What are PET, PBT, and PTT fibers?

What are PET, PBT, and PTT fibers?

Synthetic fibers differ from natural fibers in that they possess unique properties based on their molecular composition, such as high strength, lightweight, easy washing and quick drying, good elasticity, and resistance to mold and pests. Currently, their application in the textile industry is gradually surpassing that of natural fibers.

Polyester fibers, as a major category of synthetic fibers, have gained widespread favor and developed rapidly since their successful development in 1941. In recent years, their market share has gradually surpassed that of nylon fibers, making them the largest type of synthetic fiber. Although PET, PBT, and PTT fibers all belong to the polyester fiber family, they have different properties, so their application areas are not entirely the same.

I. PET Fiber

PET fiber, also known as polyethylene terephthalate fiber, is commonly referred to as polyester in China. Currently, PET fiber is primarily produced using the direct esterification method of terephthalic acid (PTA) and ethylene glycol (EG) or the ester exchange method of dimethyl terephthalate (DMT) and ethylene glycol (EG).

The cross-section of PET fibers is similar to that of PTT fibers. Under a microscope, the cross-section appears circular, with relatively uniform thickness along the length, minimal fuzz, and a smooth surface. The molecular formula of PET fibers is [-OC-Ph-COOCH₂CH₂O-]n, where each unit consists of one benzene ring, two ester groups, and two methylene groups. Due to the presence of a benzene ring in the PET molecule, it requires stretching after traditional melt spinning to facilitate rapid crystallization. This process results in fibers with high orientation and crystallinity. The resulting PET fibers exhibit high strength, good elasticity, excellent thermal setting properties, good heat resistance, and resistance to acids and alkalis.

Polyester is widely used in the apparel, decorative, and industrial sectors due to its simple processing and low cost. In the apparel sector, PET-made fabrics are easy to wash and quick to dry, earning them the nickname “wash-and-wear.” Additionally, the ester bonds in their molecules have strong antioxidant properties, making them resistant to damage from detergents and soaps. Furthermore, PET fibers are not easily degraded by microorganisms, giving the fabrics good durability. After thermal setting, polyester fabrics exhibit stable dimensions, good stiffness, and minimal shrinkage, making them suitable for shirts, men's trousers, outerwear, and jackets. The main drawbacks of polyester are its poor dyeability, moisture absorption, and anti-static properties, as well as its tendency to burn easily, due to its tightly packed molecular structure and lack of hydrophilic groups.

With the development of science and technology and people's pursuit of high-quality clothing, the multifunctional application of PET fibers is a current research direction. Li Fang improved the poor moisture absorption and static electricity issues of polyester fibers by modifying their surfaces with nano-TiO₂. This not only addressed the inherent defects of polyester but also imparted antibacterial, UV-resistant, and photocatalytic self-cleaning properties due to the addition of TiO₂. Shi Zheng developed antibacterial PET fibers using chemical modification methods involving metal ions and organic acids. Sun Pengxiao studied surface modification and weaving methods for PET fibers applied to medical artificial ligament materials.

II. PBT Fibers

Polybutylene terephthalate (PBT) is abbreviated as PBT and is synthesized through the esterification and polycondensation of dimethyl terephthalate (DMT) or terephthalic acid (TPA) with butanediol. Due to the abundance of raw materials for PBT fibers and a production process similar to that of polyester, PBT fibers have seen large-scale production in recent years. The molecular formula of PBT is [(CH₂)₄OOC₆H₄COO]_n, which has two additional methylene chains compared to PET. The main chain structure of PBT's larger methylene molecules forms a spiral shape, similar to nylon's molecular structure, while the methylene chain segments are longer than those of PET. Therefore, PBT fibers exhibit flexibility, abrasion resistance, and elasticity comparable to nylon, while their chemical properties are similar to those of PET fibers. Since the molecules of PBT fibers can move freely, PBT fibers exhibit excellent tensile compression elasticity and wrinkle resistance. Compared to PET's poor dyeability, PBT has a glass transition temperature of only 22°C, allowing it to be dyed with disperse dyes under atmospheric pressure without a carrier. However, due to the presence of a-type and B-type crystalline deformations, PBT exhibits poor dimensional stability at high temperatures.

Due to its excellent resilience, mold and moth resistance, good crimp elasticity, anti-static properties, and dyeability, PBT fiber is widely used in elastic garments such as swimwear, sportswear, skiwear, jumpsuits, and dance leotards. Spandex is relatively expensive and has poor lightfastness, prone to yellowing, while PBT fibers have elasticity second only to spandex and superior to nylon. In certain fabrics, PBT fibers can completely replace spandex, such as in elastic denim pants, where spandex is typically used as elastic yarn. However, spandex has low tensile strength and is prone to breaking after prolonged wear and friction. Replacing spandex with PBT fibers as elastic yarn can effectively address this issue. PBT fibers, with their wool-like feel, can be blended with cotton, linen, and other fibers in the woolen textile industry for autumn and winter garments, and they are also ideal for imitation down and filling materials.

In addition to being used as a standalone textile material, modified PBT fibers have seen significant research and development in recent years. For example, PBT/PET composite spun fibers not only have good spinnability but also produce fabrics with a soft feel, high loft, and ease of dyeing. They can be used as imitation wool fibers or to replace spandex. Currently, the elasticity of PBT block copolymer fibers can reach 80% of spandex, while other properties are superior to spandex. Additionally, this fiber resembles silk in appearance and can be blended with silk to create specialty-style fabrics.

III. PTT Fiber

PTT fiber (polypropylene terephthalate) is a new type of polyester fiber developed by Shell Company in the mid-1990s. PTT can be produced through ester exchange followed by melt polycondensation using 1,3-propanediol (PDO) and dimethyl terephthalate (DMT), or through melt polycondensation using PDO and terephthalic acid (PTA). PTT fibers have a smooth and glossy surface and are a semi-crystalline thermoplastic polyester. Unlike PBT and PET fibers, PTT fibers have a lowest-energy trans-cis-cis-trans conformation in their chemical structure, resulting in a distinct “Z”-shaped conformation. Additionally, while PET and PBT have two methylene units in their molecular chains, PTT has three methylene units, leading to a “odd carbon effect” between molecular chains. This molecular structure gives PTT fibers deformation capabilities akin to coil springs, with superior elasticity compared to PET and PBT. As a new type of synthetic fiber, poly(trimethylene terephthalate) (PTT) fiber, with its excellent dimensional stability, stain resistance, wrinkle resistance, abrasion resistance, and dyeability, combined with the high elasticity imparted by its unique molecular chain structure, is referred to as the “new polyester fiber of the 21st century.”

PTT fibers, as a new material, combine the advantages of PET and PBT fibers while overcoming some of their drawbacks.

Currently, most swimwear on the market uses nylon fabric, but nylon's low lightfastness and chlorine resistance limit its application in swimwear. When comparing the elasticity of nylon and PET, PTT fabric demonstrates superior elasticity compared to PET and nylon, meeting the requirements for swimwear elasticity, size adaptability, and pressure comfort. Additionally, PTT fabric's dyeability, colorfastness, chlorine resistance, and UV protection make PTT fiber an ideal material for swimwear. PTT/wool blended fabrics not only address wool supply issues but also offer a rich handfeel, excellent drape, and the combined properties of nylon and spandex. Given the ease of shaping and wrinkle recovery of PTT fabrics, the application of PTT fibers in shape-memory fabrics is also evolving. PTT fiber nonwoven fabrics can be used for carpet backing, artificial leather, protective materials, and medical applications. Additionally, due to their soft feel and excellent drape, they hold significant potential in women's sanitary napkins and disposable diapers.

IV. Summary

PBT, PET, and PTT fibers hold promising prospects in the textile industry. As technology advances and demands for comfort and functionality in clothing increase, developing multifunctional and composite new fibers will be a key focus for future efforts. For example, PET fibers are widely used in various fields due to their excellent performance. Guangzhou Yinsu Company has developed flame retardants such as PET-55D and PET-70B that can be used for PET filament drawing. These flame retardants provide the necessary fire resistance for PET fibers without compromising their other properties. As synthetic fibers, efficient, low-carbon, and environmentally friendly production processes are critical for process improvements, while the recycling and reuse of fabrics also hold potential market value.