Because of its high strength, good elasticity, good heat resistance and chemical resistance, good fabric dimensional stability, and washability, the filament has covered the disadvantage of natural fiber. And it has been the main textile raw material Since the realization of industrial production. But it also has disadvantages of poor hygroscopicity, accumulating static electricity easily, dust collection, dyeing difficultly, which motivate people to develop differentiated polyester fibers.

1 Various types of differentiated filament yarn

“Differentiation” is relative to “normalization or homogenization”. Generally speaking, the development of modified polyester fibers has gone through three stages, “specialization”, “functionalization” and “functional compound”.

Types Main Application
“specialization” Stage In order to improve the problem of the poor wearing feeling of polyester fiber fabrics, Japan took the lead in introducing special-shaped fibers with moisture-wicking functions. The “specialization” stage is improving the comfort of fabrics through the profile.
“functionalization”Stage As people’s demand for the functionality of textiles becomes stronger, polyester fibers with various functions such as antibacterial, anti-ultraviolet, flame-retardant, and anti-static have been developed one after another. This is the “functionalization” stage.
“functional compound” Stage As the contradiction becomes increasingly prominent between people’s demand for product diversified functions and the simplification of product functions, composite functions have become a new hot spot of polyester fiber. This stage is the “functional composite” stage of polyester fiber.

With the daily improvement of living standards, consumers have higher demands towards garment materials in aspects of appearance, hand feeling, comfort, function, etc. These demands accelerate the specialty filament development in elasticity, moisture absorption and quick-drying, anti-static, anti-pilling, cationic dyeing, easy dyeing, luster, fluffy, etc. As a result, there is not only a single modified fiber but also more composite modified one. At the same time, the rapid development of industrial and intelligent technology textile demand from the market has promoted the upgrading and development of high-quality functional fibers such as flame retardant, high strength, electrical conductivity, medical and environmental protection.

2 The production way of “differentiated” polyester

So how to achieve the production of “differentiated” polyester? There are three common methods, including chemical modification, physical modification, and technological modification. The corresponding “differentiated” polyester products are cationic dyeable fiber, UV protection, and other functional fiber, and fine denier, cross-sectional fiber.
In fact, Differential fibers can be divided into two categories, highly simulated differential fibers, and new functional fibers. The former one pays more attention to the imitation of natural fiber (hand feel, characteristics, etc.), which is usually achieved by technological modification and chemical modification. The latter focuses on the development of new functions, mainly through physical modification.

Types Detailed Method Examples of Products
chemical modification Conventional polyester fiber has a regular molecular structure and is a typical linear polymer. The chemical modification process connects the third or fourth monomer to the main chain of the polyester macromolecule in the form of a chemical bond through a chemical reaction and achieves the purpose of changing the properties of the fiber by changing its molecular structure. cationic dyeable fiber
physical modification Physical modification is mainly made by blending functional particles with polyester chips to prepare masterbatch, and then add the masterbatch to the chips in a certain proportion for spinning. anti-ultraviolet fiber, anti-static fiber, conductive fiber
technological modification With the continuous development of fiber preparation technology, people improve fiber performance by changing the production process parameters or changing the cross-sectional shape of the fiber during the fiber preparation process. fine-denier fiber,
different cross-section fiber

3 Fine-denier fiber acting as the most typical type

The typical types of Special filament yarn are fine denier fiber, profile fiber, and full(semi) dull fiber. Among them, fine denier is the most typical one. At present, due to the characteristics of large output and high investment, the long-term melt spinning enterprises have certain advantages in the fine fiber field. For more segmented markets, such as island fiber and functional fiber, the production is still mainly carried out by chip spinning.

Type Characteristic and Production Process   Market and Price
Fine-denier fiber Fine denier is the main differentiated variety of polyester filament. And fine denier (including monofilament size and total size) has become a trend in the production of polyester filament. The main specifications are 24D/28F, 50D/72F, 50D/144F, 75D/72F, 75D/144F, 75D/288F, 150D/576F, etc., which can be widely used in peach skin, suede, high-density waterproof, and anti-drilling fabric, high-sensitivity simulation silk, high-end knitted fashion and underwear, high-performance wipes, medical protection, etc. The fine-denier yarn has a large market capacity. And the large-capacity direct spinning production line has the characteristics of stable product quality, low energy consumption and cost, and long batch number. It has advantages in the development of fine-denier products.
Cross-sectional fiber The hot spot of polyester filament cross-section fiber is moisture absorption and sweat releasing fiber. It forms grooves on the surface of the fiber. The cross-section is cross-shaped or five-leaf-shaped. It has the characteristics of moisture conduction and quick-drying, fluffy and breathable, light and soft.  It is widely used in shirts, Jackets, sportswear, underwear, etc.
Unique luster fibers, like Full-dull, Bright By adding some additives to polyester, it is basically produced by chip spinning companies, and currently, direct spinning companies have begun to develop these products. The market capacity is limited. The output of direct spinning is relatively high. And there are problems with product sales.
Sea-island Fiber and composite fiber The ultra-fine fibers are produced by composite spinning technology. Monofilament linear density can reach 0.05 dtex. And the fabric is soft and smooth. It is widely used in clothing, home textiles, and high-grade wipes. The main composite fiber is polyester-cotton composite with orange petals, rice-shaped, and other special cross-sections. It has good moisture absorption. And many fibers with a low melting point, flame retardant, antistatic, and conductive functions are also achieved through the special structure of composite spinning.
The fiber of Flame Retardant, Anti-fungus and Anti-mildew, Antistatic, Anti-UV,  Far IR achieved by adding certain components high price and market value-added

Fine Diner filament fiber refers to filament numbers between 1.0dpf and 0.5dpf. The one between 0.5dpf and 0.1dpf is called Ultra-fine denier fiber. Filament number below 0.1dpf is micro-fine diner fiber. Dpf is short of denier per filament. Fine denier refers to the thickness of a single polyester filament, not the length of the wound yarn.