Preparation Of Epoxy Resin-based Nanocomposites And Their Application In Powder Coatings

Epoxy resin is an important category of thermosetting resin and is widely used in applications such as adhesion, coating, nonconductor materials, machine manufacturing and advanced composites due to its excellent chemical stability, shaping facility, thermal properties and low cost. But the cross-linked epoxy resin contains a large density and thus is fragile when impacted. Then the toughness improvement becomes a critical field in fundamental researches and applications of epoxy resin, and in recent years, improving toughness of epoxy resin by composing with nanomaterials is an attractive point. In this thesis, we prepared epoxy resin/CaCO₃ nanocomposites by in situ and inclusion polymerization based on studies on dispersion condition of different nanoparticles in different systems. Mechanism of the well-dispersed preparation process and the behavior of nanoparticles in the property-improving effect is studied systematically. Properties of powder coating made of the nanocomposites and their relationship with the structure is also investigated.Particle size distribution and appearance of TiO₂, CaCO₃, CeO₂ and BaSO₄ nanoparticles dispersed in water and acetone is investigated by PCS and TEM. Influences of dispersing phase, stirring, surfactant and measurement methods are studied. Difference between the two testing methods and mechanism in which the surfactant works are discussed.Condensation polymerization between bisphenol A(BisA) and epichlorohydrin(ECH) is catalyzed by NaOH in water solution and in presence of CaCO₃ nanoparticles. Period and temperature of the reaction, dosage and concentration of the NaOH solution and dosage of nanoparticles are studied to find how they affect the chemical and physical properties of the resultant resin such as epoxide value, hydrolysable chlorine, inorganic chlorine and softening point. It was found that the most appropriate preparation conditions are: M_ECH:M_BisA=1.33; MNAoh:Mech=1.3; concentration of NaOH is 10%; keeping constant in 80 for 1.5h and then 90 for 45min. Nanocomposites with different nanoparticles are prepared and result shows that epoxy/CaCO₃ nanocomposites have the best properties. Then nanocomposites with different dosage of CaCO₃ nanoparticles are prepared and the mechanism of polymerization was discussed.Traditional extruding blending and solution blending are used to prepare nanocomposites for contrast, and their dispersions, glass-transition temperature are tested. It is found that dispersion of nanoparticles in nanocomposites prepared by the new method is much more satisfying than by traditional ones. Stretch test result shows that stretch stain of the nanocomposites increases with the content of nanoparticles. Then the appearances of the stretched sections are observed by SEM. Improvement mechanism of the nanoparticles is discussed based on SEM observations.Powder coatings with different content of nanoCaCO3 are prepared using the newly prepared nanocomposites in substitute of neat resins. After sprayed to the steel baseplate, their propertiesare systematically tested. It was found that when containing 3%-5% nano CaCO₃, their impact resistance, stretch strain, and deposited stability are remarkably improved compared to the unmodified. In the range of 3%-5% CaCO₃ nanoparticles composed in, the roughness and toughness of powder coating film can be improved at the same time. Based on analysis of the crosslinked powder coating, synergistic effect of larger and smaller particles is brought forward to explain the property improvement.