Flame retardant efficiency of KH-550 modified urea-formaldehyde resin cooperating with ammonium polyphosphate on polypropylene

This paper surveys the char forming effect of urea-formaldehyde resin (UF) and the flame retardancy of UF cooperating with ammonium polyphosphate (APP) for polypropylene (PP). UF was firstly synthesized and then modified by a silane coupling agent 3-aminopropyltriethoxysilane (KH-550). UF and KH-550 modified urea-formaldehyde resin (M-UF) were characterized by field-emission scanning electron microscope (FE-SEM), energy-dispersive analysis (EDS), Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA). Compared with UF, M-UF had better thermal stability and higher mass of residue char. Afterwards the intumescent flame retardants (IFRs), consisting of UF + APP and M-UF + APP respectively, were introduced into PP. The flame retardant efficiency of PP composites was investigated by limiting oxygen index (LOI), UL-94 vertical burning, and micro combustion calorimetry (MCC). The possible decomposition mechanisms were investigated by TGA, FT-IR and EDS. When the addition of PP, APP and UF was 70, 24 and 6 wt%, the LOI value reached 23.5 and UL-94 test could not pass. However, when the loading of PP, APP and M-UF was 70, 20 and 10 wt%, the LOI value reached 29.5 and UL-94 test was V-0. The residual char layers of some PP composites were analyzed by Laser Raman spectroscopy (LRS) and FE-SEM. The LRS and FE-SEM presented that the char layer of 20%APP+10%M-UF/PP was more compact and had higher strength than 20%APP+10%UF/PP. Furthermore, tensile tests showed that M-UF/APP could improve break strength and toughness for PP compared with the same ratio of UF/APP. To sum up, M-UF + APP/PP have better flame retardant efficiency and tensile properties compared with UF + APP/PP.