Improving the flame retardancy and mechanical properties of high-density polyethylene-g-maleic anhydride with a novel organic metal phosphonate

Zinc N,N'-piperazinebis(methylenephosphonic acid) (PPMPA-Zn) was melt blended with high-density polyethylene-g-maleic anhydride (HDPE-MA) to fabricate flame-retardant HDPE-MA/PPMPA-Zn composites. The thermal stability and flame retardancy of the composites were investigated by thermogravimetric analysis (TGA) and cone calorimetry. The incorporation of PPMPA-Zn did not appreciably increase the thermal stability of HDPE-MA, but the residual char content increased to 18.7% when the content of PPMPA-Zn reached 25 wt%. X-ray diffraction and Raman spectroscopy tests showed that the residual char was composed mainly of Zn(PO3)(2), Zn-11(HPO3)(8)(OH)(6) and amorphous graphite. Scanning electron microscopy (SEM) images of samples collected after cone calorimetric tests also confirmed the formation of char in the sample with 25 wt% PPMPA-Zn loading in HDPE-MA, and the char layer acted as a compact and intact physical barrier in the condensed phase. Even at a loading as low as 5 wt% PPMPA-Zn, the peak value of the heat release rate (PHRR) was reduced by 38% compared with that of pure HDPE-MA. In contrast to other intumescent flame retardants, the introduction of PPMPA-Zn enhanced not only the flame retardancy but also the mechanical properties of HDPE-MA. For example, the yield strength and Young's modulus of HDPE-MA with 5 wt% PPMPA-Zn were 125% and 128% higher, respectively, than those of the pure HDPE-MA matrix. (c) 2013 Elsevier B.V. All rights reserved.