A Technical Case Study
United States Department of Energy
Office of Industrial Technologies
This technical case study was written for the U.S. Department of Energy by Energetics, Incorporated, Columbia, Maryland, under DOE Contract No. DE-AC01-87CE40762. Project-related information, including field test data, was supplied by the Georgia Institute of Technology's School of Textile and Fiber Engineering.
This report was prepared as an account of work sponsored by an agency of the United States government. Neither the United States government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply it endorsement, recommendation, or favoring by the United States government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States government or any agency thereof.
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Office of Industrial Technologies
Assistant Secretary for Energy Efficiency and Renewable Energy
U.S. Department of Energy
|Project Development and Status||6|
|For More Information||16|
The U.S. Department of Energy's (DOE's) Office of Industrial Technologies (OIT) sponsors research and development (R&D) to improve the energy efficiency of American industry and to provide for fuel flexibility. Working closely with industry, OIT has successfully developed more than 50 new technologies that saved industry approximately 80 trillion Btu of energy in 1992. More than 200 other projects are in various stages of development from laboratory research to field tests.
OIT's Improved Energy Productivity Program targets the energy-intensive textile industry (among others), which consumes approximately 250 trillion Btu of energy each year, equivalent to about 43 million barrels of oil. Sixty percent of this energy is spent on wet processes. These processes use water or other solvents to apply chemicals to the textile substrate and are followed by energy-intensive drying. By substituting dry processes that don't use water, the industry could save a substantial amount of energy.
To take advantage of this opportunity, OIT has sponsored a cost-shared, multiyear project with Georgia Institute of Technology's (Georgia Tech's) School of Textile and Fiber Engineering to investigate the use of solid-on-solid (SOS) processing in the production of textiles. With SOS processing, chemicals are applied directly to the textile substrate without using water or other solvents, thus eliminating the need for energy-intensive drying. SOS technologies, which are already being used in other industries (e.g., metals), can be applied to many textile production processes.
The Georgia Tech researchers conducted bench- and pilot-scale experiments using SOS technologies that were adapted for textile production lines. They investigated several applications for SOS techniques: textile xerographic printing, chemical binding and fluoropolymer finishing of nonwovens, yarn slashing, and liquid-spray coloration and finishing of textiles. All of these applications were demonstrated at the pilot scale, and yarn slashing, chemical binding, and fluoropolymer finishing were tested in full-scale, proof-of-concept trials at Nordson Corporation, West Point-Pepperell, Inc., and Electrostatic Technologies, Inc. industrial sites. The fabrics produced by the SOS processes in these trials compared well with fabrics produced by conventional wet processes. Researchers identified areas requiring further research before the development of full-scale SOS processes.
An evaluation of the energy used by conventional wet processing versus the SOS processing techniques developed by Georgia Tech showed that SOS processing reduced process energy use by approximately 90% and could save an estimated 43.4 trillion Btu/yr in the textile industry.
This technical case study describes the work conducted int eh DOE/Georgia Tech project and highlights the proof-of-concept testing of three SOS concepts. The document seeks to make the results of this project available to other researchers and private industries, particularly those interested in commercial uses of this technology. The report discusses the R&D efforts, project status, and potential impacts of this technology on the textile industry.
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Many textile manufacturing operations such as yarn slashing, dyeing, printing, and finishing of fabrics use wet processing techniques. These techniques involve using an aqueous solution or bath to apply chemicals to a textile substrate, fixing the chemicals to the fiber, scouring or washing to remove loose chemical,s and drying to produce a finished fabric or garment. Heating and later evaporating water make these wet processes very energy intensive. Industry experts estimate that wet processes use approximately 60% of the energy consumed in the textile industry.
In addition, shrinking water supplies and increased competition from residential and other industrial users in many parts of the country have prompted textile manufacturers to develop methods that reduce water and energy consumption.
These conservation methods reduce the number of washings and dryings between processes and shorten the duration of those retained, lower process temperatures, and use solvents that dry more quickly. Several R&D efforts, including some funded by DOE, have produced novel energy-conserving processes such as foam processing, beck dyeing modifications, dye bath reuse, Mach nozzle fabric drying, closed-cycle textile dyeing, ink and film applications, and air/vacuum extraction. Although many of these new processes have been extremely successful in reducing energy consumption either by reducing the amount of water used or by substituting solvents or air, all still require some liquids. Theoretically, the most energy-efficient processing methods will use waterless SOS techniques, which completely eliminate the energy-intensive drying step.
SOS processes use no extraneous liquids to apply chemicals containing a thermoplastic component are deposited on the substrate through electrostatic attraction, then fixed to the substrate by heat. Thus, SOS technology goes a step beyond the so-called low-wet-pickup systems (such as foam, film, or ink applications), which still require water or solvent. The SOS approach is widely used in the metals industry for electrostatic painting of electrified automobile body components, coating of wires and cables, and printing of aluminum cans. In these processes, resins and colorants are bound together and to the metals during thermal curing.
SOS processing offers several advantages to the textile industry.
In addition to saving energy and reducing water consumption, SOS processes can eliminate the need for steam generation, eliminate effluents, and decrease dwell times in the curing oven, thus increasing process speeds. These changes, which can increase productivity and reduce costs, can improve the competitive position of the U.S. textile industry.
In a cost-shared, multiyear project supported by DOE, Georgia Tech's School of Textile and Fiber Engineering investigated three SOS technologies from which it developed six processes applicable to the textile industry.
Two existing SOS methods are directly applicable to powder deposition on textiles: electrostatic fluidized bed systems (suitable for yarn slashing) and electrostatic powder spraygun deposition (suitable for finishing and binding). In the fluidized bed system (see Figure 1), dry air is charged, passed through a porous plate, then passed through a bed of dry powder where the charge is transferred to the powder particles. the substrate is then passed through the charged powder bed, and the particles attach to the fiber surface of the fabric. In the electrostatic spraygun process (see Figure 2), dry powder from a fluidized bed is force-fed by dry air into a spraygun. As powder particles exit the gun, they pass through a corona field generated by a charged electrode. Powder particles are thus charged and deposited onto a moving fabric, sticking to its surface. The spraygun also can be used for non-electrostatic powder deposition when the corona electrode is not charged. After powder is deposited by either of these two methods, it is melted to form a film, or sheath, of chemical around the fibers of the fabric.
Figure 1. Schematic of electrostatic fluidized bed (refer to source document)
High voltage DC negative power supply
Low velocity cloud of charged particles
Grounded substrate at room temperature
Figure 2. Construction of electrostatic powder coating spray gun (refer to source document)
Power supply tube
High tension cable
Pattern control air
Current limiting resistor
The third technology is modified xerographic printing of textiles. The basic steps of xerography are shown in Figure 3. First, the surface of a metal that is electrically grounded is coated with a layer of photoconductor (PC). The PC is then charged and a latent, or negative, electrostatic image is produced by exposing regions of the PC to light. The image is developed by cascading toner (powdered pigment plus binder) mixed with a carrier across the PC. Because the electrostatic attraction between the toner powder and the charged PC areas is greater than the attraction between the toner and the carrier, the toner is transferred to the charged areas of the PC and a positive print image is obtained. This image is then transferred to the printing substrate, and the toner is fixed to the substrate by a thermal melt/flow process. After fixation, the surface of the PC is cleaned and the process is repeated.
Figure 3. Basic steps in xerography (refer to source document)
From these three technologies, Georgia Tech developed six SOS processes for the textile industry:
Three of the SOS textile processes were demonstrated in proof-of-concept trials and three other were tested at the pilot scale. Two of these pilot technologies are ready for process scaleup.
The remainder of this report summarizes the development of these SOS processes and their potential impacts on the textile industry.
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Research on SOS processing took place at Georgia Tech from August 1984 to July 1989. First, researchers identified powder-based processes used in other industries that were amenable to continuous textile manufacturing lines. They focuses on SOS-processing alternatives to energy-intensive, water-based textile processes such as printing, dyeing, and finishing. Many resins and binders were screened to develop suitable systems for each of the SOS processes. Researchers compared the adhesive, mechanical, and durability properties of the resins and binders against those of resins used in analogous conventional wet processing operations.
This section briefly describes the bench- and pilot-scale experiments in each SOS research area. The next section summarizes proof-of-concept trials of three of the SOS processes. Further details are provided in a final report prepared for DOE by Georgia Tech.
Xerographic printing on fabric differs from printing on paper. Xerographic paper printing systems usually print individual narrow (normally 8.5 in.) sheets in sequence. Fabric printing systems need to print much wider widths and operate continuously. And the binder component of toners (normally styrene/acrylate copolymers) used for printing on paper adheres poorly to textile fibers.
Initial trials were performed on polyester/cotton sheeting using toner and carrier systems typical of paper xerography. These trials produced successful prints, but the prints did not meet the requirements of the American Association of Textile Chemists and Colorists (AATCC) for wet/dry crockfastness because of the binder components of the toner. Therefore, researchers screened several new commercial resins to develop powderable, thermoplastic binders suitable for textile xerography. They then analyzed each binder with various carriers to produce a viable toner system. The candidate toner systems used red and blue Kativo, which are modified epoxy resins produced by H.B. Fuller Co.
Subsequent printing trials were done on a Xerox Model 3100 copier, modified for continuous printing on 8.5-in.-wide sheeting fabric using the Kativo toners. The printed samples were heat treated in a 15-degree C oven and tested for wet/dry crockfastness and colorfastness in accordance with AATCC standards. Because these prints tested well, the process was scaled up for continuous, three-color, pilot-scale printing of 36-in.-wide fabric.
For these pilot-scale experiments, three modified Xerox Model 2510 copiers image loop that passed through all the copiers. The toners used in these experiments were red-, green-, and blue-pigmented Kativo resins and U.S. Industries' FE-532 polyethylene-co-vinyl acetate resin tinted with blue dispersion dye. The single-color prints obtained in trials with the tinted FE-532 toner were used only to assess the tactile properties of the fabric, since no adequate procedure was defined for incorporating pigment into the resin. The Kativo toners produced medium-depth shade prints with good fastness (see Table 1), but with greater stiffness than the unprinted fabric. The FE-532 toner outperformed the Kativo toners xerographically and produced prints wither a superior aesthetic quality. Further research is required to develop a pigmentation process for the FE-532 resin and to allow printing of darker shades with both toners.
Table 1. Fastness of Prints Produced with Kativo Toner (refer to source document)
Liquid Spray Coloration
For this coloration process, researchers screened several low-weight, oligomeric resins for ultraviolet (UV)-curable functional groups and film formation that met textile binder requirements. Candidate resins were used to form a resin system (a mixture of an oligomeric resin, a monomer diluent, and a photoinitiator) for an electrostatic liquid spraygun system obtained from Nordson Corporation. The solid-shade formulation used int he spraygun trials was composed of 70% Photoglaze U083 oligomer, 30% RC-20 monomer diluent, 1% Irgacure photoinitiator, and phthalocyanine green pigment.
Pilot-scale trials were conducted on the Nordson unit using 50/50 polyester/cotton sheeting fabric and a 22% solids-pick-up (SPU) level. Several samples of the treated fabric were predried in a convection oven at 150 degrees C for 1.5 min, and all samples were cured in an Argus International UV Processor. The cured samples were conditioned at the standards 21-degree C and 65% relative humidity. Fabric viewed under a microscope showed good solid-shade coloration. However, several properties of the treated samples rated lower than desired on AATCC colorfastness tests, indicating incomplete curing (see Table 2). The short predrying step appeared to help wick the formulation throughout the fabric, but more research is required to verify this observation. Additional investigations also are needed to optimize pigment loading, photo-initiator concentration, SPU level, UV exposure time required for complete resin curing, and combined thermal and UV curing to improve the colorfastness of the treated fabrics.
Table 2. Fastness of Fabrics Colored by SOS Process (refer to source document)
Liquid Spray Finishing
Researchers developing the liquid spray finishing process focused on reactive silicone finishes and permanent press (durable press) finishes.
The prime candidates for silicone finishing of fabrics, selected after screening of many silicones, were Ucarsil Magnasoft aminofunctional and Ucarsil T-29 epoxyfunctional reactive silicone softeners manufactured by Union Carbide Company. Samples of 50/50 polyester/cotton fabric were treated in the Nordson liquid spraygun unit; cured for 3 min in a convection oven at temperatures of 170 degrees, 180 degrees, and 190 degrees C; and conditioned at 21 degrees C and 65% relative humidity for 24 hours. Several of the samples were then repeatedly home laundered. Both washed and unwashed sample yielded good ratings on pilling tests, and the treated fabrics showed a significantly better feel than the unfinished fabric. The Magnasoft silicone performed slightly better than the T-29 silicone.
The key to an SOS durable-press finishing process was developing resins that would duplicate both the durable press and thermal responsive properties of the Polytherm wet process (developed at the Southern Regional Research Center [SRRC] of the U.S. Department of Agriculture). Researchers devised a resin mixture of methylated dimethyoldihydroxyethylene urea, polyethylene glycol (PEG), and, for curing the finish, the standard magnesium chloride/citric acid dehydration catalyst. This mixture was applied to 50/50 polyester/cotton fabric in the Nordson unit and cured in a 165-degree C convection oven for 3 min. After several treated fabric samples were laundered according to AATCC specifications, both washed and unwashed samples were tested for wrinkle recovery.
The SOS treatment greatly enhanced wrinkle recovery; recovery was comparable to that of fabric finished by the conventional wet pad-nip-cure process or by the SRRC Polytherm process (see Table 3). SOS-treated fabrics tested acceptably well in permanent press, strength, and stiffness. However, the thermal responsiveness of the resin formulation was poorer than that used by the SRRC process because of the low molecular length of the PEG used in the SOS process. Further development is required to identify polyglycols that can be sprayed and that have molecules long enough to improve thermal responsiveness.
Table 3. Wrinkle Recovery Angle Test Comparison for SOS, SRRC, and Plant Finished Fabrics (refer to source document)
Eastman's FA-252 modified polyester resin and H.B. Fuller's IF=3237 modified epoxy resin survived the screening for resin binders. Carefully controlled, multi-variable pilot experiments conducted at Georgia Tech used a 20-in. Nordson spraygun system without electrostatics. Polyester nonwoven fabrics were run through the system at a speed of 100 ft/min and at various SPU levels; they were then cured in a batch oven. Researchers found that particles <75 microns in diameter were optimum for applying the resins to the fabric. The FA-252 resin gave better results in mechanical property tests on nonwoven fabrics, but the IF-3237 resin flowed better. Both resins imparted machine-directional (MD) properties to the fabric that were comparable to those of the conventionally bound (control) fabric, and cross-machine-directional (CD) properties were twice as good. Fabrics treated with FA-252 resin at an 8% SPU level gave pilling test results equivalent to those of the control fabric; they were also softer than the control.
In preparation for proof-of-concept trials, the fabric was again run through the spray system to assess process reproducibility and the effects of using a slotted- or hinged-door batch oven for curing the treated fabric (see Table 4). The type of oven produced no variation in the final properties of the treated fabric. However, an unexpected advantage of SOS binding was revealed. Original weak points in the untreated nonwoven fabric, apparently accentuated by the liquids and stresses used in wet processing, produced vastly weaker regions in the final treated fabric. Presumably because dry fabric is under much less tension than wet fabric, any weak sections are not further weakened and the final mechanical performance of SOS-treated fabric is improved. Following these tests, the research advanced to the proof-of-concept stage.
Table 4. Repeat of Optimized Binding Trials with the FA-252 Resin (refer to source document)
Preliminary screening identified 3M Company's FC-214 fluoropolymer (FP) as the best possible FP for the finishing process. This FP was grindable to a medium-fine (75 micron), free-flowing powder that produced a clear, colorless film with good fastness to drycleaning and light. Continuous optimization trials were conducted at Georgia Tech on the 20-in. Nordson spraygun without electrostatics. These trials used FC-214 FP that was both cryogenically and air-mill ground. An optimized SPU level of 2% was obtained, which was in the 1.7% loading range required for the proof-of-concept industrial process. The standard 3M Kit Test for surface oil repellency was used to determine the effectiveness of the FP barrier. The treated fabric repelled oil and solvent well but did not repel 90% isopropanol (see Table 5). Scanning electron microscopy of the fabric surface revealed that the resin flowed well and formed a smooth film after a 3-min cure at 160 degrees C. At this point, preparations were made to start the proof-of-concept trials.
Table 5. Oil and Alcohol Drop Tests of Fabrics Treated with FC-214 Fluoropolymer (refer to source document)
In this process, sizes (the resins used in the slashing process) are applied to warp yarns to bind their fibers together and to increase their resistance to abrasion during weaving. Researchers used an electrostatic fluidized bed system obtained from Electrostatic Technologies, Inc. (ETI) to apply candidate sizes to 50/50 polyester/cotton ring-spun yarn in a continuous process. They evaluated melt blends of ground sizes to which various organic acids (adipic, sebacic, etc.) were added at various line speeds and SPU levels. The treated fabrics were cured at various oven temperatures. Several optimization runs were performed using the primary size candidate, melt-blended 60/40 Eastman WD/adipic acid (60/40 WD/AA). The yarns produced were similar to commercially slashed yarn in degree of hairiness but not in abrasion resistance. Preliminary dual-yarn runs on the ETI system showed that the size was loaded unevenly across the width of the fluidized bed.
A pilot-scale system, consisting of a 5-in. square ETI fluidized bed, which could slash up to 10 yarn ends, was designed and constructed at Georgia Tech. Five yarns that were strung and treated with 60/40 WD/AA by this system still showed uneven SPU distribution. At this point, researchers discovered that the plant that provided yarns for the trials was switching from ring-spun yarn to air jet-spun yarn production.l Therefore, they redirected research to SOS slashing of air jet-spun yarns, which have an internal structure, mechanical properties, and abrasion resistance that are very different from ring-spun yarns. To redefine the optimum settings for the process, several 10-end warp runs were made on the slashing line using the new yarn and a larger 12-in. x 14-in. fluidized bed (see Table 6). A new 65/35 WD/AA size in a fine (<75 micron) powder was chosen as the optimum size formulation for use with the air jet-spun yarns. The research than advanced to the proof-of-concept stage.
Table 6. Ruti Webtester Results and Mechanical Properties of Yarn Used in Optimized 10-end Trial
|End number||SPU (%)||Breaking load (g)||Elongation (%)||Ruti test (cycles)|
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SOS chemical binding, fluoropolymer finishing, and yarn slashing were advanced to proof-of-concept trials at industrial sites. These trials and their results are described briefly below.
The proof-of-concept trials for SOS chemical binding and fluoropolymer finishing were conducted in a spray booth system at Nordson Corporation's Research laboratories in Amherst, Ohio. A schematic diagram of the Nordson application line, which simulates full-width textile processes, is shown in Figure 4. A 60-in. width of fabric mounted on a 5-ft x 7-ft wooden frame is propelled through the spray booth at up to 200 yards per minute (ypm). Two sprayguns, each with a 30-in.-diameter application range, cover the full area of fabric. An infrared (IR) oven cures the fabric after slowing down the carrier in the dead zone. The fabric is passed through the IR oven twice, having been rotated 180 degrees before the second entrance to obtain a reasonably uniform cure.
Figure 4. Schematic of Nordson textile powder application line (refer to source document)
The proof-of-concept SOS binding trials were performed on a polyester nonwoven fabric similar to that used in the pilot trials at Georgia Tech. The trials used line speeds of 150 and 200 ypm, one-spraygun and two-spraygun arrangements, and three SPU loadings--light, medium, and heavy. The process used medium-fine (75 microns) and fine (<20 microns) grades of the FA-252 and IF-3237 resins. The treated fabrics were cured for 24 s at 195 degrees C. Researchers then compared the mechanical and pilling properties of the treated fabrics. Optimum results were obtained using the fine powders with two sprayguns. The fine-grade FA-252 resin bound nonwoven fabric as well as did conventional processes; mechanical properties of this fabric were superior to those of fabric treated with the larger grade. The IF-3237 resin yielded excellent flow characteristics but imparted inferior mechanical properties to the fabric compared to the FA-252 resin. Figure 5 shows the mechanical properties of the FA-252-bound fabric. The feel of the SOS-treated fabrics was superior to that of the conventionally bound fabric.
These trials demonstrated the successful binding of a nonwoven fabric at line speeds up to 200 ypm, and researchers postulate that even higher speeds could be accommodated.
Figure 5. Comparison of mechanical properties of treated fabric at low and medium SPUs (fine grade FA-252 resin) (consult source document)
Finishing runs were conducted using 3M's FC-214 fluoropolymer in a fine powder (<75 microns) on a 100% polypropylene nonwoven fabric. The Nordson two-spraygun system was used with line speeds of 150 and 200 ypm, SPU levels in the 1% to 2.5% range, and oven curing for 2-4 min at 160 degrees C.
Initial runs revealed three critical factors in the finishing process:
These proof-of-concept trials demonstrated for the first time that a finishing process which combines powder deposition and melt curing can impart superior barrier properties to a polypropylene nonwoven substrate. A mechanism to push powder into depressions at the thermally bonded points in the nonwoven fabric enabled a thorough film flow, which improved the barrier properties. Future systems built around an air knife or vacuum slot for this purpose, combined with more sophisticated processes, should enable the continuous finishing of nonwoven fabrics at even higher linear speeds.
Table 7. Drop Test Results for Fabrics Finished Using FC-214EP SOS Process (refer to source document)
Proof-of-concept SOS yarn slashing trials were conducted at West Point-Pepperell's (WPP) Research Center in Shawmut, Alabama. Researchers used a 60-end warp slashing line modified with the 12-in. x 14-in. ETI fluidized bed. A flow diagram of the WPP line is shown in Figure 6. Slashing runs used 50/50 polyester/cotton air jet-spun yarns and line speeds of 5 to 8 ypm, with the hope of increasing the speeds as long as SPU levels of 15% were maintainable. The yarns were then cured in a 200-degree C oven. Thirty-five section beams of slashed yarns were obtained during a two-week, round-the-clock operation. To standardize the procedure, additional powder was added manually when the level dropped to a specified line in the fluidized bed.
Figure 6. West Point-Pepperell solid-on-solid slashing process (refer to source document)
20" section beam (60 ends)
15" comb 10 dents/in.
Oven and rolls
15" comb 10 dents/in.
8" steam can area
Optional 15" comb 30 dents/in.
1/2" section beam
Acceptable SPU levels were obtained only at speeds less than 10 ypm, a limitation of the ETI system. SPU evaluations of two of the beams showed an improved cross-bed uniformity compared to the pilot runs conducted at Georgia Tech. SPU levels fluctuated widely throughout the beam diameter. This fluctuation was linked to the manual addition of powder which caused a critical loss of uniformity in yarn quality. As anticipated, the mechanical and abrasion properties of the SOS-slashed yarns were lower than those of the conventionally slashed yarn (see Table 8). The degree of hairiness, however, was quite comparable to that of the conventional yarn, and the SOS yarns possessed a lower population of frays that were 1.0 mm or more in length.
Table 8. Mechanical Properties of Griege (A), SOS-Slashed (B), and Conventionally Combed (C) Yarns (refer to source document)
Some tackiness of the 65/35 WD/AA size used for the trials caused the slashed yarns to stick together on the beams. This problem was overcome by using an aluminum beater-paddle mechanism that consolidated the remaining beams to produce a single 20-in.-wide section beam containing 1800 ends. This yarn was then merged with conventionally slashed yarn (colored blue for differentiation) on a 3600-end loom so the weaving performance of the yarns could be compared head-to-head. The weaving trial was performed on a Sulzer TW-11 Projectile Weaving Machine at Georgia Tech. A preliminary weaving run was conducted with yarn slashed in the commercial process line at WPP's Lanier Plant. A total of 1.996 million picks were used and only 452 loom stops recorded. In a weaving trial, the combined SOS- and conventionally slashed yarns broke more often than the plant-slashed yarns. Because the SOS-slashed yarns performed poorly, the trials were terminated after 114,000 picks.
This proof-of-concept test demonstrated the feasibility of slashing 50/50 polyester/cotton air jet-spun yarns using an SOS size formulation. The 65/35 WD/AA size, however, did not allow the treated yarns to withstand the tension and abrasion forces of weaving operations. The composition of the size as well as the speed of the slashing process must be improved before full-scale processes can be developed.
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This DOE project sought to determine whether energy-efficient SOS technology could be a suitable alternative to conventional wet processing of textiles. Proof-of-concept tests demonstrated that SOS processes may be suitable for use in textile binding, finishing, and yarn slashing. These processes have the potential to reduce the use of water and energy and to increase process speeds.
In general, any textile process involving applying a chemical that produces a film on fiber surfaces ("interfiber finishes") is a candidate for SOS technology. The electrostatic liquid spray approach uses oligomeric resins that require no solvent and thereby results in 100% solid deposition on the textile after film cure. This approach opens the possibility for both intrafiber finishing (e.g., permanent press resins) and solid shade coloration. Therefore, SOS technology is potentially applicable to the entire area of wet processing. Moreover, SOS processes may be able to increase process speeds because textile drying is eliminated.
Because the textile industry has moved toward shorter process runs and just-in-time delivery, the ability to change styles and colors frequently is important. SOS processing may shorten changeover times and enable the industry to respond quickly and efficiently to new trends in the marketplace. For example, current screen printing is slow and expensive, and color and pattern changes require long process times. Xerographic printing, which allows for the electronic storage of design information, can potentially permit frequent style and color changes with minimum downtime for changeover.
The SOS systems developed in this project require sufficient energy only for the treated fabric to reach its curing temperature. This energy requirement is less than that for drying textiles produced in wet processing. As part of the DOE project, Georgia Tech assessed the energy benefits of using SOS technology in textile production. Although commercial processes vary widely, a general comparison was possible between the newly developed SOS processes and conventional water-based processes (see Table 9). The SOS process reduced the process energy required by about 90%, a potential energy savings of 4075 Btu/lb of processed textiles.
Table 9. Comparison of Energy Consumption in Conventional Wet and SOS Chemical Processes (refer to source document)
These savings constitute direct reductions in process energy. Considerable indirect energy savings are also inherent in the SOS technology. For example, SOS processes eliminate the need to purify feed water or treat effluents. The SOS processes developed under this project could potentially save the textile industry 43.4 trillion Btu/yr (see Table 10). This projected energy savings is conservative, since it does not include the replacement of other wet processes by SOS techniques similar to the ones successfully developed in this project. For example, fabrics may be stiffened through interfiber finishing using the Nordson spraygun SOS technique.
Table 10. Energy Conservation Potential of SOS Processes (refer to source document)
The Georgia Institute of Technology investigators now need to resolve questions that arose in the course of the research describe here. They plan to continue research into materials and computer-aided design for textile xerography (to develop prototype machines) and to continue to develop proof-of-concept tests using SOS liquid spraygun processes.
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For additional information on the SOS processing technology for textiles describe in this document, consult the following publications:
Mr. Brian Volintine
Office of Industrial Technologies, EE-232
U.S. Department of Energy
1000 Independence Ave., SW
Washington, DC 20585
Dr. Fred L. Cook
School of Textile & Fiber Engineering
Georgia Institute of Technology
Atlanta, GA 30332
Produced by the National Renewable Energy Laboratory (NREL)
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Written by Energetics, Inc.
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Last Updated: November 15, 1995