Synthesis Of Novel Macromolecular Char Foaming Agents And Their Application In Flame Retardant Polypropylene

Polypropylene (PP) is widely used in transportation, construction, chemical industry, electronics and automobile manufacturing and other fields due to its excellent physical and mechanical properties, anti-corrosion, easy processing, low price and so on. However, PP is flammable, which limited its use in some fields, thus incorporating the flame retardant function for PP matrix is very important.The intumescent flame retardant (IFR), especially the triazine-based IFR have excellent flame retardant effect for PP martix, but there is poor dispersion and relative low flame retardant efficiency during IFR was used and investigated in PP martrix. In this paper, two novel triazine charring-foaming agent was designed and synthesized and mixed with ammonium polyphosphate (APP) and SiO2 to prepare IFR. The IFR was incorporated into PP in order to the properties of flame retardant PP materials were investigated.Firstly, the charring-foaming agent N-hydroxyethyl triazine-piperazine copolymer (HETPC) was synthesized from cyanuric chloride, ethanolamine and piperazine, and its chemical structure was characterized and confirmed by FTIR, MLA and 13C NMR. The synthsized HETPC was insoluble in common organic solvents, which domonstrated that the compound possessed excellent solvent resistance. The results of TGA tests showed that its initial thermal decomposition temperature was 330℃, and the char residues at 700℃ was 26.7 wt%, which indicated that HETPC had good thermal stability and excellent char-forming ability at high temperature. The IFR1 consisted of HETPC, APP and SiO2 was introduced into PP to prepare flame retardant PP materials. When the loading amount of IFR1 was 18 wt%, the samples with 1.6 mm thickness passed UL-94 V-0 rating and its LOI value reached 31.3%, which indicated the flame retardant has excellent flame retardant efficiency for PP martix. The mechanical properties tests showed the introducetion of IFR1 had little negative effect on the materials. The cone calorimeter test showed that the incorporation of IFR1 into PP matrix obviously decreased the combustion parameters, such as:HRR, THR, SPR and TSP, and the amount of char residue greatly increased after combustion. The char layer after cone tests was measured by scanning electron micrograph (SEM), the results domonstrated that the introduction of IFR1 promoted the formation of a continuous and dense char layer, consequently improved the flame retardancy of PP composites.In order to further improve the water resistance of flame retardant PP composites, another novel char-forming agent N-methyl-triazine-ethylenediamine copolymer (MTEC) was designed and synthesized, and its chemical structure was characterized. The synthesized MTEC also showed excellent solvent resistance. The wettability of MTEC was investigated by water contact angle test and the results showed that quasi-contact angle of MTEC reached 117 °, which indicated the MTEC possessed excellent hydrophobic properties. TGA tests showed the initial thermal decomposition temperature of MTEC was 315℃ and the char residue was 26.1 wt% at 700℃, which indicated that the compound had good thermal stability and char forming capability. The prepared IFR2 consisted of MTEC, APP and SiO2 was incorporated into PP matrix to prepare flame retardant PP composites. When the loading amount of IFR2 was 22 wt%, the samples with the thickness of 1.6 mm passed UL-94 V-0 flamability rating and its LOI value reached 29.6%, and the mechanical properties of materials remained well. The specimens were immersed into water at 70℃ for 168 h, and the mass loss rate of composites with the thickness of 1.6 and 3.2 mm was 0.62 and 0.13 wt%, respectively. After water treated, the samples remained excellent flame retardancy, which indicated the flame retardant PP composites possessed good water resistance. Cone calorimeter tests revealed that the introduction of IFR2 into PP matrix evidently reduced the combustion parameters and the residual char obviously increased. The continuous and compact char layer formed during combustion, which protected the interior material from degradation and burning, thus enhanced the flame retardant properties of PP materials.