CHEMICAL-CHANGES IN UNSATURATED OILS UPON AGING AND SUBSEQUENT EFFECTS ON FABRIC YELLOWING AND SOIL REMOVAL

Aging of unsaturated oily soils on polyester/cotton fabric was explore d with oleic acid, triolein and squalene as model soils in terms of th e relationship between changes in their chemical structure and fabric appearance. Among the three unsaturated oily soils studied, yellowing was observed only with squalene-soiled and aged fabric swatches after aging for 2 to 46 wk. The yellow material formed upon aging was not co mpletely removed by laundering or organic solvent extraction. In extra ction, the more polar solvents removed more yellow material from the f abric. Radiotracer analysis of labeled oily soils showed that all thre e soils volatilized from fabric upon aging with their characteristic v olatility patterns. The amount volatilized increased with aging time a nd temperature. Removal of triolein and squalene in creased remarkably after aging when applied as single soil. Higher aging temperature (40 degrees C) increased soil removal more dramatically than a lower temp erature (21 degrees C). In a mixed soil system, removal of triolein by detergency increased up to 8 wk of aging; a decrease in removal was o bserved for a specimen aged from 8 to 26 wk at 21 degrees C. Removal o f oleic acid decreased gradually during aging in both single and mixed soil systems. Separation of aged products by thin-layer chromatograph y (TLC) revealed that unsaturated oily soils chemically changed into v arious polar oxidation products that were more easily removed by deter gency. Infrared (IR) spectra of the aged oils substantiated the appear ance of polar groups, such as OH, C=O and C-O. Osmium tetroxide treatm ent proved disappearance of double bonds of unsaturated oils upon agin g. The fabric yellowing observed for squalene-soiled fabric is related to the formation of yellow, polar, resinous material due to rapid oxi dation, as evidenced by TLC, IR spectra, volatility pattern and rigidi ty of aged fabric. Oxidation products of squalene with conjugated C=O groups are proposed as the cause of fabric yellowing upon aging, and a possible mechanism for their formation is proposed.