Organic-inorganic hybrid materials, such as polyhedral oligomeric silsesquioxanes (POSS), have the potential to improve the mechanical properties of the methacrylate-based composites and resins used in dentistry. In this article, nanocomposites of methacryl isobutyl POSS (MI-POSS [bears only one methacrylate functional group]) and methacryl POSS (MA-POSS [bears eight methacrylate functional groups]) were investigated to determine the effect of structures on the properties of dental resin. The structures of the POSS-containing networks were determined by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy. Monofunctional POSS showed a strong tendency toward aggregation and crystallization, while multifunctional POSS showed higher miscibility with the dimethacrylate monomer. The mechanical properties and wear resistance decreased with increasing amounts of MI-POSS, indicating that the MI-POSS agglomerates act as the mechanical weak point in the dental resins. The addition of small amounts of MA-POSS improved the mechanical and shrinkage properties. However, samples with a higher MA-POSS concentration showed lower flexural strength and flexural modulus, indicating that there is a limited range in which the reinforcement properties of MA-POSS can operate. This concentration dependence is attributed to phase separation at higher concentrations of POSS, which affects the structural integrity, and thus, the mechanical and shrinkage properties of the dental resin. Our results show that resin with 3% MA-POSS is a potential candidate for resin-based dental materials.
In this study, polypropylene (PP)/nano-silica (nano-SiO2) composites were prepared by a melt blending process. Here, a novel surface treatment method which uses combined dispersant and a coupling agent is developed to treat the nano-SiO2 which is uniformly dispersed into the PP matrix. To treat the surface of nano-SiO2, the optimal content of the dispersant (SDBS) is 2.0% and the optimal amount of the coupling agent (KH-550) is 1.5%. The mechanism and synergistic effect of the combined dispersant and coupling agent are discussed based on their chemical structures. The fractography of PP/nano-SiO2 composites after notched impact testing observed by the scanning electron microscope (SEM) proves the uniform dispersion of nano-SiO2 in the PP phase. The mechanical testing results show that after surface treatment, both the tensile and notched impact strength of nanocomposites enhance markedly. The tensile strength reaches its maximum with the 4.0% of nano-SiO2 and the notched impact toughness achieves its maximum with the 5.0% of nano-SiO2. The crystallization behavior characterized by the differential scanning calorimetry (DSC) and the crystalline structure observed by the polarizing microscope (PM) indicated that nano-SiO2 has a nucleation role in the crystallization of PP which results in a higher crystallization temperature, a higher degree of crystallinity, and a smaller size of spherulites.
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