Oily stains are one of the most common stains faced by a drycleaner. These types of stains can originate from automotive oil or oily foods, such as salad dressings and mayonnaise. If the stains are brought to the attention of the drycleaner when they are fresh, before much aging has occurred, drycleaning solvent can usually remove the stain.
However, as the stain ages it becomes more difficult to remove. In the same way that oil-based paints glaze and harden, oil-ased stains oxidize. An invisible fresh stain will turn yellow and harden with age. Air and/or heat, such as the heat used during cleaning and finishing procedures, can cause this oxidation process to occur.
WHAT DO THEY LOOK LIKE?
On woven fabrics, an oxidized oil stain forms a small cross or a characteristic ragged edge as it spreads in both directions of the weave. This pattern occurs because the viscosity of the oil allows it to wick along the yarns but prevents it from forming a bridge between the yarns.
In knit fabrics, the stain is distinguished by sharp “leave-off” marks. These marks are again caused by the inability of the oil to bridge across the yarns.
HOW TO REMOVE AN OXIDIZED OIL STAIN
The first steps to follow when attempting to remove an oxidized oil stain are as follows:
• Place the stained area on the solid portion of the stain removal board and apply volatile dry solvent.
• Tamp the area with a brush.
• Keep the area saturated with volatile dry solvent.
• Use a few drops of oily type paint remover to help lubricate the oil so it can be removed.
• Flush the area well with volatile dry solvent and dry or flush and re-dryclean.
This procedure should remove most oil stains. If a stain still remains, alcoholic potassium hydroxide (KOH) may be used. Before using this solution, make sure that all other agents have been flushed thoroughly and that the fabric is completely dry.
Oxidized oil stains that have been laundered and pressed may be permanently set.
USING ALCOHOLIC KOH TO REMOVE OXIDIZED OIL STAINS
The DLI Garment Analysis Department has been using alcoholic KOH for many years with success. It is a strong alkali and should be used with caution. To avoid damaging the fabric, you should follow these precautions:
• Never apply this solution to a stained area that is wet with any other substance. A reaction with the other substance can occur very quickly and damage the dye or fabric.
• Never fog with the steam gun to speed up the process.
• Always test the solution on an unexposed area of the garment, such as a seam or hem, before using. This is especially true with wool and silk fabrics. As a strong alkali, KOH can cause permanent damage to these fabrics.
• During use, never let the alcoholic KOH solution dry on the fabric. Any dried residue will pick up moisture from the air and produce a damaging alkali.
• Never use the solution on bonded fabrics or garments containing foam.
Apply the alcoholic KOH solution to the stained area, and let it soak for about five or six minutes. As the oil stain solubilizes, you will see a yellow ring pushing outward from the stained area and the stain itself will become more intense. After the stain has been solubilized, rinse the solution well with distilled solvent and dryclean the garment. If a yellow residue remains, it may be necessary to neutralize the stained area with 28% acetic acid or a commercial tannin remover. Flush and dry.
Prolonged contact with KOH may cause some whites to yellow. This can be overcome by first flushing all the KOH out with distilled solvent and then neutralizing.
If any traces of discoloration remain, bleaching may be used as a final step. When using any bleach, take into account the fiber content and dyes used on the garment and test on an unexposed area.
PREPARATION OF ALCOHOLIC KOH
Because alcoholic KOH is not a commercial product, you will have to mix the solution yourself, or ask your pharmacist or a local chemistry laboratory to prepare it for you.
The solution consists of nine grams (0.32 ounces) of potassium hydroxide dissolved in one quart of normal butyl alcohol. Of the four types of butyl alcohol that are available, only normal butyl alcohol can be used for this purpose. Normal butyl alcohol is also known as primary butyl alcohol, butyric alcohol, or L-Butanol.
If a balance is available, you can weigh the nine grams of KOH pellets in a small, closed bottle and transfer the KOH to a quart of normal butyl alcohol. Shake to mix the two ingredients. It is best to allow the mixture to stand overnight before use. Any undissolved material that remains on the bottom of the bottle will be potassium carbonate (potash), which will not affect the solution.
If no balance is available, you can use liquid displacement to measure the potassium hydroxide. This method requires a the use of a 25 milliliter (ml) graduated cylinder. Fill the cylinder to the 20. 5 ml mark with normal butyl alcohol. Next add the KOH pellets until the volume of alcohol in the cylinder reaches the 25 ml level. Then add the contents of the cylinder to the quart bottle of normal butyl alcohol.
The following precautions must be taken during preparation:
• Do not touch the potassium hydroxide pellets with your bare hands. This material is extremely caustic and can combine with the moisture of skin to cause severe alkali burns. Use a spatula obtained from a chemical supply house or plastic spoon (be sure to discard after use).
• Always weigh the KOH pellets in a closed container. They are very hygroscopic and pick up moisture quickly from the air, producing a highly alkaline water-based solution.
• Use adequate ventilation when working with normal butyl alcohol and keep away from flames. Normal butyl alcohol has a flash point similar to Stoddard solvent and has slightly toxic vapors.
• Use safety goggles when preparing the solution.
• Keep the solution in a dark-colored glass container and away from direct light. Clearly label the container and add warnings about flammability and strong alkalis.
OBTAINING SUPPLIES
The chemicals, cylinder, spatula, and weighing bottle used in this process can be purchased from a chemical supply company. Since the chemicals are expensive, order the smallest size available.
VWR Scientific, Inc.
PO Box 626
Bridgeport, NJ 08014
(800) 932-5000
Potassium Hydroxide in n-Butanol Solution
Buy from LAB ALLEY
