| Recently, Polyurethane (PU)-based coatings have an important place in the coatings industry. In some applications they dominate the market because of their high level of quality. First, they combine outstanding resistance to solvents and chemicals with good weather stability. Secondly, the films have excellent mechanical properties and provide the idea balance of hardness and flexibility, even at low temperatures.Like the vast majority of synthetics, PU-based coatings are combustible which consequently limits their use in buildings or in transport applications. The most practical approach to enhance fire safety performances is the incorporation of flame-retardant (FR) additives in the PU polymeric matrix. The use of intumescent flame-retardant agents (IFR) allows both fire properties and mechanical behavior of the materials to be optimized. On the basis of synthesis of new-type FR agents, the properties and mechanism of FR coatings are discussed. Meanwhile, the heat transfer behavior is analyzed by establishing a three-dimensional model.This paper deals with synthesis and characterization of the carbonific. Two steps were used in synthesis process and the structure was characterized by Fourier transform infrared spectroscopy (FTIR), magic-angle spinning nuclear magnetic resonance (MAS-NMR 13C )spectroscopy, elemental analysis (ELA) and end-group analysis. Results show that structure of the carbonific was composed of triazine ring, amido and ethanolamine groups. Meanwhile, properties such as density, melting point, DSG and thermal stability of the carbonific are tested. In thefollowing part, a sole IFR additive was obtained after four steps of synthesis process including the steps of synthesis of the carbonific. Also, the structure was characterized by FTIR, MAS-NMR 13C spectroscopy and ELA. Results show that structure of the IFR agent was made up of the carbonific and pentaerythritol ramification. Finally, properties of the IFR agent are discussed.The addition of ammonium-polyphosphate (APP) and the carbonific into PU varnish leads to a great improvement in its carbonization and FR performances. So, after choosing the most effective combination of APP, carbonific and PU varnish (APP/ Carbonific/PU varnish=15: 5: 80), this paper deals with the evaluation of characteristic performances such as FR property, thermal stability of IFR/PU-based coatings, rheology of IFR/PU-based coating solutions and mechanical properties such as hardness, adhesion, flexibility of IFR/PU-based dry coating films. Meanwhile, the addition of the IFR agent (20% Wt) into PU coating also increases FR properties of the coatings. Then, the same properties similar to the APP/carbonific/PU-based coatings are characterized.Results of research made on the physics and chemistry properties of FR coating solution show that 0.4% (Wt) silane coupling agent and 1% (Wt) bentonite can improve fluidity, thixotropy and store stability properties of the two systems.FR mechanism of the above two systems is discussed. Thorough research is made on APP/Carbonific/PU system. Based on results of thermogravimetric analysis (TGA) , thermal degradation of the system is divided into five steps. Each step is characterized by SEM, FTIR, MAS -NMR 13C and ELA. Results show that FR mechanism of this system is based on the intumescent and porous char. This char is made up at least of three types of materials. One comes from the degradation product of PUpolymers , the second comes from reaction product of the degradation product of PU and APP and the third comes from the esters formed by degradation product of APP and the carbonific. Also, TGA and FTIR are used to research on the FR mechanism of IFR/PU system and results also show that amine, aromatic products and phosphoric esters are combined in the intumescent char to make the coating system have FR property.Finally, based on the conservation of mass and energy, the phenomenon in the experiment and a series of hypothesis, a three-dimensional model is developed to characterize heat transfer manner of the FR c...
|
PDF Full Text Request