(2009-2010)

Causes of yellowing during storage The intensive yellowing of white or pastel colored textile good is very often a result of the presence of phenol-based antioxidants (butylated hydroxyl toluene derivates). This chemistry is low in cost and highly effective. Due to its low vapor pressure it is volatile and can be transferred to textile goods easily. Products of this type are commonly used as stabilizers in Fibre production, Further textile processing. Packing materials (e.g. polyethylene wrapping films, packing material in general) 

• Storage yellowing

• Typical Appearance

• Lemon yellow colour of fabric

• Yellow substance is soluble in alcohol

• Yellow colour often behaves like an indicator :

• Disappearance with acid and reappearance with alkali

Factors influencing the yellowing Various factors influence the yellowing of white textile goods in presence of antioxidants :  Storage conditions

o Atmosphere composition in store, shop and home (NOX beside other pollutants)

o Humidity and temperatureo Heating and ventilationo Storage timeo Illumination

 Composition of hot air, particularly on drying / curing/heat-setting equipment with direct gas heating when nitrogen oxides are produced due to unproper burning conditions.

Causes :

Reaction of nitrous oxides (Nox) in the air with phenolic substances : Antioxidants e.g. based on butylated hydroxytoluene (BHT) often used in cardboards, synthetic materials, plastic films or plastic parts.

+ Phenolic substance + Nitrous oxides

Yellowing is favoured by pH > 6 ( yellow colour of BHT-Nox reaction products is pH – dependent )

Yellowing can be favoured by cationic charges on the fabric (affinity of BHT-NOx reaction products to cationic charges)

Fabric finished with cationic softeners or cationic after treatment : cationic charges, attract antioxidants.

Mechanism of Yellowing

Precautions lowering the risk of yellowingAs long as such antioxidants are used it is virtually very difficult to prevent such yellowing. To reduce this yellowing we recommend :

Warn customers to ensure that fibres and auxiliaries are free of phenolic antioxidants. Especially packing or wrapping materials should be free of antioxidants (phenol free low density polyethylene bags)

Adjust the final finish with some non volatile organic acid (shade and optical brightener should be acid stable)

 To avoid the presence of nitrogen oxides (NOX) during production and storage (no direct gas heat, all transportation systems such as fork-lift trucks with electric motors, good ventilation in warehouse to avoid air pollution).

Normally white PA turn yellow even under slightly acid conditions. This is due to the cationic character of the free amino end-groups of PA which interact with the antioxidant derivate. Quench APY/Quench-AY / LG are preventing such yellowing while blocking the free amino end-groups of the PA. For the application in general we recommend to use slight acid conditions. Please check also whether the optical brightener is acid stable if non-volatile acids are used.

Counter products : • Quench-AY Nylon fiber yellowing preventing agent Special nature of the applications Phenol yellow change very excellent suppression Vanillin (vanillin) and BHT (di-tert-butyl-p-cresol), yellowing caused by

the suppression effect is very excellent High affinity for the nylon fiber

• Quench-LG Highly effective anti-yellowing agent for polyamide & blends with elastane

during storage. Reduces or prevent yellowing during storage.

• Quench-APY

Is a high performance composition designed for treating fabrics & garments

from yellowing due to Storage conditions

Atmosphere composition in store, shop and home (NOX beside other pollutants)

Humidity and temperature Heating and ventilation Storage time Illumination

 

Quench – UWPIs highly effective fiber stabilizer for reducing yellowing of polyamide and PA blends during exposure of any kind of heat.It protects all types of polymide fibers and their blends with elastomer fibers against oxidative damage, thus reducing yellowing due to thermic and photochemical influence. Avoids yellowing of optical brightened polyamide and it blends during heat setting or molding processes. Prevents shade changes of pastel dyed polyamide and its blends during heat setting or molding treatments.Applicable on all textile substrates in exhaust or padding processesProducts prevent reactions of nitrous oxides and phenolic substances coming from packing material etc. during storage.No / less yellowing of stored textileNo / less complaints of retailers or consumers.

Typical appearance :

• Yellowing colour marking outer folds

or surfaces of ready made folded

denim fabrics

• Yellowish colour can be removed by

warm rinsing but leaves brightened

areas.

• Often occurring in summer, also

without light.

Causes:Unsuitable cationic softenersReaction of indigo with ozone and nitrous oxides

Prevention :Use of softeners avoiding yellowing and minimizing ozone fadingPacking of ready-made denim articles avoiding or minimizing exposure to exhaust.Fumes in stores.

Our recommendation for antiozonate:

Aquasorb-OZ / Powersil-NOZ

Avoids shade changes due to yellowing of fabrics dyed with indigo.

Gives smooth and very soft handle to cotton and yellow fabrics

Applicable in padding or exhaust process.

Causes for yellowing during heat setting or molding :

Decomposition of lubricants/spin finishes (yellowing of substances on

the fibres)

Decomposition of cationic softeners (yellowing of substances on the

fibres)

Reaction of monomers, oligomers or functional groups (yellowing of

fibre itself)

Especially PA: migration of antioxidants from within the fiber to the

surface. [ yellow reaction products with nitrous oxides, especially in

gas heated stenters]

Yellowing of substances on the fibre : Scouring the fabric prior to heat treatment Pre-emulsifying of spin finishes and lubricants by padding with

suitable products and washing off during subsequent dyeing/finishing (especially important in case of micro fibres)

Altranol-GR For PES & PA & CO/EL

A unique product that prevents yellowing of polyester, polyamide & their blends with elastane during the heat setting process. Specially designed for the production of pale shades & optically brightened whites  

Yellowing of cationic softeners

Use of suitable pseudo cationic softeners (quality of raw

materials and reaction control is crucial)

Yellowing due to reaction within or due to yellow reaction

products.

Application to fibre stabilizers [ radica / scavenger ]

Overview :

1.Storage yellowing * typical appearance

2.Storage yellowing * causes

of denim * prevention

3.Thermal yellowing * counter products

4.OBA yellowing * Lab comparison results

Conclusions :

Our products against storage yellowing : Quench-APY Quench-AY Quench-LG

Our product against thermal yellowing :• Altranol-GR

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Email ID – ketan@lnchem.in lnchem@vsnl.com