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Cellulose is one of the most abundant biopolymers in the world, occurring naturally in most plants. It is the major component of natural cotton, linen and hemp fibres. It is also transformed into man-made cellulosic fibres (MMCF), also known as ‘rayon’ in the viscose, lyocell and cupro chemical fibre-spinning processes that typically use wood-pulp feedstock. This wood pulp is produced using well-established chemical processes known as the kraft and/or sulfite pulping processes. In this process, chemicals such as hydrogen sulfide are used to break down the naturally occurring bio-polymers lignin and hemicellulose that are present in wood, liberating pure cellulose.
The main impact hot-spots in the production of man-made cellulosic fibres or rayon are the production of pulp from wood and the fibre spinning process itself, particularly in the case of the viscose process. Discharge of and the use of hazardous chemicals during the viscose process, as well as the sourcing of wood pulp from ancient and endangered forests, is also a critical issue in the supply chain which needs to be addressed.
Some of these issues can be solved by innovation, for example by focusing on cleaner fibre spinning processes, using alternative feedstocks, incorporating recycled content, improving the pulping process, and utilising traceability solutions. In this article, we break down five of the most promising innovation areas in man-made cellulosic fibres.
These technologies use different, cleaner and greener chemistry to dissolve cellulose by either exploiting physical properties to directly dissolve the cellulose in a solvent or to ‘liquify’ the cellulose via a chemical reaction, similar to the way viscose is made. There are also developing technologies that use a completely different mechanism to spin cellulose-based fibres which fall somewhere between man-made cellulosic fibres and natural fibres.
Companies such as TreeToTextile, based in Sweden, directly dissolve cellulose in novel solvents, in this case, a water-based alkali solvent, producing a new kind of rayon fibre that has properties similar to both viscose and cotton. The Finnish university spinout Ioncell is another example that uses a novel ionic solvent to produce a strong, light alternative to lyocell that can also utilise waste cotton as a feedstock. By pursuing a direct dissolution approach, these processes are analogous to the lyocell process, which is already considered as one of the lowest impact man-made cellulosic fibres. It, therefore, remains to be seen what the specific impact potential of each technology is compared to lyocell – the case for comparison to viscose is a lot easier to make. The commercialisation of these technologies will be driven by the specific aesthetic quality of the resulting fibres.
Alternatives to the much older and ‘dirtier’ viscose process also exist. Infinited Fiber Company modifies cellulose with urea, a relatively harmless chemical, instead of the hydrogen sulfide used in the viscose process, to form cellulose carbamate. After this, the cellulose carbamate is spun into an acidic water bath, leaving a pure cellulose fibre. The process is said to produce a very “cotton-like” fibre, unlike viscose.
Finnish company Spinnova is developing a unique type of fibre spinning process which is entirely water-based and requires no chemicals. They exploit the properties of microfibrillated cellulose from wood pulp in water to spin a unique kind of cellulosic fibre without any kind of chemical reaction or dissolution process. It produces a fibre that is somewhere between a rayon like viscose or lyocell and natural cotton.
The cellulose present in food and agricultural wastes can also be extracted to be used as a feedstock for rayon fibre spinning. This both valorises an otherwise low-value waste product, whilst reducing the demand for wood logging and conventional pulping. Orange Fibre, for example, extracts cellulose pulp from waste orange peel, abundant in their region of Italy, which is then used as a feedstock to produce a conventional viscose fibre. In a recent collaboration, Tencel manufacturer Lenzing produced a lyocell fibre with pulp extracted from both orange peels supplied by Orange Fibre and wood pulp. There are other companies, for example, extracting cellulose from wheat and rice straw, sugarcane bagasse, switchgrass and other waste biomass feedstocks. Key criteria in the successful commercialisation of these technologies are the yield, quality and purity of the cellulose extracted from the waste biomass.
Certain bacteria such as Komagataeibacter xylinus (K. xylinus) can create cellulose when fed sugars. These bacteria have traditionally been used in the production of the jelly-like Filipino dessert Nata de Coco from coconut water. However, the same bacteria can also be used to produce cellulose for use in spinning man-made cellulosic fibres. Nanollose is one company commercialising the production of bacterial cellulose for use in man-made cellulosic fibre production, using organic waste.
In addition to utilising a biomass source other than wood, we can also innovate on the pulping process itself. There are alternatives to kraft and sulfite pulping such as the so-called organosolv-type processes which use less harmful chemicals and, for example, operate under milder conditions requiring less energy. Historically these alternative pulping technologies have been difficult to commercialise, and a key challenge is achieving the purity needed for ‘dissolving’ grade pulp, which historically comes from the sulfite pulping process. Conventional pulping processes are currently very established and highly optimised, which makes displacing these technologies very difficult. However, some companies around the world such as Chemopolis, in Finland or Green Whisper, in the USA, are attempting to commercialise alternative and cleaner pulping processes, some with alternative feedstocks.
The easiest way to incorporate recycled content comes from the use of pre-consumer or post-industrial cotton waste – industrial scraps and offcuts that are of known quality and purity. The producer of Tencel branded lyocell fibre Lenzing produces a lyocell fibre with pre-consumer cotton content called Refibra and companies such as Renewcell have purified post-consumer cotton from denim to produce viscose fibres with recycled cotton content along with viscose spinning partners Tangshan Sanyou. Other pulp and viscose fibres companies such as Birla Cellulose are following with recycled-cotton content rayon fibres.
For most cotton-to-MMCF (rayon) recycling processes, the cotton undergoes a chemical pre-treatment, after which it can substitute the wood-pulp feedstock normally used to create viscose or lyocell fibres. The key advantage is that cotton is already pure cellulose and can therefore bypass the energy and chemical-intensive pulping of wood, reducing the overall environmental footprint of the pathway. However, as always, this depends on the specific recycling process being compared in contrast to the conventional system.
One way to trace the origin of the wood feedstock for man-made cellulosic fibre production is the use of traceability solutions that trace the origin of the material back to its source.
This helps identify and validate wood pulp that has not been sourced, for example, from ancient or endangered forests. For this, we can consider both digital solutions such as blockchain-enabled traceability solutions in combination with a physical tracer technology such as DNA. Blockchain traceability solutions such as TextileGenesis aid in the auditing and traceability of the physical supply chain, allowing the movement of material between supply chain partners to be validated.
However, it may still be possible for fraud and mistakes to creep in, so physical tracers are one way in which the origin of a material may be tested in a laboratory, by matching the information contained in the tracer to a database of tracers used by the original producers.
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Improving the sustainability of man-made cellulosic fibres production is not something that can be solved with one innovation alone. There are, inevitably, many caveats and trade-offs to consider with every new innovation and technology and the sustainability impact in many cases is not always understood in-depth. Economic feasibility and marketplace acceptance are key factors to consider too, and should not be taken for granted in the long run.
This article is a brief overview of the general areas of innovations that are of importance right now and is not a comprehensive overview of every key innovator or innovation and the possible impact of each. Rigorous analysis with life-cycle assessment is needed, not only in terms of individual innovations but also the knock-on effects on the wider system if they were to be implemented and widespread.
Circuvate is supporting the industry by undertaking and providing services for evidence-based, critical analysis of new materials, chemical technologies, and other innovations in terms of both sustainability impact (via life-cycle assessment), and their market and economic feasibility.
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Author: Dr. Ashley Holding
Principal Consultant @ Circuvate
Circuvate provides consulting and advisory services to the fashion and textiles sector. We are experts in sustainable innovation, materials, recycling, and life cycle assessment (LCA).
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