Qing Zhang,Huiyuan Liu,Junxia Guan,Xiaochun Yang,Baojing Luo
Phosphating sesbania gum (DESG) was obtained by modifying sesbania gum (SG) with 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and endic anhydride (EA). The structure of DESG was determined using Fourier transform infrared (FTIR) spectroscopy and nuclear magnetic resonance spectroscopy (1H-NMR). Flame-retardant polylactic acid (PLA) composites were prepared by melt-blending PLA with DESG, which acted as a carbon source, and ammonium polyphosphate (APP), which acted as an acid source and a gas source. The flame retardancy of the PLA composite was investigated using vertical combustion (UL-94), the limiting oxygen index (LOI) and the cone calorimeter (CONE) test. Thermal properties and morphology were characterized via thermogravimetric analysis (TGA) and field emission scanning electron microscopy (FESEM), respectively. Experimental results indicated that when the mass ratio of DESG/APP was equal to 12/8 the LOI value was 32.2%; a vertical burning test (UL-94) V-0 rating was achieved. Meanwhile, the sample showed a lowest total heat release (THR) value of 52.7 MJ/m2, which is a 32.5% reduction compared to that of neat PLA. Using FESEM, the uniform distribution of DESG and APP in the PLA matrix was observed. The synergistic effect of DESG and APP effectively enhanced the flame retardancy of PLA. Additionally, the synergistic mechanism of DESG and APP in PLA was proposed.Keywords:polylactic acid;sesbania gum;ammonium polyphosphate;flame retardancy
Poly(lactic acid)/sesbania gum/nano-TiO 2 composites were prepared by melt blending in the mixing chamber of a torque rheometer in this work. The processing rheological properties, mechanical properties, morphologies, thermal properties, and optical properties of the resulting composites were evaluated. Effects of nano-TiO 2 content and plasticizer content on the processing rheological properties and mechanical properties of composites were discussed. Scanning electron microscopy micrographs clearly revealed good dispersion of nano-TiO 2 aggregates in the matrix at the low nano-TiO 2 content, while higher content contributed to easy aggregation within the matrix, which was consistent with the results of mechanical properties, thermal properties, and optical properties. As for the processing rheological properties, a reasonable choice of nano-TiO 2 and plasticizer content should be made depending on the used processing equipment and process.
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