Bleaching performance

Tetraacetylethylenediamine (TAED) and pentaacetylglucose (PAG) are employed as bleach pre-cursors of peracetic acid this allows the bleach to occur at a temperature lower than when hydrogen peroxide is used. Perhydro-lysis of the sulfonated aromatic ester, shown in Figure 2.38, gives superb bleach performance on textiles, probably due to the surface active properties of the compound. The acyl dialkyphosphates and the N-acylimidazoles are also effective peracetic acid precursors at low temperature. 

TABLE 12. Relationship of Bleach Performance to Water Content of Soya oil Chlorophyll a (67). 

A comparative study of the bleaching performance of complexes 1-3 with hydrogen peroxide as a function of pH revealed that compounds 1 and 3 show higher activities at PH < 9.5 and compound 2 demonstrates much better results at pH > 9.5. This difference in behavior appears to be related to the generally higher stability of the mixed-valence Mn species under catalytic conditions [6] and it may suggest that catalytic fabric bleaching involves mononuclear species at pH < 9.5 and binuclear species above this pH. 

Bleach Stabilization. When added to hydrogen peroxide based bleaching systems, soluble silicates are known to significantly enhance bleach performance. Many hypotheses have been put forth to explain this process, including buffering, peroxysilicate complex formation, and modification of peroxide equilibrium. However, the most recent and plausible explanation is that the silicate inactivates iron and manganese species which catalyze peroxide decomposition (13). 

Rich, A.D. Major factors that affect bleaching performance./ Am. Oil Chem. Soc. 1967, 44, 298A-324A. 

The incorporation of a polar functional group into an alkyl peroxycarboxylic acid inaeases melting point and thermal stability. Amido and imido linkages, in particular, improve the intrinsic properties of the molecule. Optimum thermal stability, bleach performance, and accessibility are found in phthalimido peroxycaproic acid (phthaloyl amidoperoxy caproic acid, PAP) [11], which is now used in several domestic and industrial applications. 

FIGURE 16.6 Bleach performance of TAED/SPC versus peroxyacetic acid at various temperatures. 

The bleach performance profile of aerial bleach catalysts is qnite different from that of peroxide bleaching. Whereas a wide range of oxidizable stains is attacked by the activated catalyst in the presence of perhydroxyl ions, in combination with atmospheric oxygen, only oily food stains, such as tomato oil, mango or annatto-derived stains [53], are targeted. It is assumed that under aerial bleach conditions the catalyst indnces the formation of hydroperoxides in the food stain. In a second... 

FIGURE 16.22 Bleach performance of TAED/PB 4 on various stains at 40°C effect of detergent... 

Under certain conditions, positively charged quaternary imine salts may cause unacceptable levels of dye damage. Overall negatively charged or zwitterionic derivatives (IQZ) were found to provide improved safety profiles [177]. Used in relatively small amounts (0.01-0.05%) in combination with NOBS or TAED (1-5%), they have enhanced enzyme compatibility and provide effective bleach performance at an application pH of 8-10 and water temperatures below 20°C [178],... 

To achieve full bleach performance, nonactivated formulations often contain sodium carbonate or layered silicates to increase the application pH, as the perhydroxyl anion is the bleach active species. Eormulations containing bleach catalysts also work best at high pH. In contrast, TAED-based products often contain a certain amount of acidification agent, such as citric acid or sodium bicarbonate for optimum performance of peroxyacetic acid. 

Improved stability and performance Improved bleach performance Improved stability of the liquid composition Improved st age stabdity at pH 6-7, improved performance at pH 7.5-9 Improved stability of the liquid composition... 

This is the activator of choice in North America. It is superior to TAED under U.S. washing conditions, that is, low temperatures (30-40°C) and low detergent concentrations. Above 40°C, bleaching performance of NOBS and TAED is equivalent. 

Peroxide is thermodynamically unstable but kinetically rather inert and this explains the need for time or temperature to achieve effective bleaching. As a general rule, the bleaching performance of persalts increases as the pH is raised [i.e., as more OOH is generated (piC, of hydrogen peroxide is 11.6)]. Loss of actives due to transition metal action or thermal instability may alter the pH of maximum activity in practice. The optimal conditions for maximum activity of activated systems are discussed in Sec. IV. 

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