Polyester fibers, chemically modified

Pothan LA, Thomas S (2003) Polarity parameters and dynamic mechanical behaviour of chemically modified banana fiber reinforced polyester composites. Compos Sci Technol 63 1231-1240... 

Hydrophobic fibers are difficult to dye with ionic (hydrophilic) dyes. The dyes prefer to remain in the dyebath where they have a lower chemical potential. Therefore nonionic, hydrophobic dyes are used for these fibers. The exceptions to the rule are polyamide and modified polyacrylonitriles and modified polyester where the presence of a limited number of ionic groups in the polymer, or at the end of polymer chains, makes these fibers capable of being dyed by water-soluble dyes. 

By that time, W. R. Remington and I were once again separated this time my new leader was Dr. Albert Bauer, with whom I had worked at Orchem some 25 years earlier. Then, Robert Terss, Al, and I were a three-man team, which was, to identify new classes of dyes for acid-modified Dacron polyester fiber. After that work, he was transferred to a position in the Freon business. He now was transferred back to the Orchem Research Division to impart some of the wisdom that he had accumulated in that field to another business area. Bauer and I wrote several proposals for work to be undertaken by me on behalf of the Photo Products Department and submitted these to Botsolas. We set a low price tag of 25,000 on each proposal. We rationalized that this was a bargain for the Photo Products Department, but then, the Organic Chemicals Department would gain potential new business manufacturing the chemicals. 

The surface of the synthetic polymers can be modified by chemical, physical, and enzymatic methods (Figure 4.1). Chemical modification requires harsh reaction due to which strength properties of polymers get affected. Zeronian and Collins (1989) reported a 10-30% weight loss in polyester fibers after chemical treatment. Additionally, chemical treatments are difficult to control and have negative impacts on the enviromnent. 

Basic (cationic) dyes. Basic dyes are water-soluble and produce colored cations in solution. They are mostly amino and substituted amino compounds soluble in acid and made insoluble by the solution being made basic. They become attached to the fibers by formation of salt linkages (ionic bonds) with anionic groups in the fiber. They are used to dye paper, polyacrylonitrile, modified nylons, and modified polyesters. In solvents other than water, they form writing and printing inks. The principal chemical classes are triaryl methane or xanthenes. Basic brown 1 is an example of a cationic dye that is readily protonated under the pH 2 to 5 conditions of dyeing [5]. 

The world textile industry is one of the largest consumers of dyestuffs. An understanding of the chemistry of textile fibers is necessary to select an appropriate dye from each of the several dye classes so that the textile product requirements for proper shade, fastness, and economics are achieved. The properties of some of the more commercially important natural and synthetic fibers are briefly discussed in this section. The natural fibers may be from plant sources (such as cotton and flax), animal sources (such as wool and silk), or chemically modified natural materials (such as rayon and acetate fibers). The synthetic fibers include nylon, polyester, acrylics, polyolefins, and spindex. The various types of fiber along with the type of dye needed are summarized in Table 8.2. 

The natural polymers mentioned above are synthesized and grown into fibers by nature. Cotton, wool and silk are some examples. Wood is produced similarly, but not being in a form suitable for use as a textile fiber, it must be chemically modified to produce an appropriate solution, which can then be extruded into a fiber. Rayon and cellulose acetate are examples of this pro-cess.1 Synthetic materials, on the other hand, must be first polymerized into chains, by finking small molecules together end to end, and then extruded into fibers. Chains are built by either a condensation or an addition process. Nylon and polyester are examples of polymers synthesized by condensation, whereas polyethylene, polypropylene, acrylic and polytetrafluoroethylene (Teflon ) are some examples of polymers prepared by the addition process. 

The history of thermoplastic polyester goes back to 1929 with the pioneering work of Carothers. The first aromatic polyester of importance is poly(ethylene terephthalate) commonly abbreviated PET (or PETE) and was prepared by Whinfield and Dickson. In 1941, they created the first polyester fibers called Terylene and first manufactured by Imperial Chemical Industries (ICI). PET was produced commercially in 1953 as fiber for textile industry (Dacron) by Dupont using modified nylon technology. Dupont polyester research rapidly leads to a whole range of trademarked products as Mylar, a strong polyester film. 

BC-reinforced xmsaturated polyester resin nanocomposites were prepared using vinyl triethoxysilane-modified BC fibers by the resin transfer molding (RTM) methodology [180]. The X-Ray photoelectron spectroscopy (XPS) analysis revealed that chemical bonding was formed between the matrix and the modified BC fibers which resulted in composites with improved mechanical properties. 

In this survey, commercially important textile fibers are grouped by their origin. First there are the natural fibers from plant sources, cotton and flax, and those from animal sources, wool and silk. A second group consists of those fibers that are regenerated or chemically modified natural materials—the rayon and acetate fibers. The final group consists of the synthetic fibers, which include nylon, polyester, acrylics, polyolefins, and spandex. 

Zini et al. [50] prepared composites of a bacterial copolyester poly(3-hydroxybutyrate-co-3-hydroxyhexanoate], P(3HB-co-3HH), reinforced with flax fibers by compression molding. In order to improve fiber-matrix adhesion in composites, fibers chemically modified at the surface (by acetylation or by short-chain-PEG grafting] were also used. The best results were obtained with surface acetylated fibers. In the flax fiber composites the crystallization rate of P(3HB-co-3HH] remarkably increased compared with that of the plain polyester. The fibers displayed a nucleating effect on P(3HB-co-3HH] crystallization, whose magnitude depended on fiber surface chemistry. This feature was confirmed by the appearance of trans-crystallinity in isothermal crystallization experiments run in a hot stage of a polarized optical microscope. 

Maleic anhydride is important as a chemical hecause it polymerizes with other monomers while retaining the double bond, as in unsaturated polyester resins. These resins, which represent the largest end use of maleic anhydride, are employed primarily in fiber-reinforced plastics for the construction, marine, and transportation industries. Maleic anhydride can also modify drying oils such as linseed and sunflower. 

Control of fiber friction is essential to the processing of fibers, and it is sometimes desirable to modify fiber surfaces for particular end-uses. Most fiber friction modifications are accomplished by coating the fibers with lubricants or finishes. In most cases, these are temporary treatments that are removed in final processing steps before sale of the finished good. In some cases, a more permanent treatment is desired, and chemical reactions are performed to attach different species to the fiber surface, e.g. siliconized slick finishes or rubber adhesion promoters. Polyester s lack of chemical bonding sites can be modified by surface treatments that generate free radicals, such as with corrosive chemicals (e.g. acrylic acid) or by ionic bombardment with plasma treatments. The broken molecular bonds produce more polar sites, thus providing increased surface wettability and reactivity. 

Essentially, then, no new, large-volume, highly profitable fibers have been developed since the mid-1950s. Instead, the existing ones have become commodities with all the economic impact thereby implied. No major chemical engineering processes have been added, although the previously described ones have been modified to allow for spinning of liquid crystalline polymers or the formation of gel spun fibers. Research activity has been reduced and centered essentially on modifications of fiber size, shape, and properties, and many variants now are successfully marketed. Production volumes have increased enormously for nylon, polyester, and polyolefin. 

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