Investigation into the reinforcement effect of filler nanoparticles in polymer-silica nanocomposites and the effects of physical aging on SAN nanocomposites
Bremner, Amy Louise
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This work investigated the reinforcement effects of the addition of silica nanoparticles to a polymer and the aging effects on the characteristics of styrene acrylonitrile (SAN). The nanoparticles that were investigated in this study included hydrophilic silica (HDK-I) and hydrophobic silica (HDK-O), with both having the same surface area and diameter this allowed for study into the nature of the silica and if this had any effect on the aging of the nanocomposites. The final silica nanoparticle used was colloidal MEK-ST, this nanoparticle had a different diameter and surface area to the HDK samples. This allowed for the comparison between the fumed silica samples and the colloidal as well as size of nanoparticle. With regards to quantity of nanoparticle, from studies by Fu et al and Feng, a ratio of 10% silica nanoparticle to 90% polymer was used. For ease 0.1g of silica nanoparticle was combined with 0.9g of polymer. In this study the addition of silica nanoparticles appeared to have negligible reinforcement effects upon the polymers thermal and mechanical properties. The effect of this addition was seen by a limited increase in both the glass transition temperatures and storage moduli of the polymer-silica nanocomposites. An investigation of the glass transition temperatures of unaged and aged samples revealed, data for the relaxation enthalpies and free volumes of SAN nanocomposites. It was found that upon physical aging of the samples, the HDK-O and MEK-ST nanocomposites exhibited the greater reinforcement compared to the HDK-I, with respect to the DSC, DMA and master curve data. For the thermal effects upon aging of the nanocomposite samples the HDK-O sample exhibited the greatest reinforcement of +1.8ᴼC for 24 hours aged, +3.5ᴼC for 72 hours aged and +3.5ᴼC for 168 hours aged. For the mechanical effects upon aging of the nanocomposite the storage modulus increased by 4.7ᴼC for the MEK-ST sample at 24 hours aging while the other samples showed negligible increase. At 72 hours aged, once again the HDKO and MEK-ST samples exhibited an increase in the storage modulus. At 168 hours aging all samples had similar results. The HDK-I samples were found to have similar results of the unmodified polymer. This suggested that possibly the hydrophobicity of the silica played a role in the reinforcement effects.