EQUIPMENT DESIGN
The spinning solution is often filtered many times to remove foreign materials that might cause thread defects or clogging in the machine. The solution is extruded into the drying tower through which hot air or other gases pass. The concentration of the polymer increases as the solvent evaporates, leaving a solid polymer filament behind. The solvent is later recovered from the gas by condensation or absorption and is then recycled.
Solvent selection is very important, and is based on boiling point, latent heat of vaporization, thermal stability, toxicity, and inertness. Non-polar solvents are often preferred because of their low boiling points and heats of vaporization. However, non-polar solvents are prone to build-ups of electrostatic charge, which can be very dangerous.