An efficient method to improve simultaneously the water resistance, flame retardancy and mechanical properties of POE intumescent flame-retardant systems

To improve simultaneously the water resistance, flame retardancy and mechanical properties of an polyethylene-octene elastomer (POE) composite containing ammonium polyphosphate (APP), an effective method was developed, in which the APP was first coated by a silicon compound with a vinyl group, and then introduced into the POE matrix through chemical cross-linking. X-ray protoelectron spectroscopy (XPS) etc. measurements confirmed that the coated APP (CAPP) was prepared successfully. Then, together with a charring agent (CA), CAPP was used to flame retard POE. The combustible performance of the POE composites was investigated by limiting oxygen index (LOI), vertical burning (UL-94), and cone calorimeter (CC) tests. The results showed that the POE composite containing 22.5 wt% CAPP had better flame retardancy than POE containing equal amounts of APP, especially the CAPP system had much lower heat release rate (HRR), total heat release (THR), smoke production rate (SPR), and mass loss rate (MLR) than the APP system with the same amount of flame retardant. Furthermore, the CAPP system passed the UL-94 V-0 rating after water treatment at 70 degrees C for 7 days; while the APP system did not. Thermal gravimetric analysis (TGA), XPS, etc. measurements demonstrated that the formation of a rich residue containing Si-C, Si-O-C, etc. structures in the residue of the CAPP system should be the most important reason for its better flame retardancy than that of the APP system. Mechanical tests illustrated that the CAPP system had higher tensile strength and elongation at break than the APP system at the same condition, which should be due to the good interfacial adhesion resulting from the existence of silicon compounds at the surfaces of APP and its cross-linking with the POE matrix. All these results illustrate that it should be an efficient method to simultaneously improve the water resistance, flame retardancy and mechanical properties of a POE composite containing APP through functionalizing the APP and then chemically incorporating it into the polymer matrix.