Influence of Acrylonitrile Content on Processing, Morphology, Thermal Behavior, and Mechanical Properties of PA / NBR Thermoplastic Vulcanizates

ABSTRACT Polyamide (PA6/6.6)/nitrile rubber (NBR) thermoplastic vulcanizates (TPVs) were prepared by dynamic vulcanization, and their morphological evolution was tracked through aliquot collection (A2–A10), SEM, AFM, and mechanical testing. The morphology progressed from co‐continuous domains with high roughness (Ra ≈ 78 nm) to finely dispersed rubber particles (2–5 μm, Ra ≈ 27 nm) after sequential crosslinking, correlating with improved tensile strength (12.7 MPa) and elongation (195%). Crosslink density was normalized among all NBR grades to allow an accurate comparison of ACN effects, and time‐resolved aliquots enabled detailed morphology mapping during vulcanization. The acrylonitrile (ACN) content of NBR strongly affected performance. The 38% ACN TPV showed the best balance (10.0 MPa tensile strength, 149% elongation, 37 Shore D) with well‐dispersed domains (6–8 μm). In contrast, the 33% ACN grade yielded larger domains and lower strength, while 45% ACN, despite higher elongation (~230%), produced coarser morphologies due to elevated viscosity. Polyamide crystallinity (~20%) was preserved in all formulations, and solvent resistance remained high. The results clarify the combined roles of polarity, viscosity, and shear dispersion, demonstrating why 38% ACN offers the most favorable structure–property balance for PA6/6.6/NBR TPVs.