How is spandex made?
• Production of Prepolymer: The first step involves mixing macroglycol with diisocyanate monomer in a ratio of 1:2 that results in the formation of the prepolymer. The reaction is carried out in a container in carefully controlled conditions to produce a prepolymer.
• Chain Extension Reaction: The prepolymer formed in the above stage is then mixed with a diamine in equal quantities and this reaction is referred to as chain extension. The viscosity of the above-formed solution is then reduced to make it thinner for which it is diluted in a solvent and the resultant solution so obtained is a spinning solution. The spinning solution is then placed in the fiber producing cell.
• Dry Spinning: The cylindrical fiber producing cell consists of a spinneret (the sieve-like device with holes) through which the spinning solution is passed and the fibers strands are extruded which solidify in the presence of nitrogen and solvent gas.
• Twisting: The strands upon extrusion are then bundled together to attain a certain amount of thickness and this function is performed by a device that expels pressurised air that twists the fiber.
• Finishing: The spandex fiber so obtained is then immersed in a finishing solution consisting of magnesium stearate which is then wound onto the spool and can be used for further processing.