Nucleation Retardation of Polyamide 6,6 by Tuning Hydrogen Bonding Reorganization via Nigrosine for High-Speed Injection Molding Applications

Themechanism of regulating hydrogen bond organizationfor polyamide6,6 (PA 6,6) by nigrosine was investigated by temperature-dependentFTIR and in situ synchrotron X-ray diffraction duringcooling/heating processes. The intermolecular interaction betweenamide groups and nigrosine was verified by the FTIR spectroscopy method.Upon melt cooling, the formation of H-bonds is promoted by nigrosineat the initial stage (regime I) with increased enthalpy change (Delta H (1)), which results from denser molecular coilsas the interaction with nigrosine increases the ability to form H-bondsbetween adjacent amide groups, while at a lower temperature (regimeII), the Delta H (1) decreases with increasingnigrosine as nigrosine restrains the mobility of PA 6,6 chains thatretards the formation of H-bonds between nonadjacent amide groups.Moreover, the ordering arrangement of H-bonds into 2-D hydrogen bondsheets (H-sheets) is hindered for both the regime I '/II ' stages with decreased Delta H (2) due tothe decreased mobility of chain segments, which retards the nucleationof PA 6,6 crystallization. The crystal perfection index (CPI) wasinvestigated by WAXD, and it was found to decrease with the increaseof nigrosine. Combined with microstructure analysis, we proposed thatpartial nigrosine can insert between H-sheets, which therefore tunesthe Brill transition behavior of PA 6,6. Overall, the regulation mechanismof nigrosine on PA 6,6 crystallization has been established via interaction with amide groups to tune the organizationof H-sheets. The retardation effects on crystallization can improvethe flowability of PA 6,6 for high-speed injection molding applications.