Polyheral Oligomeric Silsesquioxanes (POSS) based Polymer Nanocomposites
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Date
2009-11
Authors
Hato, Mpitloane Joseph
Journal Title
Journal ISSN
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Publisher
University of the Free State
Abstract
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.
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Thesis (Ph.D) (Chemistry))--University of the Free State (Qwaqwa Campus), 2009