Influence of loop length and relaxation on the structural and dimensional behavior of recycled polyester–cotton single jersey fabrics

Purpose This study investigates the physical and dimensional properties of single jersey knitted fabrics made from a 40% post-consumer recycled polyester (rPET) and 60% virgin cotton blend. The purpose of this paper is to evaluate how loop length and relaxation/laundering processes influence fabric structure and dimensional stability for sustainable knitwear production. Design/methodology/approach Blended yarns were knitted on an 18-inch diameter, 24-gauge circular knitting machine using three loop lengths (2.8, 3.2 and 3.6 mm). Fabrics were subjected to dry, wet and full relaxation, followed by 15 laundering cycles as per AATCC TM 135-2003. Physical parameters wale, course and stitch densities and areal density (GSM) were measured using ASTM D3887 and ASTM D3776 standards, while shrinkage was analyzed in length, width and area. Findings Results showed an inverse relationship between loop length and fabric densities. Fabrics with shorter loops were denser, heavier and more dimensionally stable. Progressive relaxation improved structural compactness and dimensional equilibrium was reached after the tenth laundering cycle. The recycled polyester–cotton blend demonstrated stability comparable to virgin fiber fabrics. Originality/value This study provides practical insights for optimizing loop length and relaxation processes in sustainable knitted fabric production, proving that recycled fibers can match virgin materials in quality and performance.