Synthetic Fibers

Natural fibers, especially wool and natural silk, have existed for several thousand years, soon to be followed by cotton, flax and the like. Their processing and usage have continuously been developed. Within one hundred years the chemical fibers and within only fifty years the synthetic fibers have improved their standard from originally being “substitute products” to recently providing about 50% of the total fibers consumed. It was a long way from the first ideas by Hook (1664) and Reaumur (1734) to the first chemical fibers [4] that were produced by Nicolaus de Chardonnet (1884). ln 1898 in Oberbruch near Aachen, Paul Fremery, Bromert and Urban produced the first cooper silk filaments that after carbonization were used as incandescent filaments in light bulbs. The first fully synthetic fiber would be produced based on an idea by Klatte (1913) from polyvinyl chloride. Staudinger [6] succeeded first in 1927 under laboratory conditions to spin a fully synthetic fiber from polyoxymethylene and later from polyethylenoxide from the melt [7]. 1938 Carothers developed the first polycondensation fiber that was produced as Nylon by the company DuPont de Nemours & Co. Just one year later Schlack [10] proved that lactam can be polymerized, what resulted 1939 in Berlin-Lichtenberg in the first Perlon^® fiber production. Soon IG-Farben-Industrie obtained a license for the melt spinning process for Nylon and transferred it to Perlon. After 1934 research was conducted in Germany that allowed the first semitechnical production ofpolyacrylonitrile fibers (PAN) during 1940 to 1943 [12, 13]. Almost simultaneously and independently of the German developments similar work was done at DuPont, so that the patent registrations almost have the same dates. Already 1950 DuPont started in the Candem plant full scale production of polyacrylonitrile fibers, what was not possible in Germany until much later. The commercial production of polyester follows around 1950 after an invention by Whine.field [52], and so does polypropylene around 1958 as developed by Natta [15]. These are the fibers that today are produced worldwide in tremendous quantities.

Polymers suitable for the production of synthetic fibers are all created by linking atoms or atomic groups. This can be done by three reactions differing in their chemo-physical process [l, 6]. This chapter primarily deals with the engineering problems of the necessary equipment and machines in the process sequences. There are far more polymers that are suited for fiber formation; they are not covered here, because they can be produced on very similar equipment but are not relevant from a market or quantity point of view today. The production of the monomers from the raw materials is also briefly addressed. Figure 2.1 shows the formation mechanism of synthetic polymers [411].

In the following Chapter some of the basic knowledge and conditions will be presented that are not necessarily present in chemical or mechanical engineering and not even in textile machinery construction. These are also difficult to find in the literature. An example for this is the unit 1 tex = 1 g/1000 m yarn that is a weight unit but at the same time (because the specific weight of the yarn material is constant) is also often used as a unit for the cross-section (see Chapter 10).

The synthetic fiber plants are such an accumulation of different machines, equipment and auxiliary installations that the description of a few typical installations needs to be followed by individual descriptions - here specifically from an engineering point of view. While 1964 the plant sizes were between 1000 and 10,000 t/a, and larger installations only existed in the USA, 1990 capacities for staple fiber productions of 50,000 … 200,000 t/a were already considered as normal [l]. In the PR China runs a polyester plant with a capacity of 600,000 t/a [2], however with several production lines (it is now going to be doubled). As opposed to these large installations for PET, PA or PAN and two or three PP installations, the usual PP fiber plants have a capacity of 2000 … 20,000 t/a. Specialty fiber plants are considerably smaller. A carbon fiber plant for 3000t/a is very large, and so is a hollow filament membrane installation with 5000 t/a, and some specialty fiber installations are run with only a few 10 t/a or less.

In addition to the processes and plants for producing man-made fibers and filaments described in Chapters 2 and 4, new products and processes are continuously being developed to meet particular requirements related to polymers, production or the properties of the end products, among others. Examples here are the short-spinning process, bicomponent spinning and micro-, super micro fibers and carbon fibers. Also, many “high tech” fibers are spun in such small quantities that laboratory or pilotsized plants are more than adequate. While l t/24 h carbon fiber is a large production rate, the required ca. 2 t/24 h PAN fiber precursor is a very low production rate for PAN, which nevertheless needs to be produced on a special plant. For medical application, special fibers are produced at a rate of only a few kg/24 h; the same applies for optical fibers. As a compilation of special processes could include as many types as one likes, and as many new processes are continuously being developed, only certain processes and plants are discussed as examples in the sections below.

Trouble-free manufacture of a high quality product requires the use of auxiliary plants and equipment. Such equipment, and its requirements, are outlined in this chapter. The design and supply of such custom- made equipment is best left to specialized finns. Auxiliary equipment begins with granulate transport, package- and yarn handling, includes air conditioning, spin finish- and additive preparation and ends with the very important cleaning plants. Plant-, control- and process compressed air is required practically throughout the plant. The supply of water, steam and electricity, ensured in sufficient quantity, quality and continuity, is not discussed in this chapter. Even frequent storms and lightning strikes in the plant vicinity can cripple the electrical power supply and result in an expensive re-heating and re-starting of the plant, which can only be avoided by the installation of emergency equipment and reservoirs to keep at least the melt heating equipment in operation. An emergency lighting system must also be considered, as the production rooms are normally dark. All this must be carefully considered when designing the plant.

The most important process drives are speed-, tension- or throughput-controlled, and are differentiated (Table 7.1) into:

In 1970, one could still expect 5 … 7% waste from polymerization to finished staple or yam. Falkai [I] reported in 1981 up to 15% waste and low quality product for some processes. Owing to advances in the quality of intermediate materials and automation, including continuous processing, modern plants today produce only about 3 … 4% waste. This waste consists of lumps of oxidized polymer and low bulk density filament waste, undrawn, partly drawn and fully drawn. 2 … 3% waste is normal in fiber production. In the case of 2 staple fiber lines each producing 200 t/d, this equates to 500 kg/h waste- which, valued at l OM/kg-results in an annual cost of approximately 4 000 000 DM, thus justifying the argument for recycling. The filament waste, valued at 0.30 DM/kg, is worth approximately 900 000 DM p.a.; selling this waste does not recover its true cost. Recovery of starting materials, intermediate products or end products is nowadays significantly more economical. Table 8.1 shows production routes where waste arises and possibilities of re-using such waste. Additionally, certain production routes permit the recovery of intermediate products or auxiliary agents and their re-use, which may be necessary to make these processes economically viable.

The testing of chemical fibers is a necessary and integral part of the production process. It is multi-faceted, can be carried out at various stages in the production process and can be viewed from different aspects with the following emphasis [l].

Despite the existence of SI units and standards (ISO, DIN, etc), the literature contains a multitude of dimensional units. The units cited in the literature have, in most cases, been retained in this book in order to make comparison with the original source easier. The tables given in this chapter enable the reader to perform the conversions. In the man-made fiber and textile industry, many other non-standard units, are used, e.g., m/min, dtex =den : 0.9, Nm or Ne. Some of these have once again been officially adopted in various countries. For specific (i.e., linear density based) tenacity alone, one finds more than twelve different units in the literature. The differences are not only country-specific, but also depend on the author and the topic discussed. In many cases, the material density (mostly in g/cm³) is involved in the tenacity calculation, thereby introducing a variation of ±2%, depending on source.

The first fiber table appeared in the 1950s as “Man-made Fiber Table” in the US journal “Textile World”. In 1960 the Deutsche Forschungsinstitut für Textilindustrie (German Research Institute for the Textile Industry) translated the table into German. Fourné supplemented this with further fiber types, and generated a Fiber Table, which appeared in his book “Synthetische Fasem” (Synthetic Fibers) in 1964. This fiber table was revised once more in 1975 by E. Kleinhansl of the above German Research Institute in Denkendorf and was published in “TEXTIL PRAXIS”. With their permission, these tables have been hrther supplemented, revised and published in this book. Part of this (new) information can be found in Table 1.1. Additionally, new SEM photographs of fibers have been included, as have additional force/elongation curves due to Latzke and Fourné, as well as research work done by the Fraunhofer Institute.