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Nonwovens / Technical Textiles

Covering Nonwovens

INTC provided a forum for the presentation of new developments in nonwovens technology.

Richard G. Mansfield, Technical Editor

The nonwovens industry is using a greater diversity of processes and materials to meet the demands of its market segments. This statement is supported by the fact that, at the Nonwovens Technical Conference (INTC) in September - sponsored by the Association of the Nonwoven Fabrics Industry (INDA), Cary, N.C., and the Technical Association for the PulpandPaper Industry (TAPPI) International, Norcross, Ga. - the largest concentration of process technology papers focused on the meltblowing of polymers. Additionally, there were a number of presentations on hydroentangling and spunbonding. Virtually every process in nonwovens - with the exception of stitchbonding - was extensively covered.The abundance of such dissertations on process technologies reveals a number of trends within the industry, such as the growing use of bicomponent fibers. As well, it seems there is a tendency to use a wider range of polymers and technology combinations to develop new nonwoven products. Furthermore, there is much stronger interest in nonwoven research and development by academia, evidenced by the fact that more than one-third of the papers presented at the Baltimore conference were from colleges and universities.The lead-off paper at the conference was prepared and presented by Dr. D.K. Smith, principal, Smith JohnsonandAssociates, Salt Lake City. His review covered U.S. patent activities by company, country and process technology from the years 1996 through 2000. These 403 patents were examined and classified according to the claims and were assigned to a specific nonwoven technology (See Figure 2).

 Meltblowing TechnologyMeltblown nonwovens now play a key role in the nonwovens business, finding use in products ranging from diapers, surgical wraps, protective clothing, filtration and spill-control procedures.Such products and applications have obviously come a long way since Van A. Wente of the Naval Research Laboratory, Washington, first produced meltblown microdenier fibers from organic polymers more than 35 years ago. Meltblowing of polypropylene and other polymers was further advanced by Dr. Robert Buntin and his associates at Esso Research (now Exxon) Laboratories in Baytown, Texas, in the mid-1960s and early 1970s.An important development in the recent history of bicomponent meltblown technology was discussed by John G. McCulloch and John Hagewood, Ph.D., of Hills Inc., West Melbourne, Fla. Hills installed a 20-inch bicomponent meltblowing die, which was incorporated in the pack of the Hills spunbond bicomponent pilot line.To date, Hills has demonstrated the production of the following types of bicomponent meltblown products:meltblown sheath/core 50/50 polyethylene (PE)/polypropylene (PP);meltblown side/side split fibers PE/PP;meltblown side/side trilobal poly(butylene terephthalate) (PBT)/PP;meltblown sheath/core 10/90 PE/PP; andsegmented pie poly(ethylene terephthalate) (PET)/nylon 6.Product possibilities for bicomponent meltblown nonwovens include:respirators;heat and moisture exchangers for medical uses;improved filtration media;formation of filter and wicking rods by in-line pellets to rods process;radiation-resistant medical fabrics;artificial leather starting materials;cylindrical filter elements; andnanofibers.In further meltblown developments, the Textiles and Nonwovens Development Center (TANDEC) at the University of Tennessee (UT), Knoxville, Tenn., is playing an increasingly important role in research and development for meltblowing processing and the development of meltblown products. In its research, TANDEC took a look at multi-hole meltblowing lines operating at commercial speeds. According to Randall Bresee, Ph.D., a UT professor, measurements were obtained on-line at various locations between the die and collector, as well as off-line from webs. On-line measurements include fiber speed, fiber acceleration, fiber diameter, fiber temperature and air speed. Off-line measurements include birefringence, fiber entanglement, fiber orientation and differential scanning calorimetry. These experimental measurements provide a basis for gaining a greater understanding of the meltblowing process.Furthermore, TANDEC, in combination with the Ian Carson Shell Coordination Centre S.A. and Shell Chemical Co., Houston, presented an overview of the development and characterization of poly(trimethylene terephthalate) (PTT)-based bicomponent meltblown nonwovens. In this study, PTT-based monocomponent (mono) and bicomponent (bico) webs were produced on Germany-based Reifenhers Reicofil® bicomponent meltblown line at TANDEC. Thermal and flow properties of PTT were first examined using differential scanning calorimetry and melt indexer for an effective experimental design through the Surface Response Methodology (SRM). The processability of meltblown in a wide range of operating temperatures was investigated.Melt temperature, melt throughput, air temperature, air-flow rate and distance of collector to die (DCD) were considered as primary process-control variables. The webs produced, both mono and bico, with polypropylene were characterized for fiber diameter, bulk density, air permeability, hydrostatic head, tensile properties and heat shrinkage.Non-round and curly or twisted fibers were observed in the bico PP/PTT webs by a scanning electron microscope. It was found that the PTT grade studied is quite suitable for the meltblown process. The PTT/PP-based bico webs showed enhanced barrier properties and heat resistance.TANDEC also presented, along with the Natick Soldier Center, Natick, Mass., a study on the process properties of meltblowing polyurethane for military protective apparel garments. The objective of this work was to develop materials that are stretchable, conformable and breathable; and have the required barrier protection against biological and chemical agents. The method chosen to achieve these properties was by meltblowing thermoplastic urethane (Noveon Estane® 58227) on the 6-inch meltblowing line at TANDEC.Three promising processing conditions that were evaluated produced air and water vapor transport properties that were comparable to those of Gore-Tex® breathable materials.Spunbound Technology
Spunbond technology is now being practiced throughout the world, thanks to the availability of turnkey processing units. Polypropylene is still the major polymer used for spunbonded fabrics, but a wider range of polymers is now being used for the development of specialty products. Bico fiber technology is now being utilized for both spunbonded and meltblown nonwovens.The focus has been on spinnable resins, according to Hans GeorgGeus, research and development manager, Reifenher GmbHandCo. The characteristics of these fiber grades are relatively low viscosity, significantly high melt stability, excellent purity and homogeneity, as well as a narrow molecular weight distribution.Use of polyolefins, polyamides and polyesters has become common in the industry. Within this range of resins, there is the potential to use variations such as copolymers, terpolymers and blends with materials such as polyolefins and oligomeric materials. Some of the required properties in combining resinous materials can be found in Figure 3.The shear viscosity and an elongational viscosity at the given temperature are the most important properties. Other important items are: the degree of thermal stabilization; the degree of solubility in the second polymer; crystallization and crystallization speed; and, last but not least, the MFR of the various polymers.The melt temperature for each polymer can be set differently, until the polymers are fed into the bico system. Then the two materials are jointly passed through only one temperature. In practice, this is not a limitation, because the difference between the two set temperatures cannot continue to be very large, as the temperature of the two polymers will equalize to some degree. The two major types of processes for making spunbonds are the open systems and the closed systems (See Figure 4). The most commonly used closed system is the Reicofil III System.
 Bico NonwovensBico products from filament lines are usually produced from side/side, core/sheath or segmented pie filaments. The different cross sections of these filaments determine fabric properties. In addition to these properties, the filament shape and cross section need to be considered. Spunlaced NonwovensThe production of spunlaced nonwovens has practically doubled between 1995 and 2000, and quadrupled between 1985 and 2000, according to Alfred Watzl of Germany-based Fleissner GmbHandCo. Spunlace enjoys the highest growth rate of any nonwoven (See Figure 5).Some spunlaced products can be used directly after they are hydroentangled and dried, but many fabrics can be enhanced by further processing. Additional processing that can be applied to spunlaced fabrics includes: impregnation with chemical binders; finishing with chemicals; dyeing or printing; and thermofusion or heat-setting.An example of a spunlaced line with fiber opening, blending and two cards is shown in Figure 1. Such a production line can be further enhanced by adding additional processing lines in-line. Fleissner can supply all of the major components of a spunlaced line, from hydroentangling through dyeing and finishing.Watzl further discussed bonding and finishing with chemical binders and chemicals. Chemical binding comprises at least two steps: first, the binder is applied; then, the bonding process is triggered by a thermal treatment. Maximum strength in a nonwoven is achieved when all fiber-crossing points are bonded in a point-shaped form fit. A wide range of additives can be incorporated in the binder systems, including thickeners, softeners, colorants and flame-retardant (FR) agents.A range of application methods for applying binders, colorants or other finishing agents includes foaming, spraying and various wet-application techniques. Special techniques such as print bonding are also employed. In hot-air bonding, spunlaced nonwovens with increased strength and pilling resistance can be made by incorporating bico fibers in the blend and thermofusing the lower-melting fiber component by hot air in single- or multi-drum dryers. This method of bonding nonwovens eliminates the buildup of binders in the unit, a common occurrence when using chemical binders.Heat-setting can be done in a hot-air drum dryer when improved fabric dimensional stability is required. Heat-setting is important when processing polyester fabrics for some applications, such as coating.
 Combining Nonwoven TechnologiesFrance-based Rieter Perfojet is the only nonwoven machinery producer that makes equipment both for spunlaced and spunbonded nonwovens, according to Daniel Feroe, area sales manager, and Frederic Noelle, research and development manager. The two Reiter Perfojet executives discussed how spunlace and spunbond technology can be combined to make an improved wiping fabric.Rieter Perfojet, in its Jetlace® 3000 machine, has raised the efficiency of hydroentanglement technology by improved design of the internal chambers within the injector body. The design of the new 400-bar injector allows for a uniform and turbulence-free flow of water within the injector body, enabling a more efficient water jet created by the flow of water through the injector strip.  Editors Note: The complete set of papers presented at the INTC 2001 conference can be obtained from INTC 2001, INDA/TAPPI, P.O. Box 1288, Cary, N.C. 27512-1228. Copies of the papers are available in written form or on CD-ROM.

  December 2001