FOURNÉ POLYMERTECHNIK

LABORATORY AND PILOT PLANTS
FOR THE PRODUCTION OF ELASTANE (SPANDEX) YARNS
USING WET OR DRY SPINNING METHODS

Polyurethane elastomer threads consist of at least 85 % of segmented polyurethane with so-called soft segments providing the elasticity of the thread, as well as of hard segments which prevent the thread from initiating plastic flow under tensile stress.

The remaining 15 % or less of the PU fibres contain other chemicals such as anti oxidants, UV absorbers, delustring agents, preparative agents, etc.

The production of the polyurethane spinning solution is carried out in a continuous operation or alternatively in a two-stage batch process.

Two advantages of the batch process for pilot plants are:

     - cost-efficient for small production outputs

    - great variability of the technologies involved

In a first stage, diisocyanates are attached to highly molecular polyols (soft segments,) with a slight dilsocyanate surplus. A polymer is the result

As a preparation for the second stage, the polymer is dissolved with highly polarized organic solvent, e.g. DMF or DMAC.

In the second stage the polymer reacts with a diamine or other chain lengthener in a solvent receiver. Termination of the reaction is achieved by means of a chain stopper at a required final viscosity.

A highly molecular elastomer results. This elastomer still has to be processed into a solution ready for spinning.

The reaction stages described above react very sensitively to contamination in the reaction systems. Therefore, attention must be paid to exceptional purity and maintenance q/the other quality parameters as regards the raw materials to be used.

Due to the large number of possible reaction partners and the type of process control, the variability of the spinning solution production is extremely high.

Slight differences in the chemical structures of the segmented polyurethane spinning solution can lead to serious differences in the properties of the elastomer threads.

Therefore, prior to commencing any production of.specific elastomer yarns, extensive preliminary tests are required to work out recipes for spinning solutions as well as spinning technologies.

An experimental or pilot plant required for carrying out preliminary tests, production control and further development of the technology and products should for example be capable of fulfilling the following tasks:

    - Testing or using various raw materials such as polyols of different structure and/or molar mass, different chain lengtheners, chain stoppers, additives, solvents, etc.
   - Striving for an increased solids content of the spinning solution and consequently higher viscosity.
    - Various process technologies, such as pre-polymer melt or the production of pre-polymer solution, etc.
   - Production of elastomer yarn of different structure, count and textile physical properties.
    - Working out recommended guide values for producing large-scale mass balances.
    - Functional test of new plant and machine parts.

The Laboratory and Pilot Plants built by FEP Polymertechnik GmbH for spinning elastomer yarns permit the production of these yarns with the different properties demanded. Plants for the dry as well as the wet spinning process can be supplied.

A polymerisation plant required for this consists of the following main components:

- Storage tanks for polyols, diisocyanate solvents, amines, additives
- Reactors for the production of prepolymer and prepolymer solutions
- Polymer reactors
- Degassing tank for polymer solution
- Spinning boilers, with optional switching in
- Filter system for pre-filtering of particularly firm components
- Filter system for fine filtration or filter-medium filtration
- Filter system for additives
- Feed pumps
- Instruments, such as shut-off valves, oval wheel meter, mesh filter, etc.
- Mixing devices
- Process air extraction systems
- Complete pipe system and protective gas system for all reactors and tanks
- Central data recording and process control system

The spinning solution produced in the above mentioned pilot polymerisation plant can, for instance, be spun to elastane threads on a pilot dry spinning plant.

 

The main components of such a dry spinning plant are:

- Distribution system for spinning solution
- Metering pump system for spinning solution
- Nozzle packs with multi-hole spinnerets
- Multi-zone spinning cabinets, heated
- Spinning gas circulation system consisting of:
    -  Supply of hot spinning gas to the spinning cabinet Spinning gas flow rectifers
    -  Extraction devices for the spinning gas
    -  Condenser systems for separating the solvent from the spinning gas
   -  Spinning gas heat exchanger and blower
-  False twist devices
-  Preparation facilities
-  Pairs of draw-off godets
-  Thread guide arrangements
-  Take-up winders with automatic bobbin changer (turret type)
-  Heat transfer medium - circulation systems
-  Process air extraction devices
-  Central data recording and process control system
 

The pilot plant previously described makes the production of high quality elastane yarns possible, because it meets the high demands in terms of quality made on the spinning solution and on the thread forming process.

A homogenous solution, free of gel particles is produced by high metering accuracies, good blendings by means of appropriate agitators, exact temperature control, optimized filter systems and optionally rated protective gas systems.

Further, the precise pressure compensation control, the metering accuracy of the spinning pumps, the filtration in the spinneret pack, regularity of the spinning gas flow in the spinning cabinet, exact temperature control of the spinning cabinet zones, of the spinning solution and of the spinning gas as well as the avoidance of thread tension variations in the winding process all act towards optimizing the quality of thread formation.

The complete plant is operator friendly and designed for easy access to all important locations.

The central process control system allows a reduction in operating personnel and detailed recording of all important process parameters, as well as extensive recipe management.

In the case of pilot plants, the process data recording facility of the process control system takes over the tasks of the handwritten laboratory book Operator intervention into the process sequence is possible at any time, if required

Laboratory and pilot plants for the dry spinning process of PUR are, in accordance with the count program, usually fitted with 1 to 8 spinning positions and with up to 16 thread paths per position. Related to a count of 40 dtex f4 and 8-ends per position, a capacity of approx. 0.82 kg/h elastane yarn results for a laboratory plant with one spinning position only and for a pilot plant with 8 spinning positions, a capacity of 6.5 kg/h elastane yarn is achieved.

According to the number of batches per 24 hours, the required size of the polymerisation plant can be determined from this in each case.

In comparison with threads made out of rubber, elastane threads are approximately 3 times stronger. Because of their excellent elastic properties, high strength and resistance against aging, a large number of solvents and good dyeability they find wide use in the textile industry.

Elastane threads can be processed following cover spinning, wrap spinning or having been wrapped with twisted thread as well as in their blank state.

With blank filament yarns of the fine count range, light elastic articles, such as corset materials, swimwear and stockings are produced.

With the addition of elastane threads, the following goods are produced today:

   - Woven goods (elastic fabrics for outer clothing and sportswear and elastic cord (stretchcord)
- Hosiery goods (tulle lace for girdles and elastic washable fabrics, swimwear)
- Knitwear (elastic hosiery fabrics, stockings and socks, tights and sock bands, orthopaedic support stockings)
- Braided goods & pieces of pillow-lace (elastic ribbons and braids, elastic ropes)

Heavier counts without detectable solvent residues are also used in diapers and for foodstuff packaging.