The yellowing that we sometimes notice on cotton shirts and shirts is due to a reaction between the fibers of cellulose of which the cotton and oxygen present in the air is composed. Cotton, in fact, one of the best known and used natural fibers for clothing, is obtained from such plants Gossypium and is formed almost exclusively by cellulosea polymer consisting of long glucose chains, and if exposed to the air, undergoes a slow oxidation process that alters its chemical structure, causing a progressive yellowing. A second yellowing mechanism, said phenolicis caused by other molecules present, for example, in the plastic bags used to pack the fabrics: they also react with molecules present in the atmosphere generating yellowish compounds.
To prevent both types of yellowing, it is important limit exposure to sunlight and humidity. Scientific studies have shown that treating tissues with special slightly acidic compounds including natural ones (such as acetic acid or citric acid) helps to keep a stable a pH unfavorable to the formation of the compounds responsible for the deduction.
The causes of dejection: the oxidation of cellulose and external contaminants
Exposed to the air, the cellulose suffers a slow process of oxidation: reacting with atmospheric oxygen (or2) new groups of atoms are formed along the chain. For example, during these reactions, the obssehydrilic groups (–OH) are transformed into charcoal groups (-c = o), which have the ability to reflect and absorb different wavelengths of lightgiving the fabric a yellowish shade.
In other cases, they are the packaging materials, such as plastic bags, which react with compounds present in the atmosphere, forming yellowish compounds that they deposit on the fabricthen yellowing it in contact with it. These are in most cases of phenolic molecules such as the BHT (ButilidredSSituline), used as an antioxidant in fabric protection films: these react with nitrogen oxides in the air, forming new compounds (such as the nitrobenzene) who color the cotton yellow. This phenomenon is known by the name of phenolic yellowing.
Note how in the first case theDirect oxidation of cellulose fiberswhile instead the second phenomenon depends only from external contaminants.
How to prevent cotton yellowing
To prevent cotton yellowing, you must first of all Avoid drastic situations that can encourage or accelerate oxidation reactions, such as prolonged exposure to sunlight or humidity.
According to a study conducted by researchers of the Louisiana State Universitythe phenolic yellowing process can be prevented by treating cotton fibers through the use of neutralizing agents (even natural, such as theacetic acid ol ‘citric acid) and of softening or special products: in this way we modify the conditions of the pH of the fabric making them unfavorable to the formation of yellowish compounds and keeping the cotton visually more white over time.
