Synergistic flame retardancy of ZnO and piperazine pyrophosphate/melamine cyanurate in polypropylene

Abstract

In order to improve the flame retardant efficiency and smoke-suppression of piperazine pyrophosphate/melamine cyanurate (PPAP/MCA) in PP, the synergism of ZnO and PPAP/MCA was investigated by limiting oxygen index (LOI) determination, UL-94 test, and cone calorimetry test (CCT). It is found that ZnO performs an exceptional synergism in flame retardant effect and inhibition on the flame propagation. Besides, ZnO can significantly inhibit the production of the smoke and CO. The TGA of the PP composites, the component and structure analysis of the heated composites and CCT residues reveal that ZnO performs the synergism primarily by the following modes: ZnO promotes obviously the charring of the composite, and improves the thermal stability as well as the strength of the intumescent layer, which brings about an improved flame retardant property and inhibiting ability on the flame propagation.

Application of the PAPP/MCA/APP intumescent flame retardant system in polypropylene

“…Therefore, based on the above investigation results and previous studies, the flame‐retardant mechanism of PAPP/MCA/APP IFRS was proposed (Figure 5). 36,37,46,49–54 In the initial stage of combustion, the dehydration and ionic bond breakage reactions of APP and PAPP started, which led to the generation of the phosphoric acid, metaphosphoric, N‐P compounds, etc. with the releasing of H 2 O vapor 46,54 .…”

“…with the releasing of H 2 O vapor 46,54 . Meanwhile, MCA began to decompose to melamine and cyanuric acid 37 . The thermal and oxidative degradation of PP also happened at this stage, resulting in the formation of O‐containing functional groups such as hydroxyl and carboxyl groups on the carbon chain of PP 50–52 .…”

“…With the increase of the combustion temperature, metaphosphoric or phosphoric acid can further dehydrate to pyrophosphoric acid and continuously release H 2 O vapor 36 . The phosphoric acid derivatives and N‐P compounds reacted with the O‐containing functional groups on the carbon chain of PP by the dehydration and cross‐linking reactions leading to the formation of the multicomponent residues and the continuous char layer structure 37,46 . Meanwhile, melamine and cyanuric acid further pyrolyze into CO 2 , NH 3 , and other volatile matters leading to the expanding of the char layer 53 .…”

“…Finally, the obtained flame‐retardant PP composite was pressed by an XH‐406A parallel‐plate vulcanizer (Dongguan Xihua Testing Machine Company, China) at 180°C for 10 min under the pressure of 8 MPa to get the PP sheet used for the following studies. Table 1 listed the formulations of the prepared flame‐retardant PP composites based on the previously reported results on the flame retardancy of the APP, PAPP, and MCA 37,43,46 …”

“…However, APP, PAPP, and MCA have obvious disadvantages when they were used alone as the flame retardant. APP and PAPP have relatively high phosphorus content, and their decomposition products are mainly phosphoric acid derivatives, which make APP and PAPP play the role of flame retardance mainly in the condensed phase 36,37 . MCA can only exert the flame‐retardant effect in gas phase due to only non‐flammable gases generated during the decomposition of MCA 38,39 .…”