Swell Ratio

Solvent Impact

Organic solvents used during dry cleaning or textile finishing diffuse into the amorphous regions of the polyurethane, causing the yarn to expand. If the swell ratio of the elastomer is too high, the yarn undergoes structural deformation and loses its elastic recovery. This expansion can cause permanent damage to elastane-blended fabrics during solvent-based scouring.

Selecting resistant polymers prevents this swelling.

Polymer Network

Structural characteristics such as the concentration of physical or chemical crosslinks determine how much the elastomer will expand in a given solvent. As crosslink density increases, the polymer chain segments are held together more tightly, restricting the entry of solvent molecules. Measuring the volume change in toluene or dimethylformamide reveals this crosslink density.

Chemists use these values to predict the durability of the elastomeric fibers.

Process Application

Textile laboratories use these measurement techniques to assess whether fabrics containing elastane can withstand chemical finishing and subsequent laundering without losing stretch. The testing involves weighing the dry fabric, soaking it in a test solvent, and weighing it again after it reaches swelling equilibrium. Keeping this ratio below a specific threshold ensures that the garments do not experience bagging or dimensional distortion during wet finishing or home laundering.

Testing helps mills select the right elastane grade for fabrics destined for chemical heavy finishes.