44 . $\qquad$
$\qquad$
$\qquad$ are known as the "three major synthetic fibers".
A. Nylon, polyester, and acrylic
B. Nylon, polyester, and spandex
C. Nylon, polyester, and vinylon
D. Nylon, polyester, and acrylic
【Answer】D
【Analysis】Synthetic fibers are chemical fibers made by spinning and post-processing of linear polymers with suitable molecular weight and solubility (or meltability). Polymers with fiber-forming properties are usually referred to as fiber-forming polymers. Compared to natural fibers and regenerated fibers, the raw materials for synthetic fibers are produced by artificial synthesis methods, and production is not limited by natural conditions. In addition to the general superior properties of chemical fibers, such as high strength, light weight, easy washing and quick drying, good elasticity, and resistance to mold and insects, different types of synthetic fibers each have certain unique properties. The three major synthetic fibers usually refer to polyester, nylon, and acrylic. Polyester (PET) is an important variety of synthetic fibers and is the commercial name for polyester fibers in China. It is made from raw materials such as terephthalic acid (PTA) or dimethyl terephthalate (DMT) and ethylene glycol (MEG) through esterification or transesterification and polycondensation reactions to form a fiber-forming polymer—polyethylene terephthalate (PET)—which is then spun and post-processed into fibers. Polyester is the simplest of the three major synthetic fibers in terms of production process and is relatively inexpensive. It is also favored for its durability, good elasticity, resistance to deformation, corrosion resistance, insulation, stiffness, easy washing and quick drying, and other features. Polyester has a wide range of applications, including clothing fabrics and industrial products. Textiles: men's and women's shirts, outerwear, children's clothing, interior decorative fabrics, and carpets. Industry: tire cords, conveyor belts, fire hoses, ropes, fishing nets, etc. It can also be used as electrical insulation material, acid-resistant filter cloth, and papermaking felts; interior decorations, carpet backing, medical industrial fabrics, padding, linings, etc.

Nylon (PA) generally refers to nylon. Nylon is a type of polyamide fiber (nylon), which was developed by the American outstanding scientist Carothers and his research team. It is the first synthetic fiber in the world. Nylon has revolutionized the appearance of textiles, marking a significant breakthrough in the synthetic fiber industry and a very important milestone in polymer chemistry. In civilian use, it can be blended or used alone to make various medical and knitted products. Nylon filament is mostly used in the knitting and silk industries, while nylon staple fibers are mainly used to blend with wool or other chemical fiber wool products to make various wear-resistant and durable clothing. In industry, nylon is widely used to manufacture tire cords, industrial fabrics, ropes, conveyor belts, tents, fishing nets, etc. In defense, it is mainly used for parachutes and other military fabrics.

Acrylic (PAN) is the commercial name for polyacrylonitrile in China, known abroad as "Orlon" or "Krylon," and by DuPont as Orlon. It is the third most important synthetic fiber after polyester and polyamide. It is soft, light, warm, corrosion-resistant, and light-resistant, similar to wool short fibers. It has a lower density than wool and is known as "artificial wool." Although it is more than 10% lighter than wool, its strength is more than twice as high. Acrylic is also resistant to mold and insects and has a higher resistance to sunlight than wool and ten times that of cotton. Acrylic has a wide range of applications in clothing, accessories, and industrial fields. Polyacrylonitrile fibers can be spun alone or blended with natural fibers according to different usage requirements. It is particularly suitable for making tents, gun covers, car covers, curtains, and other outdoor fabrics. It can also be blended with wool, polyester, viscose, and cotton to produce various high-quality fabrics, artificial fur, and industrial products.

Cotton纶 (modified polypropylene fiber) has the advantages of low specific gravity, non-hygroscopicity, low thermal conductivity, good chemical resistance, and good hygiene. By adding additives to the polypropylene raw material, the fluidity of the melt can be effectively improved, and fine short fibers with a fineness of 0.6 to 0.8 d can be produced by melt spinning. The core-suction effect of cotton纶 fibers gives them excellent properties such as lightness, warmth, moisture absorption, dryness, and antibacterial properties. Products developed using it, such as ultra-cotton纶 underwear, bathrobes, T-shirts, etc., have superior warmth, moisture absorption, moisture transfer, quick drying, and antibacterial properties, making them high-end fabrics.

Spandex (PU) is the abbreviation for polyurethane fiber, a type of elastic fiber. It has excellent elasticity, capable of stretching 6 to 7 times its original length and quickly returning to its initial state when the tension is released. Its strength is 2 to 3 times that of rubber threads, and it has a finer linear density and better chemical resistance. Spandex has good acid resistance, sweat resistance, seawater resistance, dry cleaning resistance, and wear resistance. Spandex is used in clothing that requires stretchability for comfort, such as professional sports wear, fitness wear, and exercise clothing, wetsuits, swimwear, competition swimwear, basketball uniforms, bras and girdles, ski pants, disco wear, jeans, casual pants, socks, leg guards, diapers, tights, belts, underwear, bodysuits, spandex undergarments, male ballet dancers' ribbons, surgical protective clothing, logistics protective clothing, cycling shorts, wrestling vests, rowing suits, underwear, performance clothing, and custom clothing. It is also used in bras, home decor, and bead pillows. Spandex is used in a small proportion in general clothing and is usually not used alone but blended into fabrics in small amounts.

Vinalon (PV) is the commercial name for polyvinyl alcohol formal fiber, also known as Vinylon. Its properties are similar to cotton, earning it the nickname "synthetic cotton." It is the synthetic fiber with the highest moisture absorption among existing synthetic fibers. Vinalon was first produced in Germany in the 1930s but was not resistant to hot water and was mainly used for surgical sutures. In 1939, a successful method for heat treatment and acetalization was developed, making it a fiber with good hot water resistance. The raw materials for producing Vinalon are easily available, and the manufacturing cost is low. The fiber has good strength and is used not only in clothing but also in various industrial applications. However, due to its longer production process and inferior comprehensive performance compared to polyester, nylon, and acrylic, its annual production is smaller, ranking fifth among synthetic fiber varieties.