Elasthane EL

Elasthane fibers are produced in four different ways including melt extrusion, reaction spinning, solution dry spinning, and solution wet spinning. Each of these methods involve the initial step of reacting monomers to produce a prepolymer. Then the prepolymer is reacted further, in various ways, and drawn out to produce a long fiber. Since solution dry spinning is used to produce the big majority of the world's elasthane fibers, it is described.

1. Polymer reactions
   The first step in the production of spandex is the production of the prepolymer. This is done by mixing a macroglycol with a diisocyanate monomer. The compounds are mixed in a reaction vessel and under the right conditions they react to form a prepolymer. Since the ratio of the component materials produces fibers with varying characteristics, it is strictly controlled. A typical ratio of glycol to diisocyanate may be 1:2.
   
   In dry spinning fiber production, the prepolymer is further reacted with an equal amount of diamine. This is known as a chain extension reaction. The resulting solution is diluted with a solvent to produce the spinning solution. The solvent helps make the solution thinner and more easily handled. It can then be pumped into the fiber production cell.
   
    
2. Producing the fibers
   The spinning solution is pumped into a cylindrical spinning cell where it is cured and converted into fibers. In this cell, the polymer solution is forced through a metal plate, called a spinneret, which has small holes throughout. This causes the solution to be aligned in strands of liquid polymer. As the strands pass through the cell, they are heated in the presence of a nitrogen and solvent gas. These conditions cause the liquid polymer to chemically react and form solid strands.
   
   As the fibers exit the cell, a specific amount of the solid strands are bundled together to produce the desired thickness. This is done with a compressed air device that twists the fibers together. In reality, each fiber of spandex is made up of many smaller individual fibers that adhere to one another due to the natural stickiness of their surface.
   
    
3. Final processing
   The fibers are then treated with a finishing agent. This may be magnesium stearate or another polymer such as poly(dimethyl-siloxane). These finishing materials prevent the fibers from sticking together and aid in textile manufacture. After this treatment, the fibers are transferred through a series of rollers onto a spool. The windup speed of the entire process can be anywhere from 300-500 mi (482.7-804.5 km) per minute depending on the thickness of the fibers. 
   
   When the spools are filled with fiber, they are put into final packaging and shipped to textile manufacturers and other customers. Here, the fibers may be woven with other fibers such as cotton or nylon to produce the fabric that is used in clothing manufacture. This fabric can also be dyed to produce a desired color.

To ensure the quality of the spandex fibers, manufacturers monitor the product during each phase of production. Inspections begin with the evaluation of the incoming raw materials. Various chemical and physical characteristics are tested. For example, the pH, specific gravity, and viscosity of the diisocyanate may be checked. Additionally, appearance, color, and odor can also be evaluated. Only by having strict quality control checks on the starting materials can the manufacturer be sure that they will produce a consistent end product. After production, the spandex fibers are also tested. These tests may include those that evaluate fiber elasticity, resilience and absorbency.