Elastane is a synthetic fiber known for its exceptional stretch and recovery, which revolutionized the textile industry. This polymer is a long-chain synthetic material composed primarily of segmented polyurethane. The development of this elastic fiber was pioneered by DuPont in the late 1950s, providing a superior replacement for rubber threads in clothing. Although known in North America as spandex and commonly referred to by the brand name Lycra, elastane is the generic name used internationally for this type of synthetic fiber.
Primary Ingredients and Chemical Structure
The foundation of elastane’s elasticity lies in its unique chemical architecture as a segmented polyurethane. This long-chain polymer is built from two primary types of molecular segments arranged alternately to create a structure that functions much like a molecular spring.
Soft Segments
The ‘soft’ segments are typically long, flexible chains called macro-glycols, which are usually polyethers or polyesters. These soft, amorphous domains provide the material with its ability to stretch and contract easily. The soft segments make up the majority of the fiber’s mass and are responsible for the high degree of elongation.
Hard Segments
Connecting these flexible chains are the ‘hard’ segments, which are formed from diisocyanate monomers. These rigid, crystalline domains cluster together and act as physical cross-links. They anchor the soft segments and provide the necessary strength and structure.
Transforming Components into Fiber
The manufacturing of elastane fiber from its chemical components is a multi-step industrial process, with solution dry spinning accounting for the vast majority of production. The process begins with the reaction of a macroglycol with a diisocyanate monomer to create an intermediate material known as a prepolymer.
The next step involves a chain extension reaction, where the prepolymer is mixed with a diamine compound. This reaction extends the polymer chains and forms the final, high-molecular-weight polyurethane solution. This resulting solution is then diluted with a solvent, such as dimethylacetamide (DMAC), to create a spinning solution.
This spinning solution is pumped into a cylindrical spinning cell and forced through a spinneret, which contains numerous tiny holes. The liquid polymer emerges through these holes as fine strands. As the strands pass through the cell, they are heated in the presence of an inert gas, which causes the solvent to evaporate rapidly, solidifying the liquid polymer strands into continuous elastane filaments.
After solidification, individual filaments are bundled together using compressed air to achieve the desired thickness. The resulting fiber is then treated with a finishing agent, such as magnesium stearate, to prevent the naturally sticky filaments from adhering to one another. The continuous filament is then wound onto spools, ready for use in textile manufacturing.
Key Characteristics and Applications
Elastane is capable of stretching up to 500% to 600% of its relaxed length, offering unparalleled flexibility in clothing. The fiber possesses excellent resilience, meaning it quickly returns to its original shape after being stretched. Elastane is also valued for its light weight and durability, with a strong resistance to damage from body oils, perspiration, and common detergents.
Pure elastane is rarely used in clothing due to its cost and tendency to stick, so it is almost always blended with other fibers. Even a small percentage of elastane, often between 3% and 30%, is enough to impart significant stretch to natural fibers like cotton or synthetic ones like polyester and nylon.
It is extensively used in activewear, sportswear, and swimwear, where freedom of movement is paramount. Elastane blends are also common in fitted garments like jeans, leggings, and underwear, where they provide a snug fit and maintain shape over time.