Comparison of the influence of CeYAG and MCM-41 as nanofillers on the properties of polycarbonate and poly( methyl methacrylate)
Sibeko, Motshabi Alinah
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This study reports on the morphology of poly( methyl methacrylate) (PMMA) and polycarbonate (PC) filled with mesoporous silica (MCM-41) and cerium doped yttrium aluminum garnet (Ce:YAG) at contents in the range of 0.1 to 5 wt.%. The interactions between the polymer and fillers in these composites, and their thermomechanical, mechanical and thermal degradation properties were studied. The techniques used were small angle X-ray scattering (SAXS), transmission electron microscopy (TEM), CP-MAS-NMR spectroscopy, X-ray diffraction (XRD), dynamic mechanical analysis (DMA), thermogravimetric analysis (TGA), impact testing and luminescence spectroscopy. The samples containing more than 0.5 wt.% of filler were Jess transparent than those containing smaller amounts, due to the presence of agglomerates. MCM- 41 particles were well dispersed at low loadings, but formed agglomerates at higher loadings, while the Ce:Y AG particles were not too well dispersed in both polymers at low loadings. Mixing with PMMA and PC did not alter the pore dimensions in the MCM-41 structure, and it maintained its hexagonal structure, even though the polymer chains partially penetrated the pores during composite preparation. Both polymers have carbonyl groups that had hydrogen bond interactions with the silanol group (Si-OH) on the surfaces of the MCM-41 particles. In the case of Ce: Y AG the interaction was through electron donor-acceptor interaction between the carbonyl oxygen lone pair in the polymers and the yttrium cation (Y3+). PMMA, however, showed a stronger interaction than PC. The addition of MCM-41 and Ce:Y AG increased the storage and loss modulus of PMMA and PC above the glass transition temperature. In the presence of MCM- 4 I the increase in modulus was due to the interaction of the polymer chains with the porous filler which restricted the mobility of the polymer chains and increased the stiffness of the composites. The impact strength of the polymer increased with the addition of MCM-41 and Ce: Y AG, but the concentration corresponding to the maximum increase depended on the type of filler. The combination of blue LEDs with the PMMA/Ce:YAG composites loaded with 5 wt.% and PC/Ce:YAG composites loaded with 2 wt.% gave off light in the white region, making them suitable for applications in white light emitting diodes.