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Feb 19, 2016

Phenolic Yellowing

Yellowing as name called on very pale to full white fabric (Knit/Woven). Recently, had chance to visit a towel facility who is facing yellow streaks on towels.When full white OBA treated towels were tested for core ph. it was fount that ph is above 8.5 and present of Nitrogen dioxide in air has triggered the reaction.The wet storage for long period further catalyzed the yellowing.

A good definition of phenolic yellowing is expressed as "Yellowing is caused due to the presence of phenolic compounds on the textile material, reacting with the oxides of nitrogen in an alkaline medium. "

Oxides of nitrogen are generated in warehouses/households from direct heating systems or from automobile emissions in the urban environment. Neither the oxides of nitrogen nor the phenolic compounds by themselves cause yellowing, but when united, form the yellowing products.

BHT (Butyl Hydroxy Toulene) is added in polyethylene bags as anti oxidant to increase life of packaging bags and avoid air oxidation/Aging. It is good as for packaging material but, when this BHT reacts with textile material it caused yellowing. So, textile materials are often advised to not be placed in poly bags which have anti oxidents like BHT.This chemistry of BHT is low in cost and highly effective. Due to its low vapor pressure it is volatile and can be transferred to textile goods easily.

Polyamide (Nylon) is more prone to yellowing than cotton. This is due to the cationic amino groups present which react with anti oxidants.

Archroma product UMIDOL APY reacts with these cationic amino groups and block them to react with Anti oxidant and hence chances of yellowing minimizes.

Another reason of yellowing can be OBA itself. Major of the OBAs are not stable to Acidic phs and appear yellower to greener in acidic ph. so proper choice of OBA is compulsory especially when Non volatile acids are used.

Precautions which can be carried out are.

Keep fabric core ph to acidic.
keep in dry form
Avoid direct sun light.
Don't pack in BHT containing Poly bags.
Apply Umidol APY as pre caution when packaging material is not confirmed.

Find a link to james Heal Phenolic yellowing test kit.

Another excellent article on above subject.

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