The microplastics (MPs) are small fragments (length < 5 mm) of non-chemically modified and/or non-biodegradable polymers. Rough estimations point that there are between 15 to 51 trillion buoyant items of MPs in marine environments and 14 million tons in the top 9 cm of sediments of the world’s oceans.
According to the “European Chemical Agency”, chemically treated and/or nonbiodegradable textile microfibers (MFs) are a type of microplastics with a length to diameter ratio higher than 3 mm and a maximum length of 15 mm. One of the most renowned sources of MFs are those detached from every cycle of a textile article laundering. These are considered one of the most environmentally threatening pollutants as they have a continuous and cumulative entrance to the environment. Due to their small diameter they are more prone to be ingested by organisms, so high concentrations have been found in products for human consumption, as shellfish and tap water.
In this research, the microfibers’ detachment rates of finished garments were evaluated.
Results showed that MFs detachment ranges between 175 to 560 MFs/g or 30’000 to 465’000 MFs/m2 of garment. In addition, there was a high correlation between the MFs detachment and the textile article superficial density.
As there are still no accurate models to assess the MFs pollution, in this thesis a method to estimate the mass flow of MFs detached from household laundry that reaches aquatic environments was developed. The method considered the following parameters: (1) the detachment rate of microfibers from different textile garments, (2) the volume of laundry effluents, (3) the percentage of municipal water that is treated, (4) the type of used-water treatment applied, and, (5) the proportion of front- versus top-loading washing machines. In this way, 0.28 million tons of microfibers per year were estimated to reach aquatic environments. Moreover, hypothetical situations were simulated to evaluate the reduction of microfibers by modifying some parameters at different levels (consumer, government entities, and industry). It was found that depending on the implanted alternatives, microfibers that reach the aquatic environments could be reduced between 30% to 65%.
On the other hand, the current status of MFs as pollutants is reviewed, discussing possible alternatives from the manufacturing until the final disposition of MFs. There are many alternatives to reduce these pollutants but also gaps that need to be addressed.
Some viable solutions to retain them are currently on the market. However, until this thesis was over, there was no single proposal on the destination of the retained MFs.
Hence, in this research a filter has been developed to retain the MFs and a proposal to treat the retained MFs was evaluated, following the circular economy philosophy. Both processes were patented.
The developed filtering system is totally made of recycled polymers. Its performance is higher than 97% of MFs’ removal from the washers’ effluents with a replacement time for the cartridge from 30 to more than 40 washing cycles. The retained MFs are subsequently immobilized in a polymeric matrix, turning them into a composite.
Different proportions of polyester MFs were mixed with low-density polyethylene for immobilization of MFs. Results showed that the optimum composition, which improved some of the tensile mechanical properties, was 10% polyester MFs in the polymeric matrix.
Finally, other sources of MFs were studied, specifically, cigarette butts. These contains the smoked filters (SF) and unsmoked rests of tobacco. SFs are hazardous debris composed of > 15’000 strands that can be detached as MFs. Their detachment rate, acute aquatic toxicity, and the aquatic-, thermooxidative-, and photo-degradability were evaluated. It was found that SFs detach approximately 100 small MFs (< 0.2 mm) per day. About 0.3 million tons of potential MFs might be annually reaching aquatic environments from this source. A significant difference of eco-toxicity and a low degradability rate was found when MFs are present in the leachate generated by the SFs.
This implies that MFs from SFs constitute an important source of microplastics, which might partially explain the high concentration of artificial polymers found in the deep-sea sediments.
This work is the compilation of the research carried out by Ph.D. student, Francisco Belzagui Elder, during his predoctoral stage in the Environmental Engineering research group (ENMA) of the Institute of Textile Research and Industrial Cooperation of Terrassa (INTEXTER) that belong to the Polytechnic University of Catalonia (UPC).
