A Practical Valorization Approach for Mitigating Textile Fibrous Microplastics in the Environment: Collection of Textile-Processing Waste Microfibers and Direct Reuse in Green Thermal-Insulating and Mechanical-Performing Composite Construction Materials

Microplastic (MP) contamination is an urgent environmental issue to address. Fibrous microplastics (FMPs) are the principal MP type in the air and have already been found in human stool and lung tissues. FMPs are generated from the lifecycle of synthetic and blended textiles and are expected to increase due to fast fashion. Among textile processes, the finishing of fabrics is estimated to generate 5000 t/year of textile waste fibers in Italy, including FMPs. To limit FMPs spread, this paper suggests, for the first time, the direct collection of blended finishing textile waste microfibers and reuse in designing thermal-insulating and mechanical-performing fiber-reinforced cementitious composites (FRCs). The microfibers were thoroughly characterized (size, morphology, composition, and density), and their use in FRCs was additionally evaluated by considering water absorption and release capacity. Untreated, water-saturated, and NaOH-treated microfibers were considered in FRCs up to 4 wt%. Up to a +320% maximum bending load, +715% toughness, −80% linear shrinkage, and double-insulating power of Portland cement were observed by increasing microfiber contents. NaOH-treated and water-saturated microfibers better enhanced toughness and linear shrinkage reduction. Therefore, green and performant composite construction materials were obtained, allowing for the mitigation of more than 4 kg FMPs per ton of cement paste. This is a great result considering the FMP contamination (i.e., 2–8 kg/day fallout in Paris), and that FRCs are promising and shortly-widely used construction materials.