linel® (100%) Recycled Spandex Process Technology
The investment was designed and destined for a plant manufacturing linel® Spandex yarn with a name plate capacity of approx. 1.800 tons/year (330 working days production base) with the possibility to double plus its capacity to approx, 4.000 tons/year. The first step (approx. 1.800 tons/year) were a 7.500.000 UDS investment. Its completion will have passed the 10.000.000 USD mark. The linel® Heavy Deniers Spandex fibre production is based on Wet spinning technology. The Fillattice Group has been developing Wet spinning yarn manufacturing technology since the very beginning of the 1970’s in Italy. The Group has pioneered in manufacturing Eco-Friendly Heavy Denier Spandex yarn with high quality. From a 30% recycled material mix in the 80’s to 50 -50 in the 90’s and then since 2014 a 100% recipe. Spandex is commonly used for describing elastane fibres, that are synthetic, polyurethane fibres with high elasticity and recovery properties (elastics).
Elastane yarns are typically incorporated into textile constructions where their high elastic extension and high recovery forces are advantageous. Elastane yarns are never used alone in fabrics, but always in combination with other fibres (i.e. cotton, polyester, nylon, viscose, wool, etc.), either as bare yarns or as covered ones. While Heavy Deniers elastane was in the past used as a special functional fibre only, like in corsetry, bands and medical stocking as a rubber substitute, today its fields of application are much wider and continuously eroding the natural rubber market especially with the linel®tapes.
Furthermore, elastane fibres are currently used together with nylon or polyester fibres for: woven fabrics: narrow fabrics (straps and trimmings for all sorts of clothing articles), denim/jeans, leisure and sportswear, city fashions, fashionable outwear, shoes; other fabrics/applications are: diapers, sanitary articles, medical articles (support stockings, elastic bandages and compresses) and technical articles.
Elastane fibres can be produced by some different spinning processes (wet, dry, melt and reaction): but while nowadays over 95% of it is produced by dry technology all over the world, nevertheless the Wet technology can be particularly interesting and efficient to obtain good properties, mainly when producing Heavy denier yarns and now tapes too (linel®tape; the first ever elastic tape made of Spandex and from 100% recycled material).
Preparation of the polymer
The preparation of the polymer starts by thin and accurate selection, cleaning and grinding of industrial spandex waste and/or b grade – resulting from dry or wet technology -, then diluting the obtained microfilaments with a highly polar organic solvent – DMF and/or DMAc – in heated and stirred tanks, adding some chemical; additives to gain best properties, and filtering the final solution to keep off the solid impurities. As an alternative, the virgin polyurethane polymer can be produced in a first step by chemical reaction of a long-chain dyol or macrodyol (polyol PTMEG) with pure MDI (distilled isocyanate), in a DMF/DMAc solution; then in a second step, the NCO prepolymer, diluted in DMF/DMAc, reacts with low molecular weight diamines mixture in a DMF/DMAc solution, used as chain extenders and terminators to obtain the desired average molecular weight. In both cases, the final product is a high viscosity elastomer solution (called “dope”), consisting in a 25-30% total solid polymer solution in DMF/DMAc, that is stored in heated and stirred tanks under nitrogen atmosphere.
When transferred to the spinning section, the polymer is again filtered through filter-press, to remove secondary solid impurities and gels: these steps are fundamental to guarantee high performance characteristics and continuity in spinning section.
the polymer solution is extruded through a plurality of spinneret capillary holes, horizontally in a spinning bath containing a solution of DMF/DMAc in water, at controlled temperature. Here the newly born filaments or tapes loose progressively the solvent, due to its higher chemical affinity to the water solution; then, their solidification is completed passing through a washing vat and later onto a dry roll section, where they are dried in contact with steam-heated steel “godet-roll” surface. The dried yarns or tapes is lubricated with a finishing oil, that will guarantee good unwinding properties to the yarn but further adding to the tapes. For the yarn a round shaped filament cross section is often required for final application: in this case, twisters will be applied to the spinning machine, to obtain this particular property. The yarns are at the end collected on winder machines, at different speeds depending on the specific produced denier. The tapes go onto boxes with plastic lining (tail-end), 2 to 2,5 kg each. The final products are bobbins of elastane (Spandex) yarn, available in a very wide range of titres: this plant is focussed on titres between 420 to 2500 Den. The yarn will be collected on paper or plastic cylindrical tubes, of 114 mm length; 1kg standard to 3 kg (diaper’s application).
The water-DMF/DMAc liquid solution coming out from the spinning vats will be stored for successive distillation and recovery of the solvent (closed loop). The water and solvent vapours coming out from the spinning vats are blown and collected by a scrubber, where the gas stream is washed in counter-current with a water stream. The final gas emission is clean from solvent, whilst the column bottom collects a water-DMF/DMAC solution, to be treated at the solvent recovery plant (to be re-used). The spinning department is completed with a section for the preparation of spin and wash solutions, under specified thermic conditions, and with a section for the preparation of the finishing oil/silicon where required or necessary.
Solvent recovery plant
One double/triple effect distillation plant is designed for complete recovery of the solvent: after this process, DMF and or DMAc will be again available for production. The closed loop of the solvent in this technology guarantees its high economical yield and a very Eco-Friendly impact on environment. A win-win situation. The distillation plant is fed by water-solvent solution streams coming out from the spinning process (vats) and from the scrubber bottom/recovery. The secondary product is water: the obtained purity (specifications) allows to reuse this controlled water back into the plant (preparation of spinning baths and washing top stream for scrubber), so only a limited water reintegration is necessary and all parameters are under control.
Automation and control system
A PLC will maintain under control and log continuously all process parameters like temperatures, pressures, flows, dosing of single raw materials and reaction participants, viscosity, levels, as well as binary information as alarms, switch parameters, ON-OFF status, etc., in a very friendly way for the production operators. The system is relatively simple but it is able to apply complex and step procedures, it can be easily integrated with plant section outside battery limits and it can be interoperable with higher level management control system. Besides, the above mention equipment the following additional areas are necessary: Spinneret workshop: one section of spinning plant is devoted to spinneret preparation, that means cleaning (with warm solvent) after their production life and spin pack assembling, ready to be again installed on the spinning machine; The spinneret design determines the linel® yarn titre/denier and/or the mm width of the the linel®tape.
Chemical and textile laboratory
The quality control laboratory is divided in two sections: chemical analysis on raw materials coming from suppliers and process analysis (polymer, solution composition, dope viscosity, etc.); textile analysis on yarn to verify the properties and the respect of the specifications (mechanical properties like: elongation, load, tenacity, recovery, denier, etc).
An important part of workshop is devoted to machines maintenance and repair; main maintenance equipments and spare parts are available in workshop in order to guarantee continuity in production plant.
Final product packaging
The bobbins coming out from winders are put directly in carton boxes (18kg to 24kg each) by spinning operators, then final packing and labelling is made in this area; the pallets with 4 to 16 carton boxes are sent to warehouse; for the tape the boxes are also made at the machine, ready to be labelled. There are 20 up to 140 boxes per pallet (7 layers).
Raw material warehouse
A proper area is dedicated to the storage of raw materials, typically in bags or in drums; a big area is especially devoted to the spandex waste, due to the opportunity of creating a consistent safety stock producer by producer in order to be able to trace it and eventually obtain the GRS certification. Oeko -Text® Standard 100 was obtained first in 2017.
Final product warehouse
This area, equipped for pallets storage, is located downstream of the production process; pallets are handled manually by elevators and stored on shelves before picking and delivery to customers.
All main industrial utilities are needed for such a Chemical/Textile plant.