This study investigates the development of crimped poly(lactic acid) (PLA) filaments as a sustainable alternative to conventional synthetic fibers. PLA, a biodegradable and renewable fiber, exhibits promising mechanical properties but faces limitations due to restricted product diversity, particularly in bulky crimped filaments. The research is divided into two parts. This Part I focuses on the fabrication and process optimization of crimped PLA filaments with varying linear densities (150D, 450D, 600D, and 900D) using the efficient and cost-effective knit–deknit technique. Two-way analysis of variance (ANOVA) and regression (R2 = 0.837–0.979) identified 120°C for 90 s as the optimum heat-setting condition for balancing crimped and tensile properties. Under these conditions, 150D filaments exhibited a high crimp number (35.67 crimps/25 mm) and balanced tensile performance (tenacity 20.53 cN/tex, elongation 34.91%), whereas filaments of higher linear density exhibited a lower crimp number due to differences in the applicable knitting machines. Microscopy and crystallinity analyses confirmed negligible surface change and increasing crystallinity at 80–120°C, but showed deformation and reduced crystallinity at ⩾ 140°C or with longer durations, consistent with the observed property decline. To further understand performance variations, the morphological and microstructural behavior of 150D PLA filaments was analyzed throughout the heat-setting process. These findings reinforce the potential application of crimped PLA filaments in textiles, with Part II evaluating their effectiveness in weft-knitted inlaid fabrics, focusing on comfort and durability.
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