Advanced polypropylene random copolymer nanocomposites: effect of natural bentonite clay and aluminum hydroxide on morphology and properties

Abstract

This paper examines the influence of nanoparticles of the natural mineral bentonite and aluminum hydroxide on the obtain of nanocomposites based on a compatibilized polypropylene random copolymer. A random copolymer of ethylene and propylene modified with maleic anhydride was used as a compatibilizer. The total amount of filler introduced into the polypropylene random copolymer composition was 50 wt.%. To study the synergistic effect when using a mixture of fillers, bentonite was included in the formulation at five different concentrations (5, 10, 15, 20 and 25 wt.%). The composites were obtained by mechanical mixing in the melt of a compatibilized polymer matrix. The structural, morphological, physical-mechanical, thermal properties and fire resistance of the obtained composite materials were determined. The structural and morphological properties were characterized using infrared spectroscopy (IR) and scanning electron microscopy. Based on the results of IR spectroscopy and Scanning Electron Microscopy-Energy Dispersive X-ray Spectroscopy (SEM-EDX) spectra, the presence of elements and bonds corresponding to the composition of bentonite and aluminum hydroxide, which were used as fillers in the composition of the polypropylene random copolymer, was confirmed. Morphological study revealed minor agglomerates of bentonite nanoparticles. Thermal properties of the obtained composites were determined using thermogravimetric analysis and differential scanning calorimetry. Thermogravimetric analysis showed that the addition of bentonite increases the thermal stability of composites, as evidenced by a decrease in the rate of mass loss. Mechanical properties (tensile strength, elongation at break) decrease with increasing bentonite concentration. The synergistic effect obtained by the combined use of aluminum hydroxide and bentonite was manifested mainly in an increase in the melt flow index of the composite. The sample containing 25 wt. % natural bentonite showed the highest melt flow index values, up to 3.12 g/10 min.