Barbara Liukkonen, Wanda Olson, David Abazs, Karen Evens, Ruth Gubrud, Wayne Seidel
Introduction
Consumer satisfaction with ceramic laundry disks and the actual cleaning effectiveness of the disks were evaluated in a study begun in April, 1996. In the field portion of the study, conducted in Lake and Cook counties, Minnesota, households compared the use of laundry disks with their normal clothes-washing methods. The lab component of the study, conducted on the St. Paul Campus of the University of Minnesota, compared the ceramic disks with liquid laundry detergent in both front- and top-loading washing machines. Standard white cotton T-shirts were to be worn and washed six times in each study. Retention of whiteness, measured with a Gardner reflectometer, was used as a measure of soil removal.
Recent promotions, catalog sales, and popular interest in the use of alternative cleaning products, mainly related to environmental concerns, prompted the research study. Previous lab studies by Consumer Reports and the cleaning industry had indicated that the disks were not effective, but public perception was that the disks are an acceptable alternative to detergent and that they clean satisfactorily. Goals of the study were to evaluate the actual cleaning performance of the disks in a controlled lab setting and to assess consumer satisfaction under typical household conditions.
The study was a cooperative effort of Lake and Cook counties; the Department of Design, Housing, and Apparel; and the University of Minnesota Water Resources Center. Tri-Clean ceramic laundry disks were purchased from a distributor in Cold Spring, Minnesota. Typically, a set of three reusable disks sells for about $65; they are used instead of laundry detergent, and are intended to last for hundreds of wash loads. Disks were purchased with county water plan funds in Lake and Cook counties. T-shirts for the project were purchased with funds designated for housing technology research and education.
Field Study Design
For the field study, 33 volunteers were identified through public solicitation and were asked to complete a release form and a two-page household survey indicating their typical washing habits, water supply, and reasons for participating in the survey (Figure 1). Volunteers were issued a standard white cotton T-shirt and asked to wear and wash it six times with their normal laundry methods. Water hardness and normal washing temperatures were measured to allow comparison between differing water sources and washing habits. Seven of the initial 33 volunteers dropped out of the study before returning the first T-shirt and receiving the disks.
After returning the first T-shirt, volunteers received a set of laundry disks and another white cotton T-shirt. They were again asked to wear and wash the shirt six times, using the laundry disks. The three resuable ceramic disks were added to the entire wash cycle instead of the regular amount of detergent. Participants were allowed to use laundry aids of their choice (e.g. borax), to presoak or treat stains, or to add a small amount of detergent with the disks. Usually the T-shirt was washed with other clothes. Volunteers were allowed to use the disks for all or part of their normal wash loads and were allowed to keep the disks after the study.
After washing the T-shirt six times with the disks, volunteers completed a second survey (Figure 2) evaluating their satisfaction. Twenty-six volunteers received the second T-shirt and disks and returned the final survey, but one did not complete the original survey for comparison, so conclusions are based on 25 participants completing the entire project.
Campus-Based Lab Study Design
Standard white cotton T-shirts were provided to 32 volunteers who wore them and returned them six times to the Department of Design, Housing, and Apparel for washing. The T-shirts were initially assigned at random to one of four wash solutions, and washed in either a front-loading (horizontal axis) or top-loading (vertical axis) washing machine. The four wash solutions were water, laundry disks, laundry disks plus one teaspoon liquid laundry detergent, and one capful of liquid laundry detergent. Once assigned to a group, the T-shirt was washed the same way each time.
The lab study provided a more controlled situation, with water from a municipal supply (chlorinated), consistent washing methods, and no interaction with other laundry in the wash load. One front-loading washing machine (White-Westinghouse) and one top-loading model (Maytag) were used. Ultra Tide7 was used in the top-loading machines and low sudsing liquid Wisk7 was used in the front-loading model. Each load consisted of four T-shirts and enough clean cotton towels to make a six-pound load. Shirts were washed using the normal cycle with a full water level and 20 minutes of tumbling or 12 minutes of agitation.
Methods
A Gardner reflectometer was used to measure reflectance values of the white cotton T-shirts. The reflectance of new white, unwashed T-shirts was measured to serve as a baseline standard. That baseline value was subtracted from the reflectance of each T-shirt that was worn and washed as part of the study. Thus, the reported reflectance values are usually negative numbers and represent a decrease in whiteness from a new, unwashed T-shirt. Reflectance values were measured with and without a UV filter. The UV filter minimizes the effect of optical brighteners; values without the UV filter more closely represent what would be seen with the naked eye.
Reflectance measurements were taken at three locations for each T-shirt. They were tested once on the back, one inch below the neck band, and twice on the front. One measurement on the front was taken one inch above the pocket on the upper left side and one was taken on the right side in an area corresponding to one inch below the pocket. If there was an obvious stain at one of those places, the measurement was shifted as needed.
When possible in the field study, reflectance values of T-shirts washed with detergent and disks were compared for individual households. The T-shirts were measured about two months after the last washing. Statistical analyses were performed using the SPSS for MS Windows, release 6.1.
Results of the Field Study
To identify possible correlations between why people participated in the study and how satisfied they were with the disks, volunteers were asked to indicate their reasons for volunteering. On the survey, they were allowed to select more than one response or write-in their reason for participating (Table 1). Four said they had seen the disks advertised and were interested in trying them, but had been deterred by the price.
Table 1. Reasons for participating in the field research.
* Participants could check more than one reason
Twenty-three of the volunteer households used top-loading washing machines and did their laundry at home. Two used front-loading machines at a laundromat. Two-thirds of the households had a private well and eleven homes used water from a municipal supply. Typically, the water from private wells along the north shore is harder than the municipal supply, which is drawn from Lake Superior. The municipal water supply is also chlorinated. Hard water can leave a grayish film on clothes and may affect cleaning performance of laundry disks or detergent.
Table 2: Detergent and product use reported on surveys*
*N = 25 households that completed the project
Most participants (15 or 60%) used liquid detergent (Table 2). Twenty percent used powder and another 20% used either or both. One reported using a solid, heavy duty detergent. Nearly all the households (89%) added laundry products, such as bleach and spray prewash, to their detergent.
When using the disks, 72% of the households added laundry aids or presoaked their laundry. Nearly half of the households (48%) used additional products or added more of the products than they normally used when washing with detergent.
Household satisfaction with cleanliness of whites, colors, and heavily soiled clothes was measured on a scale of 1 to 10 (very satisfied) on both the original survey of normal washing methods and on the final evaluation of the laundry disks. When reported satisfaction levels for detergent and disks were also compared for individual households, thirteen households indicated they were less satisfied with whites when using the disks (Table 3).
Table 3: Change in reported satisfaction with cleaning effectiveness of disks compared with detergent.*
Of the twelve households that reported equal or greater satisfaction with whites, four are now presoaking and seven reported using more laundry aids with the disks than they did with detergent. Seven of the 25 households wrote that the T-shirts and/or whites were dingy, dull, gray, or not clean.
Twenty-one households reported equal or higher satisfaction with their colored clothes when using the disks. Twelve households reported they were less satisfied with the disks when washing heavily soiled clothes.
There was no apparent correlation between water hardness or reported washing temperature and satisfaction levels. Harder water, that is, water with higher levels of dissolved minerals, did not correlate with lower satisfaction ratings for whites or colors. Washing temperature (hot, warm, cold) did not appear to be related to satisfaction when using disks or detergent.
Twenty-three households (92%) said they will continue to use the disks; two said they will not. Seventeen households (68%) said they would purchase the disks in the future, four said they would not purchase the disks (16%), and four said maybe, probably, not sure, or it depends.
There was no significant difference in the measured reflectance values for 21 known pairs of T-shirts from individual households (see Table 4). Comparing first and second T-shirts, by household, eliminates the variability between households and strengthens statistical interpretation. Values are reported as the average difference in reflectance between a never-worn, unwashed T-shirt (baseline) and the worn T-shirt washed with either detergent or with the disks. A more negative value means less reflectance (less white).
Table 4: Average difference in reflectance values for 21 known pairs of T-shirts, field study.
Results of the Campus-Based Lab Study
Overall, in the lab study, the disks did not perform as well as detergent. The study showed that disks alone were less effective in soil removal (whiteness retention) than detergent or disks plus one teaspoon detergent (see Table 5).
Table 5: Average difference in reflectance values under laboratory and field conditions.
Values are reported as the average difference between a never-worn, unwashed T-shirt (baseline) and the worn, washed T-shirts for each treatment. A more negative value represents a greater difference between the new, unwashed T-shirt and the worn, washed ones (meaning the washed shirts were less white). In the lab study, the average reflectance value of T-shirts washed in detergent is a positive number, meaning that the T-shirts were whiter after being washed. This probably results from the optical brighteners in detergent formulations.
The small letters following the reflectance values represent the statistical significance of the difference between the treatment groups: groups having the same small letter are not significantly different at the 0.05 level (e.g. in the lab, T-shirts washed with disks and T-shirts washed with disks plus 1 teaspoon detergent weren't significantly different from each other).
In the lab study, disks alone, disks plus one teaspoon detergent, and detergent were all more effective than either disks or detergent in the field. This may be because laundry loads in the field study included more than just white T-shirts and white cotton towels.
Literature that accompanies the disks states that they work by ionizing oxygen in the water, which would change the pH of the water. No change in pH was measurable when disks were added to wash water with or without clothes in the washing machine.
Discussion
Overall, comments on the final evaluation surveys (n=25) were very positive about the disks. Two volunteers wrote that rashes had disappeared, a few mentioned that their clothes smelled fresh longer, and others were positive about minimizing their impact on the environment and their septic system by using less detergent. While some said their clothes were softer, other participants mentioned that the clothes were less soft, and some said that the clothes didn't smell as fresh.
Households that had indicated environmental concern as a reason for participating were more likely to be satisfied with the cleaning effectiveness of the disks. Comments on the
final evaluation form that indicated homeowners believed their septic system was working better correlated with those expressing concern about septic systems on the initial survey.
Personal preferences and observations vary, but overall, participants completing the field study were satisfied with the laundry disks. Although the lab study showed that the disks were less effective than detergent, people appear to be willing to accept slightly less clean clothes when they believe that they are making a choice that protects the environment.
Authors:
Barbara Liukkonen
Water Resources Center, Room 302
1518 Cleveland Avenue
St. Paul, MN 55108-6001
Wanda Olson
Design, Housing & Apparel
360 McNeal Hall
1985 Buford Avenue
St. Paul, MN 55108
David Abazs, Ruth Gubrud, Wayne Seidel
Lake County SWCD
PO Box 14
Two Harbors, MN 55616
Karen Evens
Cook County Water Planner
Cook County Courthouse
Box 1150
Grand Marais, MN 55604
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