Microblending of a Dendritic Flow Modifier Simultaneously Improves Melt Processability and Mechanical Performance of PA 66 Fibers

This study aims to improve the melt-spinning processability of polyamide 66 (PA 66) by trace blending with a dendritic polyamide-amine (701A) flow promoter. The strategy addresses inherent limitations of PA 66, including its narrow processing window and poor melt stability during spinning, which result from high melt viscosity and susceptibility to thermal degradation. The strategy is also enhancing fiber mechanical properties. Fourier transform infrared (FTIR) and nuclear magnetic resonance (NMR) analyses confirmed that incorporation of 701A did not alter the chemical structure of PA 66. Melt flow measurements showed that 701A increased the melt flow index by a factor of 2.3–2.5. Rheological studies revealed that 701A reduced the apparent viscosity, structural viscosity index, and viscous-flow activation energy under low shear rate, while increasing the non-Newtonian index and viscous-flow activation energy under high shear rate. These effects are attributed to the dendritic architecture and abundant terminal groups of 701A. Nonisothermal crystallization kinetics further indicated that 701A promoted heterogeneous nucleation, elevating both the crystallization temperature and rate of PA 66/701A blends. Notably, microblending with only 0.2 wt % 701A enabled the production of PA 66 monofilaments with superior mechanical performance at reduced processing temperatures.