Impact of Heat Setting on Dimensional Stability and Shrinkage Resistance of Polyester Knitted Fabrics

Heat setting is a crucial thermal treatment process in polyester knitted fabric production, significantly influencing dimensional stability, shrinkage resistance, elasticity, and mechanical properties. The process involves exposing the fabric to controlled heat (typically 170–210°C) under tension to stabilize the fibers and reduce internal stresses.

1. Mechanism of Heat Setting in Polyester Knits

• Polyester is a thermoplastic synthetic fiber, meaning its molecular structure can be altered through heat application.

• During heat setting, the polymer chains within polyester fibers are reoriented and locked into place, reducing their tendency to shrink when exposed to heat or moisture in subsequent use.

• The fabric is typically stretched and held under controlled tension in a stenter frame to prevent excessive contraction.

2. Key Effects on Dimensional Stability and Shrinkage Resistance

(a) Reduction in Residual Stress and Shrinkage

• Without heat setting, polyester knitted fabrics retain internal stresses from the knitting and finishing process, leading to uncontrolled shrinkage when subjected to washing or heat exposure.

• Heat setting relaxes and stabilizes the fiber structure, significantly reducing post-production shrinkage (typically improving shrinkage resistance from 5-8% to <2% in some cases).

(b) Improved Shape Retention

• Polyester knits, especially stretch fabrics blended with spandex, are prone to deformation over time.

• Heat setting ensures that the fabric retains its intended dimensions, minimizing issues like curling, twisting, and distortion after repeated washing or stretching.

(c) Enhanced Elastic Recovery and Wrinkle Resistance

• The thermal treatment allows polyester fibers to maintain better elasticity and recovery after stretching, making them ideal for sportswear, athleisure, and compression garments.

• Heat setting also improves wrinkle resistance, preventing permanent creases and maintaining a smoother surface.

(d) Improved Fabric Handle and Softness

• Properly heat-set polyester fabrics exhibit a smoother texture and softer feel, improving their drape and comfort without compromising strength.

• Overheating, however, can make the fabric feel stiff or brittle, reducing its usability for certain applications.

3. Optimizing Heat Setting Conditions for Polyester Knits

• Overheating risks: Loss of mechanical strength, increased stiffness, and potential yellowing of fabric.

• Underheating risks: Incomplete shrinkage stabilization, leading to poor dimensional stability.

4. Comparison of Heat-Set vs. Non-Heat-Set Polyester Knitted Fabrics

5. Industrial Applications Benefiting from Heat Setting

• Activewear & Sportswear: Maintains elasticity, shape retention, and stretchability under repeated use.

• Automotive & Technical Textiles: Prevents shrinkage in high-heat environments.

• Medical & Compression Textiles: Ensures precise fit and long-term stretch performance.