Polyheral Oligomeric Silsesquioxanes (POSS) based Polymer Nanocomposites
Hato, Mpitloane Joseph
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This work reports on the preparation and characterization of polyhedral oligomeric silsesquioxanes (POSS)-containing polymer nanocomposites. The nanocomposites investigated in this study consist of two different types of POSS particles [octamethyl-T8- POSS and poly((propylmethacryl-heptaisobutyl-POSS)-co-(methyl-methacrylate))] dispersed in two different polymer matrices such as linear low-density polyethylene (LLDPE) and poly(methyl methacrylate) (PMMA). The melt-blending technique was used for the preparation of various nanocomposites. The morphology and structure of various nanocomposites were characterized by using x-ray diffraction (XRD), small angle x-ray scattering (SAXS), field-emission scanning electron microscopy (FE-SEM) and polarized optical microscopy (POM). The influence of different loadings of POSS particles on the thermal, thermomechanical, tensile, impact, and melt-state viscoelastic properties of nanocomposites was investigated. The morphology of the freeze-fractured surfaces of the LLDPE/POSS nanocomposites investigated by means of FE-SEM, revealed a homogeneous dispersion of the octamethyl-T8- POSS particles into the LLDPE matrix at a low filler content. The thermal properties of pure LLDPE and various nanocomposites showed double melting behaviour of the neat LLDPE matrix and the nanocomposite samples. The thermomechanical properties were investigated by stress-strain controlled rheometry using a solid-state rectangular fixture. The results showed a moderate improvement in both the storage and loss moduli of the neat LLDPE upon the incorporation of the POSS particles. The thermal stability of pure LLDPE and its nanocomposites was investigated in both air and nitrogen atmospheres. Two degradation steps were observed for all studied samples under nitrogen atmosphere. An improvement in the thermal stability of the samples studied in air in the high-temperature region was observed. The melt-state rheological properties measurements showed that the POSS particles were highly immiscible with the LLDPE matrix. POSS-containing LLDPE composites did not show any improvement in tensile properties. A decrease in impact properties of the LLDPE at higher POSS loadings was observed. The heat distortion temperature of the LLDPE samples increased with increasing the POSS loading in the polymer matrix. In the case of PMMA/POSS nanocomposites, the FE-SEM results did not give any information about the dispersion of the POSS particles in the PMMA matrix. However, the XRD studies indicated that the POSS particles were dispersed throughout the PMMA matrix. Both differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) showed a single glass transition for all the investigated samples. A decrease in the glass transition temperature was observed with increasing POSS loading in the polymer matrix. The rheological studies showed a gel-like character for all the investigated samples. An increase in the storage modulus for the 5 wt % POSS-containing sample was observed when compared with pure PMMA.