Fundamentally, to get clothes clean, four factors in proper combination are necessary: Time, Temperature, Agitation, and Chemistry.
For example, in a typical washing machine, loose clothing is batched into a wash-wheel where various amounts of water and detergent (chemistry) are added for various amounts of time and at various temperatures. Simultaneously, the clothing is mechanically agitated by the machine's agitator and/or the rotation and oscillation of the machine's drum which act in concert with the resulting force and action of the water.
After washing, the machine rinses and centrifugally "dewaters" or extracts; the loose clothing is then batched into a tumbler for drying. In the dry-cleaning process, solvents are substituted for the water. Other than that, however, both laundry and dry cleaning processes employ the same four factors of cleaning in very similar manners. Both need time, temperature, agitation, and chemistry in proper amounts; and in both cases, a wash-wheel mechanically agitates loose, free-floating fabric.
Garment Care proposes that the traditional batch or wash-wheel process be re-configured into an in-line, continuous-flow process. More specifically, they propose that containerized and/or constrained clothing and linens be conveyed from start to finish‹from the initial staging area, through a water-based wash trough, rinse section, drying chamber and into a packaging area.
This new configuration involves three principle areas of change:
Focus on Agitation
With fabric no longer loose in a wash-wheel but conveyed through a wash trough, systemic change is needed to properly integrate the four scientific factors of cleaning.
Analogous to the age-old image of a person standing in the river beating clothes against a rock, the Team believes agitation is the most critical factor to the reintegration task. Because constrained and/or containerized garments should safely allow a high degree of agitation, and because increased agitation should mathematically equate to a decrease in one or more of the other factors, the Team believes a strong external agitation force is necessary.
Several alternative means of creating this force may be possible, but one of the most intriguing‹and the one specific to this Phase One research‹is ultrasonic agitation.
Specific to the funding limitations in this initial Phase One research, the goal of the Garment Care and Kansas City Plant Team is to determine if agitation for an in-line, continuous-flow clothes washing process can be provided by ultrasound.
In general, ultrasonic cleaning consists of immersing a substrate in a suitable liquid medium, agitating that medium with high frequency (18 kHz to 120 kHz) sound for a brief period of time (usually a few minutes), rinsing with clean solvent or water, and drying. Ultrasonic cleaning is effective due to cavitation. Cavitation is the process in which microscopic bubbles in the liquid medium implode or collapse to produce shock waves. These waves impinge on the surface of the substrate and, through a scrubbing action, displace or loosen particulate matter from the surface.
For a more in-depth review of ultrasonic theory, please see the article by Maurice O'Donoghue.
This research was broken into multiple steps which are detailed as follows.
A design for a test aqueous cleaning tank was selected and sketched. The tank's dimensions were chosen to allow cleaning of a vertically oriented, adult-sized shirt held tightly on a fixture. It was believed that this orientation would allow heavier particulate contaminants to drop to the bottom of the tank, minimizing redeposition of soils.
Because researchers from the Kansas City Plant are most familiar with ultrasonic systems in the 30 kHz to 40 kHz range, the test design was specified to operate in that range. The ultrasonic transducers were required to be mounted on the front and/or rear faces of the tank.
Although little is known about the effects of using ultrasonic agitation on sound absorbing substrates like fabrics, researchers at the Kansas City Plant have successfully cleaned rubber insulating blankets using a system having a rated power-to-volume ratio of 80 watts per gallon. Cleaning power near this value was thought necessary to clean fabrics, so a range of 50 to 100 watts per gallon was specified.
Normal clothes washing occurs in the temperature range of ambient to approximately 140 degrees Fahrenheit. In order to elevate the temperature quickly, a heater with a capacity of 200 watts of power per gallon of solution in the tank was specified.
The Team distributed copies of the sketch and written requirements of the proposed tank to various vendors. Several were interested in helping.
Crest Ultrasonics provided a cleaning tank, generator, and transducer combination that met essentially all of the original requirements. The Crest tank is a 40 kHz unit with transducers mounted on the rear wall; the power is adjustable from zero to about 80 watts per gallon; the heating system has adequate capacity, and the overall size is close to what was originally specified.
Rinsing is an integral part of any cleaning process. The original plan was to have a continuously flowing, recirculating deionized water rinse tank attached to the ultrasonic cleaning tank. However, the Crest tank was not built with an integral rinse. As a substitute for the system originally specified, two polyethylene containers were obtained for "batch" rinsing.
A decision was made at the beginning of this project to do as much testing as possible at the Garment Care facility. Fortunately, Garment Care had about 350 square feet of space it could remodel. This space was divided into two rooms: an outer office approximately 15 feet by 12 feet and an inner Laboratory approximately 14 feet by 12 feet.
Detergents made for traditional laundering and dry cleaning have not been tested with ultrasonic systems; therefore an entire reformulation appeared necessary.
However, due to time limitations and resources required for such a task, it was decided to seek the expertise of a detergent company and work with existing detergents to determine ultrasonic potential before such an investment was made.
As a result, Amway Corporation became involved in this project, and Kelly Haley joined the Team. To better understand the interrelationships of detergents and cleaning processes, Kansas City Plant researchers George Bohnert and Tom Hand attended a Short Course in Surfactant Science and Technology hosted by the University of Oklahoma in Norman.
Upon completion of the Laboratory at Garment Care, the Crest ultrasonic tank was installed. The 22-gallon tank was cleaned with an industrial detergent and rinsed several times. It was filled and switched on to verify that all components were functional. The generators drew a maximum of 1800 watts, thus making the power-to-volume ratio about 82 watts per gallon.
Pre-soiled fabric swatches are available from several sources, including Testfabrics, Inc., Scientific Services S/D Inc., and Textile Innovator Corporation.
Typical contaminants that are applied to the swatches are synthetic sebum (human "oils"), ground-in clay, grass stain, blood, coffee, tea, motor oil, greases, and other soils normally found on worn garments.
The test protocol, including wash conditions and soils to be tested, was determined by Amway in conjunction with Garment Care and the Kansas City Plant researchers.
After washing, all swatches would be evaluated based on test methods set by organizations such as The American Association of Textile Chemists and Colorists and the American Society for Testing and Materials.
Controlled testing was performed at three sites: Amway Corporation's Research Facility in Ada, Michigan; Garment Care in North Kansas City, Missouri; and Neo-Dyne Research in Las Vegas, Nevada. Amway supplied detergent (SA8 Phosphate-Free) and six sets of swatch packets to each site. Each packet consisted of four groups of swatches, and each group consisted of nine individual swatches arranged in a grid and attached to one another by plastic ties. Six swatches in each grid represented one of four different soil types: TFI (oil-grease), grass, Spangler (human oils), and clay. The remaining three swatches in each grid were uncontaminated to allow determinations to be made about soil redeposition. Each of the six sets of swatch packets came with uniform instructions as to wash times and temperatures so reliable comparative data could be obtained from each site.
Terg-O-Tometer Testing at Amway Corporation
The control swatches were cleaned at Amway's Research facility using a Terg-O-Tometer. A Terg-O-Tometer consists of a thermostatically controlled bath in which four separate two-liter containers are mounted, each fitted with a motor-driven agitator of scaled proportions. The test swatches were washed for the predetermined time at the select temperatures in one liter of solution. This laboratory cleaning method was strictly controlled and simulates washing in home machines.
Ultrasonic Cleaning at Garment Care
To make the test more feasible in terms of detergent, volume of cleaning solution, and number of swatches-per-volume, a metal tank insert was made and suspended in the ultrasonic tank at the Garment Care site.
This metal insert was sized so that a group of fabric swatches had approximately one inch of clearance on each side. Before use, the insert was ultrasonically cleaned with a highly alkaline industrial detergent to prevent any foreign contaminants from affecting the tests.
Each group of swatches was pinned firmly on a wire frame. Each group was then cleaned in a new detergent solution at the prescribed temperature and time. After cleaning, each group was removed from the tank, released from the frame, rinsed in one container of distilled water, then transferred to another container for a final rinse. After rinsing, each group of swatches was gently hand wrung, placed between clean white paper towels, pressed lightly, and left to air dry overnight. After drying, each group was separated by tissue paper, stacked by alphabetical group, packaged into their original containers, and returned to Amway for analysis.
Ultrasonic Cleaning at Neo-Dyne Research
Alvin Snaper, President of Neo-Dyne, invented, patented, and built an ultrasonic solvent-based dry-cleaning machine in 1970. In discussions among Neo-Dyne, Garment Care, and the Kansas City Plant, it was agreed that additional ultrasonic aqueous cleaning tests should be conducted at his facility.
Neo-Dyne's equipment consisted of two banks of magnetostrictive transducers bonded to a stainless steel surface plate. A plastic container to hold swatches and detergent solution was placed on the surface and a gel material was used between the container and the transducerized surface to provide good acoustical contact. One bank of transducers was powered by a 1000-watt, 20-kHz ultrasonic generator and the other by a 1000-watt, 16-kHz generator. (The power-to-volume ratio is believed to be higher than the Crest system, but due to the configuration, no value can be estimated.) Each generator could be activated separately or coaxially if desired.
The test samples processed by Neo-Dyne were in accord with the project specifications.
Amway's participation in this project consisted of the determination of the wash conditions and the preparation and evaluation of the fabric swatches tested.
Test Parameters:
Shown below is a list of the test parameters used in the study.
Conditions 7a, 7b, and 7c will show the effect of wash time on performance whereas conditions 7a and 7d will show the effect of temperature -- condition 7a is also designed to look for the best possible performance.
Test Procedure
Six sets of swatches were prepared for each set of test equipment. Four of the six sets were to be washed under specified conditions, whereas the other two were optional and to be determined by the researchers at each site.
Neo-Dyne cleaned all six (sets A-F), and Garment Care cleaned five (sets G-K). Each set included all of the soils and fabric types listed earlier and each soil was washed separately.
During actual testing, three redeposition and six soiled swatches were ultrasonically washed in about two gallons of water, followed by a hand rinse. Reflectance readings were taken on a colorimeter before and after the swatches were washed. All ultrasonically cleaned fabric swatches were compared to a set of swatches washed in a Terg-O-Tometer at Amway.
Interpretation of Data
The difference between initial and final readings is reported as reflectance difference and is shown in the Data Table (page 10). The colorimeter measures the amount of light that is reflected from the swatches. The more light that is reflected from a fabric the cleaner the fabric is, and the higher the reflectance value.
Redeposition swatches start out clean and their purpose is to show if any of the soil in the wash water redeposits on clean fabrics. When redeposition swatches get slightly cleaner, they show a very small positive increase in reflectance difference but when they pick up soil, they show a reflectance decrease, which is denoted with a negative number.
The top section of the Data Table shows the conditions by which sets A-K were ultrasonically washed followed by the conditions for sets Ta and Tb washed in a Terg-O-Tometer as controls. The bottom section of the Table shows the reflectance differences for each soil and redeposition sample tested in each swatch group.
Results
Explanation of Results
An overall assessment of the Data Table shows that ultrasonic results look very promising in terms of reflectance values when compared to Terg-O-Tometer results. Based on these data and the fact that this is only the first evaluation of this type and a number of changes can be integrated to improve this process, it is believed that ultrasonic fabric cleaning holds potential and warrants further studies.
Contrary to what was anticipated regarding the differences in ultrasonic frequency and power-to-volume ratios, the ultrasonic systems at each site produced comparable results in terms of cleaning. However, because the data obtained at the Neo-Dyne site (where the mixed power and frequencies were used) is less consistent, its interpretation is more difficult. Therefore, the analysis of the results obtained in this study is primarily based on the Garment Care data (sets G, H, I, J, and K) which were more consistent and allowed for more accurate interpretations and conclusions.
In some instances, ultrasonic cleaning performance increased as temperature decreased. This is unusual for traditional laundering and, other than some educated guesses, only further research will accurately assess the degree and the cause of this phenomenon.
Soil from the wash water was not redeposited on fabric at any of the conditions tested.
From a cleaning perspective, redeposition was anticipated as being one of the biggest obstacles in ultrasonic cleaning. Neo-Dyne Research cleaned the swatches in a horizontal position and Garment Care in a vertical.
The fact that neither showed redeposition was simply outstanding and very encouraging for the future of this process. It is important to point out that soil redeposition may be affected if detergent concentration or wash water volume is reduced.
The fact that cleaning performance decreased as wash time decreased was expected and typical of Terg-O-Tometer results. The five-minute ultrasonic wash time at 70 degrees F showed results similar to the Terg-O-Tometer for all four soils. However, the two- and one-minute wash times greatly affected the removal of TFI and grass. Grass removal is very time dependent due to enzyme performance and TFI is a very greasy soil that needs to be emulsified.
Though the four soils provided a great combination for determining overall soil removal, TFI and grass are the most critical and should definitely be included in future studies. TFI and grass deficiency could be addressed chemically with a detergent designed to complement enzyme performance and cold water. It can also be addressed by detergency adjustments and energy and equipment modifications.
Conclusions
Cleanliness evaluations of ultrasonically cleaned fabric swatches showed acceptable soil removal and sufficient potential to warrant further studies.
Unfortunately, due to limited funding, some steps that were originally planned could not be completed. These are explained below.
It is postulated that cleaning constrained fixtured fabrics, as opposed to free-floating fabrics, might yield three benefits:
Tests were not performed to determine differences between free-floating and constrained "fixtured" fabrics. Therefore, additional testing will be required to determine the need for special cleaning fixtures.
Small scale ultrasonic cleaning was successfully demonstrated during this project. "Scaling up" the power-to-volume ratios for larger tanks is not necessarily a linear function. Therefore, additional testing will be required to provide sufficient scale-up data.
Date created: 3/6/96
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