Effect of metal oxide nano-particles on the properties and degradation behaviour of polycarbonate and poly (methyl methacrylate)

[摘要] Melt compounding was used to prepare polycarbonate (PC) and poly(methyl methacrylate) (PMMA) nanocomposites with different amounts of metal-oxide fillers (silica, zirconia and titania). Zirconia and two types of titania were prepared by a sol-gel method, whereas a commercial hydrophobic silica having chemically surface bonded methyl groups was used. Titania nanoparticles were annealed at 200 and 600 °C to obtain the anatase and rutile phases, respectively. The effect of filler amount, in the range 1-5 wt.%, on the morphology, mechanical properties and thermal degradation kinetics was investigated by means of transmission electron microscopy (TEM), X-ray diffractometry (XRD), small-angle X-ray scattering (SAXS), dynamic mechanical analysis (DMA), thermogravimetric analyses (TGA), Fourier-transform infrared spectroscopy (FTIR), 13C cross-polarization magic-angle spinning nuclear magnetic resonance spectroscopy (13C{1H}CP-MAS NMR) and measures of proton spin-lattice relaxation time in the rotating frame (T1ρ(H)), in the laboratory frame (T1(H)) and cross polarization times (TCH). Results showed that the nanoparticles were well dispersed in the polymers whose structure remained amorphous, except for zirconia in a PC matrix, which showed the appearance of a local lamellar order around the nanoparticles. The silica, titania and zirconia nanopaticles increased the thermal stability of the polymers, except for the highest silica and zirconia contents in the PC system which showed a decrease. A similar trend in the activation energies of thermal degradation was observed. The presence of zirconia and silica showed a decrease in the storage and loss moduli at lower temperatures, probably due to a plasticization effect. The two types of titania nanoparticles influenced the rigidity of the polymers in different ways because of their different carbon contents, particle sizes and crystal structures. NMR results suggested that, in the presence of a metal oxide, the observations in the PMMA systems could be related to heteronuclear dipolar interactions between the carbonyl carbons and the surrounding hydrogen nuclei, and in the PC systems to intermolecular interactions involving the carbonyl groups.

[发布机构] University of the Free State