In dry spinning, the fiber-forming polymer dissolved in a volatile solvent is introduced into a heated drying chamber where the solvent is evaporated and solid fiber is obtained through a spinneret. Dry spinning is suitable for producing fire denier fibers. It also no need for washing. A flowchart of the dry spinning process is given below.
Process Flow Chart of Dry Spinning
Solidification by solvent
Dry spinning is used for polymers that need to be dissolved in a solvent. Dry spinning is similar to melt spinning. The polymer concentration in the dope ranges from 20-30 % High polymer concentration results in higher solution viscosity and difficulties in material handling.
However, the physical properties of the resulting fiber are better with higher polymer concentrations. The polymer solution is generally heated ‘to a higher temperature to reduce dope viscosity, The polymer solution is extruded into a dry spinning cell. It is a jacketed vertical box, where heated air is circulated to evaporate the solvent. After extrusion, in the solidification stage, the solvent is removed by evaporation in presence of heat and suitable inert gas current.
- In dry spinning, a volatile solvent is used to dissolve the raw materials and form a salutation.
- Then the solution is purified by filter.
- The solution is extruded through a spinneret into a warm air chamber where the solvent evaporates, solidifying the fine filaments.
- Finally, the filament yarn either is immediately wound onto bobbins or is further treated for certain desired characteristics or end-use.
Example: Dry spinning is used in the production of acetate, triacetate, and some acrylic, modacrylic, spandex, and vinyon (PVC, PVA) fibers.
Advantages: Yarn does not require purification.
Disadvantages: Flammable solvent hazards, Solvent recovery, Slow (200-400 yds/min).