Effect of fiber substrates on appearance and removal of aged oily soils

Aging of oily soils produces difficult-to-remove yellow stains on fabrics. This study examines the effect of different textile substrates on yellowing and removal of aged oily soils. Model oily soils, squalene and artificial sebum, were aged at 40 degreesC on cotton, nylon, and polyester fabrics for 8 wk. Radiotracer and spectrophotometric analyses were used to quantify volatilization and color change of soiled fabrics upon aging as well as soil and color removal after laundering. Differences in volatility of oils from three substrates were insignificant, although cotton and nylon fabrics produced significantly more yellowness than polyester fabrics. Aging of oily soil enhanced detergency from all three fabrics. The largest increase in removal upon aging was found with cotton. Difference in removal from the three substrates became very small after aging. The effect of substrate was pronounced on yellowing due to aging with cotton and nylon having higher yellowness indices. Cotton visually appeared to be cleaner than indicated by the actual amount of residual oil present after washing, whereas nylon had less residual oil present even though it visually appeared more yellow than cotton. For polyester, the amount of residual oil correlated well with appearance after washing. We conclude that discoloration mechanisms differ among cotton, polyester, and nylon substrates. For polyester, discoloration is solely discoloration of oily soil that is physically bound in the fibrous structure, whereas for cotton, discoloration is a result of discoloration of oil as well as additional yellowing caused by retention of chromophores chemically bound to the cotton substrate, In the case of nylon, yellowing of nylon itself is an additional factor contributing to yellowness even though most of the oil is removed upon washing. These results illustrate the importance of the method of detergency evaluation. Measuring color change in yellowness or reflectance is not the same as soil removal based on a quantitative measurement of soil mass. Thus, it may be necessary to measure both color and quantity of residual soil.