Preparation And Properties Of ZrO₂ Nanoparticles/Epoxy Resin Composites

Epoxy resin,as a typical thermosetting plastic material,has been widely used for aerospace parts,construction materials,and electronic component due to its low shrinkage rate,good adhesion and easy forming process,resulting to become an indispensable material.However,the brittleness and relatively weak mechanical properties of the cured pure epoxy resin restrict its application scope.The toughening of epoxy resins with inorganic nanoparticles provides a commonly used modification approach,which combines the rigidity,excellent chemical resistance and thermal stability of inorganic materials and the lightweight,flexibility,excellent impact resistance and processability of organic polymers to provide special properties.Among many nanoparticles,ZrO₂ nanoparticles may become an attractive option for reinforcement of polymers owing to their small particle size,strong chemical stability,good adsorption capacity and excellent wear resistance.Moreover,the addition of ZrO₂ nanoparticles can achieve a significant improvement in polymer properties.In this paper,well dispersive ultrafine ZrO₂ nanoparticles were prepared by a modified sol-gel process and then dispersed into epoxy resins using surface modification and ultrasonic mixing process.The effects of nanoparticle content on structure and mechanical properties of composites were also mainly studied.The thermal behavior of ZrO₂ precursor was analyzed by differential scanning calorimetry?DSC?and thermogravimetric analysis?TGA?.The morphology of ZrO₂ nanoparticles was characterized by transmission electron microscopy?TEM?and field emission scanning electron microscopy?FESEM?.The size distribution and surface area of ZrO₂ nanoparticles were examined on a laser diffraction particle size analyzer and physisorption apparatus,respectively.FTIR spectra of untreated and KH-550 treated ZrO₂were recorded using FT-IR spectrophotometer.The tensile properties and fracture toughness of ZrO₂/epoxy resin nanocomposites were measured by electro-hydraulic servo testing machine.The hardness of composites were measured using a nanoindenter.Thermal performance of the composites was evaluated with a thermogravimetric analyzer.The DSC/TGA results show that the ZrO₂ precursors have a strong redox reaction near300°C,and then the thermal decomposition is gradually completed.XRD patterns show the tetragonal phase of ZrO₂ nanoparticles calcined at 450°C.TEM and FESEM images display that the ZrO₂ particles with ultrafine particle size?about 18 nm?and good dispersion.The particle size analysis of ZrO₂ nanoparticles also reflects the smaller particle size and narrow size distribution.The specific surface area estimated using the BET method is 53.68 m²·g^-1.The FTIR spectra confirm that the KH-550 is successfully grafted onto the surface of ZrO₂nanoparticles without change of their own compositions.Mechanical tests demonstrat the increased mechanical properties for the composites with lower nanoparticle content.The maximum tensile strength,tensile modulus,fracture toughness,critical strain energy release rate,and hardness increase by 44%,29%,63%,122 and 17%compared with the neat epoxy resin,respectively.The improvement of mechanical properties is mainly ascribed to the good dispersion of modified ZrO₂ nanoparticles in the epoxy resin,improved particle/matrix interface adhesion,and some toughening mechanisms such as crack deflection,matrix-particle debonding and so on.Results of thermal analysis reveal that typical two-step degradation of polymers in O₂.Moreover,the char yield of the composites more than ZrO₂ nanoparticles content may be ascribed to the additional crosslinkage between the modified nanoparticles and matrix.