In view of the shortcomings of polyester performance, its modification research mainly includes:

The first is the physical modification method, which mainly performs physical blending modification during the production process of polyester.

The second is the chemical modification method, which uses chemical grafting or blocking methods to change the molecular chain structure of polyester and improve the wearing properties of polyester.

 

In 1941, Whenfield and Dikson in the UK synthesized polyethylene terephthalate using terephthalic acid and ethylene glycol as raw materials, and made it into fiber, which is known as polyester in my country. Polyester was industrially produced in the UK in 1946, and began to be industrially produced on a global scale in 1953. In 1971, it began to surpass nylon in quantity and became the largest synthetic fiber. Polyester has excellent properties such as high strength, good elasticity, good shape retention, and high dimensional stability. The clothes woven from it are durable, have good electrical insulation, are easy to wash and dry quickly, and are therefore widely used in clothing, decoration, industry, etc. field. However, due to the tight arrangement of internal molecules and the lack of hydrophilic structure between the molecules, polyester has a very small moisture regain and poor moisture absorption performance. Under the condition of relative humidity of 95%, its maximum moisture absorption rate is 0.7%. Due to its poor hygroscopicity and poor antistatic properties, polyester fabric has poor air permeability, poor dyeability, and poor pilling resistance.

  1. Dyeing modification of polyester

Polyester fiber is a hydrophobic synthetic fiber and lacks functional groups that can combine with direct dyes, acid dyes, basic dyes, etc.

Although it has an ester group that can form hydrogen bonds with disperse dyes, polyester has a tight molecular chain structure and it is difficult for dye molecules to enter the interior of the fiber, making dyeing difficult and monotonous in color, which directly affects the development of polyester fabric designs and colors. Due to the high crystallinity of polyester, there are only small gaps in the fiber. When the temperature is low, the thermal motion of the molecules changes their position to a smaller extent. Under humid conditions, polyester fiber does not expand the voids through violent swelling like cotton fiber, making it difficult for dye molecules to penetrate into the fiber. When polyester is dyed, it can usually only be dyed with disperse dyes, and it must be dyed under high temperature and high pressure or with the help of a carrier. In order to improve the dyeing performance of polyester, considering the molecular structure, increasing the looseness of the molecular chain will help the dye molecules enter. The main methods used to improve dyeing performance are: (1) copolymerization with compounds with bulky molecules (2) mixed spinning with compounds with plasticizing effects (3) introduction of ether bonds with affinity for disperse dyes Good group. The polyester resin modified by copolymerization has a low melting point and low crystallinity, and the thermal and mechanical properties of the fiber are damaged to a certain extent.

 

The dyeable modification method of cationic dyes is to copolymerize polyester dyeing modifier, such as sodium dimethyl phthalate-5-sulfonate (commonly known as trimonomer, English abbreviation SIPM) and polyester. After copolymerization, the polyester molecular chain The sulfonic acid group has been introduced and can be dyed with cationic dyes. The dyed fabrics are brightly colored and have a high dye absorption rate, which greatly reduces the discharge of printing and dyeing wastewater. The copolymer polyester chips can also increase antistatic, anti-pilling and hygroscopic properties. It is one of the main methods to improve the dyeing performance of polyester in recent years. Japan’s Unitika Company uses 4 parts of cationic dyeable polyester containing is ophthalate units with sulfonic acid groups and 1 part of ethylene glycol/polyethylene glycol/sodium sulfonate isophthalate/p-phenylene The block copolymer of dicarboxylic acid can be blended and spun into ultrafine fibers with high dyeing depth; before spinning or during the spinning process, a cationic active agent and a small amount of denaturant are added to copolymerize with BAET. After turning it into a random linear polymer, its spinnability becomes better. This modified polyester can not only be dyed with cationic dyes, but also has anti-pilling properties and improved wrinkle recovery.

 

In addition, at the same time that cationic dyeable fibers are launched. A modified polyester (PBT) using 1,4-butanediol instead of ethylene glycol as the second monomer has also joined the ranks of differentiated polyester. Replacing ethylene glycol with butylene glycol not only greatly increases the flexibility of the molecular chain, but also greatly improves the dyeing performance of the fiber, reaching normal pressure boiling dyeing. However, because the raw material price of 1,4-butanediol is much higher than that of ethylene glycol, PBT fiber lacks a competitive advantage in price. Therefore, at present, 1,4-butanediol is mainly added as the third monomer in conventional PET. This not only reduces the price of the fiber, but also improves its dyeing performance, and its thermal stability is much better than that of cationic dyeable fiber.

 

  1. Anti-pilling modification of polyester

 

The reason why polyester fabrics are prone to pilling is closely related to fiber properties, mainly due to the small cohesion between fibers, high fiber strength, and large elongation capacity. In particular, it has good resistance to bending fatigue, torsion fatigue and abrasion, so the fibers easily slide out of the fabric surface. Once small balls are formed on the surface, they are not easy to fall off. During the actual wearing and washing process, the fibers are constantly subjected to friction, causing the fibers on the surface of the fabric to be exposed to the fabric. There are many annoying hairs on the surface of the fabric, which is called “pilling”. If these hairs cannot fall off in time during wearing, they will become entangled with each other and be kneaded into many spherical particles, which is usually called pilling.

 

The main factors that affect fabric fluffing and pilling include:

 

(1) The fibers that make up the fabric

 

(2) Textile process parameters

 

(3) Dyeing and finishing processing

 

  • Use Conditions

 

Anti-pilling measures that have been adopted include:

 

(1) Reduce the molecular weight of polyester, which reduces the friction fastness, bending fatigue resistance and strength of the fiber, making the small balls formed by the fiber on the surface of the fabric easier to fall off.

 

(2) Change the fiber cross-sectional shape. Fibers with special-shaped cross-sections, such as “T” shape or “Y” shape, are easy to break when bent, and it is more difficult for the fibers to tangle into clusters than round fibers.

 

(3) Reduce the elongation of the fiber, increase the length of the short fiber, the twist of the short fiber yarn, or use post-finishing and other methods to obtain the anti-pilling effect, such as immersing the PET fiber in an alkali metal methanol solution of 180 to 240°C to process;

 

(4) Use blending methods to improve anti-pilling properties, such as blending 1:1 cotton and PET to produce anti-pilling fibers.

AKZO Nobel NV has developed a polyester fiber and yarn with high pilling resistance. During production, polyvinyl alcohol block copolymer is evenly added to the polyester mixture as a separate phase. This specially formulated polymer contains at least 90% mole of polyethylene terephthalate. It is added after the ester mixture is copolymerized, and its weight ratio is 1% to 7%. When the polymer and polyester mixture are evenly mixed, polyester fibers with anti-pilling properties can be produced by ordinary spinning methods.

 

  1. Antistatic, antifouling and hygroscopic modified polyester

Another serious disadvantage of polyester is that it has poor water absorption, is easily stained by oil, and is prone to electrostatic charge in low-humidity situations. The manufacturing methods of antistatic fiber are:

 

(1) Apply a durable antistatic agent to the fabric.

 

(2) Disperse the heat-resistant antistatic agent in the polyester melt and spin it into fabric.

 

(3) Copolymerize and modify the polyester molecular chain, and melt and spin the copolymer to improve the antistatic properties of the polyester fiber. Commonly used reactive and soluble antistatic additives include glycol ethers, dicarboxylic acid amides and Schiff base compounds.

To improve the antistatic and hygroscopic properties of polymer fibers, hydrophilic groups are usually introduced into the polymer through copolymerization and other methods to improve its hygroscopic properties and reduce specific resistance. For example, in the production process of PET, an appropriate amount of polyethanol (PEG) is added, and a PET-PEG block copolymer is obtained through co-condensation. Use this as a modifier to add to PET for mixed spinning to improve the antistatic and hygroscopic properties of polyester products.

 

After the 1990s, Japanese companies such as Zhongbo, Teijin, Toray, and Kuraray have all conducted series research on conductive fibers. Toray has developed high-whiteness conductive composite fibers. Kuraray has developed permanently conductive synthetic conjugate fibers composed of carbon black and thermoplastic elastomers, as well as white antistatic polyester filaments for use in military and workwear. Fabrics woven with it not only have excellent antistatic properties, but also have excellent hand feel, dyeability, strength, washing resistance and chemical resistance. Epirtopic fiber, developed by ICI Fibers, is a unique conductive fiber with a wide range of applications. The core is polyester and the skin layer is a copolymer of polyester and isophthalate, which is impregnated with black carbon particles during production.

Domestic research on conductive fibers started late. Zhejiang University, Zhejiang Institute of Metallurgy and Hangzhou Peacock Chemical Fiber Group Co., Ltd. developed a plated composite conductive polyester. It uses ordinary PET as the base, coats the surface with a layer of polyacrylonitrile, and then coats the polyacrylonitrile with composite conductive Cu2S to produce conductive fibers with basically the same physical properties as ordinary PET. The electrical conductivity of this fiber is durable, and the resistance of the 38-count yarn spun from it can be less than 100Ω. cm-1.

Conductive fiber has a wide range of uses. It was first used in carpets and is currently the largest field of use. In other fields, it is mainly used in antistatic, dust removal work clothes, general clothing and industrial materials. Antistatic dust removal work clothes are mainly used in dangerous goods workplaces such as oil and gas, semiconductors, electronics industries, precision instruments, medicine and health, and other fields. Their uses and markets are constantly expanding.

 

In recent years, domestic research and development on water-absorbent fibers have been carried out. For example, the PBT/PET hollow microporous composite fiber developed by Beijing University of Fashion Technology shows excellent water absorption and water retention. The highly water-absorbent hollow polyester staple jointly developed by Tianjin Petrochemical Company Polyester Factory and Beijing University of Fashion Technology can quickly absorb, transfer, and release moisture, and spin nearly 10 tons of 2.5 dtex highly water-absorbent staple fiber. It jointly develops highly moisture-absorbent fabrics with textile manufacturers, and the sportswear produced has good wearing comfort. The highly water-absorbent polyester fiber successfully developed by Donghua University has a water absorption rate similar to that of cotton, at 20.5%, and a moisture absorption rate of 2%, which is five times that of ordinary polyester. Teijin uses 0.1wt% to 15wt% of polyalkylene oxide with a weight average molecular weight of over 100,000 in the polyester fiber, and the polyalkylene glycol derivative is grafted onto the fiber surface, making it hygroscopic and washable. Greatly improves the hygroscopicity of polyester fibers.

Antistatic, antifouling and hygroscopicity are closely related to a certain extent. As long as the hydrophilicity of polyester is improved, these three properties can be improved accordingly. At the same time, it can also improve the dyeing performance of polyester to a certain extent.

 

  1. Flame retardant modified polyester

 

There are two methods of flame retardant modification of polyester: blending modification and copolymerization modification. Blending modification is to add flame retardant blends during the synthesis process of polyester chips to prepare flame retardant chips or to add flame retardants and blend them with the polyester melt during spinning to form flame retardant fibers. Copolymerization modification is to add copolymerized flame retardants as monomers during the synthesis of polyester to prepare flame-retardant polyester through copolymerization.

Flame retardant methods are classified according to the production process and can be summarized into the following five types:

(1) Add reactive flame retardants during the transesterification or polycondensation stage for cocondensation

 

(2) Add additive flame retardants to the melt before melt spinning

 

(3) Composite spinning of ordinary polyester and polyester containing flame retardant components

 

(4) Graft copolymerization with reactive flame retardant on polyester fiber or fabric

 

(5) Perform flame retardant post-treatment on polyester fiber fabrics.

 

There are many additive flame retardants that can be used for polyester fibers, and adding flame retardants is also the original flame retardant modification method for polyester fibers. Flame retardants mainly include halogen flame retardants and phosphorus flame retardants. Among halogen flame retardants, bromine flame retardants have the best flame retardant effect, and they can form a synergistic effect with antimony compounds (such as antimony trioxide) to improve their flame retardant effect. Among phosphorus-based flame retardants, various organic phosphates, inorganic phosphates, phosphorus oxides and other flame retardants can be used for flame retardant modification of polyester fibers. Among them, aromatic phosphates have good thermal decomposition stability, and their addition to the polyester melt will have little effect on the thermal degradation of polyester, thus not affecting the spinning process and fiber performance. At present, additive flame retardants are widely used in some small polyester fiber production companies. Reactive flame retardants for polyester fibers refer to small molecule flame retardants containing flame retardant elements (phosphorus, chlorine, bromine, fluorine) and active groups (carboxyl, hydroxyl, acid anhydride, etc.) in the molecule. Reactive flame retardants will gradually replace additive flame retardants. Usually adding a lower content (3% to 8%) of flame retardant can make the fiber have good flame retardant effect. Reactive flame retardants that can be used on polyester fibers include halogen and phosphorus flame retardants. Currently, phosphorus-based copolymer flame retardants are most commonly used internationally. Phosphorus flame retardants have good flame retardant effects on polyester fibers, and no toxic gases are generated during the combustion process. It is an environmentally friendly flame retardant system.

Reactive flame retardants are added during the transesterification or polycondensation stage for cocondensation. Since the copolymerized flame-retardant monomer is fixed on the copolyester chain through cocondensation reaction and becomes a component of the macromolecular chain, this method has less impact on the spinning properties of PET. It represents the mainstream development of flame-retardant polyester for fibers. For example, when synthesizing flame-retardant polyester, the oxygen index of polyester fiber chips made by adding 4wt% to 5wt% 2-carboxyethylphenylphosphinic acid (CEPPA) flame retardant can reach 32% to 33%. It has good reactivity and can obtain polyester chips with high molecular weight, non-toxic and odorless, high thermal stability, oxidation stability and water resistance.

 

  1. Prospects of polyester modification

With the development of the synthetic fiber industry, the continuous improvement of people’s living standards and the continuous advancement of science and technology, people’s research on the modification of polyester fibers will be further developed. Modified polyester fabrics and polyester blended fabrics will be more widely used, and the proportion of polyester for civil, decorative, and industrial use will further change. The excellent properties of polyester fabric itself, coupled with the bright color, good hand feel, anti-pilling properties, and hygroscopic and antistatic properties given to the fabric after modification, will greatly promote the development of the polyester fiber industry.

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