Viscoelastic Stress Relaxation Profiles in Heat Set Polyurethane Stretch Wovens
Controlled stenter dwell at 185-195°C stabilizes polyurethane hard segments to minimize viscoelastic force decay and garment bagging in stretch wovens.
Permanent Growth
Fabric Deformation
Irreversible elongation represents the residual stretch that remains in a textile fabric after it has been subjected to a specified tensile load and then released. Excessive permanent growth results in garments that lose their original shape and become baggy during normal wear. This mechanical property is measured as a percentage of the original sample length.
Recovery Failure
Elastic fabrics containing spandex or textured yarns must return to their initial dimensions after being stretched by body movements. The permanent growth of a knitted fabric increases when the core-spun yarn has been subjected to excessive tension during the knitting process or during heat setting. If the finishing mill fails to set the elastomer properly, the polymer chains slide past one another and cannot recover their original position.
Testing labs measure this failure using ASTM D3107 or similar standard procedures.
Yarn Evaluation
Raw materials must be carefully selected to match the performance demands of stretch garments. Lowering the permanent growth requires using high-quality elastomeric yarns and optimal stitch densities in the knitting mill. This preventive measure reduces the risk of fabric sagging in retail garments.
Garment Appearance
Apparel brands establish strict performance limits to prevent customer complaints regarding misshapen knees and elbows. A fabric with low permanent growth retains its tailored look and maintains its compression properties throughout the life of the garment. Technical datasheets from the mill must declare this parameter before production starts.