| A new type of modified epoxy coating(EP/PU?EP/PU/IFR) and commercial epoxy fireproofing coating(EP-C/IFR) has been designed in this paper, which is based on waterborne epoxy emulsion(EP) and commercial epoxy varnish(EP-C), using waterborne polyurethane(PU) as modified agent, ammonium polyphosphate(APP), novel charring-foaming agent(CFA) and nano-fillers as intumescent fire-retardant(IFR). Paint film impact tester, adhesion tester, elastic tester, thermal gravimetric analysis(TGA),scanning electron microscopy(SEM), atomic force microscopy(AFM), cone calorimeter(CONE) and back-side temperature test were used to carry out the following research.(1) Impact strength, adhesion, flexibility, thermal stability, section microstructure and interpenetrating polymer network(IPN) of polyurethane-modified epoxy coating were studied.(2) The effect of polyurethane on the thermal stability, heat release, fire resistance and carbon residue microstructure of epoxy fireproofing coatings was studied.(3) The effect of polyurethane on the aging resistance of epoxy fireproofing coatings was studied.Both Boltzmann and Linear fitting methods were used to predict the service life of the coatings, and the suitability was studied. The research results indicate that:(1) After modified by PU, the impact strength of EP/PU coatings is higher than that of neat EP coating. When the addition amount of PU(TF-680) is 15 wt%, the compatibility between EP and PU is better and the density of interpenetrating network is higher. The synergistic effect of interpenetrating polymer network is remarkable. The impact strength,flexibility and thermal stability are better, meanwhile, the adhesion does not reduce.(2) The thermal stability and fire resistance of epoxy fireproofing coatings do not get worse while modified by PU, of which the thermal stability of EP-C/IFR is the best, while the fire resistance is poor. The ignition time of fireproofing coatings modified with PU is little earlier. The peak heat release rate and total heat release reduce 7.6% and 33.3%,respectively. After combustion, EP/IFR and EP/PU/IFR form a lot of small holes in the carbon residue, while the aperture of EP-C/IFR carbon residue increases, which results in the poor fire resistance.(3) The results of hot air accelerated aging indicate that PU is helpful to improve the aging resistance of epoxy fireproofing coatings. The service life at room temperature of EP/IFR, EP/PU/IFR, EP-C/IFR is 568 d, 648 d, 1597 d and 326 d, 335 d, 940 d corresponding to Boltzmann and Linear fitting method, respectively. The measured aging time andtheoretical analysis indicate that Linear fitting method gravely deviates from the coating's real aging situation, while Boltzmann fitting method can better reflect the mass loss of the coatings during aging. |
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