The Effect of Textile Dyes on the HCl-Based Polycotton Recycling Process

The growing volume of textile waste increases the need for effective chemical recycling methods. The hydrochloric acid-based polycotton recycling process offers a route to valorize polycotton textiles (polyester/cotton blends in any ratio) in two steps. First, cotton is selectively hydrolyzed with superconcentrated hydrochloric acid at ambient temperature, enabling its separation from polyester. The resulting saccharides are then converted and simultaneously extracted at 91 °C as 5-chloromethylfurfural (CMF). This preliminary study examined whether dye molecules present in polycotton waste textiles affect the performance and product of the recycling process. The CMF production was not affected by the presence of dyes; however, the heat required for this step caused dye degradation. To prevent contamination of the product by the dye molecules and their degradation products, two types of activated carbon (AC) were evaluated as dye adsorbents. Both proved effective at removing dye molecules from hydrolysates produced from four types of post-consumer polycotton waste. However, although the use of ACs resulted in decolorized hydrolysates, it resulted in lower CMF yields in the subsequent conversion step. Therefore, the use of AC is not recommended in the current laboratory setup.