Multilayer nanofilled polymer systems under extensional flow: Role of filler aspect ratio and interfacial chain dynamics

The influence of carbon nanofillers on the melt extensional behavior of multilayer polymer nanocomposites was investigated using linear low-density polyethylene (LLDPE) as matrices embedded with either carbon nanostructures (CNS) or multi-walled carbon nanotubes (MWCNTs). Multilayer films with controlled layer architectures were fabricated via forced-assembly co-extrusion. Extensional rheology tests revealed that CNS, due to their higher aspect ratio and stronger interfacial interactions with LLDPE chains, significantly enhanced the extensional viscosity and strain hardening behavior, especially in highly layered (1025L) systems. By contrast, MWCNT-filled films exhibited extensional responses similar to the neat LLDPE matrix, indicating minimal nanofiller–polymer interaction. Microstructural analyses via SEM, TEM, and SAXS confirmed the alignment of CNS under extension and the presence of thick interfacial bound polymer layers, leading to complex interfacial chain relaxation dynamics. Furthermore, stress yielding observed in CNS-filled systems with fewer layers (e.g., 9L) was attributed to structural instabilities and filler-rich layer breakup. These findings provide new insights into the role of nanofiller morphology and interfacial dynamics in tuning extensional rheology, with implications for advanced polymer processing and modeling of nanocomposite systems.