New Insight into the Microstructure Changes and Molecular Mobility of Polyamides Exposed to H2S Scavengers

Polyamides (PAs) are widely used as barrier materials in offshore oil and gas (O&G) equipment due to their mechanical strength and chemical resistance. However, long-term exposure to hydrogen sulfide scavengers (H2S-SCVs) may significantly affect their physicochemical properties. Previous studies using thermal analysis and 1H time-domain NMR (1H TD-NMR) suggest that ethoxylated H2S-SCVs impose molecular constraints, increasing the glass transition temperature (Tg) and reducing chain mobility above Tg. The present study builds upon these findings using a multi-technique analytical approach, including FTIR, Raman, 1H DQ-TD-NMR, and 13C solid-state NMR (ssNMR), to provide a more comprehensive understanding of the molecular alterations in PA materials. The results clearly demonstrate that H2S-SCV exposure leads to the progressive exudation of plasticizers from the PA matrix. This plasticizer loss is a key factor contributing to the observed shift in Tg and the reduction in molecular mobility. 1H DQ-TD-NMR data confirmed an increase in the density of dynamically constrained chains over time and allowed for the characterization of heterogeneity in these constraints throughout the PA matrix. Moreover, 13C ssNMR spectra revealed the presence of immobilized H2S-SCV chemical groups within the polymer matrix, strongly supporting the early statement that the mobility constraints observed in 1H DQ-TD-NMR are associated with the formation of crosslinks induced by the H2S-SCV: H2S-SCV acts as a crosslinking agent. Taken together, our findings indicate that both plasticizer loss and H2S-SCV-induced crosslinking contribute significantly to the microstructural evolution of PAs when exposed to ethoxylated H2S-SCVs, offering important insights into their degradation mechanisms and long-term behavior in aggressive operational environments.