PERP Program Nylon Fiber Spinning Technology New Report Alert February 2006 Nexant s ChemSystems Process Evaluation/Research Planning program has published a new report, Nylon Fiber Spinning Technology (04/05S5). To view the table of contents or order this report, please click on the link below: http://www.nexant.com/products/csreports/index.asp?body=http://www.chemsystems.com/reports/show_cat.cfm?catid=2 Introduction Three commercially important textile fibers, nylon, polyester and polypropylene are produced by the melt spinning process. Melt spinning is the most critical operation in the production of nylon, as number of fiber properties such as yarn uniformity, crystallinity, and orientation are imparted to the yarn during this process. In comparison to wet and dry spinning methods, the melt spinning process offers a number of advantages, such as high throughput, solvent-free workplace, and no toxic hazards. In the 1950s, nylon fiber spinning occurred at speeds of 1,200-1500 m/min. followed by a drawing stage where the fibers were stretched to three to five times their initial length. Drawing improves fiber properties by increasing orientation, crystallinity, and strength. Higher fiber spinning speeds increase orientation and crystallinity prior to drawing. By 1988, speeds of 6,000 to 8,000 m/min. were achieved which reduced drawing requirements and increased throughput. Considerable work continues to increase fiber production speeds as a means to further improve productivity and reduce costs. Additionally, nylon fibers are spun into packages called cones or bobbins. A considerable amount of research has resulted in an increase in package sizes from 10 kilograms to around 40 kilograms. The progress in high speed spinning has resulted in higher productivity, higher storage stability of filaments, more uniform dyeability, and elimination of the need for a separate stretching operation (as yarn is partially oriented during spinning followed by a finishing step on a draw texturing machine). Fiber spinners can now adjust their processes to produce fibers with varying properties. Consequently, fibers with a broader range of properties are available on the market. Spinning plants are taking advantage of this by producing more of these higher valued products such as fleece, microfibers, and bacteria/odor resistant fibers. Nylon fibers are used in everything from hosiery to parachutes. The tenacity of nylon fibers finds large industrial applications such as conveyor and automotive belts, as well as ballistic nylon for travel luggage.
- 2 - Nylon fibers contain amide groups (CO-NH), that provide hydrogen bonding between polyamide chains resulting in high strength at elevated temperatures in addition to nylon s abrasion resistance, resistance to chemicals, and low coefficient of friction. The chief drawback for nylon in some applications, such as fishing nets, is its ready absorption of water. A bonding agent is coated onto nylon in such cases, though repeated usage can lower the efficiency of the coating. Overview of Nylon Fiber Nylon fiber is defined as a manufactured fiber in which the fiber-forming substance is a long-chain synthetic polyamide in which less than 85 percent of the amide linkages are attached directly to two aromatic rings. Nylon fibers are highly crystalline; crystallinity can be altered and controlled through various processing techniques. The strength of nylon fiber is a result of molecular orientation and crystallinity introduced during fiber spinning or during subsequent drawing, texturizing, and heattreating. It is this non-rigid structure that allows the fibers to be stretched and their properties to be tuned by post-spinning processing. The more crystalline a fiber structure becomes, the less stretchable it will be. Properties of nylon used in fibers are shown in Table 1. Properties of nylon fibers in comparison to polyester fibers are shown in Table 2. Table 1 Nylon Properties Property Nylon 6 Nylon 6,6 Tm ( C) 220 265 Tg ( C) 90 50 Tenacity (g/d) 4.6-8.8 4.6-8.8 Coefficient of Friction (µm) 0.35 0.5 Tensile Stress at Yield (MPa) 76 80 Water absorption (%) 1.9 2.8 Elongation at Break (%) 100-200 80-100 Nylon Fiber Types Essentially all nylon fiber is produced by melt spinning, which involves forcing a polymer melt through a spinneret and into air to cause the polymer to solidify.
- 3 - Table 2 Fiber Characteristics and Properties Property PTT PET Nylon 6 Nylon 6,6 Abrasion resistance Good Good Good Excellent Bulk and loft Excellent Fairly good Fairly good Good Wrinkle and crush resistance Excellent Excellent Fairly good Good Static electricity Low Very high High High Stretch recovery Very good Poor Good Very good Water absorbency Poor Poor Fair Fair Tenacity (strength) (g/denier) 3.15 2.8-6.0 4.6-8.8 4.6-8.8 Loop tenacity (g/denier) - 2-5 6-8 6-8 Degree of fibrillation None None None None Water absorption (% by wt) 24 hours 0.03 0.09 1.9 2.8 14 days 0.15 0.49 9.5 8.9 Flammability Low Low Low Low Elastic recovery (stretch) at 99-100% 75-80% 99-100% 99-100% 5% elongation Melting point ( C) 228 265 220 265 Glass transition temperature 45-65 80 40-87 50-90 (Tg C) Density (g/cm 3 ) 1.33 1.40 1.13 1.14 Source: Shell and trade sources It is important to understand that there are two very distinct forms of nylon fibers. One form is for the nylon fiber to be cut into short pieces, called staple fibers, which are blended with other fibers, such as cotton or cellulosics. These fiber blends are then carded, and spun into thread or yarn in traditional yarn manufacturing techniques. Material that goes into these applications is called nylon staple fiber, and the un-cut precursor fiber is called nylon staple filament (NSF) or nylon staple yarn (NSY). Nylon staple yarn is spun at rates below 2500 meters per minute, and additional orientation is added in subsequent processing. The second form of nylon fibers is as a continuous filament or filament yarn. Following meltspinning, nylon filament is then drawn, texturized (crimped) and used directly as a continuous thread or filament. Another way of categorizing nylon fibers is by the degree of orientation introduced into the fiber during melt spinning. These categories are low, medium or partial, high, and fully oriented fiber. Low oriented polyester fiber is used to make staple products. Of the oriented fiber categories, partially oriented yarn (POY) is by far the most common material in commercial production. POY has gained rapidly in popularity since its introduction in the early 1980s, and now accounts for the
- 4 - majority of the nylon filament category. Highly oriented yarn (HOY) is spun at 4000-6500 meters per minute, whereas fully oriented yarn (FOY) is spun at greater than 6500 meters per minute. Both of these latter categories are still developing, as these spinning rates have proven challenging to achieve in commercial operations. Fiber Spinning Modern textile nylon fiber operations now typically consist of a continuous polymerization train directly feeding one or more spin packs. The resulting fibers can be fully or partially oriented during spinning by varying the spinning speed, depending on subsequent processing requirements. Low and medium oriented yarns have more limited storage stability, whereas partial or highly oriented yarns require higher spinning speeds. Figure 1 shows the relationship between degree of nylon fiber orientation and spinning speed. Figure 1 Nylon Fiber Orientation versus Spinning Speed Residual Draw 1.5 1.4 1.3 1.2 Slow or Conventional Speed spinning Medium Speed spinning High speed spinning 1.1 LOY MOY POY HOY FOY 1000 2000 3000 4000 5000 6000 Spinning Speed (take-up speed), m/min LOY is low orientation yarn; MOY, medium oriented yarn; POY, partially oriented yarn; HOY, highly oriented yarn; and FOY, fully oriented yarn. Source: Journal of Textile Research Q405_00101.0005_4110.ppt An indirect spinning process (re-melting of nylon chip) is employed where a higher viscosity resin is needed than can be produced directly in the melt polymerization process (requiring solid stating of
- 5 - the resin) or where small batches of fiber might be required, making production on a continuous line inefficient. Although most nylon fiber is produced in filament form, some staple is also produced. Staple manufacturing consists of spinning, drawing, crimping, cutting and baling. Nylon staple is used in blends with other natural or synthetic fibers, or even in 100 percent form. Additives can be introduced at several points in the overall process, including salt preparation, polymerization, or just prior to spinning. Delusterants reduce the transparency, increase the whiteness, and change the reflection of light. They are used in most nylon textile and home furnishing applications to reduce fabric sheen. Titanium dioxide is commonly employed for this purpose. Other additives include colorants, antioxidants, antistatic agents, anti-microbial agents, and flame-retardants. However, a number of these additives also interfere with fiber spinning, so they are best added during fabric finishing. Due to its physical and chemical structure (amine endgroups), nylon has an affinity for every dye class. Spinning temperatures range from 280-310 C, whereas spinning pressures can be up to 70 Mpa. The high pressure of the spinning operation necessitates a minimal spinner plate thickness of 10 mm. The number of capillaries in a spinneret can be as many as 500 holes for large disk spinnerettes, and 4,000 holes for rectangular spinnerettes. In practice, fibers are spun in bundles. One spinning machine will have multiple spinning stations. Several yarn ends can be spun, quenched, finished, and wound at each spinning location. As filaments leave the spinnerette, they are narrowed while still in a fluid state by drawing off the filaments at a constant take-up velocity. Quenching conditions can vary considerably from filament to filament in the bundle leading to inconsistent fiber properties across the bundle. Nylon fibers are spun in a number of cross-sectional shapes, ranging from round to irregular solid and even hollow shapes. The cross-sectional shape impacts to functionality and luster of the resulting fabric. Round fibers provide the highest strength and are used in industrial, apparel and upholstery applications. Multi-global cross sections enhance bulk, and find use in carpet and upholstery yarns. Indirect fiber spinning tends to be used in smaller spinning operations producing specialty fibers of varying cross-sections and deniers. Chips are melted in an extruder and metered to the spin pack with a pump. Once the melted nylon passes through the spinneret, downstream fiber handling alternatives are the same for indirect fiber spinning as for direct fiber spinning. Most nylon plants today employ direct spinning due to cost savings opportunities. Since polymer chips no longer need to be produced,
- 6 - dried, or remelted, energy consumption is lower for direct spinning. Consequently, investment capital for buildings and equipment is also lower for direct spinning. In direct fiber spinning, molten nylon from a continuous polymerization unit is pumped by a gear pump directly into the spin pack. In the case of nylon 6,6, this does not represent any particular problems as the polycondensation reaction goes essentially to completion and only a small amount of low molecular weight species are produced. Economics Third quarter 2005 economics were developed for three different cases: USGC economics, designed to illustrate nylon fiber spinning costs in a developed region; China economics using imported equipment, developed to illustrate the case of a nylon fiber producer using imported equipment in a low-cost labor region; China economics using Chinese equipment and technology, illustrating a case of locallyproduced equipment in a low labor cost region. Economics have been developed for all three cases (USGC, China with imported equipment and China with locally made equipment) for both nylon 6 and 6,6. To simplify the analysis, the economics for nylon 6 are for textile filament products, whereas the economics for nylon 6,6 are for industrial filament products. Economics were developed for nylon 6 textile grade chip, nylon 6 textile filament, nylon 6,6 industrial grade chip, and nylon 6,6 industrial filament. In the indirect production of filament (e.g. from chip), the nylon chip was assumed to be purchased (or transferred) at prevailing market prices. Interestingly, a large-scale continuous polymerization facility located in the USGC has a nylon 6 resin production cost plus ROCE that is only 2.5 percent higher than that from the Chinese process illustrating that leading nylon 6 resin producers in developed regions can be competitive with their Chinese counterparts at least on a resin manufacturing cost basis. The disadvantages of batch nylon 6 resin production, on a cost basis, are also evident. Partly for this reason, and partly due to the problems in maintaining consistent product quality inherent in batch processes, new nylon 6 resin lines being built are virtually all continuous processes. The normalized production costs for nylon 6 textile filament are illustrated in Figure 2. Overall, the indirect spinning of nylon 6 textile filament from chip using Chinese equipment has the lowest production cost, due to its lower investment base. However, the production costs from the Chinese process are estimated to be only about one percent lower than the costs from either direct spinning in the USGC, or indirect spinning in China using imported equipment meaning that continuous nylon 6 textile filament production from the melt on a large scale in the USGC or elsewhere, can be competitive with indirect textile filament production in China. For example, it is scale and
- 7 - technological advantage which fiber producers in Taiwan are exploiting as a means of competing against Chinese producers. Figure 2 Cost Comparison of Nylon 6 Textile Filament in Production Costs Filament Unit Cost Nylon 6 Textile Filament - Direct Spinning from Melt Nylon 6 Textile Filament - Indirect Spinning from Chip USGC, 60kta International Equipment China, 20kta Chinese Equipment China, 20kta InternationaI Equipment USGC, 60kta International Equipment Net Raw Materials Costs Utility Costs Direct Fixed Costs Allocated Fixed Costs Depreciation 10% ROCE Related data for nylon 6,6 resin and industrial filament production are provided in the report. Commercial Analysis Nylon has a very high strength-to-weight ratio, which is particularly valued in industrial applications such as tire cord. In industrial applications, nylon fiber competes against polyester and steel. Nylon s stiffness and crush resistance has made it the material of choice in carpet fiber applications, where it competes against polypropylene, and to a lesser extent polyester and natural fibers. While nylon fibers are used in textile applications, nylon fiber is higher cost than polyester fibers, and thus is increasingly being relegated to more specialized textile end-use applications, such as sportswear. On a global basis, an estimated 35 percent of nylon fiber production is for carpet fiber, 35 percent is textile fiber, and the remaining 30 percent industrial fiber. Note, however, that the break-down in nylon fiber production varies widely by region nylon carpet fiber is largely a U.S. and to a lesser extent West European product, with very little produced in all other regions. Conversely, textile
- 8 - fiber production has moved to Asia and Rest of World (ROW), especially from North America. Industrial nylon fiber production is also increasingly centered in Asia. Nylon carpet fiber production is growing at an annual rate of about 0.5 percent per year on a global basis. The trend toward hardwood flooring in North America is dampening growth, as is continued displacement of nylon fiber by polypropylene fiber in commercial applications on a cost basis. Competition with polytrimethylene terephthalate will also hurt nylon carpet fiber production growth rates. On the positive side, Central and Eastern Europe represent an area of above average growth in nylon carpet fiber production, as these countries develop and adopt consumption patterns more typical of Western Europe. Growth of nylon carpet fiber is also occurring in Asia, albeit from a very low base. Textile fiber production is forecast to exhibit global growth of about 1 percent per year, largely due to displacement by polyester fiber on a cost basis. There is also a trend away from casual and sports wear - key textile sub-segments for nylon fiber - which is dampening growth. Industrial fiber applications represent the most promising growth areas for nylon fibers, with global production forecast to increase at about 3.3 percent per year, which is in line with global GDP growth of about 3.2 percent per year. While growth in nylon tire cord production is slowing, this is being offset by rapidly rising production of nylon fibers for air-bags. Estimates for nylon fiber production and capacity by country/region are provided in the report, emphasizing the growing importance of China as a center of nylon fiber production. = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Copyright by Nexant, Inc. 2006. All Rights Reserved. Nexant, Inc. (www.nexant.com) is a leading management consultancy to the global energy, chemical, and related industries. For over 38 years, Nexant s ChemSystems Solutions has helped clients increase business value through assistance in all aspects of business strategy, including business intelligence, project feasibility and implementation, operational improvement, portfolio planning, and growth through M&A activities. Nexant has its main offices in San Francisco (California), White Plains (New York), and London (UK), and satellite offices worldwide. These reports are for the exclusive use of the purchasing company or its subsidiaries, from Nexant, Inc., 44 South Broadway, 5 th Floor, White Plains, New York 10601-4425 U.S.A. For further information about these reports contact Dr. Jeffrey S. Plotkin, Vice President and Global Director, PERP Program, phone: 1-914-609-0315; fax: 1-914-609-0399; e-mail: jplotkin@nexant.com; or Heidi Junker Coleman, phone: 1-914-609-0381, e-mail address: hcoleman@nexant.com, Website: http://www.nexant.com.