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 vo latilization 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 prod uced significantly more yellowness than polyester fabrics. Aging of oily so il enhanced detergency from all three fabrics. The largest increase in remo val upon aging was found with cotton. Difference in removal from the three substrates became very small after aging. The effect of substrate was prono unced on yellowing due to aging with cotton and nylon having higher yellown ess indices. Cotton visually appeared to be cleaner than indicated by the a ctual amount of residual oil present after washing, whereas nylon had less residual oil present even though it visually appeared more yellow than cott on. For polyester, the amount of residual oil correlated well with appearan ce after washing. We conclude that discoloration mechanisms differ among co tton, polyester, and nylon substrates. For polyester, discoloration is sole ly discoloration of oily soil that is physically bound in the fibrous struc ture, whereas for cotton, discoloration is a result of discoloration of oil as well as additional yellowing caused by retention of chromophores chemic ally bound to the cotton substrate, In the case of nylon, yellowing of nylo n itself is an additional factor contributing to yellowness even though mos t of the oil is removed upon washing. These results illustrate the importan ce of the method of detergency evaluation. Measuring color change in yellow ness 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.