Blog written by Aidé Gaona, R&D Project Manager at AITEX
A wide range of industrial sectors, from the textile industry to automotive and construction, have been significant consumers of large quantities of synthetic polymers in recent decades. These sectors have operated under a paradigm of linear production, distribution, and consumption, which has proven unsustainable due to the increasing generation and accumulation of waste. Traditionally, most synthetic polymers have been designed to offer performance and durability, implying low degradability. This has exacerbated the problem of waste accumulation.
The global textile industry has had a considerable environmental impact. To put it into perspective, in 2020, this industry consumed approximately 93 billion cubic meters of water, representing over 20% of global water resource pollution. Additionally, it has been responsible for generating 92 million tons of waste, contributing significantly, between 3 and 10%, to total greenhouse gas emissions [1]. Consequently, the environmental impact associated with the textile industry has become one of the most pressing issues on the current global agenda.
In March 2020, the European Commission (EC) introduced the Circular Economy Action Plan (CEAP) (COM(2020)98), one of the main building blocks of the European Green Deal, a blueprint for sustainable growth in Europe. This transition to a circular economy within the EU holds the potential to alleviate strain on natural resources, foster sustainable economic expansion, and generate employment opportunities. Additionally, it serves as a prerequisite for attaining the EU’s objective of achieving climate neutrality by 2050 and halting biodiversity loss. The CEAP addresses product design, promotes circular economy practices, encourages responsible consumption, and strives to minimize waste generation while retaining resources within the EU economy for as long as possible.
- PET recycling technologies
With the current recycling technologies available in Europe, less than half of the total amount of used clothing is collected for reuse or recycling when it is no longer needed, and only 1% is recycled into new clothing. In recent years, various technologies based on chemical recycling have emerged to address the problem of poor recyclability of fossil-based polymers since traditional methods, such as primary (reuse) and secondary recycling (mechanical/thermo-mechanical), have not yielded satisfactory results. This focus on chemical recycling not only does align with the goals of the European Green Deal, that promotes a circular and sustainable economy, but also underscores the pressing need to innovate in textile waste management to mitigate the negative effects of fast fashion and garment waste. Circularity, in this context, becomes a fundamental part of the European strategy to reduce the environmental impact of the fashion industry and promote more sustainable practices throughout the value chain.
Specifically, in the textile sector, out of the 116 million tons of fibres produced worldwide in 2022, approximately 65% were synthetic fibres, 29% natural fibres, and 6% artificial fibres. Among synthetic fibres, polyester stands out, with a market share of approximately 85% of total synthetic fibres, representing an annual production of 63 million tons and a global share of 54% (Figure 1) [2].
Figure 1. Global fiber production in 2022
Thus, in recent decades, polyester has become the most widely used fibre thanks to its lightweight, low cost, and high mechanical performance. Currently, the primary technology for polyester recycling is thermo-mechanical recycling, due to its simplicity and low cost. Thermo-mechanical recycling involves a physical process in which textile waste is sorted, washed, and reprocessed through an extrusion (melting) process. The disadvantages of this method mainly lie in the heterogeneity of solid waste and the deterioration of product properties in each extrusion cycle. Therefore, most mechanically recycled garments experience value and quality loss, so they are not usually used to manufacture new textile products. Instead, they are transformed into materials with lower technical requirements, such as injection pieces or fillers. [3]
On the other hand, among the different chemical recycling technologies, thermal depolymerization and catalytic depolymerization are noteworthy. Due to the numerous advantages of catalytic depolymerization over other technologies, this strategy is being studied in greater depth by the scientific community, with the first industrial plants located in countries such as Japan, the United States, or India. [4]
Specifically, catalytic depolymerization of polyester involves breaking down the polymeric chains into their fundamental units or monomers through catalytic reactions. Depending on the solvent used in the depolymerization reaction, the process is called glycolysis (glycols), hydrolysis (water), methanolysis (methanol), aminolysis (amines), or ammonolysis (ammonia). Once the reaction is complete, the monomer is isolated, purified, and used in a new polymerization process to obtain virgin polymer. The main advantage of this process is that it allows waste to be recycled an infinite number of times without experiencing mechanical properties loss (Figure 2).
Figure 2. Schematic representation of the catalytic depolymerization process.
- The textile value chain in the REDOL project
The textile value chain will be redesigned in the REDOL project, starting with a novel textile waste sorting technology based on hyperspectral imaging selection by colour, composition, and fabric/garment structure. The next step will be the management of polyester textile fibres through a depolymerisation-polymerisation process. The glycolysis using ionic liquids as catalyst will be optimised by AITEX, followed by post-condensation and spinning steps at pre-industrial demonstration level by BRILEN TECH, S.A. Finally, BRILEN will use the recycled polyester yarns to produce geotextiles for civil infrastructures applications, enhancing the readiness of the textile Circular Economy Hub.
As commented before, the AITEX main role in the REDOL project focuses on the development and optimization of polyester chemical recycling, so as to achieve technical advancements in this line of research and progressively facilitating the transition towards a circular economy.
To carry out the chemical recycling of post-consumer textile waste, it has been necessary to study and optimize the reaction conditions of glycolysis, as well as subsequent treatments such as isolation and purification. After sorting the waste at the source by composition and colour using Fibersort technology, it is shredded and pelletized to efficiently feed the process. Subsequently, it is depolymerized through a glycolysis process, which, as introduced earlier, involves the use of ethylene glycol as a solvent. In a first stage, polyester depolymerization is carried out in a batch reactor, allowing to obtain, isolate and purify the monomer (BHET) with yields exceeding 90% and purity exceeding 99.5%. Subsequently, in a second stage, the BHET polymerization process can be carried out, resulting in a polyester product with suitable viscosity for the production of new fibres (IV = 0.62-0.65 g/dl) (Figure 3).
[1] Mc Kinsey &Company. 2022. Scaling textile recycling in Europe–turning waste into value.
[2] https://textileexchange.org/app/uploads/2023/11/Materials-Market-Report-2023.pdf
[3] S. Park, et al., Poly (Ethylene Terephthalate) Recycling for High Value Added Textiles. Fash. Text., 2014, 1.
[4] Simon, J.M., and Martin, S. (2019) El Dorado of Chemical Recycling – State of play and policy challenges.
Blog written by Aidé Gaona, R&D Project Manager at AITEX
