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

The first is the physical modification method, mainly in the production process of polyester physical blending modification;

The second is chemical modification method, using chemical grafting or block method to change the molecular chain structure of polyester, improve the wear performance of polyester.

In 1941, British Whenfield and Dikson synthesized polyethylene terephthalate with terephthalic acid and ethylene glycol as raw materials, and made a fiber, which was named polyester in China. Polyester was industrially produced in the United Kingdom in 1946, began large-scale industrial production in the world in 1953, and began to exceed nylon in quantity in 1971, becoming DIYi large synthetic fiber. Because polyester has high strength, good elasticity, good shape preservation, high dimensional stability and excellent performance, the woven clothes are durable, good electrical insulation, easy to wash and dry, and have the reputation of "washable and wearable", so it is widely used in clothing, decoration, industry and other fields. However, due to the tight arrangement of internal molecules and the lack of hydrophilic structure between molecules, the moisture recovery rate is very small and the moisture absorption performance is poor. Under the condition of relative humidity of 95%, the moisture absorption rate of ZuiGao is 0.7%, due to its poor moisture absorption, poor antistatic property, poor air permeability of polyester fabric, poor dyeing, poor pilling resistance.

Frist. Dyeing modification of polyester

Polyester fiber is a hydrophobic synthetic fiber, which lacks functional groups that can be combined with direct dyes, acidic dyes, alkaline dyes, etc.

Although there is an ester group that can form hydrogen bond with disperse dyes, the structure of polyester molecular chain is tight, and the dye molecules are not easy to enter the interior of the fiber, which makes dyeing difficult and the color is monotonous, which directly affects the development of polyester fabric varieties. Due to the high crystallinity of polyester, there is only a small gap in the fiber, when the temperature is low, the molecular thermal motion to change its position is small, under humid conditions, polyester fiber will not be like cotton fiber through violent swelling and make the gap increase, dye molecules are difficult to penetrate into the fiber. Polyester is usually dyed only with disperse dyes, and must be dyed under high temperature and pressure or with the aid of a carrier. In order to improve the dyeing performance of polyester, from the perspective of molecular structure, improving the degree of molecular chain porosity will help dye molecules to enter. The main methods used to improve the dyeing properties are: (1) copolymerization with chemical substrates with large molecular volume; (2) Spinning mixed with compounds with plasticizing effect; (3) Introduce groups with ether bonds and good affinity for dispersive dyes. The polyester resin modified by copolymerization method has low melting point and 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-5-sulfonate (commonly known as trimonomer, English abbreviation SIPM) with polyester, and introduce sulfonic acid groups into the polyester molecular chain after copolymerization. Cationic dyes can be dyed, the dyed fabric has bright colors, high dye absorption rate, and greatly reduce the discharge of printing and dyeing wastewater. Copolymer polyester slicing can also increase the anti-static, anti-pilling and hygroscopic properties, which is one of the main methods to improve the dyeing properties of polyester in recent years. The microfiber with high dyeing depth can be made by blending 4 parts cationic dyeable polyester containing sulfonic acid group isophenate unit with 1 part ethylene glycol/polyethylene glycol/sulfonic acid sodium isophenate/terephthalic acid block copolymer in Unijica Company of Japan. Before spinning or during spinning, a cationic active agent and a small amount of denaturant are added to copolymerize with BAET. The spinnability of the polymer is improved by making it into random linear polymer. This modified polyester can not only be dyed with cationic dyes, but also has pilling resistance and improved wrinkle recovery.

In addition, the cationic dyeable fiber is introduced at the same time. A modified polyester (PBT) with 1,4 butanediol instead of ethylene glycol as the second monomer has also joined the ranks of differential polyester. The substitution of butanediol for ethylene glycol not only greatly increased the flexibility of the molecular chain, but also greatly improved the dyeing property of the fiber, and reached the atmospheric pressure boiling dyeing. However, because the raw material price of 1,4 butanediol is much higher than that of ethylene glycol, PBT fiber lacks competitive advantage in price. Therefore, at present, l, 4 butanediol is mainly added as the third monomer in conventional PET, which not only reduces the price of the fiber, but also improves its dyeing performance, and the thermal stability is much better than that of cationic dyeable fiber.

Second, anti-pilling modification of polyester

The reason why polyester fabric is easy to pilling is closely related to fiber properties, mainly small adhesion between fibers, high fiber strength, large elongation, especially good resistance to bending fatigue, torsion fatigue and wear resistance, so the fiber is easy to slip out of the fabric surface, once the ball is formed on the surface, it is not easy to fall off. In the actual wearing and washing process. The fibers are constantly subjected to friction, exposing the fibers on the surface of the fabric. On the surface of the fabric presents a lot of annoying fur, that is, "fuzz", if these fur can not fall off in time during wearing, they are entangled with each other, and are kneaded into many spherical small particles, usually called pilling.

The main factors affecting fabric fuzz and pilling are:

(1) The fibers constituting the fabric;

(2) textile process parameters;

(3) dyeing and finishing processing;

(4) Taking conditions.

The anti-pilling measures that have been adopted are:

(1) Reduce the molecular weight of polyester, so that the fiber friction fastness, bending fatigue resistance and strength decline, so that the fiber formed on the surface of the fabric ball is easier to fall off;

(2) Change the fiber section shape. Special-section fibers, such as "T" shape or "Y" shape, are easy to break when bent, and it is more difficult for fibers to form clusters than circular fibers.

(3) Reduce the elongation of the fiber, increase the length of the staple fiber, the twist of the staple fiber yarn, or use post-finishing processing methods to obtain the anti-pilling effect, such as the PET fiber immersed in the alkali metal methanol solution of 180 ~ 240℃ for treatment;

(4) The use of blending methods to improve pilling resistance, such as l: 1 cotton and PET blended to produce pilling resistance fiber.

AKZO Nobel NV has developed a polyester fiber and yarn with high pilling resistance. The polyvinyl alcohol block copolymer is uniformly added to the polyester mixture as a separation phase during production. This special polymer contains at least 90% moles of polyethylene terephthalate. The polymer is added after copolymerization of the polyester mixture, and its weight ratio is 1% ~ 7%. When the polymer and polyester mixture are mixed evenly, the polyester fiber with anti-pilling properties can be prepared by ordinary spinning method.

Third, anti-static, anti-fouling and hygroscopic modified polyester

Another serious disadvantage of polyester is poor water absorption, easy to be stained by oil, and easy to carry static charge in low humidity situations. Antistatic fiber manufacturing methods are:

(1) Coating the fabric with durable antistatic agent;

(2) The heat-resistant antistatic agent is dispersed in the polyester melt and spun into a fabric;

(3) The polyester molecular chain is copolymerized, and the copolymer is fused and spun to improve the antistatic properties of the polyester fiber. The commonly used reactive and soluble antistatic additives are glycol ethers and dicarboxylic amides and Seifer base compounds.

To improve the antistatic and hygroscopic properties of polymer fiber, hydrophilic groups are usually introduced into the polymer by copolymerization, so as 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 to produce PET-PEG block copolymer through co-condensation, which is added to PET as a modifier to mix spinning to improve the antistatic property and hygroscopic property of polyester products.

After the 1990s, Japan's bell textile, Teijin, Toray, Cola and other companies have carried out a series of conductive fiber research. The high whiteness conductive composite fiber developed by Toray Company, the synthetic conjugated fiber with YongJiu conductive property composed of carbon black and thermoplastic elastomer developed by Corolli company, and the white antistatic polyester filament used in military and work clothes was also developed. The fabric woven with it not only has excellent antistatic property, but also has excellent anti-static property. It also has excellent hand feel, dyeing, strength, washing resistance and chemical resistance. Epirtopic fiber, developed by ICI Fiber Company, is a unique conductive fiber with a very wide range of applications, its core is polyester, the skin is a copolymer of polyester and isophthalic acid ester, and at the time of production, it is impregnated in black carbon grains.

Domestic conductive fiber research started late, Zhejiang University, Zhejiang Metallurgical Research Institute and Hangzhou Peacock Chemical Fiber Group Co., Ltd. developed a plated composite conductive polyester, which uses common PET as a matrix, plated on its surface a layer of polyacrylonitrile, and then plated on the polyacrylonitrile composite conductive Cu2S. The conductive fiber with the same physical properties as common PET is prepared, and the conductive properties of the fiber are durable, and the resistance of the 38 yarn spun by it can be less than 100Ω. cm-1.

Conductive fiber is widely used, among which the earliest used in carpet, is the current amount of ZuiDa field, other aspects are mainly used in antistatic, dust removal work clothes, general clothing and industrial materials and other fields. Antistatic dust removal work clothes are mainly used in oil, natural gas and other dangerous goods workplaces, semiconductors, electronics industry, precision instruments, medicine and health and other fields, and its use and market are constantly expanding.

Absorbent fibers have been researched and developed in China in recent years, such as PBT/PET hollow microporous composite fibers developed by Beijing University of Fashion Technology, which show excellent water absorption and water retention. The high absorbent hollow polyester staple fiber developed by the Polyester plant of Tianjin Petrochemical Company and Beijing University of Fashion Technology can quickly absorb, transfer and release water, and spin the high absorbent staple fiber of nearly l0t 2.5dtex. The high absorbent fabric is jointly developed with textile manufacturers, and the sportwear is made of good wearing comfort. The water absorption of the highly absorbent polyester fiber developed by Donghua University is similar to cotton, which is 20.5% and 2%, which is 5 times that of ordinary polyester. Teijin Company polyester fiber internal with an average weight of more than 100,000 molecular weight of polyalkylene oxide is O.1wt % ~ 15wt %, and polyalkylene glycol derivatives grafted on the surface of the fiber, moisture absorption and washable, greatly improving the moisture absorption of polyester fiber.

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, and the dyeing performance of polyester can also be improved to a certain extent.

Four, flame retardant modified polyester

There are two methods of flame retardant modification of polyester: blending modification and copolymerization modification. Blending modification is to prepare flame retardant slices by adding flame retardant in the process of polyester slice synthesis or to blend flame retardant with polyester melt in spinning. Copolymerization modification is the preparation of flame retardant polyester by copolymerization by adding copolymerized flame retardant as monomer in the process of polyester synthesis.

According to the production process, the flame retardant method is classified, which can be summarized as the following 5 kinds:

(1) Adding reactive flame retardants in transesterification or polycondensation stage for co-polycondensation;

(2) Adding 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 retardants on polyester fibers or fabrics;

(5) Flame retardant post-treatment of polyester fiber fabric.

There are many additive flame retardants that can be used for polyester fiber, and the addition of flame retardants is also the initial flame retardancy modification method of polyester fiber. The main flame retardants are halogen flame retardants and phosphorus flame retardants. In halogen flame retardants, the flame retardant effect of bromine flame retardants is ZuiHao, and it can be improved by the formation of synergistic interaction with antimony compounds (such as antimony trioxide). In phosphorous flame retardants, various flame retardants such as organophosphate ester, inorganic phosphate ester and phosphorus oxide can be used for flame retardancy modification of polyester fiber. The aromatic phosphate ester has good thermal decomposition stability, and its addition to the polyester melt has little effect on the thermal degradation of the polyester, so it will not affect the spinning process and fiber performance. At present, additive flame retardants have been widely used in some small polyester fiber production enterprises. Reactive flame retardants for polyester fibers refer to small molecular flame retardants containing flame retardant elements (phosphorus, chlorine, bromine, fluorine) and active groups (carboxyl, hydroxyl and acid anhydride, etc.). 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 a good flame retardant effect. Reactive flame retardants available for polyester fibers include halogen and phosphorus based flame retardants. At present, the most commonly used in the world is phosphorous copolymerized flame retardants. Phosphorous flame retardants have good flame retardancy effect on polyester fiber, and no toxic gas is generated during combustion. It belongs to environmentally friendly flame retardant system.

In transesterification or polycondensation stage, reactive flame retardants are added to co-polycondensation, because the copolymerized flame retardant monomer is fixed on the copolyester chain through the co-polycondensation reaction, and becomes a component of the macromolecular chain, so this method has little impact on the spinning performance of PET, representing the mainstream of the development of flame retardant polyester for fibers. For example, when synthesizing flame retardant polyester, adding 4wt % ~ 5wt % 2 carboxyethyl phenyl phosphonic acid (CEPPA) flame retardant made of polyester fiber slices, the oxygen index can reach 32% ~ 33%; With good reactivity, polyester chips with high molecular weight, non-toxic, odorless, high thermal stability, oxidation stability and water resistance can be obtained.

Fifth, the prospect of polyester modification

With the development of synthetic fiber industry, the continuous improvement of people's living standards and the continuous progress of science and technology, people's research on the modification of polyester fiber will be more in-depth development, the application of modified polyester fabric and polyester blended fabric will be more extensive, and the proportion of civilian, decorative and industrial polyester will be further changed. The excellent properties of polyester fabric itself, coupled with the bright color, good hand feel, anti-pilling and hygroscopic anti-static properties of the modified fabric, will greatly promote the development of polyester fiber industry.