Polyester most commercially useful

Polyesters are made in one of two ways by either direct reaction of a diacid and a diol or ester interchange of a diester and a diol. By far the most commercially useful polyester is poly(ethylene terephthalate) (PET). Both methods are illustrated here. 

However, most of the aliphatic polyesters presently commercially used for biodegradable materials exhibit serious disadvantages. Beside the relatively high price level, properties are often limited and exclude these materials from many applications. For example, PCL has a very low melting point of about 60 °C. 

This mixture is known as Quinoline Yellow A [8003-22-3] (Cl 47000) and is most widely used with polyester fibers (109). Upon sulfonation, the water-soluble Quinoline Yellow S or Acid Yellow 3 [8004-92-0] (Cl 47005) is obtained. This dye is used with wool and its aluminum salt as a pigment. Foron Yellow SE-3GL (Cl Disperse Yellow 64) is the 3-hydroxy-4-bromo derivative. Several other quinoline dyes are commercially available and find apphcations as biological stains and analytical reagents (110). 

Plastics. Almost all commercial plastics find some use both dry and lubricated for sliding at low speeds and light loads the most commonly used thermoplastics are nylon, acetal resins, and polytetrafluoroethylene (PTFE). Typical thermosetting resins for bearing appHcations are phenoHcs, polyesters, and polyimides. Table 8 compares the characteristics of plastic bearing materials with those of graphite, wood, and mbber which find use in somewhat similar appHcations. 

Ethylene oxide is a precursor for many chemicals of great commercial importance, including ethylene glycols, ethanolamines, and alcohol ethoxylates. Ethylene glycol is one of the monomers for polyesters, the most widely-used synthetic fiber polymers. The current US production of EO is approximately 8.1 hillion pounds. 

For most commercial resins, the diluent is styrene monomer, but it is possible to use other vinyl monomers such as methyl styrene and alkyl methacrylate monomers. These diluents serve two vital roles for the system. They reduce viscosity so the resins can be processed, and they cross-link with the double bonds in the polyester. The later, however, is the focus of this section. For more detailed reviews on this subject, readers are directed to the references listed at the end of this chapter [1-3]. 

This mixture is known as Quinoline Yellow A and is most widely used with polyester fibers. Several other quinoline dyes are commercially available and find applications as pigments, biological stains, and analytical reagents. 

Polyester. The most common polyester in use is derived from the homopolymer poly (ethylene terephthalate). Many types of this fiber contain a delustrant, usually titanium dioxide. Optically brightened polymers are quite common. The optical brightener, such as specially stabilized derivatives of either stilbenes or phenylcoumarins, can be added to the polyester before formation of the fiber (107). Some commercial fibers contain minor amounts of copolymerized modifier to confer such properties as basic dyeability. A wide range of polyester fibers is used for consumer end-uses. Both staple fiber and filament yarn are available. Filament yarns with noncircular cross-sections are made (107). 

Polysacharides such as starch are the most prevalent naturally biodegradable polymer in commercial use. Aliphatic polyesters such as polyhydroxyalkanoates (PHA) are also a family of easily biodegradable polymers found in nature that are beginning to find commercial use. 

Organic matrices are divided into thermosets and thermoplastics. The main thermoset matrices are polyesters, epoxies, phenolics, and polyimides, polyesters being the most widely used in commercial applications (3,4). Epoxy and polyimide resins are applied in advanced composites for structural aerospace applications (1,5). Thermoplastics Uke polyolefins, nylons, and polyesters are reinforced with short fibers (3). They are known as traditional polymeric matrices. Advanced thermoplastic polymeric matrices like poly(ether ketones) and polysulfones have a higher service temperature than the traditional ones (1,6). They have service properties similar to those of thermoset matrices and are reinforced with continuous fibers. Of course, composites reinforced with discontinuous fibers have weaker mechanical properties than those with continuous fibers. Elastomers are generally reinforced by the addition of carbon black or silica. Although they are reinforced polymers, traditionally they are studied separately due to their singular properties (see Chap. 3). 

Polyesters are step-growth polymers in which the monomer units are joined together by ester groups. They have found wide commercial use as fibers, plastics, and coatings. The most common polyester is known by the trade name Dacron and is made by the transesterification (Section 17.10) of dimethyl terephthalate with ethylene glycol. High resilience, durability, and moisture resistance are the properties of this polymer that contribute to its wash-and-wear characteristics. 

---