PET Fiber

Standard polyester fibers contain no reactive dye sites. PET fibers are typically dyed by diffusiag dispersed dyestuffs iato the amorphous regions ia the fibers. Copolyesters from a variety of copolymeri2able glycol or diacid comonomers open the fiber stmcture to achieve deep dyeabiHty (7,28—30). This approach is useful when the attendant effects on the copolyester thermal or physical properties are not of concern (31,32). The addition of anionic sites to polyester usiag sodium dimethyl 5-sulfoisophthalate [3965-55-7] has been practiced to make fibers receptive to cationic dyes (33). Yams and fabrics made from mixtures of disperse and cationicaHy dyeable PET show a visual range from subde heather tones to striking contrasts (see Dyes, application and evaluation). 

In addition to dyeabiHty, polyesters with a high percentage of comonomer to reduce the melting poiat have found use as fusible biader fibers ia nonwoven fabrics (32,34,35). Specially designed copolymers have also been evaluated for flame-retardant PET fibers (36,37). 

Most textile fibers are delustered with 0.1—3.0 wt % Ti02 to reduce the gHtter and plastic appearance. Many PET fibers also contain optical bTighteners (17). Through the use of soluble dyes or pigments, including photochromic pigments (19), a wide variety of producer-colored fibers and effects is available. 

Physically or chemically modifying the surface of PET fiber is another route to diversified products. Hydrophilicity, moisture absorption, moisture transport, soil release, color depth, tactile aesthetics, and comfort all can be affected by surface modification. Examples iaclude coatiag the surface with multiple hydroxyl groups (40), creatiag surface pores and cavities by adding a gas or gas-forming additive to the polymer melt (41), roughening the surface... 

Eig. 1. Typical stress—strain curves for cotton and PET fibers. A, industrial B, high tenacity, staple C, regular tenacity, filament D, regular tenacity, staple ... 

Polyester fibers have exceUent resistance to soap, detergent, bleach, and other oxidiziag agents. PET fibers are generally iasoluble ia organic solvents, including cleaning fluids, but are soluble ia some phenoHc compounds, eg, (9-chlorophenol. 

Other Properties. Polyester fibers have good resistance to uv radiation although prolonged exposure weakens the fibers (47,51). PET is not affected by iasects or microorganisms and can be designed to kill bacteria by the iacorporation of antimicrobial agents (19). The oleophilic surface of PET fibers attracts and holds oils. Other PET fiber properties can be found ia the Hterature (47,49). 

Terephthahc acid (TA) or dimethyl terephthalate [120-61 -6] (DMT) reacts with ethyleae glycol (2G) to form bis(2-hydroxyethyl) terephthalate [959-26-2] (BHET) which is coadeasatioa polymerized to PET with the elimination of 2G. Moltea polymer is extmded through a die (spinneret) forming filaments that are solidified by air cooling. Combinations of stress, strain, and thermal treatments are appHed to the filaments to orient and crystallize the molecular chains. These steps develop the fiber properties required for specific uses. The two general physical forms of PET fibers are continuous filament and cut staple. 

Woddwide, the production capacity for polyester fiber is approximately 11 million tons about 55% of the capacity is staple. Annual production capacity iu the United States is approximately 1.2 million tons of staple and 0.4 million tons of filament. Capacity utilization values of about 85% for staple and about 93% for filament show a good balance of domestic production vs capacity (105). However, polyester has become a woddwide market with over half of the production capacity located iu the Asia/Pacific region (106). The top ranked PET fiber-produciug countries are as follows Taiwan, 16% United States, 15% People s RepubHc of China, 11% Korea, 9% and Japan, 7% (107—109). Woddwide, the top produciug companies of PET fibers are shown iu Table 3 (107-109). 

Health Safety. PET fibers pose no health risk to humans or animals. Eibers have been used extensively iu textiles with no adverse physiological effects from prolonged skin contact. PET has been approved by the U.S. Eood and Dmg Administration for food packagiug and botties. PET is considered biologically iuert and has been widely used iu medical iaserts such as vascular implants and artificial blood vessels, artificial bone, and eye sutures (19). Other polyester homopolymers including polylactide and polyglycoHde are used iu resorbable sutures (19,47). 

Peculiarities of the Fine Structure of PET Fibers and the Relationship to Their Basic Physical Properties... 

In 1994, the proportion of PET fibers in the world production of synthetic fibers was 62.9% and of chemical fibers was 55.3%, while in the total volume of all kinds of fibers it was 27.4%. Out of PET fibers presently produced, 38% are staple fibers and 52.5% are filament yarns, with a marked tendency toward an increase in the latter. A 55% proportion is anticipated in the year 2000, At present, about 75% of PET fibers are used for textile purposes and 25% for nontextile purposes. 

This dynamic increase in production was accompanied by the qualitative development of PET fibers, which manifested itself in the widening of assortment of the fibers being produced (e.g., staple microfibers and filament yarns of the POY, MOY, FOY, and HOY type) and in the manufacture of second-generation fibers on... 

PET fibers in final form are semi-crystalline polymeric objects of an axial orientation of structural elements, characterized by the rotational symmetry of their location in relation to the geometrical axis of the fiber. The semi-crystalline character manifests itself in the occurrence of three qualitatively different polymeric phases crystalline phase, intermediate phase (the so-called mes-ophase), and amorphous phase. When considering the fine structure, attention should be paid to its three fundamental aspects morphological structure, in other words, super- or suprastructure microstructure and preferred orientation. 

PET fibers and filaments are characterized by a fibrillar superstructure that corresponds to the general concept of the fibrillar structure of synthetic fibers. The fibrillar... 

Microfibrils are formed in PET fibers during the stretching of a solidified polymer stream. With an increase in the draw ratio, microfibrils become increasingly slender. The microfibril length is assumed to be proportional to the draw ratio (R), their lateral dimension proportional to Jr, while the length-to-lateral dimension ratio is proportional to... 

Another type of fibril substructure in PET fibers, besides the microfibrillar type already discussed, is the lamellar substructure, also referred to as the lateral substructure. The basic structural unit of this kind of substructure is the crystalline lamella. Formation of crystalline lamellae is a result of lateral adjustment of crystalline blocks occurring in neighboring microfibrils on the same level. Particular lamellae are placed laterally in relation to the axis of the fibrils, which explains the name—lateral substructure. The principle of the lamellar substructure is shown in Fig. 2. 

The distinction between the types of substructures of the microfibrils occurring in the PET fiber is possible based on the value of the substructure parameter (yl). 

Table 1 Values of the Long Period of Differently Drawn PET Fibers...

Characteristic of the microstructure of PET fibers in their final production form is the occurrence of three types of polymer phases crystalline, mesomorphous, and amorphous. The first phase is the result of crystalline aggregation of PET molecules, the second phase—of mesomorphous or, in other words, paracrys-talline aggregation, the third phase—of amorphous aggregation. The mesomorphous and amorphous phases together form a noncrystalline part of the fiber. 

A univocal confirmation of the development of crystalline aggregation in the fiber is the occurrence of layer reflexes Oil, HI, ill, and 101 on the textural x-ray diffraction pattern. The details of organization of the space lattice are defined by the parameters of the unit cell and the number of polymers felling into one cell. The data, established by different authors, are presented in Table 2. Daubenny and Bunn s [8] pioneer findings are considered the most probable for space lattices occurring in PET fibers. 

A specific attribute of unit cell building is the inclination of the axis of macromolecule chains, in relation to the normal, to the plane of the base of the cell (ab). According to Yamashita [11] this inclination is within the range of 25-35° (Fig. 4). Against the background of space lattices of other types of fibers, the lattice of crystalline regions in PET fibers is characterized by a number of specific features. These are ... 

The space lattice does not undergo polymorphous transformation. As with other kinds of fibers, no transformation of the space lattice under the effect of any physical or chemical treatment of PET fibers has yet been found. 

Crystallites occurring in PET fibers can assume two kinds of morphological forms. The first form represents the crystallite formed by molecules of folded conformation, while the other is formed from molecules of extended-chain conformation. The first form is sometimes called a flexural morphological form, whereas the other is called a straightened morphological form. The flexural form is the typical and prevailing morphological form in PET fibers. However, it should be stressed that no... 

Figure 5 X-ray reflexes of PET fibers differentiated by draw ratio (in %).

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