Appliance of Science
It is a well known fact that wool is sensitive to high pH chemicals: strong alkali (pH=11 and above) may cause yellowing and even fi bre degradation on wool (-rich) carpets. In the case of patterned carpet, colour bleeding is an issue too, since wool is dyed in acid conditions. So it is no surprise that when it comes to WoolSafe testing of carpet cleaning chemicals, checking the pH and the alkalinity comes high on the list.
We take a reading of the pH of the cleaning chemical both in its concentrated form and after diluting it according to the manufacturer’s instructions. Here, as in all our testing, we work on the principle of the “worst case scenario”, which means that we perform all defensive tests at the highest recommended concentration, whilst doing the cleaning trials at the lowest.
pH is easy to measure (in the lab we use a glass electrode for accurate reading), but unfortunately this does not provide ultimate information on whether the cleaning chemical in question will cause a problem on a wool carpet or not. T at’s why we do the alkalinity test, which tells us how stable the pH is, i.e. how well the chemical is buff ered. ‘Buff ering’ generally means a certain ‘resistance to change’. In a chemical sense it is the resistance to any change in the pH. A variety of chemicals, added to the cleaning products during formulation for all sorts of reasons, can act as buff ers. In some cases, for example in heavy duty degreasers, they are useful, but in products formulated for cleaning wool they can cause problems. As the acid dyes generally used on wool (and nylon) carpets are only stable in acid conditions, a repeat use of a cleaner buff ered at pH=7 or higher is likely to cause the colours to run. On the other hand, even a higher pH product can be used safely
WOOLSAFE Chemical Tests, Part 2 - pH and Alkalinity...
if it is not buff ered, since the residual acidity in the wool carpet will neutralise it. A word of caution: it is the cleaner’s responsibility to ensure that the carpet is left acidic. So do check the pH before the carpet has dried and use an acid rinse if necessary. Do take particular care on printed nylon carpet (mainly in commercial locations): their colourfastness could be just within industry standard with no margin for error!
Colour fastness testing
WoolSafe testing does not rely on the alkalinity test alone to discover whether the product might promote bleeding. Instead, a supplementary test is carried out based upon an ISO Standard 105-E01 for determining colour fastness to water.
In the test, a standard-dyed carpet in a dark red shade is incubated at 37°C in contact with a small piece of standard undyed wool fabric, and a small piece of standard undyed cotton fabric whilst immersed in the product under test at working strength. Bleeding inevitably occurs (even water causes the standard dyed carpet to bleed to a certain degree) and staining of the white adjacent cloths takes place. It is clearly desirable that the product should cause the minimum amount of bleeding when measured either in terms of colour loss from the test carpet, or in terms of the discolouration of the undyed wool and cotton.
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