Effect of ionomer interfacial compatibilization on highly filled HDPE/Al2O3/ionomer composites: Morphology and rheological behavior

Highly filled high-density polyethylene/alumina (HDPE/Al2O3) composites were fabricated by melt mixing with direct incorporation of poly(ethylene-co-methacrylic)-based ionomer (EMAA-Na) as an interfacial compatibilizer. SEM and EDX micrographs indicate EMAA-Na interfacial adhesion on the Al2O3 spheres. Under low EMAA-Na content conditions, the FT-IR characterization and an EMAA-Na neutralization degree analysis revealed the priority of the melt neutralization interaction between the acid groups of the ionomer and the Al2O3 spheres in the composite. Under high EMAA-Na content conditions, an AFM phase characterization revealed the formation of an EMAA-Na ionomer spherical domain (300 nm) dispersed in an HDPE matrix due to the microphase separation of ionic chains. Capillary and dynamic rheology measurements were also conducted to investigate the phase morphology evolution. The polymeric adhesion on the Al2O3 sphere surfaces contributed to the increase of the melt viscosity and gradual elongation thickening behavior of the composite melts. The formed spherical domain structure of EMAA-Na of the composite melts contributed to the shear thickening, elongation thickening and yield behavior. Three rheology criteria plots indicate large complex formation in the composite melts. The EMAA-Na incorporation in the highly filled HDPE/Al2O3 composite matrix not only improved the strength and toughness performance, with a 27% improvement in the elongation at break (EMAA-Na content 1 wt.%) and 21% improvement in the tensile strength (EMAA-Na content 10 wt.%), but also preserved the good thermal conductivity (1.5 W/(m.K)). This study reveals the potential application of the EMAA-Na ionomer to resolve the challenge of the strength and toughness performance degradation in highly filled polymer composites.