CHEMICALS

Getting the right chemistry

1 May 2009



Richard Neale discusses the role that chemicals play at different stages in the drycleaning process


Drycleaners use chemicals at four different stages in the process and the best operators are adept choosing the right solvent or reagent for each.

Stain removal: Most operators are skilled in the selection, testing and use of the standard three-bottle kit. The mildly acidic oxidising agent used for red wine and beetroot is designed to remove tannins and will reduce stains from plants grown in the ground. The mildly alkaline protein remover is for blood, sweat and tears and can be used on a stain from an animal-based product such as cream or gravy made from meat juices. The third reagent is used for solvent-based stains such as paint and glue.

It is best to test each reagent before trying to remove the stain. Apply to a hidden area, leave it for the time needed to take the stain out, then flush the area, feather it dry and examine for damage.

Detergent pre-brushing: Water is a superb solvent for treating a wide range of collar and cuff grime and pre-brushing with detergent is a good and safe way to moisten these areas to help the drycleaning process dissolve perspiration and skin sebum and clean them up.

Pre-treatment detergents differ from machine detergents in that they may have more moisture in them. They are also free from optical brightening agents so they can be applied locally without creating areas of higher fluorescence that can cause extra marks that become visible after cleaning.

The drycleaning machine process: The main chemical used in the machine is the drycleaning solvent. Perc is the most powerful with a solvency of 90 on the Kauri-butanol (Kb) scale. Hydrocarbon has a power of 30 while cyclosiloxane is the mildest with a power of around 12. Perc probably needs the least pre-treatment (especially for oily stains) whilst cyclosiloxane is the least likely to cause any colour damage.

The addition of the machine detergent to the process is essential for obtaining a good result in most cases. Modern machine detergents are designed to be cationic, which means they are attracted to the textiles being cleaned just like a fabric conditioner in a washing process. A good detergent eliminates static, gives the fabrics body and texture (especially important with silks after cleaning in perc) and generally leaves the fabric with a soft feel.

Other additives essential for comprehensive cleaning include reproofing agents for rainwear, deodorisers for smoke-damaged work, stain repellents and leather oils.

Post spotting: Stains that are difficult to remove and therefore survive the machine process and those that contain sugars or proteins, which can darken and become visible in the cleaning process, may need post-spotting with a stronger reagent. There are three available (to match the three for pre-spotting for vegetable dyes, proteins from the body and solvent-based stains). The best post-spotters are not only stronger but can also be removed by flushing alone, without re-cleaning.

There is a full armoury of chemicals to assist the modern cleaner, which allows the skilled and experienced to do a good job. However, the untrained cleaner may make the wrong choice producing poor, if not disastrous, results.


Confusion Confusion
Testing misses a step Testing misses a step


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