Technical fibers, whether natural or synthetic in origin, are produced via a series of steps which transform the raw material into a viscous, homogenous, degassed spinning dope.
For any fibers which require a dissolving step LIST KneaderReactor technology can produce high quality spinning dope which results in high fiber quality with maximum throughput and at minimum costs.
The unique process characteristics of the KneaderReactor provide intensive mixing and kneading, constant surface renewal and variable residence times. The scale-up to large industrial capacities in one single line is one of the many advantages of the LIST Technology.
- Effective self-cleaning to minimize dead zones, product accumulation and product degradation
- Excellent kneading and mixing for better homogenization
- Low shear processing
- Effective heat transfer
- High surface renewal efficiency
- Large free vapour volume
- Precise and uniform temperature control due to large heat transfer areas
- Continuous processing
- Processing of sticky and highly viscous products
- Narrow residence time distributions (plug flow)
- Wide and flexible range of average residence times
- Reliable process scale-up from pilot to industrial units
Cellulose and additives are dissolved continuously in the LIST KneaderReactor, which provides thermal treatment, evaporation, and degassing along with intensive mixing. The result is a glass-clear, light yellow spinning solution that is highly homogeneous and free from bubbles and dissolved gases.
Depending on the process the solvent might be N-Methylmorpholine-N-Oxide (NMMNO), various ionic liquids, acids or caustics.
Aramid fibers are typically wet-spun from a viscous solution made of poly(p-phenylene terephthalamide) (PPTA) polymer in concentrated sulfuric acid. The thermal energy released during the exothermic dissolving process helps to melt and dissolve the polymer. The polymer solution is viscous and non-Newtonian. The requirement is to create a homogenous, degassed solution with a controlled high polymer concentration.
|Perfect dissolving technology for very good fiber quality|
For decades, conventional polymerisation has been the norm in the production of elastomers. The time and cost involved in removing and treating solvents in the final stages of production were acceptable. Yet as pressure builds on manufacturers to reduce operating costs, there is greater urgency to develop processes that can help streamline costs and production techniques. One such effort has yielded extremely promising results.
|Direkt in der Polymerlösung entgasen|
Der zunehmende Kostendruck macht keinen Halt vor der Produktion von Elastomeren. Gefragt sind intensivierte Prozesse, die unnötige Verfahrensschritte ersparen und sowohl Zeitaufwand wie auch Kosten senken. Nun liefert ein innovativer Ansatz aus der Schweiz, die sogenannte Direct Devolatilization (direkte Entgasung) von Polymerlösungen, vielversprechende Ergebnisse.
|Perfect fiber quality from perfect dissolving technology|
Fiber, filament, flies and foil are the final products of a complex process of mixing, dissolving, spinning, washing and drying of raw material. Many specialists believe that the spinning part is the only relevant processing step for the final fiber quality. This belief falls short, as the fiber quality also depends on the dissolving step before the spinning step.
|Concentrated dissolving for homogeneous spinning dope|
In conventional spinning dope production, capacity is typically a function of the maximum processing viscosity the spinning plant can handle. Often the prior dissolving process step is limited by this fact. In a typical wet spinning operation, dope viscosity ranges from 500-2500 Pa ·s (zero shear viscosity at 95 °C) can be handled. For processors looking to meet rising demand with world-sca le plants, the limitations imposed by high viscosity dope sol utions are challenging and costly. List AG, Arisdorf/Switzerland, have now adapted the company’s high viscosity processing technology in order to meet the difficult processing challenges of today’s high-production fiber lines. The technology can easily handle 20,000-200,000 Pa·s (zero shear viscosity).
|Improved Lyocell dissolving system|
The Iyo cell fiber process is developed to transform cellulose to a man-made cotton-like fiber. The lyocell process includes a number of processing steps. The dissolving step is the most important one. It represents the heart of the lyocell technology. Kneaders developed by List AG, Arisdorf/Switzerland, are successfully applied for the continuous dissolving step whereby raw materials of different origin can be processed and transferred into a spinabie dope.
|Process flexibility and process safety|
As world consumption of textile fibers expands with the rapid growth of Asia and other developing countries, sources of fibers other than cotton and rayon must be developed and brought to market to meet demand. Cellulose fibers (Lyocell fibers) can meet these expanding needs because of the specific qualities and characteristics of the fiber, as well as the vast availability of the raw materials.
|Innovative Weiterentwicklung der Lyocell Tehnologie|
Der LYOCELL-Prozess ist eine moderne umweltfreundliche Möglichkeit zur Umwandlung von verschiedensten cellulosischen Rohmaterialien der Natur in Fasern, Filamente und Folien zur weiteren Verarbeitung in der Textilindustrie, der Verpackungsindustrie oder als Strukturbildner in technischen Anwendungen. Die Nassreißfestigkeit der LYOCELL-Faser übertrifft sogar die der Bauwollfaser.
|Optimization of cellulose dissolution stage|
LIST further optimized the cellulose dissolution technology, which was introduced in 1992. This succeeded the production of excellent spinning solution qualities, produced from a variety of low cost raw materials. The technology fulfils the current high safety standards.
|Continous dissolution process of cellulose in NMMO|
A new dissolution process for cellulose spinning solution was developed. As Basis for the new process served the classic cellulosic fiber production process. In the last 30 years or so the conventional viscose process became environmentally critical. Evaluated with regard to its environmental viability it was found to create considerable water and air pollution. This conclusion ignited the research and development of new technologies with less environmental impact.