Electrospun Films from Recycled rPET Functionalized with Nano-Hydroxyapatite and Natural Phosphate for Enhanced Thermal Stability

Recycled polyethylene terephthalate (rPET) from post-consumer water bottles was valorized into electrospun fibrous films using a trifluoroacetic acid/chloroform solvent system and functionalized with phosphate-based additives, namely nano-hydroxyapatite (“nano-HAP”) and natural phosphate (patented mineral additive), at 1 and 3 wt%. The electrospun rPET fibers exhibited an average diameter of 710 ± 249 nm, while FTIR confirmed the characteristic rPET bands at 1714, 1240, 1092 and 722 cm−1 together with phosphate-related signals for the mineral phase (1093 and 565 cm−1). In the flame exposure test, the control rPET exhibited a total burning time of 3 s and a residue of 54.59 ± 2.10%, whereas functionalized films exhibited burning times ranging from 6 to 20 s and higher residues, reaching 96.73 ± 3.45% (rPET +3% nano-HAP) and 97.89 ± 1.84% (rPET +3% natural phosphate). Thermogravimetric analysis under nitrogen revealed an increase in the final residue from 20% for neat rPET to 35% for nano-HAP-modified rPET and 50% for natural phosphate-modified rPET. Overall, the results demonstrate that phosphate functionalization modifies the residue formation of electrospun recycled rPET films under the investigated experimental conditions. These findings highlight the potential of mineral-functionalized recycled rPET for applications requiring controlled thermal degradation and residue formation, contributing to plastic waste valorization within a circular economy framework.Waste rPET transformed into electrospun fibrous films.Phosphate additives increase the final TGA residue up to 50%.Mineral functionalization increases the residue after flame exposure.Natural phosphate exhibits a higher final TGA residue than nano-HAP.