The Influence Of Curing Conversion On The Structure-Property Relationship Of Epoxy Materials

Epoxy material is widely used in adhesive, coating, matrix of composites and electric packaging. The performance of the final products is largely determined by the properties of epoxy resins. In general, it is assumed that the optimistic performance of epoxy resin is achieved when epoxy is fully cured. However, in practice curing conditions are typically controlled to balance the final properties, the effect on other components and processing condition, rather than to achieve complete functional group conversion. Therefore, it is of great significance to study the influence of curing conversion on the structure-property relationship of epoxy materials.In this work, to simplify the study, we adopt a model epoxy-amine system, which has a binary composition and a simple reaction, to find some general methods and trends. DSC is employed, first to establish the curing conditions for different curing conversion, and to study the curing kinetics of the model system. DMA is a sensitive and simple method to characterize curing conversion, by measuring the glass transition. At the mean time, DMA could provide a lot of information on the structure-property relationship, such as, glass transition, crosslinking density, secondary relaxation transition, apparent activation energy and so on. Mechanical properties of the model system with different conversion are tested; it is interesting that the best performance is not necessarily obtained at highest conversion.The influence of curing conversion on the water sorption behavior of DGEBA-DDS system is thoroughly investigated. Interestingly, the equivalent water sorption increases as curing conversion increases at lower temperature, while decreases as curing conversion increases at higher temperature. To try to understand this phenomenon, IR and two-dimensional correlation method are adopted to study how water molecules diffuse into and interact with the epoxy network for different curing conversion, at lower and higher temperatures, respectively.Finally, rheology method is applied to monitor the curing process of epoxy materials, which not only provides useful information on the structure evolution, but also serves as a guideline for actual processing of the materials. The viscosity evolutionoand the gelation behavior of the material are discussed in details. Three different systems are under study:simple epoxy-amine system, thermoplastic-modified thermosetting epoxy where viscoelastic phase separation plays an important role, and epoxy material with reinforcing mesoscale fillers.