POLYMER APPLICATIONS SYNTHETIC FIBERS

For some applications, a combination of materials may be required to achieve a composite with the desired properties and performance. Property-improved lignocellulosic fibers can be combined with materials such as metal, glass, plastic, natural polymers, and synthetic fiber to yield a new generation of composite materials. New composites will be developed that utilize the unique properties obtainable by combining many different materials. This trend will increase significantly in the future. 

Fiber-reinforced composites contain strong fibers embedded in a continuous phase. They form the basis of many of the advanced and space-age products. They are important because they offer strength without weight and good resistance to weathering. Typical fibers are fiberous glass, carbon-based, aromatic nylons, and polyolefins. Typical resins are polyimides, polyesters, epoxys, PF, and many synthetic polymers. Applications include biomedical, boating, aerospace and outer space, sports, automotive, and industry. 

Wallace Carothers and coworkers at DuPont synthesized aliphatic polyesters in the 1930s [Furukawa, 1998 Hounshell and Smith, 1988]. These had melting points below 100°C, which made them unsuitable for firber use. Carothers then turned successfully to polyamides, based on the theoretical consideration that amides melt higher than esters. Polyamides were the first synthetic fibers to be produced commercially. The polyester and polyamide research at DuPont had a major impact on all of polymer science. Carothers laid the foundation for much of our understanding of how to synthesize polymeric materials. Out of that work came other discoveries in the late 1930s, including neoprene, an elastomer produced from chloro-prene, and Teflon, produced from tetrafluoroethylene. The initial commercial application for nylon 6/6 was women s hosiery, but this was short-lived with the intrusion of World War II. The entire nylon 6/6 production was allocated to the war effort in applications for parachutes, tire cord, sewing thread, and rope. The civilian applications for nylon products burst forth and expanded rapidly after the war. 

Like polyester, polyamides are synthetic fibers made from semicrystalline polymers which find use in a variety of applications in textiles almost similar to those of polyester. A recent work of Horrocks et al.55 has investigated the effect of adding selected intumescent FRs based on APP, MP,... 

As the title suggests, this approach is applicable to synthetic fibers only where either one of the monomer/ homopolymer can be flame retarded or the FR molecules can be attached to the polymer chain during... 

ANs are those that contain a majority of nitrile polymers. They provide good gas barrier, chemical resistance, and low taste and odor transfer with good impact properties when modified with rubber. Extruded sheet is used extensively in food packaging and rigid packaging applications. This crystalline TP is most useful in copolymers. Its copolymer with butadiene is nitrile rubber. Acrylonitrile-butadiene copolymers with styrene (SAN) exist that are tougher than PS. It is also used as a synthetic fiber and as a chemical intermediate. 

Synthetic fibers are generally made from polymers whose chemical composition and geometry enhance intermolecular attractive forces and crystallization. A certain degree of moisture affinity is also desirable for wearer comfort in textile applications. The same chemical species can be used as a plastic, without fiber-like axial orientation. Thus most fiber forming polymers can also be used as plastics, with adjustment of molecular size if necessary to optimize properties for particular fabrication conditions and end u.ses. Not all plastics can form practical fibers, however, because the intermolecular forces or... 

An important practical application of organic chemistiy has been the synthesis of synthetic fibers, many of which have properties that are different from and sometimes superior to their naturally occurring counterparts. The two most common classes of synthetic polymers are based on polyamides and polyesters. 

The major use of polymers has been as replacements for naturally occurring materials. Synthetic fibers such as nylon and polyester have substantially replaced natural textiles synthetic rubber is vastly superior to natural rubber, and the wide variety of engineering polymers (both thermosets and thermoplastics) have replaced traditional, naturally occurring materials such as metals and cellulosic compounds in many applications. 

Itaconic acid was isolated in 1836 from the pyrolysis products of citric acid (7) and the pol3mierization of the ethyl ester was observed by SwAETS in 1873 (2). While many patents relating to the acid and its esters as monomers have issued since that time, only recently have reports begun to appear in the scientific journals. The voluminous patent literature describes the use of polymeric itaconic acid derivatives in such applications as protective and decorative coatings, synthetic fibers, oil additives and rigid plastics as well as many others. Several summaries of the patent art and present commercial applications are available (3). Such information has been omitted from this review, which is directed primarily toward chemical behavior of the itaconic monomers and polymers. 

A recently developed one-step ammonoxidation process to acrylonitrile developed by BP Chemicals uses propane instead of propylene feed [21]. Key to the feasibility of this lower cost option was the development of the new catalyst system, which is now at the commercial demonstration stage. Almost all the acrylonitrile production goes into synthetic polymers and copolymers mostly for applications as fibers, some for plastics applications, and a small percentage to elastomer markets (the nitrile rubbers). 

Epoxy resin systems with fiber reinforcements are called "reinforced systems" or "composites." Composites are made by impregnating reinforcing fibers such as glass, synthetic polymer, or graphite fibers, by one of several processes with the desired epoxy resin system, and then curing in a heated mold or die. Epoxy composite systems are formulated with either liquid or solid resins with selection of the type of system dependent on the fabrication process, the cure temperature, and the final part application. 

PET is a thermoplastic polymer resin of the polyester family. PET is used in synthetic fibers beverage, food and other liquid containers thermoforming applications and engineering resins often in combination with glass fiber. 

Polyesters form a large class of commercially important polymers. A typical polyester is poly(ethylene terephthalate) (PETP), the largest volume synthetic fiber. It is also used as film (mylar) and in bottle applications. We have already discussed in the preceding section one of the routes for the preparation of PETP. The traditional route for the production of commercial PETP is through two successive ester interchange reactions, as shown below ... 

Indonesia is a tropical country with about 144 million Ha of tropical forest, producing a large amount of natural polymers, mainly natural rubber and wood products. In 1991 the total production of natural rubber was about 1.36 million tonnes while the production of log was about 40 million. Such large amount and various kinds of natural polymers were subject to investigation by a number of research centers since before the second WW. Center for the Application of Isotopes and Radiation, using radiation technique as a tool to modify the property of various natural polymers in order to meet the industries. Several Cobalt-60 sources and electron beam machine (EBM) from a small scale to a pilot scale are available. Other polymers such as synthetic fibers also becoming a subject of investigation. 

Schmack et al. [126] spun PLA fibers through the reactive extrusion polymerization of L-lactide (92 wt%) and meso-lactide (8 wt%). In many potential textile technological applications (e.g., for nonwoven materials) the fiber forming process is of general importance. An effective polymer synthesis requires also an effective spinning process to reduce the still high cost of the PLA fibers compared with those of established synthetic fibers. 

Fibers are classified as natural or synthetic. Fibers are used as a reinforcement material to increase the mechanical properties of polymer composites [31]. Synthetic fibers have been successfully used as the reinforcing material in composites such as carbon fiber, glass fiber, and Kevlar fiber. Glass fiber is a well-known example of a reinforcement material for polyolefin matrix. Polypropylene is a composite of increasing interest in automotive and other applications [32]. Figure 6.3 illustrates a glass fiber-reinforced polypropylene matrix. 

The focus in this chapter will be on the two main polyolefin polymers, namely polyethylene (PE) and polypropylene (PP). The latter especially has established itself as a very versatile fiber with unique applications in the textile and nonwoven industry. Polyethylene, on the other hand, has not been widely used as a fiber compared to other synthetic polymers such as PET, PP, and nylon, due in part to its low melting point. This chapter will, however, discuss ultra-high molecular weight polyethylene (UHMWPE) fiber that given its success and uniqueness in the synthetic fiber industry. 

The earliest applications of polymer chemistry involved chemical modification designed to improve the physical properties of naturally occurring polymers. In 1839, Charles Goodyear transformed natural rubber, which is brittle when cold and tacky when warm, to a substance that maintains its elasticity over a wider temperature range by heating it with sulfur (vulcanization). The first synthetic fibers— called rayons—were made by chemical modification of cellulose near the end of the nineteenth century. 

Synthetic polymers are relatively recently introduced materials. The natural fiber wool has already been used since antiquity, but the first completely synthetic fibers have only been in use since 1940. Iron has been known as a working material for thousands of years, but the oldest thermoset, phenolic resin, has only been known since 1906, and the oldest completely synthetic thermoplast, poly(vinyl chloride-co-acetate), has only been commercially produced since 1928. Large-scale application of elastomers has only been known since the beginning of the 19th century, when natural rubber was used, but the first commercial synthesis of a completely synthetic elastomer, poly(2,3-dimethyl butadiene), was only made in 1916. Since this time, the commercial production of thermoplasts, thermosets, chemical fibers, and synthetic rubbers has increased strongly (Figure 33-2). 

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