Washing temperature

Detergency is mainly affected by the concentration and stmcture of surfactant, hardness and builders present, and the nature of the soil and substrate. Other important factors include wash temperature length of time of washing process mechanical action relative amounts of sod, substrate, and bath, generally expressed as the bath ratio, ie, the ratio of the bath weight to substrate weight and rinse conditions. 

Fig. 2. Effect of wash temperature on removal of sebum, O lanolin, and lard from cotton (0.25% built detergent) (48). D, Represents sebum removal...

Proteia and starch stains are removed by proteases and amylases, respectively. Fats and oils are generally difficult to remove at low wash temperatures by conventional detergents. By usiag Upases, it is possible to improve the removal of fats/oils of animal and vegetable origin even at temperatures where the fatty material is ia a soUd form. Particulate soils can be difficult to remove, especially if the particle sise is small. Removal of particulate soil from cotton fabric can be improved by use of a ceUulase which removes cellulose fibrils from the surface of the yam. 

AH detergent proteases are destabilized by linear alkylbenzenesulfonate (LAS), the most common type of anionic surfactant in detergents. The higher the LAS concentration and wash temperature, the greater the inactivation of the enzyme. The presence of nonionic surfactants, however, counteracts the negative effect of LAS. Almost aH detergents contain some nonionic surfactant therefore, the stabHity of proteases in a washing context is not problematic. 

Earlier formulations contained mainly chlorine bleach, metasiUcates, triphosphate, and nonionic surfactants. Modem manufacturers have switched to more compHcated formulations with disiUcates, phosphates or citrate, phosphonates, polycarboxylates, nonionic surfactants, oxygen bleach, bleach activator, and enzymes. The replacement of metasiUcates by disilicates lowers pH from approximately 12 to 10.5, at 1 g ADD/L water. The combined effect of decreased pH, the absence of hypochlorite, and the trend toward lower wash temperatures has paved the way for the introduction of enzymes into ADDs. Most ADD brands in Europe are part of the new generation of ADD products with enzymes. The new formulations are described in the patent hterature (55—57). 

It has been reported that the LAS/AS mixed active system was produced by continuous oleum sulfonation of LAB followed by addition of the alcohol and more oleum to provide a tandem sulfation [40]. Tallow range alcohol sulfate (Ci6-is AS) was used in the past when U.S. wash temperatures were as high as 60°C. At these wash temperatures and in phosphate-built formulations the Ci6 18 AS gave very good detergency performance [41]. However, as U.S. washing temperatures decreased, C16.,8 AS was replaced by the more soluble shorter-chain ASs, such as C12.I8 or C,4, 5. 

The instability of DAST-type brighteners towards chlorine-containing bleaches has been mentioned already. They also show limited stability towards per-acids. As recommended washing temperatures have tended to fall in recent years, a bleach consisting of sodium perborate activated by addition of tetra-acetylethylenediamine (11.63) has become an important component of household detergent formulations. This system is effective at temperatures as low as 40-50 °C. Since the FBA may be sensitive to the activated oxidant, however, in some formulations it is necessary to protect compounds such as 11.60 or 11.61 by encapsulating either the brightener or the activator, if adequate shelf-life is to be maintained. 

The poor performance of the distyryldiphenyl derivative 11.15 at higher washing temperatures is a serious drawback in some countries. In an attempt to overcome this disadvantage, product 11.15 has been marketed in admixture with an analogous FBA (11.64) derived from 4-chlorobenzaldehyde-3-sulphonic acid (see Scheme 11.5). This much less soluble variant is highly effective at high washing temperatures. 

Japanese washing machines in particular frequently operate with large 7-segment or LCD displays. In Europe as well such technology, although cost-intensive, is being introduced in more and more machines. Until now it would be used to display the set spin speed, wash temperature or program duration. Fig. 3.12 shows a modern fascia with some additional features. 

When looking at Sinner s famous circle that describes wash performance as the result of four components - temperature, time, mechanical and chemical action, it becomes clear that with decreasing wash temperature and time, chemistry has to become all the more sophisticated. 

Krafft point (for ionic surfactants) and cloud point (for nonionic surfactants) are both a limit to surfactant solubility. The solubility of ionic surfactants decreases significantly below the Krafft point, since its concentration falls below the CMC and individual surfactant molecules cannot form micelles. Therefore, the Krafft point of an ionic surfactant must be below the desired wash temperature for maximum soil removal. In contrast, the solubility of some nonionic surfactants decreases with increasing temperature. Above the cloud point, the surfactant becomes insoluble. Thus, the cloud point of a nonionic surfactant should be 15-30°C above the intended wash temperature [8],... 

Suds suppressors (LD, DW, ADW, HC) Limit suds amount when suds will interfere with cleaning Sensitivity to wash temperature, water hardness, and builder system Efficiency on the surfactant system Alkyl phosphates Silicones Soap 0-5% 0-5%... 

Choose enzymes which have alkaline optimum pH, are most effective at low wash temperatures of 2CM0°C and stable for temperatures up to 60 °C. 

The level of alcohol-extractables remaining on the fiber also decreased as washing temperature increased (Figure 2). However, the quantity of material removed at the lowest wash temperature was significant and did not increase markedly with increases in wash temperature. Apparently, little would be gained in using the higher temperatures to remove these types of extractables. 

Washing temperatures above 60°C tended to lower fiber length... 

Figure 1. Plot of wax content vs. wash temperature. Laboratory washing conditions. Key O unwashed , washed.

Effects of Washing Temperatures on Fiber Length Characteristics(3)... 

Wash Temperature (°C) Upper Quartile Length (mm) Mean Length (mm) Short Fibers (%)... 

---