Effect of Concentration of Microencapsulated 1-Methyl Imidazole Curing Agent with Solid Epoxy Shell on the Mechanical Properties of Epoxy Resin

 Epoxy resin is used in various industries such as adhesives, paints and coatings, aerospace and electronics due to its unique attributes. Epoxy curing agents can be generally classified in two groups of normal (room or high temperature) and latent curing agents. Latent curing agents are mixed with epoxy resins to obtain stable compounds at normal conditions. These compounds can cure epoxy resins rapidly when exposed to external stimulation, such as heat. Capsulation of curing agent as a cost-effective method has attracted an extensive attention to prepare non-reactive or latent curing agents. The concentration of microencapsulated latent curing agent significantly affects the final mechanical properties of cured epoxy resins.

The effect of concentration of microcapsules containing curing agent of 1-methyl imidazole by solid epoxy shell on the mechanical properties of epoxy resin was investigated using dynamic mechanical thermal analysis.

The effect of 20, 25, 30 and 35 phr (per hundred resin) microcapsules concentration in liquid epoxy on storage modulus (E′) and phase angle tangent (Tanδ) was investigated. The results showed that increasing the concentration of microcapsules in cured samples causes to advance storage modulus due to increasing the amount of curing agent and consequently increasing the density of crosslinks. On the other hand, it was found that liquid epoxy resin cured with 30 phr microcapsules has the highest glass transition temperature (48°C). The hardness test results also confirmed the results of thermal-mechanical dynamic test at the optimum microcapsule concentration. The results also indicated that at 30°C the storage module decreased by increasing microcapsule concentration from 20 to 25 phr.  The storage modulus of cured epoxy resins increased to higher values by increases in microcapsule concentration. Therefore, the epoxy resin cured by 35 phr microcapsule showed the highest storage module (723 MPa).