| Ian Holme discusses recent pretreatment developments that allow users to attain desirable pretreatment effects more easily and avoid possible dyeing problems in subsequent processes |
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| Tanatex responds to market needs with greener pre-treatment agents |
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Modern fabric pretreatment systems are designed to perform and to yield fabric that is of uniform whiteness, absorbency and wettability. The level of pretreatment given to a fabric is often dependent upon the subsequent processing sequence to be carried out. With many cotton fabrics a thorough scour may be all that is required for subsequently dyeing to a dark colour, and there are now many combined scour / dye systems that can be used to save processing time, water and energy. However for high whites and pastel colours a high standard of pretreatment is essential.
Fabric pretreatment is more critical for fabrics scheduled for open width pad dyeing methods because dyeing uniformity and levelness must be achieved within a very short time, whereas in exhaust dyeing methods the longer dyeing process is more tolerant of fabric pretreatment variations. The current trend towards pad-batch dyeing of cellulosic knitted fabrics to achieve a higher quality dyed and finished fabric will therefore require that fabric pretreatment be optimised to the high quality levels demanded for pad-dyeing.
Pretreatment chemicals / auxiliaries are chemically formulated to provide maximum removal and suspension of fabric impurities as well as maximising bleaching performance with minimum fibre damage. Thus fabric pretreatment recipes may contain surfactants / detergents / wetting agents, chelating or sequestering agents for heavy metal ions, bleach stabilisers and accelerators, and fluorescent brightening agents for high whites.
Sarex, India has recently introduced a new cost-effective and economical low foaming wetting and detergent agent termed Celldet R. This product has been designed for application in the bleaching of cellulosic yarns or fabrics. Celldet R is APEO (alkyl phenol ethylene oxide)-free and NPEO-free (nonyl phenol ethylene oxide-free). Celldet R offers excellent wetting of cellulosic fibres enabling high levels of whiteness and absorbency to be achieved. Of particular importance are the good fabric rewetting characteristics after bleaching, which ensures rapid wetting out in subsequent pad-dyeing and exhaust dyeing processes.
Friendly to the Earth with biodegradable chemicals
Biodegradability of surfactants is an important factor for many textile wet processing plants. Dow Chemical has recently introduced a range of three new biodegradable surfactants, namely, Ecosurf EH3, Ecosurf EH6 and Ecosurf EH9. All three products are readily biodegradable and have low aquatic toxicity. The Ecosurf range of surfactants has been accepted and listed on the CleanGredients Database as meeting the Design for Environment (DfE) screening criteria of the US EPA (Environmental Protection Agency). The CleanGredients Database enables producers to identify cleaning product ingredients with optimal performance / environmental characteristics and has been established through the DfE program in partnership with the GreenBlue Institute. The market potential for biodegradable surfactants and auxiliaries is increasing globally because of the greater restrictions imposed through tighter regulations in many countries on effluent quality standards.
Greener pretreatment agents are on demand as Asian producers are under a mounting pressure to minimize their environmental footprint in their manufacturing activities. Responding to the market needs, Tanatex has introduced an improved version of their well-established Tannex Rena Liquid. This improved formulation is termed Tannex Rena Liquid 01 and is now a transparent formulation that is phosphorus-free and more environmentally friendly. An advantage of this pretreatment agent is that the amount of caustic soda used can be much lower with Tannex Rena Liquid 01 than with other classical organic stabilisers. As a result, less acid and water are required in the subsequent neutralisation treatment with clear cost savings in chemicals, water consumption and effluent treatment.
A novel multi-purpose pretreatment agent is Tannex Noveco, which has been designed by Tanatex for all kinds of discontinuous operations. Readily soluble in cold water Tannex Noveco can be dosed automatically and possesses low foaming properties. This new pretreatment agent provides an excellent stabilising action in full-white bleaching and in preparing white fabric for dyeing as well as in other treatments, e.g. scouring of elastane bands, stripping fluorocarbons and more. Tannex Noveco is claimed to be harmless to the aquatic environment and meets all modern environmental guidelines / ecological standards, e.g. Oeko-Tex 100, EKO label and GOTS. Tannex Noveco provides fabrics with excellent rewetting characteristics, good DP (degree of polymerisation) values, and the pretreatment agent also offers good lubrication properties thereby helping to eliminate formation of fabric crease marks.
Whiter than white with new bleach
Sera Fil SBS of DyStar is a new high performance multifunctional auxiliary for the bleaching of cotton and cotton blends. It is effective on blends containing elastane because Sera Fil SBS contains specific natural minerals with a large surface area enabling the absorption of oily substances like the silicone oils used on elastane. These are often very difficult to remove efficiently and can give rise to problems in subsequent dyeing, printing and finishing operations. Similarly, coning, twisting and needle oils are also effectively removed.
A big benefit customers can get from Sera Fil SBS is an improved right-first-time rate, or in other words, a reduced number of dyeing faults, according to DyStar.
Sera Fil SBS softens hard water and sequesters iron impurities out of the fabric as well as providing stabilisation of hydrogen peroxide bleach liquors thereby increasing the efficiency of bleaching. It also provides a crease-preventing action and imparts excellent fabric absorbency. An additional advantage is that the heavy metal / alkaline earth contents of the fabric are reduced to a minimum, thereby giving rise to a higher whiteness and avoiding dyeing problems due to the presence of metallic impurities.
Good full whites can be achieved on regenerated cellulosic fibres using the Gentle Power Bleach system introduced by Huntsman Textile Effects and Genencor. It is a new bleaching technology based upon "first-to-market" enzyme innovation from Genencor. Compared with traditional peroxide bleaching under highly alkaline conditions the novel Gentle Power Bleach system offers low temperature bleaching at 65°C and in a neutral pH range. This reduction in the bleaching and in the rinsing temperature can lead to savings in water and energy consumption of up to 40%.
With this product, extremely soft, bulky natural handle effects are delivered on cotton fabrics. Of special importance is that high levels of fabric whiteness are achieved with less fabric weight loss and Gentle Power Bleach delivers brighter and more brilliant colours after dyeing together with an enhanced colour yield. There is clearly considerable market potential in Asia for enzyme bleaching systems that operate under neutral pH conditions.
Another approach to attain full white is the use of fluorescent brightener. Clariant’s Leucophor BMBB liq is a fluorescent brightener that imparts a brilliant bluish white to cellulosic fibres and their blends with synthetic fibres.
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