Abstract:

In this investigation,the waterborne ultra-thin fire-retardant coatings for steel structures were prepared respectively with the silicone-acrylic, acrylic, styrene-acrylic and VAc-VeoVa latexes as the binder. Then,the effects of the binders on the fire-retardant performance of the coatings were discussed in terms of the thermal stability and the high-temperature rheology. The combustion test results of analoging large panels show that the expansion
ratio,17.4 times that of the fire-retardant coatings from the VAc-VeoVa latex,is the largest,and its fire-retardant performance is the best with a steel backside temperature of 304℃ after a 30-min combustion. It is seen from TGA curves that the VAc-VeoVa polymer is of good thermal stability and its average thermal degradation rate is the lowest,and that those characteristics of the VAc-VeoVa polymer provide enough time for its reaction with ammonium polyphosphate,thus generating a dense char layer which can remarkably improve the fire-retardant performance of the coating. Moreover, the results of the dynamic rheological test demonstrate that,for the acrylic and styreneacrylic molten polymers,the storage modulus ( G') are higher than the loss modulus ( G″) ,which means that the elastic flow is predominant in these melts,and their complex viscosities are more than 1 000 Pa·s, while for the VAc-VeoVa molten polymer,G″ is higher than G',which means that the viscous flow is predominant in this melt,and its complex viscosity is 33 Pa·s,and that,for the VAc-VeoVa melt,a Newtonian fluid property is displayed at the low frequency stage,and the complex viscosity slightly decreases at the end of the high frequency stage. The above-mentioned results show that the viscous fluid with good thermal stability and low complex viscosity can be used as the binder of fire-retardant coatings,which is helpful in the expansion and fire retardancy of the coatings.

Key words: waterborne ultra-thin fire-retardant coating, binder, dynamic rheological property, fire-retardant performance