Preparation And Properties Of Transparent Poly(Methyl Methacrylate)/Zirconia Nanocomposites

In the past decades, incorporation of inorganic nanoparticles into polymer matrix received tremendous interests, since it can obviously improve the properties of polymers and/or render polymers with novel functions. Among all these studies, special attentions have been focused on polymethyl methacrylate (PMMA)-based nanocomposites, because the small size effect of nanoparticles could retain the original transparency of PMMA.ZrO2 nanoparticles is well known for its high hardness, chemical inertness, high refractive index and excellent thermal stabilities and thus is a good candidate to improve the properties of PMMA.In this paper, highly-crystalline ZrO2 nanoparticles, synthesized from a solvothermal reaction of zirconium(â…£) isopropoxide isopropanol complex (99.9%) in anhydrous benzyl alcohol, were dispersed in MMA with the help of vinyl group-containing ligands, methacryloxypropyltrimethoxylsilane (MPS) and 2-hydroxyethyl methacrylate (HEMA), forming transparent MMA/ZrO2 dispersion. Transparent PMMA/ZrO2 nanocomposites were then prepared through in-situ bulk polymerization of MMA/ZrO2 dispersions. The optical, mechanical, and thermal properties of the nanocomposites were determined. The relationship between the structure and the properties of the PMMA/ZrO2 nanocomposites was discussed. Details are as follows:Non-aqueous synthesized ZrO2 nanoparticles were first modified with MPS in tetrahydrofuran and then dispersed in MMA to form transparent MMA/ZrO2 dispersion. In-situ bulk polymerization with controlled pre-polymerization time was then carried out to obtain PMMA/ZrO2 nanocomposites with ZrO2 content of as high as 15 wt%.The MPS-functionalized ZrO2 nanoparticles showed an efficient crosslinking role in the polymerization, leading to a complete gel of PMMA at 5 wt% of ZrO2 content. Homogeneous dispersion of the ZrO2 nanopartiles at primary particle size level was observed in all nanocomposites, which results in good clarity of the obtained nanocomposites. Hardness tests (pendulum hardness tests and indentation tests) and anti-scratch tests (abrasion tests and nano scratch tests) were employed to probe the surface mechanical properties of the nanocomposites. The properties of nanocomposites as a function of ZrO2 content, revealing from various characterization techniques, are not consistent and discussed in detail.At low ZrO2 content, the mechanical properties are enhanced by the formed crosslinking structure. However, remarkable improvements of hardness and scratch resistance of PMMA were achieved when 15 wt% of ZrO2 content was embedded.Non-aqueous synthesized ZrO2 nanoparticles were directly dispersed in MMA using HEMA as a ligand. In-situ bulk polymerization of MMA/ZrO2 dispersions was conducted to obtain transparent PMMA/ZrO2 nanocomposites with ZrO2 contents of as high as 7 wt%. The dispersion behavior of ZrO2 nanoparticles in MMA, structure, mechanical and thermal properties of the PMMA/ZrO2 nanocomposites were investigated by optical appearance, variable temperature FTIR spectra, tensile tests, DMA and TGA. It was found that ZrO2 nanoparticles could be well dispersed in MMA with HEMA ligand. But the MMA/ZrO2 dispersions easily destabilized in air as well as at elevated temperature. The destabilization temperature of the dispersion could be raised by increasing the molar ratio of HEMA/ZrO2 to match the temperature of bulk polymerization. The PMMA/ZrO2 nanocomposites revealed an interesting chemical structure (namely, highly cross-linked structure even at ZrO2 content of as low as 0.8% and hydrogen bonding interaction between polymer matrix and ZrO2 nanoparticles), enhanced rigidity without loss of the toughness of PMMA, and improved thermal stability.