Polyheral Oligomeric Silsesquioxanes (POSS) based Polymer Nanocomposites

[摘要] This work reports on the preparation and characterization of polyhedral oligomericsilsesquioxanes (POSS)-containing polymer nanocomposites. The nanocompositesinvestigated in this study consist of two different types of POSS particles [octamethyl-T8-POSS and poly((propylmethacryl-heptaisobutyl-POSS)-co-(methyl-methacrylate))] dispersedin two different polymer matrices such as linear low-density polyethylene (LLDPE) andpoly(methyl methacrylate) (PMMA). The melt-blending technique was used for thepreparation of various nanocomposites. The morphology and structure of variousnanocomposites were characterized by using x-ray diffraction (XRD), small angle x-rayscattering (SAXS), field-emission scanning electron microscopy (FE-SEM) and polarizedoptical microscopy (POM). The influence of different loadings of POSS particles on thethermal, thermomechanical, tensile, impact, and melt-state viscoelastic properties ofnanocomposites was investigated.The morphology of the freeze-fractured surfaces of the LLDPE/POSS nanocompositesinvestigated 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 pureLLDPE and various nanocomposites showed double melting behaviour of the neat LLDPEmatrix and the nanocomposite samples. The thermomechanical properties were investigatedby stress-strain controlled rheometry using a solid-state rectangular fixture. The resultsshowed a moderate improvement in both the storage and loss moduli of the neat LLDPE uponthe incorporation of the POSS particles. The thermal stability of pure LLDPE and itsnanocomposites was investigated in both air and nitrogen atmospheres. Two degradation stepswere observed for all studied samples under nitrogen atmosphere. An improvement in thethermal 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 werehighly immiscible with the LLDPE matrix. POSS-containing LLDPE composites did notshow any improvement in tensile properties. A decrease in impact properties of the LLDPE athigher POSS loadings was observed. The heat distortion temperature of the LLDPE samplesincreased with increasing the POSS loading in the polymer matrix. In the case of PMMA/POSS nanocomposites, the FE-SEM results did not give anyinformation about the dispersion of the POSS particles in the PMMA matrix. However, theXRD 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 glasstransition temperature was observed with increasing POSS loading in the polymer matrix. Therheological studies showed a gel-like character for all the investigated samples. An increase inthe storage modulus for the 5 wt % POSS-containing sample was observed when comparedwith pure PMMA.

[发布机构] University of the Free State