The continuously increasing consumption of elastane fibres over the last few years shows that nobody wants to do without the advantages imparted to the textiles substrates with high stretching properties & high elastic force, but today these fibres are also used for women's & men's outerwear in order to impart a better & permanent form stability.
Textile articles especially whites and pale shades are susceptible to yellowing. This can happen during or after textile processing at the plant but also during storage & in shops or even at home. There are many causes which can be responsible for this phenomenon: Yellowing Effects Gas Fading Temperature Storage Miscellaneous Light Packaging
<ul><li>The yellowing effects may be due to substrate itself, or due to the products used such as oils & softeners. It requires an analysis to detect the problem. </li></ul><ul><li>Gas Fading: NO x fumes of stenters & NO X fumes during storage & Ozone exposure </li></ul><ul><li>Temperature: Heat setting, Moulding, Softeners & heat exposure </li></ul><ul><li>Packaging: Phenolic & amine related yellowing </li></ul><ul><li>Light: Fading of optical brighteners & dyestuffs, Deterioration of fibres </li></ul><ul><li>Micro-organisms: Attack by fungi & bacteria </li></ul><ul><li>Miscellaneous:Interaction of softener & fluorescent whitening agent </li></ul>
Directly heated stenters One of the most important causes of textile yellowing of synthetic fibres is gas fading. The combustion of gas and fuel introduces NO x into the heated air. This NO x - gas is able to react with the fibre and with products (oils, waxes and anti-oxidants) on the fibre. By applying Altranol-GR on the fabric, a reaction of the NO x with the active ingredients of Altranol-GR takes place. The resulting reaction product is easily washed off. The fibres are not attacked. At the end the result is a cleaner, whiter fabric.
Stenters In the textile industry we meet two different types of stenters. Stenters heated by burning gas and oil as well as indirectly oil-heated stenters. The combustion heated stenters produce more harmful nitrogen oxides as the air is in direct contact with the flame. In the indirectly heated stenter type air is not mixed with fuel or gas to heat the textile materials. By using Altranol-GR the difference in whiteness between similar lots heat set on different stenters can be minimized (reproducibility). As explained before, the NO x produced in the direct heated stenter is scavenged away by the Altranol-GR product. The levelness in the width and also in the length of the lot as well as between similar lots is far better when Altranol-GR is used.
Gas fading and storage Some fibres and applied lubricants, but especially packaging materials, can contain anti-oxidants, based on steric hindered phenols, like BHT. This anti-oxidant can react with NO x fumes present in shops and ware houses, due to air pollution especially through traffic (traffic in or close to ware houses). Avoiding BHT containing packaging and an acid pH value of the finished goods can minimize this problem. Ozone fading Ozone fading is actually an issue in the garment industry, especially on denim articles. This causes a yellowing effect which is caused by a certain type of softeners. Special anti-ozonate softeners can reduce this problem to a minimum (e.g. Aquasorb-OZ)
High temperatures Exposure of textile materials to heat can cause yellowing due to oxidation of fibres, fibre and spinning lubricants, fibre impurities (cotton). Fibre oxidation of Polyamide fibres results in loss of end-amino groups. As a consequence a loss of colour-yield will be observed. If oils are present, the heat transfer can be irregular from fibre to fibre and oxidation takes place unevenly. Differences in dye-sites (end-amino groups) automatically will then show up as barriness . Another yellowing defect can occur during moulding of articles made of synthetic fibres, especially for lady’s lingerie ( e.g. PA/EL bra.) Altranol-GR can be of great help to maintain whiteness and overcome inconsistency problems. Especially cationic fatty amide derived softeners as well as some amino modified silicones (high nitrogen contents) are sensitive to oxidation and thus yellowing effects. Drying and finishing conditions should be well balanced out with the choice of softeners and the required end-results.
Packaging Some remarks were already made, on this topic, under Nitrous fumes and storage. It is important to set the right final acid pH-value for the finished goods, as the yellowing only appears under neutral to alkaline conditions. It can easily be checked if the fabric turns white after exposure to acid. The reason for this yellowing is the combination of phenolic compounds like BHT and nitrous gases, coming mainly from air pollution. It occurs much more in cities than in the countryside. BHT may be present in packaging materials like plastics, foams, recycled paper and adhesives (try to sue BHT-free plastic and avoid paper boxes made of recycled paper)
Light The light fastness of Fluorescent Whitening Agents (FWA) is generally rather low. Articles or parts of them, which are exposed to direct sunlight, will look yellowish. Light, as an energy source, can also deteriorate fibres. Glass does not filter out all UV light (only < 320 nm). PA is a very susceptible fibre, especially the Titanium oxide containing dull versions. This photo oxidation causes yellowing and strength-loss. The presence of moisture accelerates this effect. Micro-organisms Fungi and bacteria can cause yellowish or even brown or black stains. These species need nutrition to grow, such as residual organic chemicals on the fabric (e.g. organic acids, leveling agents, surfactants, softeners, lubricants). Humidity and ambient temperatures will speed up their growth.
Miscellaneous Cationic softeners can interact with anionic fluorescent whitening agents, reducing the hue of whiteness. The rate of quenching depends on the type of softener and the accessibility of the nitrogen-atoms. The pH also plays an important role. Strong acid conditions should be avoided. Acid pH values of the fabric may also lead to shade change of the FWA to greenish, which may already happen at pH of <5. Select the right FWA if slightly acid conditions on the fabrics are required (e.g. to avoid phenolic yellowing)
Untreated fabric can be full of different preparations & impurities. Especially mineral oil / natural oils, silicone oils, paraffin waxes, antistats etc affect the fabric. Normally these impurities would be removed by washing. However this is impossible due to curling of textile & hence forced to set the fabric with all contaminating substances. This have negative effect on the fabric quality. The most frequent negative appearances are yellowing, poorer dyeability caused by the oxidation of the fibre, reservations which are observed after dyeing & poor fastness properties. Volatile preparations indirectly affect the fixing aggregates because these preparations precipitate on colder machine parts & drop back onto the fabric , which too cause a typical faulty appearance.
This special product contains selected scavengers to avoid yellowing effects due to NO x fumes in direct heated stenters as well as heat-related oxidation. This product is efficient on PA, PA/EL, PES and PES/EL. Pre-fixation of greige goods EASTANE containing fabrics and especially knitwear need a presenting to relax the fabric and to obtain form stability of the goods (changing the micro-structure of the synthetic fibre and partly fusing the Elastane fibres). Of course in respect to the weight per m 2 , the length and the width per all settings should be within the final specifications of the goods. Additionally the undesirable tendency of curling edges can be eliminated or at least be minimized. Heat-setting of Polyester/EL and Polyamide/EL is done at approx. 185º - 195º C, depending on the type of Elastane – fibre.
Logistically it is preferred to do the heat-setting operation on greige goods, but impurities such as fibre and spinning lubricants / oils and emulsifiers may lead to increased yellowing tendency . Some industries tend to pre-scour before setting for this reason. It solves however the yellowing of oils but not that of the Polyamide and Elastane. Heat-setting wet fabric will moreover cause increased yellowing. However, the circumstances on the stenter play an even greater influence. Direct or indirect heating. Reliability and consistency of the temperature. Direct heated stenters produce NO x fumes by oxidation of nitrogen. These fumes are attacking the oils and the fibres during the setting operation, thereby causing yellowing. Altranol-GR prevents this reaction as it contains special scavengers.
In a gas chamber combustion fumes (among others NO x ) are brought into contact with fabric and treated at 160ºC. Moulding of finished fabrics (e.g. women’s brassiers) PA/EL especially blends are susceptible to yellowing during moulding to obtain a good fit especially for lady’s underwear. Oxidation of the Elastane and polyamide fibres can easily occur. Residual scavenger from the previous treatment or newly applied Altranol-GR will avoid this to a large extend. BLANKOPHOR CLE and BLANKOPHOR CLE Liquid have the highest moulding resistance of all Fluorescent Whitening Agents for PA/Elastane.
PA/EL knitted fabric was treated with 20 ml/l Altranol-GR Pick-up : 60 % Dried at 120ºC and heat-setted at 195ºC. Part of the samples were washed with reduction agent at 85ºC, rinsed and dried. Contact head was applied on the FIXOTEST according ISO 105-P01. The treated fabrics, either washed or unwashed, are showing clearly much less yellowing after the Fixotest-treatment. Light fastness Altranol-GR shows only very little improvement of the light fastness. To increase the light fastness of the fibres and the dyestuffs special UV-absorbers are recommended. Untreated Altranol-GR treated After heat setting 60 secs at 195ºC After heat setting 60 secs at 210ºC
Influence of amount of product The amount of scavenger (and thus the amount of product) depends on the amount of fumes and oxygen in stenter. Good stenters need lower amounts than critical ones. For moulding articles it is advised to use some more product as residual scavenger will remain on the fabric after washing and reduction bleaching. This will help to overcome yellowing during forming cups etc. Application: It can be applied by pad and/or exhaust method. Pad application “Altranol-GR” 20-40 ml/l Exhaust application “Altranol-GR” 2-4% o.w.f
Recipe The following variation in processing are suggested. For use on Greige goods: 1. Padding: 20-40ml/l Altranol-GR 0.3-0.5ml/l Sequestering agent Padding 50-75% pick-up Drying 100ºC Heat setting 180-200ºC For use on Pre scoured goods: 2. Exhaust : 2 -4% Altranol-GR 0.25-0.5ml/l Sequestering agent Process for about 10-15 mins at 50-60ºC,spin or put through a mangle & finally dry & heat set.
For use during moulding The conditions during moulding are principally the same as in heat setting. At temperatures above 200ºC & exposure times between 20-80 seconds some fibres show a tendency to yellowing. This problem is aggravated through softeners on the fabric which cause yellowing under the influence of temperature. If one optimises this finish by a combination of thermostable hydrophilic softeners & an additional wetting agent with antioxidative effects: Guide Recipe: 10-30g/l Altranol-GR 10-30g/l Powersil-SIQ or Luballen-AH X g/l Altraplex-GA (To adjust pH to 4.5-5.0) Subsequent heat setting
<ul><li>Antioxidative effect. </li></ul><ul><li>Prevents yellowing induced by heat processing </li></ul><ul><li>specifically for articles which have to be heat set e.g. </li></ul><ul><li>because of curled edges, or for stability reasons. </li></ul><ul><li>Maintains the dyeability. </li></ul><ul><li>Very good wetting effect on hydrophobic untreated </li></ul><ul><li>fabric. </li></ul><ul><li>Good washing effect. </li></ul><ul><li>Reduces evaporation of spinning lubricants at the </li></ul><ul><li>stenter. </li></ul><ul><li>Prevents soiling of the stenter. </li></ul><ul><li>Suitable for articles with a tendency to yellowing in </li></ul><ul><li>subsequent heat treatments (e.g. on a rotary press). </li></ul><ul><li>Preferred application is by padding. </li></ul><ul><li>An exhaust application can be used. </li></ul>