New routes for functionalised nanoparticles for polymer nanocomposites

Polymer nanocomposites represent a class of advanced, multifunctional materials, combining the attractive features of both nanomaterials and polymers. The level of dispersion of the nanoparticles directly controls the extent to which nanocomposites can maximize the unique attributes of their nano-scale fillers. However, as a consequence of the tendency of nanofillers to agglomerate, the anticipated superior properties of polymer nanocomposites are yet to be realised, and remain merely a theoretical prediction. As a result, the surface chemistry of nanofillers is often tailored to reduce the attractive interparticle interactions that promote agglomeration. This modification can also be used to enhance the interfacial interactions between the nanofiller and polymer matrices to achieve improved filler dispersion. Accordingly, this thesis addresses this challenge in nanocomposite technology by investigating the chemical surface functionalisation of various nanoparticles in order to produce polypropylene (PP) nanocomposites with superior electrical, mechanical and thermal properties.
Part I describes covalent modification of nanosilica, microsilica, furnace Carbon Black (CB), acetylene black (ACB) and carbon nanotube (CNT) nanomaterials by carbene insertion and azo-coupling reactions, in a series of studies, in order to tailor their surfaces for application in polypropylene (PP) nanocomposites. The surface characterisation of the modified nanomaterials was assessed in detail using XPS, CHN, SSNMR, BET, ATR-IR and thermal analysis techniques. The surface grafting densities were estimated to be of the order of 1013 and 1014 molecules/cm2 and additionally, SSNMR provided direct evidence of the diarylcarbene reaction to the silica surface. Following nanocomposite production with PP by solvent mixing methods, the macroscopic properties were studied demonstrating altered electrical, mechanical and thermal properties following assessment of the DC conductivity, dielectric properties, thermal analysis (TGA, DSC, DMA) and morphological measurements. In particular, the introduction to the CB surface of a diaryl complex with terminal dodecyl hydrocarbon chains demonstrated substantial improvements to the DC electrical and dielectric properties of the PP nanocomposites.
Part II explores the non-covalent surface functionalisation of CB and ACB by the physisorption of the non-ionic surfactant Triton-X-100. Various protocols were developed in which an optimal surface loading for CB was determined by treatment at 0.024 mM(aq). In addition, the modification procedure was combined with the granulation protocol of ACB in an effort to evaluate the potential for industrial applications. The degree of surface functionalisation was extensively characterised by BET, XPS, thermal analysis, UV-Vis and ATR-IR analyses. PP nanocomposites produced by solvent and melt mixing methods demonstrated similar conductive properties following the nanoscale modification, however morphological, dielectric and thermal analysis indicated altered interfacial interactions demonstrating improved mechanical properties.

Keywords: Silica
Nanocomposites
Carbon Black
Polypropylene
Advisor: Foord, J
Moloney, M