Study On Intumescent Flame Retardant And Synergistic Mechanism Of THEIC Based Charring Agent

Polypropylene (PP) is one of the three major synthetic materials in the world, it has been widely used in many fields such as automotive, chemical engineering, construction due to its advantage of light-mass, cheap prices, easy molding as well as good performance. However, PP is highly flammable and its limiting oxygen index (LOI) is only 18%, this seriously limits its application in fields such as electronics, wire and cable. Traditionally, halogen compounds are used as additives to enhance PP’s flame resistant properties, however, the practice and research confirms that toxic gases and corrosive fume can be released during their decomposition, which threats human health. The EU, the United States and some other countries have issued a series of laws and regulations to prohibit some halogen containing flame retardants used in fields of electronics. The development of non-halogen and environmental friendly flame retardant is very clear. Intumescent flame retardants (IFRs) have drawn much attention in recent years, its flame retardant mechanism is based on the char layer which is formed when the IFR was heated to a certain temperature. The char layer could effectively slow down heat and mass transfer between gas and condensed phase, so that the flame retardancy is achieved. Although developments on IFR have been conducted for many years, only a few of IFR products have been commercialized, most products are still halogen containing flame retardants. The fundamental issues of IFR are not resolved, such as high adding amount, low flame retardant efficiency, poor compatibility, etc. In this paper, a series of novel components in IFR including acid source and charring agent were synthesized, which provide a new way to solve the mentioned problems, on that basis, the mechanisms of synergistic effect between sepiolite as well as zinc oxide and the novel IFR were investigated in detail. The works in this paper can be summarized as below:(1) Ammonium polyphosphate with crystalline form Ⅴ (APP-Ⅴ) was synthesized using diammonium phosphate (DAP) and melamine polyphosphate salt (MPP) as raw materials, its structure was characterized by flourier transform infrared spectrum (FTIR) and X-ray diffraction spectra(XRD) and was compared with that of commercial APP-Ⅰ and APP-Ⅱ. The physical properties of the three APPs were also studied and compared by thermogravimetric analysis (TGA), water solubility, crystal morphology analysis as well as the contents of phosphorus and nitrogen. TG-FTIR was used to analyze the gaseous products of APP-Ⅴ. Finally, the synthesized mechanism of APP-Ⅴ from DAP and MPP was proposed.(2) The flame retardancy of PP/APP/PER composites was investigated by LOI, UL-94 vertical burning tests as well as cone calorimeter test, the results showed that single addition of any kind of APP had little effect on the flame retardancy of PP. When PER was added with APP, the flame retardancy was improved obviously. In the LOI tests, PP/APP-I/PER composites showed the highest LOI values, however, PP/APP-Ⅱ/PER composites presented the best performance on anti-heat release. Meanwhile, the synergistic effect between 4A zeolite and the three types of APP was also studied, the results showed this synergistic effect was not influenced by the crystal form of APP. Finally, the effect of crystal form of APP on flame retardancy was discussed in detail.(3) THEIC was used as charring agent in IFR system, the flame retardancy of PP/APP/THEIC composites was evaluated by LOI, UL-94 vertical burning test as well as cone calorimeter test. The results showed that when the mass ratio of APP to THEIC was 2:1 and the loading was at 30 wt% level, the PP/APP/THEIC composite showed the best flame retardancy. However, the flame retardancy was strongly affected by hot water, when PP/APP/THEIC composites were soaked in water at 70 ℃ for 36 h, it could not pass UL-94 V-0 rating, indicating its bad water resistant property. Finally, the esterification process between APP and THEIC was proposed.(4) The THEIC-based charring agent (TBCA) was synthesized from THEIC and TPA by melt polymerization, it was characterized by FTIR,1H NMR, element analysis and TGA. On that basis, the effect of APP/TBCA on flame retardancy, water resistant property, combustion properties as well as thermal stability of PP was studied and compared with that of APP/THEIC. It was found that the flame retardant efficiency of APP/TBCA was not better than that of APP/THEIC, however, the water resistant property improved a lot, molecular dynamics was used to explain this phenomenon, the results showed that the interaction between PP and TBCA was stronger than that of PP and THEIC. Finally, the gaseous products and the morphology of the char were studied by TG-FTIR and SEM.(5) THEIC-based charring agent (TT) was synthesized by changing the mass ratio of THEIC to TPA, and it was characterized by FTIR,1H NMR and TGA. TT was mixed with APP to form IFR. The synergistic effect of IFR and ZnO as well as sepiolite (SEP) was studied by testing the flame retardancy, combustion behavior, thermal stability, morphology and the structure of the char. The synergistic effect of IFR/ZnO and IFR/SEP was investigated in detail. The results showed that there exists synergistic effect between IFR and SEP, however, the antagonism effect between IFR and ZnO was found. Finally, the synergistic mechanisms were proposed.(6) A novel triazine-based charring agent (CA) was synthesized by THEIC, formaldehyde and melamine, its structure and thermal stability were characterized by FTIR and TGA. The synergistic effect between CA and APP was studied by testing the flame retardancy of PP/APP/CA composites by LOI, UL-94 vertical burning tests, TG, and cone calorimeter test. Finally, the char morphology and structure were investigated by SEM, XPS and FTIR.