Effect of d-isomer concentration on the coloration properties of poly(lactic acid)

Poly(lactic acid) (PLA) fibre is derived from annually renewable crops, it is 100% compostable and its life cycle potentially reduces the earth's carbon dioxide level. In this work PLA fabrics containing variable concentrations of the d- and l-isomers have been studied to ascertain their dyeability, the characteristics of those dyed polymers, and their subsequent performance and properties. Comparison of poly(lactic acid) fabrics with varying d-isomer content revealed differences in melting temperature; by virtue of a higher d-isomer concentration, ‘high d-’ fibres have greater fibre entropy which causes a decrease in melting temperature. As a result of greater fibre entropy, high d- fibres have more amorphous and less crystalline regions in the polymer, with respect to low d- fibres, hence, high d- fabrics display greater dye exhaustion and colour strength in comparison with their low d- counterpart in all dyes and all concentrations. In application of a dye mixture for a black shade, high d- fibres are able to be dyed to an excellent black shade, whereas low d- fibres appear very brown, due to lower exhaustion of the blue component of the mix. In terms of wash fastness, there is very little difference between high d- fibres and low d- fibres; this is because the glass transition temperature for both fibres is very similar.