Effects of composition of hardener on the curing and aging for an epoxy resin system

Different Mixture ratios of Shell Epon 828 (based on diglycidyl ether of bisphenol A, DGEBA) and Shell EPI-CURE 3046 (based on triethylenetetramine, TETA) were evaluated under different environments of isothermal curing at 80 degrees C in DSC, room temperature Curing in air, and aging in water at 45 degrees C. The Curing reactions were monitored using differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and infrared spectroscopy (IR). It was shown that the initial curing rate increased with the amount of hardener. However, the epoxy groups in samples with excess hardener were prone to reaction with primary amines located at the ends of TETA molecules, resulting in a less dense epoxy network. During aging in water at 45 degrees C, significant effects of water on the postcure and the increased water absorption with an increase of hardener amount were observed. The DMA results show that the samples with hardener around stoichiometric composition have the greatest storage modulus while curing in air environment. However, the samples with hardener Much less than stoichiometric composition have greater storage modulus under aging in water at 45 degrees C. (c) 2005 Wiley Periodicals, Inc.