Role of Softeners in Textile Wet-Processing

Any operation that improves the physical characteristics of the fabric is termed asFinishing. Softener is an finishing agent that when applied to textile material improves its handle giving pleasing touch. As a general rule, the softening agents applied are lubricating agents, which facilitate the fiber sliding within the fabric structure, thus granting easier deformation and creasing of the fabric. In most cases, the duration of the effect is limited since the products applied during the treatment are eliminated by subsequent washing; for this reason they must be applied in the final stage of the treatment. The most common softeners are explained below :

***Non-ionic softeners : These are generally ethers and polyglycol esters, ethoxylated products, paraffins and fats. These softening agents are generally less efficient than anionic and cationic ones but they withstand the effects of hard waters, acid or basic environment and also stable in presence of cations and anions. As they do not bear any charge, they are mainly applied by forced application like padding methods. We at Matex have developed a complete range of Non-ionic softeners like Matsoft NISB paste, Matsoft NI flakes, Matsoft NISIL liquid, Matsoft NYS emulsion and NISPE.

***Anionic softeners :  Anionic softeners are produced by the condensation of fatty acids. They have good characteristics as lubricating softening agents and give the fabric a full hand.  They are unstable in hard water and acid environment. Anionic finishing agents have negatively charged hydrophilic group. The cellulose acquires negative charge when wetted out and attracts the positively charged hydrophobic group, with hydrophilic group orienting away from the fiber surface.

Anionic softeners are heat stable at normal textile processing temperature and compatible with other components of dye and bleach baths. They can easily be washed off and provide strong antistatic effects and good rewetting properties because their anionic groups are oriented outward and are surrounded by a thick hydration layer. They are often used for special applications, such as medical textiles, or in combination with anionic fluorescent brightening agents.

***Cationic softeners : They are usually quaternary ammonium salts, amino-esters and amino-amides. They are recommended for all types of fiber, and can be also applied with exhaustion process in acid environment (pH 4-5). These are also called molecular finishing agents because they form bonds with the cationic group on the surface of the fiber generally with negative electric potential. They can give some problem in presence of large anions, and they can cause change in dye toning, or a reduction in fastness to light values in the presence of direct and reactive dyes.

They are considered as the best softeners and are reasonably durable to laundering. They can be applied by exhaustion to all fibers from a high liquor to goods ratio bath they provide a hydrophobic surface and poor rewetting properties, because their hydrophobic group are oriented away from the fiber surface. They are usually not compatible with anionic products.

Cationic softeners attract soil, may cause yellowing upon exposure to high temperatures. Yellowing is associated with cationic finishes of quaternary ammonium compounds with free hydrogen attached to the nitrogen atom that can bind with chlorine to form ‘Chloramines’, the main cause for the coloration. Inherent ecological disadvantages of many conventional (unmodified) quaternary ammonium compounds (quaternaries) are fish toxicity and poor biodegradability. But they are easily removed from waste water by adsorption and by precipitation with anionic compound. At Matex, we have cationic softeners that are cold soluble like Matsoft VSC flakes, hot soluble like Matsoft HCS flakes, Matsoft CES flakes etc. that impart super softness properties to the fabric. We also have combined softeners for inner softness and surface silky feel like Matsoft CSIL, CSIL-JET for shear stability, and CSPE for abrasion resistance & improving tear strength.

***Amphoteric softeners :  Typical properties are good softening effects, low permanence to washing and high antistatic effects. They have fewer ecological problems than similar cationic products. Examples are betaine and the amine oxide type.

***Reactive softeners : N-methylol derivatives of superior fatty amides or urea compounds replaced with fatty acids. The products have to be cross-linked. They provide permanent softness and water repellency.

***Polyethylene-based softeners : Polyethylene can be modified by air oxidation in the melt at high pressure to add hydrophilic character (mainly carboxylic acid group). Emulsification in the presence of alkali provides higher quality and more stable products. They show high lubricity that is not durable to dry cleaning. They are stable to extreme pH conditions and heat at normal textile processing condition, and compatible with resins and fluorescent brightening agents. They impart lubricity especially required for yarns. They are very strong in improving properties like tensile strength/tear strength, sewability, abrasion resistance and rubbing. Matsoft PE emulsion and Matsoft PEW emulsion belongs to this category.

***Silicone-based softeners : Silicones are macromolecules comprised of a polymer backbone of alternating Silicon and Oxygen atoms with organic groups attached to silicon. Silicone’s softening capability comes from the siloxane backbone’s flexibility and its freedom of rotation along the Si-O bonds.

They are insoluble in water, and therefore must be applied on fabrics after emulsification or dissolution in organic solvents. They feature quite good fastness to washing. They create a lubricating and moderately waterproof film on the surface and give fabrics a silky hand.

They provide very special unique hand, high lubricity, good sewability, elastic resilience, crease recovery, abrasion resistance and tear strength. They show good temperature stability and durability, with high degree of permanence for those products that form cross linked films and a range of properties from hydrophobic to hydrophilic. As per the required properties the organoreactive group is modified and the results are achieved. Matex has a developed a complete range of silicone softeners like Diamino silicone(DAS), Reactive aminosilicone (RAS), Aminofunctional silicone (AFS), Organofunctional silicone (OFS), Premium aminofunctional silicone (PAS), polyether silicone (HYS) and epoxy silicone (NYS).

***Mechanism of softeners : Softeners provide their main effects on the surface of the fabrics. Small softener molecules, in addition, penetrate the fiber and provide an internal plasticization of the fiber forming polymer by reducing of the glass transition temperature.

Depending on the ionic nature of the softener molecule and the relative hydrophobicity of the fiber surface, cationic softeners orient themselves with their positively charged ends toward the partially negatively charged fabrics (zeta potential), creating a new surface of hydrophobic carbon chain that provide the characteristic excellent softening and lubricity seen with cationic softeners.

Anionic softeners, on the other hand, orient themselves with their negatively charged ends repelled away from the negatively charged fiber surface. This leads to higher hydrophilicity, but less softening compared to cationic softeners.

The orientation of non-ionic softeners depends on the nature of the fiber surface, with the hydrophilic portion of the softener being attracted to hydrophilic surfaces and the hydrophobic portion being attracted to hydrophobic surface, thus imparting hydrophilicity or hydrophobicity.

***Application methods : Softeners are mostly applied by forced application (padding, spraying) from relatively concentrated solutions, which transfers all of the liquor onto the fabric. In batch processing softeners are often applied by exhaustion from diluted baths on machines such as jet, overflow or winch. Here the exhaustion rate is relevant to ecological considerations of waste water loads. Applications by foam applicator by spray techniques are common in the case of made-up-garments. Thus it depends upon the substrate and the feasibility of adopting either of the processes.

As explained previously, even though some softeners can be applied with exhaustion processes on yarns, when softening fabrics, the best technique is the continuous pad-wetting process followed by a drying stage in a stenter. This treatment must be carried out at the end of the finishing process; for this reason, softening is usually performed simultaneously with other dimensional stability processes (width stabilization, weft and warp straightening). The use of softeners can reduce the fastness to rubbing of synthetic fibers dyed with disperse dyes, as the fatty surface layer tend to attract the dye molecules after hot treatments. Thus, it is worth remembering that the final selection of softener should be as per the requirement of the end user/buyer.