Magnetically Soft and Hard Polypropylene/Cobalt Nanocomposites: Role of Maleic Anhydride Grafted Polypropylene

Polypropylene (PP) magnetic polymer nanocomposites (MPNCs) filled with different loadings of cobalt (Co) nanoparticles (NPs) were synthesized through a one-pot bottom-up method, i.e., thermal decomposition of soluble dicobalt octacarbonyl (Co-2(CO)(8)) in the refluxing xylene solution. Maleic anhydride grafted PP (PP-g-MA) served as surfactant to stabilize the in-situ formed Co NPs and control the particle morphology and served as compatibilzier to promote the particle dispersion in the hosting PP matrix. Transmission electron microscopy (TEM) micrographs revealed that the Co core NPs with a Co3O4 shell were well distributed with an average size of 12.6 nm for 5.0 wt % Co loading, while an interconnected network structure was formed when the particle loading reached 10.0 wt %. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) results indicated that a thin Co3O4 layer was formed on the surface of Co NPs together with chemisorbed hydrolyzed PP-g-MA. Differential scanning calorimetry (DSC) analysis demonstrated that the fusion heat and the crystalline fraction of the PP matrix decreased with the introduction of these NPs. Except the PP/5.0 wt % NPs sample, the observed monotonically decreased complex viscosity indicated a strong shear thinning behavior in the MPNC melts; meanwhile, the percolation took place at the particle loading between 5.0 and 10.0 wt %. The damping property suggested a strong interaction between the Co NPs and the hosting PP/PP-g-MA matrix. Thermal gravimetric analysis (TGA) and microscale combustion calorimetry (MCC) revealed an enhanced thermal stability and reduced flammability in the MPNCs. A magnetically soft behavior (coercivity of 47.0 Oe) was observed for the MPNCs at 5.0 wt % particle loading, while a magnetically hard behavior (coercivity of similar to 900-1000 Oe) was observed for the MPNCs at a loading of 10.0 wt % at room temperature.