Poliester Febers

POLYESTER FIBERS
Updated: April, 2004- Raghavendra R. Hegde, Atul Dahiya, M. G. Kamath
(Ramaiah Kotra and Xiao Gao)
1. INTRODUCTION
In 1996, 24.1 million metric tons of manmade fibers were produced worldwide. The main volume gain took place in production of PET fibers (PET filament 9%, PET staple 4%) [1]. The primary drive for this growth is demand for fiber and container resin. Seventyfive percent of the entire PET production is directed toward fiber manufacturing. Hoechst, Dupont and Eastman are the three world largest polyester producers. Additional current U.S. Polyester Fiber Producers are: Acordis Industrial Fibers, Inc.; AlliedSignal Inc; Cookson Fibers, Inc.; KoSa; Intercontinental Polymers, Inc., Martin Color-Fi. Nan Ya Plastics Corp., Wellman, Inc. [24] Dramatic growthin PET fiber production is foreseen inAsia in the near future [22].
The cost of polyester, with the combination of its superior strength and resilience, is lower than that of rayon. Polyester fibers are hydrophobic, which is desirable for lightweight facing fabrics used in the disposable industry. They provide a perceptible dry feel on the facing, even when the inner absorbent media issaturated. As new methods of processing and bonding of PET are developed, rayon is being replaced by polyester on the market. According to David Harrison [2], 49% of the total nonwovens market share in the USAbelongs to polyester staple, reaching 291 million pounds in 1996 and ranking number one among all kind of fiber supplies. If one were to assume that the filament fiber consumption is half of that ofstaple, the total PET consumption in the USA nonwovens industry alone would be over 450 million pounds. Even if the estimate is not completely accurate, polyester has become the most widely used polymer in the nonwovens industry since 1995. The next most popular was polypropylene [2]. But in 1996, poly-olefins, particularly polypropylene (PP) moved ahead of PET fibers. They had 46% market shares infibers used for nonwovens, whereas, PET had a 45% share. By the end of 1998, olefin fibers increased their share to 49% and PET dropped to 42%[25].
Mechanical properties of nonwoven fabrics depend on many parameters, including fiber properties, web structure and processing. It is, therefore, useful to review some of the elementary knowledge of fiber properties and other factors like webprocessing techniques and structure. What follows is a brief review of PET fiber properties, which should serve as background information for better understanding the subject.
2. POLYESTER FIBERS
Polyester fiber is a " manufactured fiber in which the fiber forming substance is any long chain synthetic polymer composed at least 85% by weight of an ester of a dihydric alcohol (HOROH) and terephthalicacid (p-HOOC-C6H4COOH)" [3]. The most widely used polyester fiber is made from the linear polymer poly (ethylene terephtalate), and this polyester class is generally referred to simply as PET. High strength, high modulus, low _shrinkage, heat set stability, light fastness and chemical resistance account for the great versatility of PET.
3. POLYMER FORMATION
Polyethylene Teraphthalate (PET) is acondensation polymer and is industrially produced by either terephthalic acid or dimethyl terephthalate with ethylene glycol. [26] Other polyester fibers of interest to the nonwovens field include:
(a) Terephthalic Acid (PTA), produced directly from p-xylene with bromide-controlled oxidation.
(b) Dimethyl Terephthalate (DMT), made in the early stages by esterification of terephthalic acid.However, a different process involving two oxidation and esterification stages now accounts for most DMT.
(c) Ethylene Glycol (EG) initially generated as an intermediate product by oxidation of ethylene. Further ethylene glycol is obtained by reaction of ethylene oxide with water. 2

Fig.1: Production of polyethylene terephthalate
4. SYNTHESIS OF POLYMER
4.4 LINEAR POLYESTERS
A...