Synthesis Of A Novel Hyperbranched Charring Agent Containing Triazine And Polyurea Group And Its Application To Polypropylene

Polypropylene(PP) is widely used in many fields, including building materials, packaging materials and daily necessities. Due to high flammability of PP and melt drops in the combustion process, which leading to the fire is difficult to prevent from spreading and it is difficult to rescue. Application of PP is limited in some areas because of these shortcomings. So improving the flame retardant property of PP is the focus to the researchers.With the improvement of the quality of living environment, intumescent flame retardant system(IFRs), which have low smoke and low toxic, are gradually replacing the halogen flame retardant system. IFR generally include acid source, charring agent and blowing agent. Although the acid source plays a key role in the whole flame retardant system, the role of charring agent is not tobe ignored. Traditional charring agents are mostly small-molecular structures,although they also have better flame effectancy on formation of char, they also have some disadvantages, such as easy to move to the substrate surface, the poor compatibility with the matrix and easy to absorb moisture and so on. Therefore,in order to improve the shortcomings of small-molecule charring agents, this paper synthesize a kind of novel hyperbranched charring agent with macromolecular structure via one step method.Melamine(MEL) has a large amount of N element and 4’4-diphenyl methane diisocyanate(MDI) contains a lot of C element. Therefore, this paper shows MEL and MDI with N, N- dimethyl formamide(DMF) as a solvent obtain a novel hyperbranched charring agent(MM) containing triazine and polyurea group.The structure of MM was characterized by X-ray diffraction(XRD), fourier transform infrared spectrometry(FTIR), nuclear magnetic resonance spectrometry(1H NMR); thermal stability and hydrophobicity were tested by thermogravimetric analysis(TGA) and water contact angle metering system(WCA). The flammability of PP and its composites were tested by limiting oxygen index(LOI), vertical flame test(UL-94) and cone calorimetry(CONE).The Micro-morphology and medical structure of char residues of PP composites were studied using field emission scanning electron microscopy(FESEM) and fourier transform infrared spectrometry(FTIR).The results show that: a novel hyperbranched charring agent(MM)containing triazine and polyurea group was successful synthesized. Water contact angle of MM reached 90°, suggesting its good hydrophobic performance;initial decomposition temperature of MM was 250℃, which can satisfy with the polymer processing requirements, preventing the occurrence of degradation of flame retardant during material processing; when the temperature increases to800℃, the residual amount of MM was 40 wt%, showing that the effect of char formation of MM on PP was outstanding.The combustion properties and mechanical properties of PP composites showed that LOI value of composite increased to 29.5% from 18% for pure PP,and get the UL-94 V-0 level, no molten drop during combustion process when30 wt% APP/MM(APP:MM=3:1) was loaded into PP; the peak of heat release rate(PHRR) decreased to 223 kW/m2, the total heat release(THR) was reduced to 66 MJ/m2; char layer after cone calorimeter tests with a dense, continuous and smooth characteristics, can not only effectively prevent PP6 from combustion but also enhance the performance of molten PP anti-dripping, hindering further spread of the flame, therefore, the PP composite material has good flame retardancy; in the combustion process, the cross-linking reaction of APP and MM formed P-O-C and P-N structure, so the benzene ring in the combustion process and phosphoric acid can be formed char layer can be as a protective layer, a good inhibited further combustion of materials; tensile strength of PP/APP/MM composite can achieve 34.19 MPa, impact strength also can reach3.45 J/m2. Compared with pure PP, the mechanical properties of PP compositeshave no remarkable change.Thus it can be seen that combination of APP and novel charring agent containing triazine and polyurea group has a good synergistic effect. Because of its hydrophobic surface, the compatibility between PP matrix and charring agent could be improved, as a result good flame retardancy and mechanical properties of the flame retardant PP composites have been obtained.