Softening finishes are among the most important of textile chemical after treatments. With chemical softeners, textiles can achieve an agreeable, soft hand (supple, pliant, sleek and fluffy), some smoothness, more flexibility and better drape and pliability. The hand of a fabric is a subjective sensation felt by the skin when a textile fabric is touched with the finger tips and gently compressed. The perceived softness of a textile is the combination of several measurable physical phenomena such as elasticity, compressibility and smoothness. During preparation, textiles can become embrittled because natural oils and waxes or fibre preparations are improved. Finishing with softeners can overcome this deficiency and even improve on the original suppleness. Other properties improved by softeners include the feeling of added fullness, antistatic properties and sewability. Disadvantages sometimes seen with chemical softeners include reduced crockfastness, yellowing of white goods, changes in hue of dyed goods and fabric structure slippage.
Mechanisms of the softening effect
Softeners provide their main effects on the surface of the fibres. Small softener molecules, in addition, penetrate the fibre and provide an internal plasticization of the fibre forming polymer by reducing of the glass transition temperature T. The physical arrangement of the usual softener molecules on the fibre surface is important. It depends on the ionic nature of the softener molecule and the relative hydrophobicity of the fibre surface .Cationic softeners orient themselves with their positively charged ends toward the partially negatively charged fibre (zeta potential), creating a new surface of hydrophobic carbon chains 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 fibre surface .This leads to higher hydrophilicity, but less softening than with cationic softeners. The orientation of non-ionic softeners depends on the nature of the fibre surface, with the hydrophilic portion of the softener being attracted to hydrophilic surfaces and the hydrophobic portion being attracted to hydrophobic surfaces.