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Latent curing epoxy systems with reduced curing temperature and improved stability

Zhang, Pengbo, Ali Shah, Sayyed Asim, Gao, Feng, Sun, Hao, Cui, Zhichao, Cheng, Jue, Zhang, Junying
Thermochimica acta 2019 v.676 pp. 130-138
adhesives, bisphenol A, curing agents, epoxides, imidazoles, molecular weight, polymers, shear strength, shelf life, temperature, tensile strength
As a representative single component epoxy resin, diglycidyl ether of bisphenol A resin (DGEBA) is the most widely used matrix in adhesives. However, challenges are still remained including high curing temperature and short shelf life. Herein, bisphenol A (BPA), Tetrachlorobisphenol A (TCBPA), and Tetrabromobisphenol A (TBBPA) as latent curing agents and imidazole as accelerator were used in adhesives. Curing kinetics was studied by non-isothermal DSC, using a model-fitting Málek approach and a model-free advanced isoconversional method of Vyazovkin. Results indicated that curing temperature of EP-BPA, EP-TCBPA, and EP-TBBPA was reduced to 126 ℃, 94 ℃, and 106 ℃, respectively. Storage stability evaluated by DSC indicated the shelf life was up to five months. After curing, molecular weights of the as-prepared linear polymers (EP-BPA, EP-TCBPA, and EP-TBBPA) were 33,822 g/mol, 14,913 g/mol, and 18,846 g/mol, and their tensile strength and shear strength were more than 40.06 MPa and 13.64 MPa, respectively.