Interplay Between Octene Content and Grafting-Induced Molecular Weight Deviations and Their Effect on the Impact Toughness of Ethylene/1-Octene-Modified Polyamide 6

The impact modification of polyamide 6 (PA6) using maleic anhydride-grafted ethylene/1-octene copolymers (EOR-g-MAH) involves a trade-off between improved compatibilization, grafting-induced changes in modifier molecular weight MW, and melt processability. In this study, EOR modifiers with comparable initial MW but different octene contents (coct = 13, 15, and 16 mol%) were grafted to two MAH levels (cMAH = 0.5 and 1.0 wt%) and incorporated into PA6 at a fixed composition. The system was designed to maintain a comparable microstructure, enabling the isolation of grafting-induced changes in modifier properties from microstructural effects. MW distributions were analyzed by gel permeation chromatography, and the impact behavior was evaluated over a wide temperature range, using an instrumented Charpy impact test. The results reveal a strong, interrelated, coct- and cMAH-dependent competition between β-scission and cross-linking during grafting, which governs the modifier’s MW distribution and particle strength. Higher coct (15 and 16 mol%) enhances the impact performance up to ≈ 0 °C, well above the brittle–ductile transition temperature (BDTT), through increased elastic and plastic deformation capability of the modifiers. At elevated temperatures, however, successive melting of the modifiers leads to a loss of particle strength. At high coct and cMAH = 1.0 wt%, susceptibility to β-scission increases, leading to MW reduction that, for coct = 16 mol%, is detrimental to impact performance, particularly above the BDTT. This effect is further amplified by reduced ductility due to stronger polar intermolecular interactions at high grafting levels. A moderate cMAH = 0.5 wt% and coct = 15 mol% provides an optimal compromise between strength and ductility, delivering high impact strength across a broad temperature range. At this cMAH level, the number of PA6 chains covalently anchored to the modifier particles is moderate, resulting in lower compound viscosity and supporting favorable melt processability.