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Popular Science | Fiber Knowledge: Modified Polyester

In 1941, Whenfield and Dikson in the UK synthesized polyethylene from terephthalic acid and ethylene glycol. Ethylene terephthalate is made into fiber, and its trade name is polyes…

In 1941, Whenfield and Dikson in the UK synthesized polyethylene from terephthalic acid and ethylene glycol. Ethylene terephthalate is made into fiber, and its trade name is 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. Because polyester has excellent properties such as high strength, good elasticity, good shape retention, and high dimensional stability, clothes woven from it are durable, have good electrical insulation, are easy to wash and dry quickly, and have the reputation of “wash and wear”. Therefore, 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 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, the molecular chain structure of polyester is tight and it is difficult for dye molecules to enter the interior of the fiber, making dyeing difficult and the color monotonous, 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 its position to a smaller extent. Under humid conditions, polyester fiber will not be able to pass through as violently as cotton fiber. Swelling increases the voids and makes 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 properties are: (1) copolymerization with compounds with bulky molecules; (2) mixed spinning with compounds with plasticizing effects; (3) introduction of compounds with ether bonds that are compatible with disperse dyes. and good group. The polyester resin modified by the copolymerization method has a low melting point and low crystallinity, and the thermal and mechanical properties of the fiber are damaged to a certain extent.�.

Cationic dye dyeable modification method is to add polyester dyeing modifier, such as Dimethyl Phthalate-5-Sodium Sulfonate (commonly known as trimonomer, English abbreviation SIPM) is copolymerized with polyester. After copolymerization, sulfonic acid groups are introduced into the polyester molecular chain, which can be dyed with cationic dyes to achieve different colors of dyed fabrics. It is bright and has high dye absorption rate, which greatly reduces the discharge of printing and dyeing wastewater. Copolyester 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 isophthalate 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 as cationic dyeable fiber is 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. .

2. Anti-pilling modification of polyester

The reason why polyester fabrics are prone to pilling is closely related to fiber properties, mainly fiber The cohesion force is small, the fiber strength is high, the elongation capacity is large, and the resistance to bending fatigue, torsion fatigue and abrasion is good, so the fiber easily slides out of the fabric surface, and 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 exposed to friction on the surface of the fabric, which is called “fluffing”. If they cannot fall off in time, they become entangled with each other and are rolled into many spherical particles, which is usually called pilling.

The main factors affecting fabric fluffing and pilling are:

(1) The fibers that make up the fabric;

(2) Textile technology Parameters;

(3) Dyeing and finishing;

(4) Taking conditions.

The anti-pilling measures that have been adopted are:

(1) Reduce the molecular weight of polyester to improve the fiber’s friction fastness, bending fatigue resistance and strength Decreasing, making the small balls formed by fibers on the surface of the fabric easier to fall off;

( 2) Change the fiber cross-section 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 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 processing to obtain the anti-pilling effect , such as immersing PET fiber in an alkali metal methanol solution at 180~240℃ for treatment;

(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.

3. 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) Antistatic with durability The agent is applied to the fabric;

(2) Apply heat-resistant antistatic agent Dispersed in polyester melt, spun into fabric;

(3 ) Copolymerizes and modifies polyester molecular chains, and melts and spins the copolymer to improve the antistatic properties of polyester fiber. Commonly used reactive and soluble antistatic additives include glycol ethers, dicarboxylic acid amides and Schiff base compounds.

Improve the antistatic properties and hygroscopic properties of polymer fibers, usually through copolymerization Methods such as introducing hydrophilic groups into polymers can improve their 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. This is used as a modifier to be added to PET for mixed spinning to improve the quality of polyester products. Antistatic and hygroscopic.

After the 1990s, Japan’s Companies such as Zhongbo, Teijin, Toray, and Kuraray have all conducted series research on conductive fibers. Toray has developed high-whiteness conductive composite fibers, and Kuraray has developed permanent conductive fibers composed of carbon black and thermoplastic elastomers. The synthetic conjugate fiber has also developed white antistatic polyester filament for military uniforms and work clothes. Fabrics woven with it not only have excellent antistatic properties, but also have excellent hand feel, dyeability, strength, and washing resistance. and chemical resistance. Epirtopic fiber, developed by ICI Fibers, is a unique conductive fiber that has a wide range of applications. Its core is polyester and the skin layer is a copolymer of polyester and isophthalate. , which is impregnated with black carbon particles.
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, which uses ordinary PET As a matrix, a layer of polyacrylonitrile is plated on its surface, and then composite conductive Cu2S is plated on the polyacrylonitrile to obtain a conductive fiber with basically the same physical properties as ordinary PET. The conductive performance of the fiber is durable, and it is The resistance of the spun 38-count yarn 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 area of ​​use. In other aspects, it is mainly used in anti-static, dust removal work clothes, and general clothing. and industrial materials and other fields. 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.

Domestic research and development on water-absorbent fibers has been carried out in recent years, such as those developed by Beijing University of Fashion Technology The PBT/PET hollow microporous composite fiber shows excellent water absorption and water retention; the highly water-absorbent hollow polyester staple fiber jointly developed by Tianjin Petrochemical Company Polyester Factory and Beijing University of Fashion Technology can quickly absorb, transfer and release water, and spin Produced nearly 10t of 2.5dtex highly absorbent staple fiber, and jointly developed highly absorbent fabrics with textile manufacturers. The sportswear produced has good wearing comfort; the highly absorbent polyester fiber successfully developed by Donghua University has a water absorption rate similar to that of cotton. , is 20.5%, and the moisture absorption rate is 2%, which is 5 times that of ordinary polyester. Teijin incorporates 0.1wt% to 15wt% of polyalkylene oxide with a weight average molecular weight of over 100,000 into the polyester fiber, and the polyalkylene glycol derivative is grafted onto the surface of the fiber, making it hygroscopic and washable, which greatly improves 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, and at the same time, they can also be improved to a certain extent. Dyeing properties of polyester.

4. Flame-retardant modified polyester

There are two methods of flame retardant modification of polyester: blending modification and copolymerization modification. Blending modification is to add blending flame retardants during the polyester chip synthesis process to prepare flame retardant chips or add flame retardants to blend with the polyester melt during spinning to form flame retardant fibers; copolymerization modification is to synthesize polyester During the process, a copolymerized flame retardant is added as a monomer 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 retardant during the transesterification or polycondensation stage for co-condensation;

(2) Add additive flame retardant to the melt before melt spinning;

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

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

(5) After flame retardant the polyester fabric deal with.

There are many additive flame retardants that can be used for polyester fibers. Flame retardant is also the original flame retardant modification method for polyester fiber. 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 phosphate ester has good thermal decomposition stability, and its addition to the polyester melt has 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 additives��Flame retardant. 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.
In the transesterification or polycondensation stage, reactive flame retardants are added for copolycondensation. Since the copolymerized flame retardant monomer is fixed on the copolyester chain through the copolycondensation reaction and becomes a component of the macromolecular chain, this This method has little impact on the spinning properties of PET and represents the mainstream of the 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%; reaction It has good activity and can obtain polyester chips with high molecular weight, non-toxic and odorless, high thermal stability, oxidation stability and water resistance.

5. Prospects of polyester modification

With the development of the 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 fibers will be further developed. Modification The future polyester fabrics and polyester blended fabrics will be more widely used, and the proportion of polyester used in civil, decorative, and industrial applications 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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Author: clsrich