Why do white bed sheets develop yellow stains after washing?
Release Time:
2011-04-22 09:08
Source:
China Laundry
If yellow stains appear on white sheets after washing and cannot be removed by oxalic acid treatment, the possibility of rust or iron ion factors can be ruled out. If bleach treatment also fails to remove the stains, the possibility of pigment causing the yellow stains can be excluded.
Let's analyze one of the main factors causing yellow stains on white fabrics after washing. Some fabrics such as white sheets, white shirts, white underwear, and white tablecloths contain a certain amount of cotton (some do not, but they are few). Some have a high cotton content. These fabrics (except tablecloths) come into direct contact with human skin to some extent during use, which inevitably contains some skin secretions. The main secretion from the skin is sweat from sweat glands. Sweat is 99% water, with 1% residue after evaporation, containing a certain proportion of protein. The protein content in sweat varies depending on the person, diet, season, etc. When these proteins remain on white clothes or sheets, they do not show any color in dry or wet states and can be considered in a "latent state." However, when exposed to a certain amount of heat, they easily coagulate and firmly fix to the fabric, causing yellowing.
Using bleach, oxalic acid, and other treatments is very ineffective in dealing with this. This yellowing phenomenon mostly occurs on white or light-colored fabrics containing cotton. There is no way to restore the original color of the fabric once yellowing has occurred. Enzymes can decompose proteins, but they are not effective on proteins that have already solidified and are "closely" bonded to the fabric. The best way to reduce yellowing on white fabrics is to take effective measures during the washing process. For example, when washing white sheets, the main wash is generally done at 60-70°C. When heating, do not quickly raise the temperature to the preset level; it can be done in stages. First, add detergent at 40°C water temperature, then gradually increase to the preset temperature after some time. For white shirts or underwear, enzyme-containing detergent can be used, or pre-treat with 5% saline solution before washing with detergent. For tablecloths, which often have food stains rich in protein, the treatment method can refer to that used for sheets.
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