Switzerland's Uster outlines challenges & solutions of recycled yarn

The European Union has defined a strategy for sustainable and circular textile production, to make the sector greener and more competitive. Part of this 2030 Vision for Textiles calls for all textile products on the EU market to be durable, repairable and recyclable – and largely made of recycled fibres. Many leading retailers are also championing the use of recycled materials from 2030 onwards, Uster said in a press release.

The use of mechanically recycled fibres in spinning has specific quality considerations: such fibres have a higher short fibre and nep content and may often be coloured, particularly if post-consumer material is used. It’s also true that recycled yarns have limitations in terms of fineness. Officially, a yarn can only be branded `recycled´ when spun with more than 20 per cent recycled fibres. This is set by the Global Recycled Standard (GRS), a voluntary product specification for tracking and verifying the recycled content of materials in a final product.

Blending virgin and recycled cotton together is well known as a challenge for spinners. The smartest spinners and world-class processes simply can’t overcome the fact that some important quality parameters will be adversely affected. It’s clear that the use of recycled cotton in a blend with new fibre will impact on both the overall yarn strength and its CV per cent. Even the most sophisticated spinning machinery won’t fix the problem.

Awareness of the risk of yarn quality deterioration with recycled fibre blends means that quality control is the only way to assure customer satisfaction. Even then, the task is far from simple. When spinning new materials, Uster strongly recommends taking both numeric test results and graphic evaluations into account, to eliminate the risk of problems in further processing.

Spinners face major difficulties because of the high proportion of short fibres in recycled cotton (CO-R) and the fact that, when mixing with virgin cotton (CO), the fibre length distribution is sometimes suboptimal. This results, for example, in incorrect guidance of short fibres in the drafting system and potential draft errors.

In tests, a Ne 20 rotor yarn of 75 per cent CO and 25 per cent CO-R was compared with a 100 per cent cotton yarn. The values for evenness, imperfections and hairiness were measured and produced a CVm per cent of 22 per cent in Uster Statistics, which might appear to indicate excellent quality for the recycled yarn if relying on numeric values alone. In fact, closer analysis with Uster Tester spectrograms showed a draft error at the draw frame. In this case, the problem was detected before causing an uneven structure in the subsequent fabric made from the yarn, the release added.

It is an unavoidable fact that blending virgin and recycled cotton will make some quality parameters worse. Using recycled fibre is often desirable, but it creates a new reality for the industry. To cope with the risks, better communication and a common understanding are needed throughout the textile value chain.

Uster’s common language of quality will be – once more – vital in improving communication throughout the textile industry. For 66 years, Uster Statistics have been the only globally-accepted quality benchmark and the foundation for industry-wide quality improvement. The new edition, to be launched at ITMA 2023, includes for the first time a section for recycled yarn.

The Uster Statistics 2023 edition features an extended range of fibre data, supporting sustainability goals. An ideal fibre mix – with or without recycled content – also ensures meeting quality requirements for least waste. Fibre graphs will be newly available for every process step.

Spinners need to find a way to transform their mills to a more sustainable future. The challenge of spinning recycled yarns must be acknowledged, and the big goal here is to succeed with it. Spinners already have the tools they need, allowing them to benefit from both laboratory instruments and quality monitoring systems to optimise quality and productivity. Their experience, combined with Uster knowledge and latest technology in quality control and analysis systems, are a promising basis for a sustainable future for the textile industry.

The new reality of the need for closer communication and cooperation will include all players from fibre to fabric. It’s an essential debate for everyone – and Uster is ready to take the lead, the company futher said in the release.

Fibre2Fashion News Desk (RR)