Studies On Preparation And Properties Of Epoxy Resin/Silica-Titania Hybrid Materials

Epoxy resin possesses many excellent properties of materials, however, as the kind of thermosetting material is with a high cross-link density, the behavior of its crack growth shows that it is of typical brittleness, which leads to some weak points, such as the great brittleness in the curing state, low heat-resistance, low impact strength, easy crackness. So it difficult to satisfy the requirements of the developing engineering technology, .In this paper, on the basis of the structure characteristic of nanocomposites , toughening method, toughening effect, toughening mechanism of epoxy resin have been studied in detail. Three kinds of EP/SiO₂-TiO₂ hybrid materials have been synthesized. The experimental results are given as follows: 1.Three kinds of EP/SiO₂-TiO₂ hybrid materials containing grafted compound, rigid-flexible spacers and hyperbranched polymer have been synthesized via sol-gel process. Those materials were characterized by FTIR, XRD, 1HNRM, AFM, DSC ,UV-Vis, TEM and SEM, etc. The experimental results indicated that the transparency of EP/SiO₂-TiO₂ hybrid films is over 80%. SiO₂-TiO₂ inorganic networks and epoxy matrix combined with chemical bonding, and was not the simple blend. The results of AFM and TEM indicated that SiO₂-TiO₂ particle sizes is about 10¹00nm. 2. The non-isothemal curing kinetics of EP/SiO₂-TiO₂ prepolymer and DDS systems was studied by dynamic differential scanning calorimetry (DSC) through three kinds of kinetic methods(Kissinger, Ozawa and Crane kinetic model). The results showed that SiO₂-TiO₂ can enhance curing reaction activation energy (Ea), and do not change the reaction order. This shows that the curing mechanism is not changed by addition of SiO₂-TiO₂ , and the curing reaction is a complex process. 3. The mechanical properties and the fracture surface of SEM indicated that the toughness of epoxy resins was enhanced greatly by adding SiO₂-TiO₂ , the tensile strength and bending strength were also improved to some extent. The impact strength of the modified systems was enhanced to 2-3 times in the range of SiO₂-TiO₂ contents. 4. From SEM analyzing of impact fracture surface, the roughness mechanism of SiO2-TiO2 inorganic networks was mainly craze and hole. It is that SiO2-TiO2 nano-particles could induce epoxy matrix yielding deformation and resistance to crack propagation.. 5. The experimental results of the creep behavior and the stress relaxation of the curing systems indicated that the crosslinking points of the curing networks increased the formation of SiO2-TiO2 inorganic networks. Which led to the difficult deformation for the linear curled segments between crosslinking points, the increased the balance force values ,so it made the crosslink density and resistance deformation of epoxy resin improved greatly. 6. The investigation on dynamic mechanical properties of cured materials showed that the storage modulus of materials was improved and damping decreased by adding SiO2-TiO2 nanoparticles. It might be due to the fact that the crosslink intensity of curing systems enhanced, and the motion of epoxy resin molecular chain was hindered. The glass transition temperature (Tg) was about 30⁴0℃higher than that of pure epoxy resin. 7. The investigation on the activation energy of the glass transition temperature for α-relaxation peaks at different frequency showed that, when SiO2-TiO2 contents was 3.25%, the activation energy of α-relaxation peaks is 455KJ/mol, it is 62KJ/mol higher than that of the pure epoxy resin (392KJ/mol). The results mean that the internal tribological performance, strength and the glass transition temperature of composites materials improved. It was due to the fact that SiO2-TiO2 networks can restrict effectively the epoxy resin molecular chains movement. 8. The results of DSC and TG showed that the glass temperature and the decomposition temperature of EP/ SiO2-TiO2 hybrid materials improved greatly with contents of SiO2-TiO2 increasing. This indicated that SiO2-TiO2 inorganic networks can improve not only the mechanical properties of materials, but also improve thermal properties. 9. When SiO2-TiO2 contents is 0.67¹.97wt.%, EP/ SiO2-TiO2 hybrid materialshave a good antibacterical behavior under the light of fluorescent. This is because TiO2 can absorb electron-hole pairs, and has photocatalytic effect. It is the mainly reason that SiO2-TiO2 has a good antibacterial and bactericide function. 10. According to the experimental results of the wear and the SEM images of the wear surface. The friction coefficient and wear loss of the modified systems could be effectively decreased at a relatively low level (1.32².60 wt.% SiO2-TiO2). It was found that the incorporation of SiO2-TiO2 networks into epoxy caused a considerable improvement of tribological characteristics. The micro-hardness was also improved. The wear mechanisms are mainly abrasive and fatigue wear. 11. Based on the electrical property, nano-SiO2-TiO2 can be dispersed in epoxy matrix homogeneously, which made the crosslink intensty of materials improve. So due to the motion of molecular chains of materials was hindered which made the surface resistivity, the bulk resistivity, the dielectric constant and the dielectric loss decrease, While the electrical breakdown strength and arc resistance improved.