The Environmental Engineering Research Group (GI2AM), thanks to funding from the Valencian Innovation Agency (AVI), is completing the project "Recycling of complex plastic waste from cotton-polyester mixtures (INNEST/2022/205)" (RECIMAP), executed in the period between September 2022 and June 2024.
The GI2AM group, from the University of Valencia, has participated in the project with the entities AIMPLAS, Consorcio Valencia Interior V3 and Bespoke Factory Group SL.
Firstly, as a result of the first tasks of analysis of textile waste collection, the lack of efficient textile collection systems was confirmed and, therefore, the need for an improvement in the collection systems for this waste. Also, the difficulty of subsequent identification and sorting of materials into pure streams suitable for recycling could be observed. This fact has been mainly associated with three reasons: (1) Inefficiency of current optical detection systems (NIR) when dealing with textile waste; (2) high presence of multi-material garments that make classification laborious and alter the composition of the pure streams and; (3) the need for further processing to remove zips, buttons, inks, shredding, etc. in order to obtain a stream suitable for recycling. These aspects are a critical bottleneck for the success of downstream processes and need to be addressed urgently.
Secondly, in terms of research into new recycling techniques for complex textiles, the process studied in the RECIMAP project has proved to be highly successful and positioned itself as a promising option for the treatment of multi-material waste. The pre-treatment carried out with Ionic Liquids (IL) allowed a separation of textiles composed of cotton and polyester with an efficiency of more than 90%, with no subsequent harmful effects on the enzymatic hydrolysis process of the cotton. Furthermore, it was demonstrated the possibility of recovering 80% of the ionic liquid used in the process with less than 10% water content and being reused in up to 4 subsequent cycles with cotton digestibilities of more than 80%.
Thirdly, in terms of obtaining new materials with high added value from the streams obtained. The possibility of recycling the polyester fraction recovered after the separation process with LI using mechanochemical techniques was demonstrated, with a terephthalic acid (TPA) recovery efficiency of 56% and a purity of over 80%, these results being very similar to those obtained for the recycling of virgin PET.
Regarding the cotton fraction, the possibility of being enzymatically hydrolysed and fermented to obtain lactic acid with a sugar transformation ratio close to 100% was demonstrated. The lactic acid obtained was combined with virgin lactic acid in a polymerisation process to obtain PLA.
Thus, the RECIMAP project proposes an innovative process, with high yields, that allows the separation of complex textile waste and the subsequent recycling of its fractions for the production of high added value molecules that can be subsequently used in polymerisation processes.
