The textile industry is in a revolution: Fast fashion has damaged its reputation. Demand is rising. The strong growth of polyester fibers contrasts the necessity to reduce microplastics. Cotton is limited. Viscose is not sustainable. Lyocell is in. New technological initiatives are on the way. New cellulose sources are needed. Global supply chains are fragile. Raw material dependency is a concern. Global brands face a reputational risk. In the middle: LIST Dissolving Technology - the versatile dissolving technology platform for cellulose from any kind of biomass, from lab to world scale, for any solvents - unleashing Lyocell’s full potential.
The LIST Dissolving Technology has always been here - now its time has come!
Discover here the story of Lyocell 2.0:
Market Environment of LIST Lyocell
Why KneaderReactors for Lyocell?
LIST Lyocell - Why now?
Lyocell from Recycle Pulp
The power of Re-Recycling
Are you prepared for the upcoming dynamics of the Lyocell market?
Director Business Development
Market Environment of LIST Lyocell
LIST specializes in KneaderReactors for various high-viscosity processes in the chemical industry. These include a wide variety of applications in all sizes - from laboratory kneaders to 100 ton heavy machines. Since about 2018, one of LIST's most dynamic business areas is in the textile industry.
What exactly is it about?
With its KneaderReactors, LIST specializes in the mixing and kneading of viscous materials. For this purpose, LIST operates a pilot plant center in Switzerland, in Arisdorf nearby Basel, where the products of LIST customers are tested and process design data is collected. One of these applications is the production of a homogeneous highviscosity solution of cellulose, which can be pressed through a spinneret to produce cellulose-based fibers. The process is a direct dissolving process, the most common of which is known as Lyocell.
Lyocell is very much in vogue in the industry today. Cellulose-based fibers are more and more popular because they are made from a renewable raw material and biodegrade in a short period of time. It also avoids the generation of microplastics. This contrasts with polyester fibers, whose biodegradation takes an unimaginable 400 years and also releases microplastics with each washing cycle, ultimately entering the food chain. In addition, cellulose-based fibers are more comfortable to wear than polyester fibers because they absorb moisture. Due to this property, cotton fibers have traditionally been used and are still very popular. However, cotton production areas stagnate because cultivation is so water-intensive that entire stretches of land are being dried out, such as the Aral Sea. However, the rapidly growing middle class worldwide is demanding higher quantities of cotton.
Until now, the only man-made cellulose-based fiber was viscose - also called rayon. However, viscose fibers do not achieve the qualities of traditional cotton and use chemicals that are very toxic to humans and the environment. This is why Lyocell's hour has come. Lyocell uses no toxic chemicals and surpasses viscose in terms of quality and sustainability. And the hour has come for LIST, because the use of KneaderReactors has shown that the quality potential of Lyocell has not yet been fully realized.
The market environment is very dynamic. Many different types of biomasses are currently being tested, ranging from cellulose from agricultural waste, used clothing or bacterial cellulose. Also being tested are various non-toxic solvents. Each case has its merit but must be embedded in different business models. LIST accompanies its customers from the initial idea, through customer-specific development, to industrial implementation and commissioning. Always in focus is the customer's market competitiveness.
Why KneaderReactors for Lyocell?
1. Dissolving process
The Lyocell process uses N-methylmorpholine-N-oxide (NMMO) as a solvent. NMMO is very hygroscopic and quickly and easily absorbs water and atmospheric moisture. It dissolves a pulp only within a certain concentration range, the so-called dissolving window, in which NMMO forms a monohydrate with water.
The usual manufacturing process of a Lyocell spinning solution from pulp starts with an excess of water, allowing the NMMO to strongly penetrate the pulp without dissolving it. Thus, the NMMO, the water and the pulp form a suspension. By adding energy, the water begins to evaporate until the dissolution window is reached. The pulp begins to dissolve, the suspension becomes a solution, and the viscosity increases sharply. During these processing steps, a good mixture of the components is essential for the success of the process ultimately targeting a high degree of homogeneity.
LIST KneaderReactors are specialized in mixing highly viscous substances and evaporating volatile components.
NMMO is in itself harmless to humans and the environment. However, overheating of the solvent can, under certain circumstances, lead to an autocatalytic reaction with a sudden release of gases, i.e. an explosion.
Water evaporation requires high heating temperatures. Constant temperature control is therefore very important. If a temperature rise is detected, the energy supply must be reduced immediately.
In LIST KneaderReactors, the energy input occurs largely through mechanical energy from the rotation of the shaft and interaction of the mixing elements. The high viscosity causes friction, which heats the product. This frictional heat is used to evaporate the water. The good mixing of the mass in the process chamber of the LIST KneaderReactor ensures that no overheated spots (hotspots) are formed. Since the frictional heat is directly dependent on the rotational speed of the shaft, the product temperature can be precisely controlled. In an emergency, the shaft rotation can thus be quickly and greatly reduced or even stopped altogether, thus immediately stopping the energy input. This input of mechanical energy is an advantage over a thin-film evaporator, whose energy input is via heated surfaces that remain hot even after the heating energy has been stopped and can continue to heat the thin film of product (here more about thin-film evaporators).
Therefore, LIST KneaderReactors increase process reliability.
LIST KneaderReactors are specialized in mixing and kneading of viscous materials due to the following unique properties:
- Unlimited residence time and selectively adjustable mixing intensity, which sets no technological limits to the dissolving of alternative biomasses.
- Tight temperature control due to
a. mechanical energy input through shaft rotation speed (see also "Safety")
combined with a
b. high accuracy of the temperature measurement due to the good mixing of the product mass
- No hotspots can be formed in the process chamber due to the good mixing of the product
This accurate temperature control heats the product just enough to evaporate the water without overheating the rest of the product while concurrently mixing it with a biomassspecific intensity to reach the required homogeneity. This makes it possible to dissolve pulps from alternative biomass, such as hemp or cotton from recycled textiles, to 100% and process them into fibers.
LIST has been in the Lyocell business since the 1990s with their KneadReactors. But why has LIST experienced a boom since 2018?
In the direct dissolving processes, a pulp is dissolved in a special solvent, resulting in a sufficiently homogeneous high-viscosity solution that it can be pressed through a spinneret, thus producing cellulose-based fibers. LIST KneaderReactors are particularly suitable to produce a homogeneous high viscosity spinning solution. But why actually?
LIST KneaderReactors have been specially developed for various high-viscosity processes in the chemical industry. Their strength lies in the continuous conversion and processing of highly viscous masses, whereby these can be kneaded at any intensity for any length of time. This technology allows to set a processing time and intensity specifically for any pulp. LIST KneaderReactor based plants have never faced any quality limitations and could easily dissolve alternative biomasses, such as 100% hempbased pulp (Lyohemp©). But to dissolve wood pulp, originally developed for viscose, limited processing time and mixing intensity could also be used.
2. New technology need since 2018
Around 2018, the textile industry’s lack of sustainability was generally accepted and the interest in producing sustainable cellulosic fibers grew quickly. The realization took hold that pulp sources for alternative biomasses must be developed to meet the raw material demand that could replace even a small portion of polyester fibers. This has since been reflected in several technology innovation initiatives. Hereto, more technological flexibility in processing time and intensity is needed - and LIST KneaderReactors provide this.
Lyocell plants equipped with LIST KneaderReactors enable the plant owner to change the pulp source and adjust the relevant process parameters without having to rebuild the plant. Lyocell producers can thus confidently follow developments on the pulp side and react flexibly to them at any time whether they are striving for cost leadership with low-cost pulp or want to differentiate themselves on the market through high fiber quality using high-quality pulp.
3. Invention of LIST Combo System
In the 1990s, thin film evaporators were used in conjunction with the LIST KneaderReactor for the development of the manufacturing process for Lyocell spinning solutions. As the name suggests, a thin film evaporator is characterized as an efficient evaporator. Above a certain water concentration in the NMMO, a monohydrate is formed, which begins to dissolve the cellulose and causes the product viscosity to increase. In this range of high product viscosities, thin film technology reaches its limits. However, it is precisely in this part of the process that the LIST KneaderReactor shows its strength. The LIST Combo System combines the strengths of both technologies, the thin film evaporator evaporates the water until the viscosities increase such that a LIST KneaderReactor can handle the product better. The process can then be completed to a homogeneous spinning solution without limiting the residence time or mixing intensity.
This combination has several advantages:
1. Safety & efficiency
In the thin film evaporator, no consideration has to be given to excessive shear and product overheating in the highly viscous section as this is relocated to the LIST KneaderReactor. In the thin film evaporation without a LIST Combo System, this higher shear could lead to product damage or autocatalytic decomposition (explosion).
In the LIST KneaderReactor, cellulose from any biomass can be dissolved and homogenized with any mixing intensity and for any length of time. Thanks to the exact temperature measurement and the energy input via the shaft rotation, the product temperature can also be controlled precisely and "fail-safe".
The division of evaporation and dissolving into two separate pieces of equipment avoids a compromise between efficiency on the one hand and safety and quality on the other. This makes the operation more robust, safer and easier to operate.
2. Unlimited biomass
The unlimited mixing intensity and residence time range of the LIST KneaderReactor allows the processing of cellulose from any biomass. The Lyocell producer can thus easily switch to other cellulose sources that may be cheaper, more sustainable or higher quality.
3. Maximum capacity
The largest thin film evaporators do not require the largest LIST KneaderReactors. Conversely, this means that a large LIST KneaderReactor can be combined with more than one thin film evaporator in a LIST Combo system set-up. Further, all of the heating surface of a thin film evaporator can be used for heating and no areas need to be reserved for a dissolving section, where hot surfaces must be avoided for safety reasons. This increases the capacity of spinning solution production because the entire surface of a thin film evaporator is available for evaporation and several thin film evaporators can be connected in parallel to a LIST KneaderReactor (see also "Energy savings").
4. Energy savings
In the LIST Combo mode, the thin film evaporator does not have a homogenization section in which it would have to cool the product due to consideration of product quality and process safety, which means avoiding a loss of energy.
In short, these advantages have become more and more relevant in recent years, due to the increasing demand for
- large capacities
- pulp from alternative biomasses
- a robust process that is especially suitable for newcomers to the market
Lyocell from Recycle Pulp
What's the "kicker" in recycling cotton textiles into Lyocell fibers?
1. Higher fiber strengths
Fibers have been obtained from cotton for thousands of years. Their cellulose-based cell structure makes them absorbent and comfortable to wear. Cotton cellulose is of higher quality than wood-based cellulose. The polymer chains are longer from cellulose than from wood. It also contains fewer foreign substances such as lignin.
In a direct dissolution process, as used in the Lyocell process, the cellulose is physically dissolved and the polymer chain lengths are largely retained. These polymer chain lengths are measured in DP (Degree of Polymerization). If cellulose with long polymer chains is used in the Lyocell process, these remain and increase the tensile strength of the Lyocell fibers.
2. New supply chains
Cotton textiles are produced near the end consumer. This enables
- completely new, local supply and value chains with shorter transport routes,
- less dependence on foreign countries and, in addition,
- involvement of the end consumer – enabling completely new branding strategies.
Brand owners can also better control the supply chain and more credibly guarantee the sustainability of their value chain, which will in any case experience greater customer awareness through the use of recycled pulp.
Recycle Pulp (RePulp) - FAQ:
A. Why not the viscose process?
The Lyocell process is fundamentally different from the viscose process: The viscose process is a chemical process that converts the cellulose polymer chains into an intermediate (or derivative, specifically a xanthogenate) through a chemical reaction. Cellulose fibers are then obtained from this - again through a chemical reaction. This process results in more uniform polymer lengths than the Lyocell process, regardless of whether the original polymer chain was long or short.
In addition, unlike the Lyocell process, the viscose process uses chemicals that are highly harmful to humans and the environment. This is contrary to the sustainability of recycled fibers.
B. Why not generally use cotton-based cellulose instead of wood-based cellulose for Lyocell?
The reason lies in the economy with which the cellulose can be obtained. Wood has a much higher density than cotton bales. Cultivation therefore requires much less land and no artificial irrigation, harvesting is not labor-intensive, and logistics costs are lower. In addition, cotton is already a fiber. It would not be economical to make a replica from the original.
C. What is the contribution of LIST in an industrial implementation?
Today's Lyocell plants are built to process wood pulp. They cannot process 100% recycled pulp. Typically, only proportions on the order of 30% RePulp are possible in pulp blends. 70% is still virgin wood-based pulp so that the process is similar to that of pure wood pulp. LIST KneaderReactors do not have this limitation. The higher quality cellulose of RePulp requires a higher mixing intensity in processing and LIST KneaderReactors make it possible to obtain Lyocell fibers from 100% RePulp.
Lyocell made from 100% RePulp is not an isolated technical-academic excercise but has very tangible strategic implications. It enables the establishment of closed supply chain cycles in the first place. After all, the limit of only 30% RePulp would mean that a production plant for Lyocell from used clothing would in fact still have to process an additional 70% pulp from virgin wood. In other words, in order to recycle used clothing, twice as many trees would have to be felled - measured in cellulose equivalents.
D. How to recover pulp from textiles (RePulp)?
Recycled pulp is obtained from textiles containing cotton fibers. Most of them are blended fabrics. Most are polycotton, namely blended fabrics made of cotton and polyester fibers. Here, the polyester must first be separated from the cotton. Most easy is the processing of pre-consumer (pre-use) cuttings from pure cotton textiles, which are produced by textile processors. Their composition is known, and the textiles are not contaminated. Most costly are used (post-use or post-consumer) polycotton fabrics. Like with wood-based pulp, they must meet a specific requirement profile. These requirement profiles are different for viscose and Lyocell and vary from fiber manufacturer to fiber manufacturer.
Various manufacturing processes are currently being developed and launched on the market for this purpose. They are at different stages of development. They all go through several process steps, typically starting with a pre-selection in the supply logistics through cooperation with the textile collection organizations, then start with mechanical process steps followed by chemical processes to produce a RePulp with the required specifications.
The power of Re-Recycling
As soon as Lyocell textiles made from recycled cotton textiles come onto the market, the question of their further recycling arises immediately. Lyocell fibers can be recycled at least five (5) times.
Since cotton fibers account for just over one-fifth of the total fiber market, using cotton fibers for the first time followed by recycling them four more times would equal the total biomass to produce all synthetic and natural cellulose-based fibers combined - without cutting down a single tree.
This consideration is not about how much of the polyester fiber market could be replaced by cellulosic fibers. It is simply about showing the potential that lies in rerecycling.
Closing the textile loop not only improves sustainability, but also reduces dependence on raw materials and shortens transport distances.