Evaluation of colour fastness and thermal migration in softened polylactic acid fabrics dyed with disperse dyes of differing hydrophobicity

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This paper addresses the relative effects of softeners having different properties and their method of application (exhaust vs pad) on the colour fastness of poly(lactic acid) fabrics dyed with a range of disperse dyes with different levels of hydrophobicity. A comparison was made with a correspondingly finished polyethylene terephthalate fabric. Possible relationships between the levels of hydrophilicity/hydrophobicity of the dye, and softener, and the colour fastness were explored. Finally, the amount of dye thermally migrated into the finish on the softened poly(lactic acid) and polyethylene terephthalate fabrics was examined in comparison with their colour fastness. Softened poly(lactic acid) fabrics dyed with CI Disperse Red 167.1 exhibited more thermal migration, and hence lower colour fastness, than the corresponding polyethylene terephthalate fabrics. Conversely, softened poly(lactic acid) fabrics dyed with Dianix Deep Red SF exhibited less thermal migration, and hence better colour fastness, than the corresponding polyethylene terephthalate fabrics. Overall, no clear relationship was found between the hydrophobic nature of the disperse dye and the hydrophobic character of the softener on the colour fastness.