Investigation on the mechanical, thermal, structural and morphological properties of polypropylene/ethylene-vinyl acetate copolymer/graphene oxide nanocomposites: effect of nanofiller surface functionalization and compatibilizers

Rubber toughened PP nanocomposites with desirable thermal properties and tensile strength (TS) found applications in automotive and packaging industries. This article reports on the mechanical, thermal, structural, and morphological properties of polypropylene (PP)/ethylene-vinyl acetate copolymer (EVA) blend reinforced with graphene oxide (GO) and silane-functionalized GO (f-GO). GO was modified with two silanes: gamma-glycidoxypropyltrimethoxysilane (GPTMS) and gamma-mercaptopropyltrimethoxysilane (MPTMS). The influence of three compatibilizer systems: (PP-g-OH, PP-g-COOH, and PP-g-NH2) on the properties of the composites was also evaluated. The structure and thermal behavior of GO and f-GO were comparatively studied for the first time. The attenuated total reflectance Fourier transform infrared (ATR-FTIR), Raman spectroscopy measurements, and X-ray diffraction (XRD) brought evidence for the successful interactions of silanes with GO. Thermogravimetric analysis (TGA) showed that f-GO exhibited higher thermal stability compared to GO. According to the mechanical analysis, PP/EVA/GPTMS-GO/PP-g-NH2 displayed higher TS and stiffness than the other compatibilized nanocomposites. TGA results indicated that the presence of both f-GO and compatibilizers caused a drastic improvement in the thermal stability. DSC analyses revealed that the addition of nanoparticles led to an increase in PP melting and crystallization temperatures, as well as the degree of crystallinity. XRD patterns revealed the formation of intercalated-delaminated nanocomposites and the promotion of beta-phase crystals of PP for the samples containing PP-g-COOH and PP-g-NH2. The scanning electron microscopy (SEM) showed that the addition of compatibilizers drastically reduces the domain size of the EVA particles. All results suggest that GO nanoparticles enhance the mechanical and thermal properties of PP/EVA blend.