Seawater and Sunlight as Critical Ageing Factors Affecting the Mechanical Performance of Knitted Swimwear Fabrics.

This study investigates the effects of seawater and sunlight ageing on the structural and mechanical properties of knitted fabrics designed for swimwear. Nine fabrics with varying polyamide, polyester, and elastane ratios in yarn were subjected to 200 h seawater exposure, with and without sunlight, followed by washing and drying cycles to simulate real training and use conditions. The evaluated properties included mass per unit area, thickness, horizontal and vertical density, bursting strength, breaking force, and breaking elongation. Results showed a slight increase in mass and thickness after ageing, reflecting fabric shrinkage in the course direction. Breaking force decreased on average after ageing, with statistically significant reductions in the wale direction under combined seawater and sunlight exposure, whereas shrinkage occasionally produced apparent strengthening effects. Breaking elongation increased in the wale direction and decreased in the course direction, though without statistical significance. Correlation analysis revealed that ageing alters the dependence of mechanical properties on fabric mass per unit area and thickness, with seawater enhancing strength in the wale direction, while sunlight shifted the effects toward the strength in the course direction. These findings demonstrate that seawater and sunlight are critical ageing factors that affect swimwear performance, emphasising the need for their inclusion in durability assessments.