White or light-colored fabrics of nylon, elastic fibers and their blends are particularly susceptible to yellowing. Yellowing may occur during the dyeing and finishing process, during storage or hanging in store windows, or even in at home. There are many reasons that may cause yellowing. For example, the fiber itself is prone to yellowing (material-related), or chemicals used on the fabric, such as oil residues and softeners (chemical-related).
Further analysis is usually necessary to know the cause of yellowing, how to set processing conditions, which chemicals should be used or only which chemicals should be used, and what influencing factors interact to cause yellowing, packaging and packaging of fabrics. How is the storage situation?
We mainly focus on the high-heat yellowing and storage yellowing of blended fabrics of nylon, polyester fiber and elastic fiber, such as Lycra, Dorlastan, Spandex, etc.
Causes of fabric yellowing
Gas fading:
NOx flue gas of setting machine
NOx flue gas during storage
Ozone exposure
Temperature:
High heat setting
High temperature die
Softener and high temperature treatment
Packaging&Storage:
Phenol and amine-related yellowing sunlight (Light):
Fading of dyes and fluorescers
Degeneration of fibers
Microorganisms:
Suffering damage from bacteria and mold
Miscellaneous:
The relationship between softeners and fluorescent essence
Analysis of the source of the problem or countermeasures
Styling machine
There are several different types of setting machines used in the textile industry. There are setting machines that are directly heated by combustion gas and oil or indirectly heated by hot oil. The combustion-heated setting machine produces more harmful NOx because the heated air is in direct contact with the burning gas and fuel; while the setting machine heated by hot oil will not mix the burning gas with the hot air used to set the fabric.
To avoid excess NOx produced by the direct heating setting machine during the high-temperature setting process, it can usually be removed by using our SPANSCOUR.
Smoke fading and storage
Some fibers and some packaging materials, such as plastics, foam, and recycled paper, add phenolic antioxidants such as BHT (Butylated Hydroxy Toluene) during the processing of these auxiliary materials. These antioxidants will interact with stores and warehouses. NOx smoke reaction in the air, these NOx smoke comes from air pollution (including air pollution caused by traffic, for example).
We can: firstly, avoid using packaging materials containing BHT, and secondly, make the pH value of the fabric lower than 6 (you can use fiber to neutralize the acid) to avoid this problem. In addition, anti-phenol yellowing treatment is carried out during the dyeing and finishing process to avoid the problem of phenol yellowing.
Ozone fade
Ozone fading is mainly a problem that occurs in the garment industry, because some softeners can cause fabric yellowing due to ozone. Special anti-ozone softeners can minimize this problem.
In particular, cationic amino-aliphatic softeners and some amine-modified silicone softeners (high nitrogen content) are very sensitive to high-temperature oxidation, thus causing yellowing. The choice of softener and the desired end result must be carefully considered with the drying and finishing conditions to reduce the chance of yellowing.
High temperature
When textiles are exposed to high temperatures, they will cause yellowing due to oxidation of the fibers, impurities in the fibers and spinning lubricants, and fibers. Other yellowing problems can occur when molding synthetic fabrics, especially women’s lingerie (such as PA/EL bras). Some anti-yellowing products can be extremely helpful in overcoming this type of problem.
Packaging material
The relationship between gases containing nitrogen oxides and yellowing during storage has been confirmed. The traditional method is to adjust the final pH value of the fabric to between 5.5-6.0, because storage yellowing only occurs under neutral to alkaline conditions. , this kind of yellowing can be easily confirmed by pickling, because the yellowing will disappear when stored under acidic conditions. Anti-phenol yellowing products from companies such as Clariant and Tona can effectively prevent the occurrence of stored phenol yellowing.
The main reason for this type of yellowing is that phenolic substances such as (BHT) combine with NOx from air pollution to produce yellowing substances. BHT may be present in plastic bags, recycled paper cartons, glue, etc. You can try to use BHT-free plastic bags to reduce the occurrence of such problems.
Daylight
Generally speaking, the light fastness of fluorescent whitening agents is low. If the fluorescent whitening fabric is exposed to the sun for too long, it will gradually turn yellow. It is recommended that for fabrics with high quality requirements, use fluorescent whitening agents with high light fastness. Whitening agent. Sunlight, as an energy source, will degrade fibers; glass cannot filter all ultraviolet rays (it can only filter light waves below 320 nm). Nylon is a fiber that is very prone to yellowing, especially semi-glossy or matte fibers containing pigments. This type of photo-oxidation will cause yellowing and loss of strength. If the fiber contains high moisture content, the problem will be more serious.
Microorganisms
Mold and bacteria can also cause fabrics to turn yellow, brown or black.pollute. Mold and bacteria need nutrients to grow, such as residual organic chemicals (such as organic acids, leveling agents, surfactants) on the fabric. Humid environments and ambient temperatures will accelerate the growth of microorganisms.
Others
Cationic softeners will interact with anionic fluorescent whitening agents to reduce the whiteness value of the fabric. The rate of reduction is related to the type of softener and the chance of contact with nitrogen atoms. The influence of PH value is also important, but it is also Strongly acidic conditions should be avoided. If the PH of the fabric is lower than PH 5.0, the hue of the fluorescent whitening agent will also become greenish. If fabrics must be exposed to acidic conditioning to avoid phenolic yellowing, an appropriate fluorescent whitening agent must be selected.
Phenol yellowing test method (Adidas method)
There are many reasons for phenol yellowing, the main reason being the antioxidants used in packaging materials. In most cases, blocking phenolic compounds (BHT: Butylated Hydroxy Toluene) are used as antioxidants in packaging materials. oxidizing agent. During storage, BHT and nitrogen oxides in the air will form yellow 2,6-di-tert-butyl-1,4-quinonemethide, which is one of the possible causes of storage yellowing.
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