Dyed substrate comprising poly(lactic acid) fibres

A method of preparing a dyed substrate comprising at least 70 wt. % of dyed PLA-fibres having a poly(lactic) acid content of at least 70 wt. %, the dyed substrate having a total poly(lactic) acid content of at least 70 wt. %, wherein the dyed PLA-fibres are dyed with one or more disperse dyes and wherein the dyed substrate has the following CIELAB colour:

• 0
• ≤
• L
• *
• ≤
• 25
• ;
• ⁢
• -
• 128
• ≤
• a
• *
• ≤
• 10
• ;
• ⁢
• -
• 128
• ≤
• b
• *
• ≤
• 128
• ,
• said method comprising:
• providing a substrate comprising at least 70 wt. % of fibres having a poly(lactic) acid content of at least 70 wt. %, said substrate having a total poly(lactic) acid content of at least 70 wt. %;
• introducing the substrate into a dyeing chamber;
• passing a stream of dyeing medium through the dyeing chamber containing the substrate during a period of 30 to 300 minutes to produce a dyed substrate, said dyeing medium having a pressure of 12-50 MPa and a temperature of 70-100° C., and comprising at least 80 wt. % of supercritical carbon dioxide, one or more disperse dyes and less than 3 wt. % water;
• wherein the disperse dye is employed in a concentration of 0.2-3% by weight of substrate;
• and
• wherein the dyeing conditions employed during the dyeing period meet the following condition:
• W
• CO
• ⁢
• 2
• /
• W
• dye
• ≥
• 100
• ⁢
• kg
• /
• g
• wherein:
• WCO2 represents the total mass of supercritical dioxide that is passed through the dyeing chamber during the dyeing period, expressed in kg;
• Wdye represents the total amount of disperse dye that is retained in the dyed substrate after the dyeing period, expressed in g.