Acrilyc DMF Process

PROCESS CHARACTERISTICS

 

The whole process develops continuously from the monomers inlet into the polymerization solution preparation tanks up to the finished fibre baling (tow or staple). In order to obtain this continuity, the process has the following main features:

 

• Monomer continuous polymerization in the polymer solvent, so as to directly obtain the dope ready to be spun

• Fibre continuous drying under relaxation, so as to obtain a fibre ready to be processed in the wool system spinning, both via staple carding or tow-to-top transformation using stretch breaking machines

• Fibre continuous annealing with saturated stream under pressure (when annealing is required) so as to get a fibre ready to be processed in the cotton system spinning (both ring and open end), or to be heat stretched and cut to give high shrinkage staple

 

PROCESS DESCRIPTION

 

Polymerization

The polymerization mixture is continuously prepared by dosing the fresh monomers (ACN and MA or VA) and the solvent (DMF) into the solution of unreacted monomers, recovered by distillation. Organic catalyst is added to the polymerization solution.

The polymerization reaction takes place in three reactors, in series. The reaction is exothermic and the reactors are operated at constant temperature.

The reaction product, a solution of polymer and unreacted monomers from the dope are fed to a thin layer distiller. The recovered monomers from the top are recycled to the mixture preparation.

The polymer solution is extracted from the bottom of the distiller. Before filtration through filter presses, dulling or blueing agents or pigments or cationic dyestuffs are dosed into the polymer solution. Upon request, a technology for mass dyeing with pigments can be provided.

 

Spinning

The spinning line is of double front type. The coagulation takes place in a bath consisting of a solution of water and DMF with controlled composition, temperature and flow rate.

The coagulated fibre undergoes first a prestretching treatment in hot solvent-water solution, then a washing to eliminate the residual solvent and finally a second stretching in water.

After the first finishing application, the fibre is fed to the perforated drums drier, where the water is removed from the fibre and a fibre shrinkage occurs. At the outlet of the dryer, after the second finishing application, the fibre undergoes the crimping treatment.

The crimped tow does not require any further treatment if a wool type fibre has to be produced and max 3% residual shrinkage can be accepted. If a cotton type fibre has to be produced, then a continuous annealing can be provided after crimping.

Upon request gel dyeing equipment can be included in the spinning line to obtain dyed fibre together with computerized system for recipes preparation, cationic dyestuffs solution feeding and colour parameters continuous monitoring in line.

 

Circulation of spinning bath and solvent recovery

The DMF excess, introduced in the bath through the polymer solution the coagulation process, is sent to the solvent recovery plant, which consists of a concentration tower, working under vacuum and of separation tower working at atmospheric pressure.

An anhydrous solvent is obtained from the bottom of this latter tower. The purified solvent is sent back again to the production line. The bottom products of the solvent recovery plant are sent to the solid removal system.

For further energy saving, solvent recovery can be obtained through a triple effect distillation provided that the towers are filled with special packings.

 

© Ing. A. Maurer S.A.

 

 

 

 

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