Comparative analysis of poly(ether-ether-ketone) properties aged in different conditions for application in pipelines

This study aimed to evaluate the aging of poly(ether-ether-ketone) (PEEK) submitted to different media: in air, in water bubbled with nitrogen, in water bubbled with air, and in water at pH 4, for 90 days at temperatures of 120, 140 and 160 degrees C. The physical, thermal and mechanical properties of PEEK specimens were evaluated before and after aging. The density measurements showed that the aging conditions employed did not promote water absorption or mass loss; thermogravimetric analyses (TGA) showed that all aging media exerted the same effects on the material's thermal stability, with variation in the initial thermal degradation (T-onset) below 5 degrees C concerning the unaged polymer. The thermal history obtained by differential scanning calorimetry (DSC) did not show significant variations in thermal transition temperatures in the first heating cycle, indicating that the aging conditions did not cause internal degradation in PEEK samples within the studied period. The degree of crystallinity calculated by X-ray diffractometry (XRD) and DSC demonstrated a slight increase over time due to thermal annealing at temperatures above the T-g of the unaged PEEK. The mechanical properties of the aged PEEK showed low variations in Young's modulus and greater variations in the tension at rupture and elongation at rupture, being more drastic in the aqueous media saturated in air and acid solution.