| Fiber cement board possesses many excellent properties and is widely used in the field of home decoration.The water-based primer used for fiber cement board needs a long drying time,which brings low production efficiency.The permeability of ultraviolet(UV)light-cured primer is poor,which decreases the service life and weakens decorative effect of later functionalized fiber cement board.Moreover,the high content of volatile organic compounds(VOCs)pollutes the environment and also endangers human health.In view of the current problems for the coating of fiber cement board,the fast-drying and high-permeability waterborne epoxy primer and its key raw materials including waterborne epoxy dispersion and waterborne epoxy curing agent are developed.The hydrophilic intermediate was synthesized from ethanolamine and polyethylene glycol diglycidyl ether.After reacting with epoxy resin,it was used to modify triethylenetetramine.Finally,it was terminated with phenyl glycidyl ether to obtain a non-ionic waterborne epoxy curing agent with emulsifying and curing functions.The reaction conditions of each step were determined,and the effects of different polyamines,end-capping agents and end-capping ratios on the properties of the curing agent were discussed.The curing agent was characterized by Fourier transform infrared spectroscopy(FTIR),which confirmed the successful incorporation of the hydrophilic intermediate and epoxy resin into the curing agent molecule.The obtained curing agent is a light yellow transparent viscous liquid,with good compatibility with epoxy resin,excellent water dispersibility,solid content of 60%,viscosity of 7000 cp,active hydrogen equivalent of 280 g/mol,and shelf life over 6 months.Waterborne epoxy dispersion was prepared by phase inversion method with solid-state epoxy resin E-20 as the main resin.The effects of operating paramters such as emulsifier dosage,emulsifying temperature,emulsifying time and emulsifying speed on the particle size and stability of epoxy dispersion were discussed.When the amount of emulsifier is 25 wt% of the resin,the emulsifying temperature is 65 ～ 75 ℃,the emulsifying time is 40 min,and the emulsifying speed is 2500 ～ 3000 r/min,the obtained epoxy dispersion occupies a small particle size(169 nm),good stability,viscosity of 3000 cp,epoxy equivalent of 960 g/mol,and the storage stability at room temperature is more than 6 months.The self-made waterborne epoxy dispersion and waterborne epoxy curing agent were used to prepare the primer for the fiber cement board.When the curing agent and the epoxy dispersion mixed with the molar ratio of amine hydrogen and epoxy group of 1:1,the optimal performance of the primer film is obtained,in which the drying time at 60 ℃ is 2 min,achieving the effect of fast drying,and the adhesion of the pull-out method is 2.34 ～ 2.61 MPa,more than the blank control of 1.80 MPa,which obviously enhances the strength of the board.The pencil hardness is 4H and the application period is 4 h.The fast-drying mechanism and strengthening mechanism of waterborne epoxy primer are attributing to small particle size waterborne epoxy dispersion and the unique molecular structure design of the curing agent.Scanning electron microscope(SEM)results showed that,compared with the film prepared by epoxy resin E-51 and self-made curing agent,the film obtained by waterborne epoxy dispersion and waterborne epoxy curing agent was denser.The results of thermogravimetric(TG)and differential scanning calorimetry(DSC)showed that the latter has better thermal stability and higher glass transition temperature. |
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