Engineered thermoregulatory filament fabrication from recycled polyester sources

The widespread application of polyethylene terephthalate (PET) in textiles and packaging has resulted in the continuous buildup of non-biodegradable waste, while current recycling systems are still inadequate to fully recirculate the material. Although recycled polyester (rPET) is widely regarded as a more sustainable option, its full potential remains underexplored. To address this issue, this study proposes a practical and potentially scalable waste recycling and upcycling methodology for transforming rPET chips into functional thermoregulatory filaments, creating a more valuable alternative to virgin polyester (vPET). In this method, rPET chips were carefully dried and subsequently melt-blended with paraffin wax (PW) as a phase change material (PCM), at different loadings from 5 to 20 wt%. This process is followed by melt extrusion to develop continuous thermoregulatory filaments. The reversible phase change behavior of PW within the rPET matrix was confirmed by DSC analysis. The normalized enthalpy of fusion (ΔH) increased from 11.6 ± 0.6 to 47.1 ± 0.7 J·g−1 as the PW content increased from 5 to 20 wt%, respectively. Among the fabricated compositions, the filament containing 10 wt% PW exhibited the most favorable balance between functional and mechanical properties. It delivered a reversible energy storage capacity of 23.4 ± 0.3 J·g−1 while maintaining a tenacity of 51.4 ± 1.2 cN·Tex−1, which is comparable to that typically achieved with virgin PET filaments. Notably, this optimized composition preserved both its thermal storage capability and mechanical strength even after 100 laundering cycles, indicating strong durability under realistic service conditions. The findings confirm that rPET chips can be successfully converted into thermally responsive filaments by directly incorporating PW, thereby offering a practical route for upgrading PET waste into value-added functional products.