Combination of montmorillonite and a Schiff-base polyphosphate ester to improve the flame retardancy of ethylene-vinyl acetate copolymer

Different flame retardant ethylene-vinyl acetate copolymer (EVA) formulations were prepared to evaluate the synergistic effect between organo-montmorillonite (OMMT) and a Schiff-base polyphosphate ester (PAB) on the combustion behavior of EVA. X-ray diffraction (XRD) and transmission electron microscopy (TEM) results revealed that montmorillonite platelets selectively dispersed in the PAB phase. EVA/PAB/OMMT(80/15/5) had better thermal stability and flame retardancy than EVA/PAB(80/20), as indicated by the results of thermogravimetric analysis (TGA), limited oxygen index (LOI), vertical burning test (UL-94) and microscale combustion colorimeter (MCC), showing a synergism between OMMT and PAB. For example, the onset decomposition temperature (T-5%) increased from 233 degrees C to 296 degrees C, the char residue at 600 degrees C increased from 6.6% to 11.0%, and the peak heat release rate (PHRR) decreased from 718.1 W/g to 706.6 W/g. This is caused by the silicoaluminophosphate (SAPO) structure formed by reactions between the phosphoric acid generated from PAB and OMMT.