Abstract:

Objective This study aimed to establish a feasible approach for recycling high-performance fibers from waste flame-retardant clothing and blending them with meta-aramid fibers to develop flame-retardant yarns. The findings are expected to provide a theoretical basis for understanding fiber blend compatibility and offer technical support for recycling waste textiles, thereby promoting the circular economy and sustainable practices within the specialty textiles industry.

Method Recycled fibers were obtained from waste aramid flame-retardant clothing through mechanical opening. Both recycled and meta-aramid fibers were characterized using scanning electron microscopy (SEM), Fourier tranform intrared spectroscopy (FT-IR), X-ray diffraction (XRD), Thermogravimetric analysis (TGA), and mechanical tests. A series of 29.5 tex blended yarns with four blending ratios of recycled to virgin fibers (50/50, 60/40, 70/30 and 0/100) were produced using ring spinning at three twist coefficients (300, 320 and 340). The resulting yarns were subsequently characterized for their morphological properties, tensile strength, and thermal shrinkage at 260 ℃.

Results SEM images showed that recycled fibers had a rougher surface with visible cracks and fractures, in contrast to the smooth surface of meta-aramid fibers. The average length of recycled fibers was 31.85 mm (ranging from 15 to 54 mm), while meta-aramid fibers had a uniform length of 51 mm. The breaking strength of meta-aramid fibers was 6.75 cN, which decreased to 6.07 cN after use, and further dropped to 5.69 cN after 10 opening cycles. FT-IR results showed that both fibers exhibited characteristic peaks of aromatic rings and amide bonds at 1 640, 1 540 and 1 510 cm^-1, indicating the main molecular chain structure remained intact. The intensity of the amide bond stretching vibration peak near 3 300 cm^-1 was decreased slightly in recycled fibers, and that of the aliphatic characteristic peaks at 2 851 and 2 925 cm^-1 was weakened. XRD characterization showed that, both fibers had double crystalline peaks at 2θ=23° and 26°, and an amorphous peak at 2θ=19°, indicating unchanged crystal form. However, the diffraction peak intensity of recycled fibers was decreased, suggesting a lower crystallinity compared to virgin fibers. TG analysis showed that both fibers had similar three-stage thermal degradation behavior, with char residues at 800 ℃ of 54.87% (meta-aramid fibers) and 53.73% (recycled fibers). The LOI value of recycled fibers was 29.8%, slightly higher than 29.3% of that of the meta-aramid fibers, indicating retention of flame retardancy. For yarns spun with a twist coefficient of 300, the breaking strength was decreased from 735 cN (0/100) to 513 cN (50/50), 384 cN (60/40) and 266 cN (70/30), while thermal shrinkage at 260 ℃ was increased from 0.85% (0/100) to 2.10% (50/50), 3.60% (60/40) and 4.90% (70/30) as recycled fiber content increased. Increasing the twist coefficient caused improvement in yarn breaking strength and reduction in thermal shrinkage. For instance, for the yarn with 50/50 blending ratio, the breaking strength increased from 370 cN to 450 cN when the twist coefficient was raised from 300 to 340.

Conclusion This study demonstrates that mechanical recycling is a viable method for recovering meta-aramid fibers from waste flame-retardant clothing where their essential flame-retardant properties were maintained. Although recycled fibers exhibit reduced length uniformity and tensile strength, their thermal stability and flame retardancy remain comparative to the meta-aramid fibers, highlighting the potential for high-value reuse in textile applications. The incorporation of recycled fibers into flame-retardant yarns inevitably affects their performance characteristics. However, these effects can be mitigated through optimized processing parameters. A blending ratio of 50/50 recycled fibers to meta-aramid fibers with a twist coefficient of 320 is recommended for producing yarns suitable for flame-retardant applications, achieving a balance between recycled content utilization and mechanical performance. These findings offer guidance for textile manufacturers integrating recycled high-performance fibers into flame-retardant products. Furthermore, the developed approach may serve as a reference for repurposing other types of high-performance fibers in future applications.

Key words: waste textiles, meta-aramid fibers, flame-retardant clothing, recycled fiber, blended yarn, thermal stability, flame retardancy