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THE EFFECTS OF WASHING CONDITIONS ON SOIL REMOVAL IN DOMESTIC LAUNDERING PROCESSES
Dokuz Eylül University, Department of Textile Engineering, Izmir- Turkey *Günkol Güneş Enerjisi ve Klima Sistemleri A.Ş. (TEBA), Izmir-Turkey E-mail: merih.sariisik@deu.edu.tr
In the domestic laundering process, relatively high wash temperatures and long wash times have traditionally been used for optimum soil removal. The use of lower wash temperatures could result in a substantial reduction in the amount of energy used in laundering. The purpose of this study was to determine soil removal from cotton, polyester, polyester/cotton, wool and wool/polyester fabrics at a range of wash temperatures, wash times, pre-wash times and liquor ratios. The samples were soiled with sebum, coke, instant coffee, sour cherry juice and meat sauce. Soil removal was determined by the differences between remission values of fabrics before and after washing. Optimum temperature and times for soil removal was estimated for all soils and fabrics.
soil removal, washing machine programs, laundering,
Maintaining textile products consumes significant amounts of energy, and is extremely important to the satisfactory performance of these products. The laundering process uses approximately nine percent of the total household consumption of energy, and much of this energy is used in heating water. Traditionally it has been considered that hot wash temperatures were required for satisfactory soil removal from cotton fabrics, while lower temperatures would give adequate soil removal from fabrics of synthetic fibre. The use of lower wash temperatures for all fabrics could result in a substantial reduction in the amount of energy used in laundering [1]. Numerous variables affect the rate of soil removal and the cleanliness of the washed garment:
− washing equipment, − time (length of the wash cycle and the pre-soak cycle, if included), − agitation, − temperature, − detergent composition (and the structure of the surfactants), − detergent concentration, − bleach, if added separately, − water hardness, − load size and cloth-liquor ratio, − rinse conditions (time, temperature, volume, agitation, and so on), − drying conditions [2].
Table 1 shows the washing conditions of washing machines in Japan, the United States and Western Europe [3]. Washing is usually done within one of three temperature ranges: 90-100, 40-60˘C and at ambient temperature. The ASTM method recommends washing at 21, 37 and 54˘C. The maximum wash temperature depends on the type of washing machine used. Front loading washers used in Europe are equipped with heaters for raising the water temperature to 95˘C. In the United States, top loading washers are by far more popular, and wash temperatures are in the 40-60˘C range, usually at 55˘C, or washing is done at ambient temperature. Wash temperatures are decreasing, especially in Europe, mainly because of the increased cost of heating.
Table 1. Washing conditions in different continents [3]
| Washing conditions | United States/Canada | Japan | Western Europe |
|---|---|---|---|
| Washing machine | agitator type | impeller type | drum type |
| Heating coils | no | no | yes |
| Fabric load, kg | 2-3 | 1-1.5 | 3-4 |
| Amount of wash liquor, L | extra small: ca.35 medium: ca. 50 large: ca. 65 extra large: ca. 80 | low: 30 high: 45 | low: 18-20 high: 25 |
| Total water consumption, L (regular heavy cycle) | 140 | 150 | 120 |
| Wash liquor ratio | 1:15- 1:30 | 1:20-1:30 | 1:5-1:25 |
| Washing time, min | 10-15 | 5-15 | 60-70 (90C) 20-30 (30C) |
| Washing, rinsing and spinning time, min | 20-35 | 15-35 | 100-120 (90C) 40-50 (30C) |
| Washing temperature,ºC | hot: 50 (122F) warm: 27-43 (80-110F) cold: 10-27 (50-80F) | 10-40 | 90 60 40 30 |
| Water hardness, ppm CaCO3 | relatively low, 100 | very low, 50 | relatively high, 250 |
| Automatic detergent addition | mostly no | mostly no | dispenser |
| Recommended detergent dose, g/L g/kg fabric | 1.5 35-50 | 1.3 30-40 | 8-10 60-80 |
| Peroxide bleach | + | (+)** | + |
| Chlorine bleach | + | (+) | (+) |
| Drying process by automatic dryer | + | (+) | (+) |
* In the United States and Japan without bleaching components. ** Parentheses indicate that this element is less important.
The length of the wash cycle depends on the construction of the washing machine and the cycle selected in accord with the type of fabrics washed. The wash cycles of washers built in the United States are usually 8 to 15 min. Standard test procedures recommend washing for 10 to 12 min [2]. There are numerous publications, including several up-to-date textbooks, which deal comprehensively with aspects of surfactant science relating to the theory and technology of detergency [4-6]. The physical and chemical effects of domestic laundering process have been investigated by several researchers [7]. The purpose of this study was to determine soil removal from cotton, polyester, polyester/cotton, wool and wool/polyester fabrics at a range of wash temperatures, wash times, pre-wash times and liquor ratios. The samples were soiled with sebum, coke, instant coffee, sour cherry juice and meat sauce. Soil removal was determined by the differences between the remission values of fabrics before and after washing. Optimum temperature and times for soil removal was estimated for all soils and fabrics.
For this study, five different types of white fabrics, which were pre-treated without optical brightener, were used. They are described in Table 2. When choosing, soils were considered to be those that a person was likely to encounter during a normal day. The soils chosen were coke, sour cherry juice, instant coffee, sebum and meat sauce. Fabrics were padded with instant coffee, coke and sour cherry juice at room temperature. For padding, sour cherry juice and coke were opened and then used immediately. 0.01 g/l coffee solution
was prepared and 69 g/l sugars was added to the solution. The padding temperature of the solution was 70ºC. Pick-up ratio was 90%. Fabrics were dried flat. Cotton, cotton/polyester blend, polyester and wool fabrics soiled with meat sauce and sebum were obtained from WFK Testgewebe GmbH. No wool/polyester blend fabric was soiled with these soils, and so the wool/polyester blend fabric with these soils was not used. A good quality detergent, which is commercially available, was used in the proportions of 5 g/l for cotton, polyester and cotton/polyester fabrics and 3 g/l for wool and wool/polyester blend fabrics. The amount used for pre-wash cycles was 2.5 g/l. The detergent was composed of the following agents:
Table 2. Description of fabrics
| Fabric | Weight (g/m2) | Yarn Setts (cm-1) | Yarn Counts (Nm) | ||
|---|---|---|---|---|---|
| Weft | Warp | Weft | Warp | ||
| 100% Cotton (Co) | 138 | 20 | 24 | 32 | 32 |
| 65% Cotton / 35% Polyester | 208 | 17 | 41 | 14 | 60 |
| 100% Polyester (PES) | 144 | 21 | 21 | 46 | 46 |
| 45% Wool / 55% Polyester | 236 | 22 | 38 | 56/2 | 56/2 |
| 100% Wool | 271 | 35 | 45 | 60/2 | 60/2 |
The study was designed as a factorial experiment with four factors; main wash temperatures (five), wash liquor ratios (two), main wash times (four) and pre-wash times (three). Two samples were prepared for each possible combination of factors. The plan of the experiments is given in Table 3.
Table 3. Plan of Experiments
| Temperature (˘C) | |||||||
|---|---|---|---|---|---|---|---|
| 30 | 40 | 50 | 60 | 80 | |||
| Fabric | Co | Wo | Co | Wo | Co | Co | Co |
| Co / PES | Co / PES | Co / PES | Co / PES | Co / PES | |||
| PES | Wo / PES | PES | Wo / PES | PES | PES | PES | |
| Reversing Rhythm | 12s rotation / 4s pause | 4s rotation / 12s pause | 12s rotation / 4s pause | 4s rotation / 12s pause | 12s rotation / 4s pause | 12s rotation / 4s pause | 12s rotation / 4s pause |
| Liquor Ratio | 1:3 | 1:10 | 1:3 | 1:10 | 1:3 | 1:3 | 1:3 |
| 1:5 | 1:5 | 1:5 | 1:5 | 1:5 | |||
| 10 | 10 | 10 | 10 | 10 | 10 | 10 | |
| Main Wash | 15 | 15 | 15 | 15 | 15 | 15 | 15 |
| Times (min) | 20 | 20 | 20 | 20 | 20 | 20 | 20 |
| 25 | 25 | 25 | 25 | 25 | 25 | 25 | |
| Pre-wash Times (min) | 0 | 0 | 0 | 0 | 0 | ||
| 5 | 5 | 5 | 5 | 5 | |||
| 10 | 10 | 10 | 10 | 10 | |||
An automatic washing machine, whose wash temperatures, amount of water, operation times, drum speed, reversing rhythm and wash steps order can be set, was used for the study. The temperature of pre-wash cycle was set at 30˘C. The drum speeds of machine were 50 rpm for washing steps and 60 rpm for rinsing steps. Rinsing was completed in two steps, both of which lasted five minutes. A reversing rhythm of 12 s of rotation / 4 s of pause was chosen for low wash liquor ratios (for cotton, cotton/polyester blend and polyester fabrics), and a reversing rhythm of 4 s of rotation / 12 s of pause was chosen for high liquor ratio (for wool and wool/polyester fabrics). Before washing, the soiled fabrics were cut into 5 cm þ 5 cm pieces. The cut fabrics were stitched to a cotton fabric with dimensions of 70 cm þ 100 cm. The total wash load was 1.5 kg, and the ballast load was 100% polyester fabric. Five different wash temperatures were chosen; 30, 40, 50, 60 and 80˘C. The wash liquor ratios were 1:3 and 1:5. The main wash times were 10, 15, 20 and 25 minutes, and the 3 levels of pre-wash times were 0, 5 and 10 minutes. Before and after washing, the colours of fabrics were measured by a Minolta CM-3600D spectrophotometer using a UV filter. Three measurements were made for each fabric. The reflectance values of fabrics at 460 nm were recorded. Soil removal from fabrics was calculated by subtracting reflectance values after washings from reflectance values before washings [8].
∆R = RA - RB Eq.1
RA: Reflectance values after washings, RB: Reflectance values before washings, ∆R: Amount of soil removal, the difference between RA and RB. The results were evaluated according to variation analysis (α=0.05). Multiple comparisons between factor levels were evaluated according to the Duncan test.
The results of soil removal depending on several factors at 30˘C are given in Table 4. For wool and wool/polyester blend fabrics, the only liquor ratio used was 1:10, because liquor ratios of 1:3 and 1:5 were not used for these fabrics in delicate programs of conventional washing machines. Again regarding conventional washing machines, pre-washing steps were not applied for these fabrics. For removal of coke soil at 30˘C, the amount of soil removal increased with increasing liquor ratios for cotton fabrics, while for others it did not change. The main wash and pre-wash times had no effect on soil removal degree. For removal of sour cherry juice soil, it was seen that the liquor ratio and the main wash times were effective for cotton fabric, but the pre-wash time had no effect on soil removal. The liquor ratios, main wash times and pre-wash times were not effective for cotton/polyester and polyester fabrics. For all the fabrics soiled with instant coffee, the amount of soil removed increased with the increase in liquor ratios. Although soil removal increased with the increase in main wash times, different pre-wash times had no effect on the amount of soil removed. The best soil removal was observed at a liquor ratio of 1:5 for fabrics soiled with sebum. Soil removal degree was variable depending on fibre types. For cotton fabrics, the soil removal degree increased with increasing liquor ratios, although for cotton/polyester blend and polyester fabrics, the soil removal degree decreased. It was demonstrated that main and pre-wash times had no significant effect on soil removal.
As seen in Table 5, for cotton and cotton/polyester fabrics soiled with coke, the highest soil removal degree was observed at the liquor ratio of 1:5. However, liquor ratios were not effective for polyester fabrics. It was demonstrated that main wash times had no significant effect on soil removal degree. Due to the increasing pre-wash times, the soil removal degree for cotton/polyester fabrics increased, although this had no effect on the other fabrics. For the removal of sour cherry juice soil, the increase in the liquor ratios had no significant effect on the polyester fabric, although the soil removal degree increased with the increase in liquor ratios for the other fabrics. Regarding main wash times, the soil removal degree showed changes for cotton, cotton/polyester and wool/polyester fabrics, and it was demonstrated that the best result was observed at main wash times of 20 minutes. Soil removal degree at liquor ratio of 1:5 was best for the fabrics soiled with instant coffee. The increase in the main wash times was significant for cotton, cotton/polyester and polyester fabrics, while it was not effective for wool and wool/polyester fabrics. For cotton and cotton/polyester fabrics, the soil removal degree increased with the increase in pre-wash times. The best results of removing sebum soil at 40˘C were observed at a liquor ratio of 1:5 for all the fabrics. Regarding main and pre-wash times, soil removal degree increased with increasing time for all the fabrics. For the removal of meat sauce soil, the liquor ratios did not show any significant effects. The main wash times were not effective for cotton fabrics, but they enhanced the soil removal degree for the other fabrics. Pre-wash times for all test fabrics were effective.
| SOİL TYPE: | COKE | FABRICS | |||||||
|---|---|---|---|---|---|---|---|---|---|
| Liquor Rstio | Co | Co/PES | PES | Wo | Wo/PES | ||||
| 1_3 | 11.99 | 8.64 | 19.11 | ||||||
| 1_5 | 13.72 | 10.5 | 19.36 | ||||||
| 1_10 | 4.43 | 10.2 | |||||||
| Main Wash Times | |||||||||
| 10 min | 12.46 | 9.71 | 18.83 | 5.1 | 10.6 | ||||
| 15 min | 13.16 | 9.26 | 19.08 | 3.89 | 10.14 | ||||
| 20 min | 12.36 | 9.38 | 19.2 | 3.31 | 9.94 | ||||
| 25 min | 13.46 | 9.93 | 19.83 | 5.43 | 10.12 | ||||
| Pre-wash Times | |||||||||
| 0 | 12.85 | 9.33 | 19.24 | 4.43 | 10.2 | ||||
| 5 min | 12.95 | 9.41 | 18.92 | ||||||
| 10 min | 12.78 | 9.98 | 19.53 | ||||||
| SOİL TYPE:SOUR CHERRY JUİCE | FABRICS | ||||||||
| Liquor Ratio | Co | Co/PES | PES | Wo | Wo/PES | ||||
| 1_3 | 9.78 | 14.59 | 14.83 | ||||||
| 1_5 | 16.7 | 15.22 | 23.63 | ||||||
| 1_10 | 6.79 | 14.3 | |||||||
| Main Wash Times | |||||||||
| 10 min | 11.98 | 12.92 | 19.18 | 5.93 | 14.1 | ||||
| 15 min | 12.2 | 15.67 | 18.33 | 6.94 | 13.99 | ||||
| 20 min | 13.58 | 15.04 | 19.47 | 7.2 | 14.46 | ||||
| 25 min | 15.19 | 15.99 | 19.95 | 7.1 | 14.68 | ||||
| Pre-wash Times | |||||||||
| 0 | 12.96 | 15.78 | 19.9 | 6.79 | 14.3 | ||||
| 5 min | 13.32 | 12.6 | |||||||