stretching

Stretching, also known as drawing, is a crucial step in manufacturing man-made fibers. This process aligns the long polymer chains within the fiber along its longitudinal axis, causing them to pack closely together. This close packing leads to the formation of ordered regions called crystallites, embedded in amorphous material.1

The degree of molecular alignment directly impacts the fiber's properties. Increased alignment enhances ultimate strength and rigidity while reducing elongation before breaking. It also lowers moisture absorption and can affect dyeing properties, as dye molecules struggle to penetrate the tightly packed crystalline regions. Highly oriented fibers are generally more chemically stable and can develop a lustrous appearance.1

Stretch yarns, often made from synthetic continuous-filament yarns, achieve their elasticity through tight twisting, heat-setting, and then untwisting, creating a spiral crimp. Spandex, a highly elastic synthetic fiber, is frequently used as the core of such yarns, covered by a non-stretch fiber.2