The use of hypochlorite bleach should be limited to temperatures below 60C to avoid damage to cotton and other cellulosic fabrics. It is therefore used typically in the rinse stages. But in this case the pH of the rinse liquor is critical!
Even with temperatures below 60C, damage can be accelerated where the liquor is taken below pH 8.5 – 9. Where launderers have a problem with high alkalinity levels in raw water supplies and to avoid problems of discolouration or galling of work in drying, they may be tempted to use an acid sour to neutralise this excess alkalinity, or reduce the pH of the rinse liquors. However, by so doing, is there not a danger of any retained hypochlorite bleach creating accelerated damage to workloads?
Even with “safe bleaches”, such as hydrogen peroxide and sodium perborate, there may be some risks. When these are used in the main wash at temperatures in excess of 70C to be effective, problems can occur if the wash liquor is higher than pH11 – typical of many wash processes.
In addition to these conditions, the catalytic effect of free metallic ions in the wash – from iron contamination, copper or even metallic components from articles in the workload – can result in the catalytic breakdown of bleaches causing both general and severe localised chemical damage to fabrics.
No one said laundering was easy!
