What is polyester fiber

History of polyester fiber

In 1941, British J.R. Winfield and j.t. Dixon first developed polyester fiber in the laboratory with terephthalic acid and ethylene glycol as raw materials, named terylene. In 1953, the United States produced a polyester fiber with the trade name Dacron. Subsequently, polyester fiber has developed rapidly all over the world. In 1960, the world output of polyester fiber exceeded that of polyacrylonitrile fiber, and in 1972, it exceeded that of polyamide fiber, becoming the largest variety of synthetic fiber.

Classification and properties of polyester fibers

Short fiber classification: according to the fiber used for blending, long fiber can be divided into cotton type, wool type, and medium-length type according to the degree.
Classification of polyester long fiber:

  1. Polyester full draft yarn: it adopts low-speed spinning and high-speed drawing and winding.
    Features: high strength, good forming of silk cylinder, small size, strength, uneven elongation, uniform dyeing, etc.
  2. Polyester pre oriented yarn: when the high-speed spinning speed is 3000 ~ 3600 / min, the pre oriented yarn can be prepared.
    Characteristics: high degree of pre orientation, stable properties, good mechanical properties, high uniformity and good processing properties.
    Glass transition temperature: 67 ℃ – 81 ℃
    High strength: the strength of short fiber is 2.6 ~ 5.7cn/dtex, and that of high strength fiber is 5.6 ~ 8.0cn/dtex. The impact strength is 4 times higher than that of nylon and 20 times higher than that of viscose fiber, so the polyester fabric product is very strong and durable.
    Good elasticity: the elasticity is close to that of wool. When the elongation is 5% ~ 6%, it is almost completely restored. Crease resistance is better than other fibers, that is, the fabric does not wrinkle and has good dimensional stability. The elastic modulus is 22 ~ 141cn / dtex, 2 ~ 3 times higher than that of nylon.
    Good wear resistance: wear resistance is second only to nylon with the best wear resistance, which is better than other natural fibers and synthetic fibers.
    Good light resistance: second only to acrylic fiber. Its sun resistance is better than that of natural fiber fabrics.
    Corrosion resistance: resistant to bleach, oxidant, hydrocarbon, ketone, petroleum products and inorganic acids. It is resistant to dilute alkali and is not afraid of mold, but hot alkali can decompose it.
    Dyeability: polyester has poor dyeability, but good labor and is not easy to fade.
    Hygroscopicity: the hygroscopicity is very small, the relative humidity is 100%, and the hygroscopicity is only 0.6% ~ 0.8%. Poor moisture absorption, easy to wash and dry. However, it is stuffy and hot to wear, which is easy to carry static electricity and stain dust, affecting beauty and comfort.

Synthesis of polyester fiber

Synthetic process
The production process of polyester includes two parts: polyester melt synthesis and melt spinning. The raw materials for polyester synthesis are poly terephthalic acid and ethylene glycol, which are mainly obtained from oil cracking, coal, and natural gas. Toluene, xylene, and ethylene are obtained by heating and cracking petroleum. Terephthalic acid or dimethyl terephthalate and ethylene glycol can be obtained after the chemical processing of polyester chips.
In the early polyester production, dimethyl terephthalate and ethylene glycol were used as raw materials because terephthalic acid was not easy to refine. In 1965, the refining of terephthalic acid was successful, which reduced the polyester production process and cost. Polyester produced from terephthalic acid and ethylene glycol has increased year by year.
Polycondensation is to exchange dimethyl terephthalate and ethylene glycol to produce diethylene terephthalate oligomer, which is polycondensation under 280 ~ 290 ℃ and vacuum to obtain polyethylene terephthalate; Or terephthalic acid is directly esterified with ethylene glycol, and then ethylene terephthalate is polycondensation to obtain polyester melt. Polyester melt can be used to prepare polyester chips and melt direct spinning. Polyester chip is obtained by casting polyester melt and cutting particles.
Production method
At present, there are two main production methods of ethylene terephthalate (BHET), transesterification (DMT) and direct esterification (PTA).
After drying and melting, polyester chips can be used for spinning, preparation of the polyester film, polyester bottle, etc. During the melting process, the moisture contained in the polyester chip spinning can hydrolyze the polyester and affect the spinning performance and fiber quality. Therefore, it must be dried before spinning to reduce the moisture content of the chip to less than 0.01%. For chip spinning, the dried polyester chip is heated and melted in the screw, extruded and sent to each spinning part of the spinning box, accurately measured and filtered by the metering pump, and then ejected from the spinneret hole of the spinneret. The diameter of the spinneret hole is generally 0.15 ~ 0.30 mm. The ejected melt stream is cooled by the cooling airflow and solidified into filaments. The cooled filament is divided into polyester filament and polyester staple according to different processing technologies.
Polyester staple
When spinning staple fiber, multiple lines are gathered together and fall into the silk barrel after being wet and oiled. The finished product is obtained through the processes of bunching, stretching, crimping, heat setting, and cutting. After tension heat setting at about 180 ℃ after drawing, high strength and low elongation staple fibers with strength above 6cn / dtex and elongation below 30% can be obtained. Polyester staple fiber is divided into cotton staple fiber (length 38mm) and wool staple fiber (length 56mm), which are used for blending with cotton fiber and wool respectively.
Polyester filament
When spinning filament, after wet oiling, the solidified filament is wound on the bobbin at a speed of about 3500m / min to obtain pre-oriented filament (POY). POY can not be directly used for weaving. POY can be directly used for weaving or deformation processing to obtain stretch wire (DT), stretch deformation wire (DTY) or twist wire after stretching, shaping, springing, or twisting. After solidification, the filament is directly stretched by oiling and wound at 4500-5000m / min to obtain fully stretched filament (FDY), which can be used for weaving.

Modification of polyester fiber

Polyester modification: its properties are improved by physical and/or chemical methods, commonly known as a polyester modification. The improvement is divided into two directions. One is to improve the performance of polyester fiber which is not as good as natural fiber, and the other is to improve the inherent excellent performance of polyester fiber and give full play to its advantages.
Polyester modification method
Copolymerization: by adding modified components (monomers) for copolymerization, the molecular chain structure is changed, that is, the method of molecular design is adopted.
Blending: mechanical (physical) blending with other polymers to obtain modification effect.
Composite (addition): in the process of synthesis and processing, composite technologies such as additives, fillers, and reinforcing materials are used to improve the morphology and properties of polyester.
Modified polyester fiber
Cationic dye dyeable polyester (CDP): in the process of pet synthesis, a third monomer containing anionic groups is introduced for copolymerization.
Cationic dyeable polyester (ECDP) fiber: Based on the addition of the third monomer and the flexible fourth monomer, the cationic dyeable copolyester is developed and produced, that is, it can be boiled and dyed under normal pressure.
Easily hydrolyzable polyester (COPET): copolyester prepared by adding a variety of copolymer components in the production of conventional polyester. It can be dissolved in dilute alkali solution at 100 ℃.
High shrinkage polyester (aspect) fiber: through copolymerization of modified polymer, and further adopting the physical modification method of combining high-power drawing and low-temperature settings, the boiling water shrinkage can reach more than 50%.
Low melting point polyester (let) and fiber: lower melting point than the conventional pet is prepared by adding copolymerization components (IPA, adipic acid, DEG, 1.4-bg, 1.6-HD, PEG, etc.) to meet the requirements of different thermal bonding temperatures.
Flame retardant polyester fiber: flame retardant additives are added in the polymerization or spinning process, mainly phosphorus and halogen compounds.

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