Biodegradation pathways in compost-enriched soil of cotton fabrics treated with chitosan and a natural dye: Chemical and biological evaluation

This study investigated the biodegradation of cotton fabrics finished with chitosan, a natural antimicrobial biomacromolecule. Chitosan also possesses crosslinking properties that favor the attachment of anionic natural dyes, such as Carmine Red, onto cellulosic textile fibers. Herein, dyed and undyed chitosan-finished cotton samples were buried in compost-added soil (in its original form, rich in microorganisms, or after sterilization at 105 °C) for 10, 30, 90 days. The comparison between dyed and undyed fabric behavior suggested that the dyed samples were more degradable in terms of fabric disruption and weight loss (e.g., +83 %), probably due to the availability of Carmine Red to microorganisms' attack. Nevertheless, the soil medium (sterilized/non-sterilized) and burial time emerged as the most impactful parameters in the biodegradation process. Indeed, fabrics buried 90 days in non-sterilized soil showed the strongest modifications related to chemical functional groups, morphology (fiber rupture) and thermal features (loss in crystallinity). In a multifaceted and novel approach, high-throughput sequencing combined with bioinformatics analysis was used to qualitatively analyze soil in contact with the various treated cotton specimens. The outcomes showed different biota communities in correspondence with the diverse burying conditions and fabric finishing, thus evidencing the non-negligible effect of bio-based textiles in soil.