Soil biodegradation of finished fabrics: from lab-scale studies to a real environment

The stability of textile materials in the natural environment is a cutting-edge topic: on the one hand, significant durability is required for specific applications (e.g., geotextiles) to guarantee long-term performance; on the other hand, when textile materials are discarded, easy degradation without secondary pollutants is preferred. In this framework, this research was based on different biodegradation studies carried out on cotton fabrics treated with (i) polypyrrole, (ii) chitosan, and (iii) chitosan+carmine and on polyamide 6.6 fabrics treated with chitosan+carmine. Polypyrrole is a dark nitrogen-containing polymer obtained by pyrrole polymerization; chitosan is a biopolymer that comes from crustacean exoskeleton; carmine is a natural red dye derived from Cochineal insects. These finishes were applied to impart specific properties and functions to the textile substrate, ranging from color to antibacterial features and electrical conductivity. In controlled lab-scale experiments, bare cotton/polyamide and the different functionalized fabrics were buried in commercial compost-enriched soil over time (up to 90 days) to determine whether the considered finishes promoted or delayed the natural biodegradation process. A set of polyamide 6.6 fabrics (bare and finished) was also placed in an outdoor house garden to simulate real landfill conditions. Physicochemical changes during different biodegradation periods were determined using scanning electron microscopy, thermal analysis, and spectroscopy, in addition to specific characterizations based on the treatment type, such as surface resistivity measurements for polypyrrole-coated samples or the determination of surface hydrophilicity variation for chitosan-treated samples. An insight into microbiota communities found in the soil kept in a lab-scale environment, where cotton fabrics coated with chitosan and chitosan+carmine were buried, enriched knowledge about the biodegradation pathways of so-treated textile materials. In conclusion, the overall results showed that the coating/finishing interacts with the surrounding media, protecting or exposing the substrate to biochemical agents in the soil, and the extent of these effects depends, on the one hand, on soil characteristics and, on the other hand, on the finishing type. For instance, polypyrrole and chitosan, inherently antibacterial, preserved the integrity of cotton that, in its bare form, completely disappeared in 90 days; particularly, in the case of polypyrrole, the shielding effect toward the cotton substrate from the soil microbiota was almost complete, although signs of polypyrrole depletion were revealed. Polyamide fabrics, well-known for their recalcitrance to biodegradation, were expected to be more damaged in the presence of the bio-based finishing (as a point of attack for microbiota), but only mild degradation effects were detected, more related to microorganism colonization and the adsorption of water and soil-derived substances.