Graphene nanoplatelets reinforced Polyamide-11 nanocomposites thermal stability and aging for application in flexible pipelines

Novel nanocomposites of polyamide-11 (PA11) reinforced with commercial graphene nanoplatelets (GNP) in amounts of 1.0, 2.5, and 5.0 wt.% were prepared and characterized for their thermal stability and aging performance. The processing of the nanocomposites was carried out by mixing PA11 in the molten state employing a double screw mini-extruder at 200 °C under 60 rpm screw speed, with a residence time of 7 min. The incorporation of GNP increased the thermal stability of PA11, particularly in the amount of 1.0 wt.%, as observed by thermogravimetric analysis. X-ray diffraction indicated that the composites' crystallinity increased with 1.0 and 2.5 wt.% of GNP. Evidence of agglomerates formation in the sample with 5.0 wt.% of GNP suggests it to be less dispersed in the PA11 matrix and associated with reduction in crystallinity. The dynamic mechanical analysis showed that GNP promoted an increase in the storage and loss moduli. The increase of GNP in the PA11 matrix enhanced the water contact angle and, therefore, provided greater hydrophilicity of the nanocomposite. The GNP reinforcement prevents the decrease in the molar mass of PA11, estimated by the corrected inherent viscosity (CIV) measured with aging time into water at 85 °C, when compared to the performance of neat PA11. All nanocomposites had CIV values above 1.20 dL/g before and after the aging test. Therefore, using the lowest GNP content of 1.0 wt.% proved to be the more efficient for application in flexible oil/gas pipelines.