Mild valorisation process of polycotton waste using a recyclable ionic liquid for lactic acid production, combined with polyester recovery

Textile waste, commonly found in blends, is a potential raw material that needs recycling due to the rise of the fast-fashion model. In this study, a method to valorise cotton-polyester textile waste (average composition 60% cotton, 40% polyester) into a value-added chemical, such as lactic acid was investigated. As pretreatment, the most effective ionic liquid was the 1-ethyl-3-methylimidazolium acetate, [Emim][OAc]. This one at a relatively low temperature (60 ºC) and a short duration (15 min) drastically increased the digestibility of treated cotton textiles to levels exceeding 95%. Furthermore, the proposed method enabled the recovery of the polyester fraction with a high similarity (96%) to commercial polyester. The recovery and reuse of the [Emim][OAc] were assessed, with up to four recycling cycles conducted, showing minimal differences between cycles, with recovery values ranging from 81.8% to 89.2%. The pretreated textile waste was hydrolysed, and lactic acid was successfully produced with the same glucose uptake and lactic acid fermentation profiles regardless of the cycle of [Emim][OAc] utilisation. The lactic acid yields were excellent, ranging from 0.92 to 0.97 g/g and an overall yield of ~0.5 kg of lactic acid per kg of textile waste was achieved. The lack of differences in enzymatic hydrolysis and fermentation showed that there was no adverse effect on the reutilisation of [Emim][OAc] in the overall process; therefore, this approach may enhance the circularity of polycotton waste into high-value bioproducts. • Efficient recycling of polycotton (60% cotton) waste into lactic acid. • [Emim][OAc] rapidly dissolves 95% of cellulose at low temperatures. • Minimal loss in ionic liquid efficiency across four recycling cycles. • 96% of the original PET was recovered after saccharification. • Overall yield of ~0.5 kg LA/kg waste enables PLA production from textiles.