| Intumescent flame retardants (IFR) are an important class of additives for flame-retardant polymer materials, which usually consists of carbon source, acid source and air source. While the traditional intumescent flame retardants were mainly prepared with ammonium polyphosphate (APP) for the acid source, pentaerythritol (PER)for the carbon source and melamine(MEL)for the gas source. In this paper, processing byproducts tea saponin (TS) of camellia oleifera was selected as a blowing agent, insteading of melamine, combined with ammonium polyphosphate(APP), pentaerythritol physical(PER) to synthesis green tea saponin intumescent flame retardants (TS-IFR) by the method of composition, esterification and coupling agent modification, and the tea saponin intumescent flame retardants (TS-IFR) was used in environmental friendly intumescent flame retardant coatings.The methods and processes of the preparation of tea saponin intumescent flame retardants was studied, and the flame retardancy, pyrolysis process, flame-retardant mechanism and pyrolysis kinetics of tea saponin intumescent flame-retardant coatings(TS-IFRC) were discussed by the methods of FT-IR, SEM-EDS, TG-DSC, CONE analysis. The main research contents and results are as follows:1.Complex tea saponin intumescent flame retardants(CTS-IFR) was prepared by mixing the acid source ammonium polyphosphate, the carbon source pentaerythritol and the gas source tea saponin physically, and was used in alkyd resin varnish to prepare intumescent flame retardant coatings(CTS-IFRC). The preparation process of CTS-IFR and flame retardancy, thermal degradation of its application in flame retardant coating was studied. By orthogonal design test, the appropriate formulation of CTS-IFR had been investigated, and with this formulation of CTS-IFR the intumescent flame retardant coatings had a good flame retardancy. CONE experiments showed that samples coated CTS-IFRC had low values of heat release rate (HRR), total heat release (THR), effective heat of combustion (EHC) and other indicators, which were significantly superior to traditional melamine flame-retardant coatings and flame-retardant coatings without tea saponin. In addition, TG-DSC analysis indicated that CTS-IFR had greatly improved the thermal stability and carbon residue performance at high temperature of the flame retardant coatings.2. Based on the theoretical basis of tea saponin structure being rich in hydroxyl and carboxyl group, trinity tea saponin intumescent flame retardants(TTS-IFR) were synthesized by esterification reaction of tea saponin, ammonium polyphosphate and pentaerythritol, and also were applied in flame-retardant coatings. The TTS-IFR was characterized using FT-IR and SEM, and the flame retardancy and pyrolysis performance of flame-retardant coatings containing TTS-IFR (TTS-IFRC) also were investigated systematacially. The results showed that when the material ratio m(APP):m(PER):m(TS) is of 2:1:0.25～0.5,the prepared TTS-IFR had a high carbon residue rate of 68.40% and a expansion coefficient of 38mL/g at 500℃. TTS-IFRC had an excellent flame retardance, thermal stability and quality of residual rate, flame-retardant efficiency had been greatly improved. When the amount of TTS-IFR was 50% of the solids content of flame-retardant coatings, the LOI of TTS-IFRC was up to 34.2%, the fire-resistance time was 11.1min, and the mass loss was a minimum of 21.29%. CONE experiments show samples coated with TTS-IFRC had a significantly lower values of HRR, EHC,THR and other performance indicators than those of samples coated with flame retardant coating with unreacted flame retardant of the same material ratio, and the flame retardancy of which had been greatly improved. Meanwhile, the thermal degradation performance analysis shows that TTS-IFR can significantly improve the thermal stability and heat resistance of flame retardant coatings.3.In order to improve the application performance of the complex tea saponin intumescent flame retardant(CTS-IFR) used in flame-retardant coatings, silane coupling agent was selected as a modifier to modify the CTS-IFR. By investigating the moisture absorption and dispersion properties of the modified flame retardants(MTS-IFR),the suitable conditions of the modification reaction were obtained for the temperature of 80℃, the modification time of 4h, and the amount of silane coupling agent added of 2.5%.Under this condition, the flame retardant system reacted well with silane coupling agent, form a good chemical crosslinking in the modification reaction, and the modified flame retardants had a good thermal stability. Besides, the combustion properties and flame retardancy of the flame-retardant coatings containing modified flame retardants(MTS-IFRC) were discussed. It was concluded that the MTS-IFR had a good flame retardancy and a good carbon residue performance, which were much improved compared with the flame retardant coatings containing unmodified flame retardants. When the amount of modified flame retardants was 50% of the solids content of flame-retardant coatings, the MTS-IFRC had a LOI value of 32.4%, a fire-resistance time of 13.2min and a smaller quality loss and carbonized area. Meanwhile, the mean heat release rate (m-HRR), total heat release(THR), mean effective heat of combustion(m-EHC) and mean mass loss rate(m-MLR) of samples coated with MTS-IFRC had been decreased significantly compared with the samples coated with flame retardant coating with unmodified flame retardant. And the flame retardancy, painting properties and film property of MTS-IFRC was obviously improved.4. The flame retardant mechanism and thermal degradation kinetics of tea saponin retardant intumescent flame retardant coatings (TS-IFRC) were discussed. By analysing the thermal properties of each component of TS-IFR by using TG-DSC respectively, it was disclosed that APP, PER and TS in the flame retardant system occurred synergistic mechanism, at the same time, it was also proved that tea saponin as gas source of TS-IFR could occur synergistic effect with other components, play a good flame-retardant effect. Furthermore, the thermal reaction process and content changes of the main elements of TS-IFRC and the formation law of intumescent char in various temperature phase was studied by FT-IR^ SEM-ESD. In addition, thermal decomposition reaction kinetics of TS-IFRC were solved by the integral method of Coats-Redfern. And the process of pyrolysis reactions and pyrolysis kinetics model at different stages of TS-IFRC were obtained. The results shown that at the early flame retardant stage of TS-IFRC, ammonium polyphosphate(APP) and tea saponin(TS) was degraded into gases such as NH3, H2O to prevent from the invasion of oxygen, which was mainly called gas phase mechanism. With the increasing of temperature, phosphoric acid generated at the early stage catalyzed tea saponin and pentaerythritol to inflate into carbon, and combined with the carbonized layer to form a dense char layer containing aromatic phosphate esters, which can effectively prevent the combustion of the protecting material, mainly occurring the condensed phase mechanism. |
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