple fiber (length 38mm) and wool type staple fiber (length 56mm), which are used to blend with cotton fiber and wool, respectively.

• polyester filament. When spinning filament, the solidified filament is wet with oil, that is, it is wound on the bobbin at a speed of about 3500 m/min to obtain pre-oriented filament (POY). POY can not be directly used for weaving, POY after stretching shape, elastic or twisting to get a stretch wire (DT), stretch deformation wire (DTY) or twisted wire, can be directly used for weaving or deformation processing into deformation yarn. After solidification, the strips are oiled and stretched directly at 4500-5000m/min for winding to obtain fully stretched silk (FDY), which can be used for weaving. The American commodity kodel is another polyester fiber that has been produced industrially. It is produced by spinning a high polymer from the condensation of terephthalic acid and 1, 4-cyclohexanedimethanol. Compared with polyester, the specific gravity is lighter, 1.22, the melting point is higher, 290 ~ 295℃, the decomposition resistance is strong, and the strength and elongation of the fiber are slightly lower. Suitable for blending with cotton, wool, etc., the fabric made has good elasticity, feel, wrinkle resistance and pilling resistance, but poor strength and wear resistance.

Polyester modification

Compared with natural fiber, polyester has some disadvantages such as low moisture content, poor air permeability, poor dyeing, easy pilling and flaking, and easy staining. In order to improve these shortcomings, chemical modification and physical deformation are adopted. Chemical modification methods are:

① Adding monomer or oligomer polyethylene glycol with hydrophilic groups for copolymerization can improve the moisture absorption rate of the fiber;

②The anti-static and anti-fouling properties of fiber can be improved by adding monomer with antistatic properties for copolymerization;

③ Compounds containing phosphorus, halogen and antimony were added to improve the combustion resistance of the fiber;

④ The use of polyester spinning with lower polymerization degree to improve the pilling resistance;

⑤ Copolymerization with dyephilic monomer (such as sulfonate, etc.) to improve the dyeing property of the fiber.

After physical deformation there are a variety of profiled polyester, with other polymers composite spinning, colored polyester, fine denier polyester and high shrinkage polyester.

use

Polyester fiber has high strength, high modulus and low water absorption, and is widely used as civil fabric and industrial fabric. As a textile material, polyester staple fiber can be spun purely and is especially suitable for blending with other fibers. It can be blended with natural fibers such as cotton, linen, wool, and other chemical staple fibers such as viscose fiber, acetate fiber, polyacrylonitrile fiber and other short fibers. Its pure spinning or blending made of imitation cotton, wool, linen fabric generally has the original excellent characteristics of polyester fiber, such as fabric wrinkle resistance and pleat retention, dimensional stability, wear resistance, washable and wearable, and some of the original shortcomings of polyester fiber, such as electrostatic phenomenon and dyeing difficulties in textile processing, poor sweat absorption and air permeability, and easy to melt into a hole in the event of Mars, etc. It can be alleviated and improved to a certain extent with the inclusion of hydrophilic fibers. Polyester twisted filament (DT) is mainly used to weave a variety of imitation silk fabrics, can also be interwoven with natural fiber or chemical staple fiber yarn, can also be interwoven with silk or other chemical fiber filament, this interweaving material maintains a series of advantages of polyester.

Polyester textured yarn (mainly low-elasticity DTY) is one of the main varieties in China in recent years. It is different from ordinary filament is high fluffy, large crimp, strong wool, soft, and has a high elastic elongation (up to 400%). The fabric woven with it has the characteristics of good warmth, good covering and drape, soft luster, etc., especially suitable for weaving wool-like cloth, serge and other suit fabrics, coats, coats and various decorative fabrics such as curtains, tablecloths, sofa fabrics. Polyester air textured silk ATY and network silk have good adhesion and smoothness, and can be directly used in water jet loom in the form of tube silk, suitable for weaving artificial silk and thin fabric, and can also weave medium and thick fabric. Polyester fiber is increasingly widely used in industry, agriculture and new technology fields, such as cord, conveyor belt, rope, electrical insulation materials. Polyester filament has high strength and initial modulus, good heat resistance, fatigue resistance and form stability, and is especially suitable for spinning tire cord. The use of polyester cord to make tires can reduce their flat spot phenomenon.