Soil-release finishes mechanisms

The colour of the treated and stained fabric cannot be ignored. Very dark fabrics and very light fabrics can appear to have less soil simply from optical effects. Table 7.2 gives an overview on the chemical mechanisms of soil-release finishing. 

Table 7.2 Chemical mechanisms of soil-release finishes...

Although soil retardants reduce soiling, the deposition of soil onto a textile cannot be entirely prevented. If the textile can be washed, soil-release finishes can facilitate the removal of soil considerably. The term soil release suggests a separation of soil from a fabric immersed in water, but such a spontaneous separation is possible only with liquid oily soils. Solid soils cannot separate spontaneously and require mechanical action for their removal. 

Of these mechanisms, solubilisation and emulsification of soils are controlled by detergent composition, hydrodynamic flow is controlled by washing machine design and fibre flexing is controlled by fabric construction. The textile chemist can only influence the mechanisms that involve the fibre surface, i.e. rollup of oily soil, penetration of soil-fibre interface, surface abrasion and finish swelling. Finishes have been developed that provide soil release performance by taking advantage of all of these mechanisms. 

Particulate soil is removed from fibres by a two-step process. First, a thin layer of wash liquid penetrates between the particle and the fibre surface, enabling surfactants to adsorb onto the particle surface (Fig. 7.1). Then, the particle becomes solvated and is transported away from the fibre and into the bulk of the wash liquid by mechanical action. Finishes that are hydrophilic (enhancing penetration of the fibre-soil interface) with low adhesion to soil under washing conditions should improve particulate soil release. Ablative or sacrificial finishes... 

Additional finish characteristics that should facilitate oily soil release include the ability of the finish to swell during the washing process and flexibility under mechanical action. As in particulate soil release, sacrificial finishes are expected to benefit oily soil release. 

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