Since past ages, fabrics and fibres have always been an integral part of every human activity. We find the application of fabrics in clothing to protect and cover the human body from bad weather or simply to identify social status and respond to different fashions and trends. There are fabrics in each home for sheets and bed linen and towels, napkins, tea towels, table cloths, rugs, sofas, armchairs, chairs, curtains. There are fabrics in transport means, cars, trains, craft, and airplanes for airbags, seat belts, carpets, seat upholstery, and tires. Fabrics are also used as structural reinforcement elements in construction fields. Statistical studies by Garside M. (2019) report that the production of chemical and textile fibres from 1975 to 2018 has increased approximately from 23.94 million metric tons to 105.6 million metric tons: this means an increment of more than four times in about 40 years.
As the demand for fabrics has grown, aspects linked to the environmental impact of fibre production, and the following disposal operations, have also become increasingly present. Numerous and recent studies show the danger of the textile industry for the freshwater and atmosphere micro-system, due to the usage of significant amounts of industrial harmful and toxic chemicals during the manufacturing process and the release of pollutants during the lifecycle of a textile product. Other forms of contamination arise from high energy consumption, heavy transportation, and excessive packing material. Finally, given the huge waste generation, the problem of disposing of large solid volumes has arisen. Twenty percent of earth pollution has been attributed to the textile industry, which for these reasons has been considered among the most harmful and detrimental manufacturing processes for our ecosystem. In the light of these complex ecological issues, over the years until 2020, European directives have promoted and encouraged the recovery of textiles in a board plan for new circular economic action for a cleaner and more competitive country.
Textile production ,right from fibre production, yarn production, fabric production, pre-treatment, dyeing and printing and finishing treatment involved, the environmental impact in different aspects all connected to each other that take into account the usage of harmful chemicals, the water and energy consumption, the air emission, the transportation, and the packaging.
The raw materials involved in the textile manufacturing are divided into two main categories: (i) natural fibres, deriving from vegetables and plants (cotton, flax, sisal, hemp, ramie, jute, banana, pineapple, coir, and oil palm), animals (wool, angora, cashmere, and silk), and minerals (asbestos); and (ii) man-made fibres, synthetic or regenerated, coming from petroleum-based resources, such as polyester, nylon, spandex, acrylic, and polypropylene. These primary materials, depending on their nature, require being treated with different chemical agents.
For instance, in the fibre production, pesticides, insecticides, and fertilizers are applied in the case of cellulose or natural fibres, to allow and facilitate the growth and development of plants, whereas for protein fibres, parasites are used for the animal, and after the fibres shredding, the utilization of chemicals for the cleaning operations. In the case of the synthetic fibres, the preparation of the agents, polymerization, polymer recovery and extrusion, and spinning for arriving to the filaments required the use of monomers and catalyst that generate a series of by-products.
Then, during the yarn production, particularly in the spinning, oil is required for reducing the friction among the parts, and again, in the fabric production, the sizing species together with the lubricants should be used for avoiding the breakage of the fibres during the process. Once obtained, and before the dyeing step, the fabric should be suitably prepared with a multiple pre-treatments through the following processes: (i) de-sizing, consisted in the removal of the starch (sizing chemical) and the improvement of the absorbent capability, since the starch hampers the diffusion of the dye molecule into the yarn/fabric; through enzymatic, or dilute mineral acid hydrolysis, or oxidation, the starch is transformed in water soluble constituents; (ii) scouring, during which wax, fats, pectin, and lubrication oil are removed by using aqueous sodium hydroxide together with the surfactant; (iii) bleaching, to get white fibres by decolorizing their natural creamy appearance, during which oxidant agents, such as sodium hypochlorite, sodium chlorite, and hydrogen peroxide, are always applied; and (iv) mercerizing, realized by immersion in a high concentration of sodium hydroxide solution to improve fabric features, in terms of tensile strength, hygroscopicity, and dye absorbency, brightness, and dimensional stability, occurred through the swelling, the untwisting, and the fibre re-orientation.
In fact, during the mercerizing, the wetted fibres go through a longitudinal shrinkage that can be avoided by elongation and holding the fibres under an applied uniaxial stress. The excess of caustic soda is removed by water washing, (v) dying, and printing to impart the colour to the fabric or yarns. All the chromophore agents, such as azo (-N=N-), carbonyl (-C=O), nitro (-N=O), and also amine, carboxyl, sulfonate, and hydroxyl groups are considered water contaminants, because they confer unacceptable colour to the wash water. Several other chemicals are involved in the dyeing and printing depending on the chemical nature of the fibres: reactive dyes, direct dyes, naphthol dyes, and indigo dyes in the case of cellulose fibres, acid dyes and Lana set dyes in the case of protein fibres, and finally dispersed dyes, basic dyes, and direct dyes for the synthetic fibres. In order to promote the link between fibres and pigments, binder and polymeric resins should be applied, while the pigments in excess should be removed by washing with detergents, such as alkyl aryl-sulfonates, sulphated alkyl phenol polyglycol, alkylphenol ethoxylates, sodium palmitate, and sodium stearate.
Finally, specific finishing treatments should be designed for imparting particular features to the latest products: in the case of water and oil repellency, paraffin (waxes), silicones, fluorocarbon, and stearic-acid melamine may be suggested ;for the antibacterial activity metallic salts (Ag+ and Cu2+), triclorosan (2,4,4-hydrophenyl trichloro (II) ether), quaternary ammonium compounds, chitosan, and cyclodextrin are the most common antiseptic products ;again, for the flame retardancy halogen based formulations, phosphor, or nitrogen based coating systems, silicone based species are usually implied .
In general, all the listed components implied in the fabric production can have different life paths: they can remain attached to the fabric or can evaporate, end up in the wastewater, and be poured into the environment. Although the dilution in large volume of air and water, many of these species may not degrade rapidly, and therefore can be transported at very high distances and accumulate in sediments or organisms (“persistence”); additionally, they can enter the body absorbed through food and skin and accumulate in it (“bio-accumulation”). Many of these species can be considered toxic (“toxicity”) due to the potential or established carcinogenic and/or mutagenic effects, the risk of physical malformation for the fetuses, and the unleashing of allergies of various kinds.
Recently, research attention has been devoted to the possible reuse of industrial textile waste, or recovery of the used fabrics, for realizing recycled fibres, to be applied as fillers, in compounding with polymer or concrete matrices. In this way, the eco-sustainability of the textile manufacturing process and the realization of useful goods, adaptable to the different requirements, have been simultaneously satisfied.
In this framework, the aim is to provide an overview of the current issues related to the environmental concerns of the textile productions, and of the alternative solutions for limiting the production of solid textile waste to be disposed. In detail, attention was devoted to collecting the most recent studies, written in the last decade that dealt with the possible applications of the recycled fibres, coming from textile waste, into the world of composite materials.
(Writer can be reached at:sjugeshwor7@gmail.com)