Elastane is a synthetic fiber renowned for its exceptional elasticity, allowing it to stretch dramatically and return to its original shape. This unique property makes it a highly sought-after component in the textile industry for clothing that requires significant movement and comfort. While known generically as elastane, it is also widely recognized by the common trade names Spandex (North America) and Lycra (other regions). It is almost always blended with natural or rigid synthetic fibers, bringing stretch and shape retention to textiles from athletic wear to everyday denim.
Chemical Foundations
The creation of elastane fiber begins with a precise chemical reaction combining two primary liquid components to form a specialized polymer. The first is a long-chain polyglycol, which forms the “soft” segment providing flexibility and stretch. Another element is a diisocyanate, which forms the “hard” segment, linking the soft chains together to provide structure and recovery force.
These two molecules are mixed under controlled conditions to initiate polymerization, often using a molar ratio of one part polyglycol to two parts diisocyanate. This initial step results in a highly reactive liquid polyurethane known as a prepolymer. To convert this prepolymer into a high molecular weight polymer suitable for spinning, it undergoes a chain extension reaction. A diamine compound is added, which rapidly links the prepolymer chains together into much longer chains, forming a polyurethaneurea polymer solution. This chemical structure, with alternating soft and hard segments, gives elastane its unique ability to elongate and snap back.
The Dry Spinning Process
The most common industrial method used to transform the liquid polymer solution into solid elastane filaments is known as solution dry spinning, which accounts for up to 95% of worldwide production. This process begins by dissolving the newly formed polymer in a highly polar solvent, such as dimethylacetamide (DMAc), which thins the mixture to a workable viscosity. This liquid spinning solution is then carefully pumped through a device called a spinneret, which forces the solution out as fine liquid streams.
As these streams exit the spinneret, they enter a tall, cylindrical spinning cell where they are met with a current of heated, inert gas, such as nitrogen. The heat causes the solvent to rapidly evaporate from the liquid streams, simultaneously curing and solidifying the polymer into continuous filaments. The solvent vapor is then collected and condensed for recycling. This physical transformation occurs almost instantly, leaving behind the cured elastane filaments.
Preparing the Fiber for Textiles
Once the individual solid filaments exit the spinning cell, they are immediately collected and prepared for textile manufacturing. The filaments possess a natural stickiness, which manufacturers utilize to bundle multiple strands together to achieve the desired yarn thickness, or linear density. To prevent excessive sticking and to aid in later handling, the filaments are typically treated with a finishing agent, such as magnesium stearate or polydimethyl siloxane.
Following the formation of the yarn, the fiber undergoes a crucial process called heat setting, which is necessary to stabilize its structure and permanently fix its elastic properties. The yarn is subjected to controlled heat, often in the range of 182°C to 196°C, which relaxes internal tensions. After stabilization, the finished elastane yarn is wound onto spools or bobbins at high speeds for distribution to fabric manufacturers.
The yarn is rarely used alone. Instead, it is combined with non-elastic fibers, frequently by wrapping them around the elastane core. This creates a blended yarn that offers both the comfort of the other fiber and the stretch of the elastane.