Department of Textile Technology, Dr. B R Ambedkar National Institute of Technology Jalandhar, G.T. Road, Amritsar Bypass, Jalandhar (Punjab), India – 144027
It is undoubtful that the twenty-first century will be devastating if the issues about efficient energy and water utilization, pollution control and waste management are not addressed appropriately. With an increase in population, the need for the textile has increased. Today, the world consumes over a hundred million tonnes of different textile fibres, of which synthetic fibre consumption has gone more than fifty per cent by weight (Figure 1). Consequently, textile waste also increased. Further, the COVID-19 pandemic has substantially increased the use of protective gear, namely, face masks, protective suits, shoe covers, etc. Thus the huge quantity of this medical textile waste also became a great challenge. Textile waste is an important category of waste and was always neglected. The various forms of textile waste are fibre, yarn, and fabrics. Textile waste can be classified as pre-and post-consumer waste. However, the fibrous waste generated during the production of textiles from recycled textiles and the waste generated at the end of the life of recycled textile material also needs to be categorised separately to quantify these wastes. The microfibres that form from openly dumped textile waste travel readily with waterways. About 1.5 million trillion microfibres are floating around in the sea. These microfibers have been introduced to the food chain by biomagnification. Synthetic finishing chemicals and swallowed microfibres have devastating effects on aquatic animals and human health.
Materials like ethanol, glucose, nitrocellulose and cellulose nanocrystals, biogas, thermal and acoustic insulation, concrete and bricks, fibres, yarns, fabrics, polymeric composites, etc., may all be made from textile waste. Waste textiles have a significant perspective in polymeric composites. The collecting, sorting, storage, and distribution of used textiles are some of the challenges in textile waste recycling.
Different techniques of textile waste-based composite development
Textile waste can be used in four ways as a reinforcement material for the development of composite material; namely, 1) Discarded fabric as a preform, 2) Fibrous material (shoddy) obtained by shredding waste textiles, 3) Converting the shoddy to yarns and woven or nonwoven fabrics to be used as a preform, and 4) Developing Nano or microstructures from cellulosic waste textiles via mechanical or chemical methods. The decision on how to use the given waste textile is based on its form, physical condition, desired performance of the product to be developed, cost, etc.
Discarded fabrics as a reinforcement
The waste textiles in the fabric form can be obtained from a landfill or collected through a retail chain, or it may be a donated fabric. However, the fabric form and composition are important factors in deciding the matrix material. Let’s say that the fabric has more than fifty per cent of the weight of a polyester component. Then, in this case, this fabric can be directly hot pressed to develop a composite material with enough mechanical properties for the application, such as secondary load-bearing components. The thermoset composite can also be developed using discarded fabrics as a reinforcement. However, the physical properties of the reinforcement material and the desired mechanical performance must be understood well before opting for the thermoset composites manufacturing route. Since thermoset matrix materials are costly, manufacturing can be cheap if the composite materials are cured at room temperature, and the break-even fibre volume fraction is determined.
Shoddy as reinforcement
The fibrous material obtained by shredding the waste textiles is called shoddy. The discarded textiles in the fabric form, which cannot be used directly as a reinforcement, necessitate cutting into pieces followed by rag tearing to form the shoddy. The rag-tearing machine consists of a series of pinned rollers. The shoddy can be processed directly on an injection moulding machine along with thermoplastic fibrous waste (polyester/polypropylene) to produce beads. These beads can be reprocessed on injection or compression moulding to produce the composite components. The other route is producing the carded web from shoddy, which can be converted to thermoset composites by compression moulding. The mechanical performance of the shoddy reinforced composites can be further enhanced by adding filler materials such as cellulosic and non-cellulosic nano/microparticles. However, one should take care of the colour or hue of the shoddy used for composite production. The textile waste with similar colour or hue must be processed separately to maintain the final product aesthetics.
Yarn, woven or non-woven fabrics developed from waste textiles as reinforcement
The technology of converting the shoddy into the rotor spun yarn is well established. Compared to ring spinning, rotor spinning is a method for making fast and cheap yarn. Further, it has been established that adding 25% waste fibres to the virgin fibres does not alter the rotor yarn tenacity, irregularity, and elongation. Most importantly, the recycled fibre-based yarns have enough strength to be used for weaving. The recycled fibre-based yarns are already in use for applications such as bedsheets, doormats, school blazer fabrics, etc. However, the potential of recycled fibre-based yarns for 2D and 3D woven forms for composite development is not yet realised. Further, Nonwoven fabric manufacturing is the cheapest way of turning recycled fibres into fabric form. These nonwoven fabrics can be tailored to develop thermoplastic and thermoset composite materials as per the requirements. For example, the composite nonwoven fabric produced by blending thermoplastic fibres with shoddy can be directly used to produce compression moulded component production.
Nano/microstructures developed from waste textiles as reinforcement
The large specific surface area of the nano or microparticle enhances the interface with the matrix material in the composite. This helps in distributing the stress applied onto the composite material. The nanomaterials, such as cellulose nanocrystals, can be extracted from the waste textiles by milling or chemical hydrolysis. However, the removal of the dye within the textile is important for nanocrystal extraction. Further, recycled fibres such as hemp, jute, and banana can be milled directly to produce nano/microparticles. These microparticles can be directly used as filler in composite materials. These particles have been reported to enhance the mechanical performance of composite materials.