Abstract:In this work, a series of molar ratios composed with YD-128 and DDM were chosen based on the viscosity analysis. The mixtures of YD-128 and DDM with the different molar ratios were cured at 170°C for 15 min followed by post cure at 190°C for two hours. The thermal properties of the cured samples were investigated with DSC, TGA, DMA, and TMA. The conversion ratio of the mixtures of YD-128 and DDM (1 : 1.1) was calculated by dividing ΔH obtained from DSC experiments for each cured sample by ΔH. The TGA data of the cured samples showed that the thermal stability and thermal degradation activation energy were proportional to the amount of DDM in the mixtures. However, the highest tan δ, and the lowest thermal expansion data with DMA and TMA respectively were obtained from the stoichiometric mixture of YD-128 and DDM. Furthermore, the different ratio of mixtures were applied to test specimens to be cured at 170°C to measure single lap shear strength with universal testing machine.

Epoxy resin toughening agents such as core/shell nanoparticles, CTBN epoxy, polyester polyols, and polyurethane have been widely used in order to compensate for the brittleness and improve the impact resistance of the epoxy resin. In this work, a few tougheners mentioned above were individually added into adhesive compositions to observe the effects of physical and mechanical properties. Both flexural strength and flexural modulus were measured with UTM while impact strength was analyzed with Izod impact tester. The obtained results showed that the addition of toughening agents afforded positive performance in terms of flexibility and impact resistance of the cured epoxy resin. Furthermore, DMA experiments suggested that the trends of storage modulus data of each epoxy resin composition coincided with the trends of flexural modulus data. FE-SEM images showed that toughening agents formed circled-shape particles when it was cured in epoxy resin composition at high temperature by phase separation. The existence of particles in the cured samples explains why epoxy resin with toughener has higher impact resistance.

: Volatile organic compounds (VOC) free adhesives have been interested by many scientists and engineers due to environmental regulations and the safety of industrial workers. In this work, a series of composites composed with bisphenol A epoxy resin used as solvent, dicyandiamide, and promoter were prepared to investigate the most appropriate molar ratio for steel-steel adhesion. The cured test specimen of each composite were measured with universal testing machine (UTM) to figure out mechanical properties such as tensile strength, Young's modulus, and elongation. Furthermore, the lap shear strength of the specimen was tested with UTM while impact resistance was measured with Izod impact tester. The composite whose molar ratio of epoxy resin to curing agent is 1 : 0.9 (sample 3), showed better tensile strength, coefficient of elastic modulus, elongation, and impact strength than other composites did. The highest tanδ from dynamic mechanical analysis (DMA) was observed from sample 2 (epoxy resin: dicy = 1 : 0.7) while sample 3 showed slightly lower tanδ than that of 2. The morphology of the fracture surface of the cured composites from SEM showed that the number of subtle lines on the surface caused by impact increase as the contents of amine curing agent accrete. Furthermore, the viscosity change of sample 5 (epoxy resin: dicy = 1 : 1.3) was observed to confirm its storage stability.