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High Density Polyethylene(HDPE) has been widely used in many fields as general plastic due to its good comprehensive properties. However, there is a hidden fire trouble because it is rather flammable with low limited oxygen index (LOI), the burning is too fast and will generate a lot of melt dripping,thus it is particularly important to do research on resisting flammability of HDPE. As more and more requires of environmental protection in flame-retardant field and forbid use of conventional halogen-containing flame retardants, the research of halogen-free flame retardant HDPE is of important value.A great deal of attention has been paid to intumescent flame retardants(IFRs) due to they have advantages like no toxicity, less smoke, no melt dripping and so on. In recent years, the application of IFRs have achieved significant results in flame-retardant field, especially used in polyolefin. However, there are some disadvantantages of IFR systems, such as weak compatibility with resin, easy moisture absorption and so on.To solve the existence problems of IFR systems,this work based on molecular scale, design a macromolecular flame retatdant which is composed of three components---an acid source,a carbon source and a gas source, then make it graft p-bond which can react with HDPE, thus improving the compatibility of rIFR in HDPE matrix; In order to further enhance interfacial combination between the two phases, rIFR was surface-modified with siloxane coupling agent(KH570). Then HDPE/rIFR composites with good flame retardant properties and mechanical properties were prepared by thermol-mechanical blending. Subsequently, we studied the synthesis process,chemical structure, thermal stability of rIFR and the chemical structure,fracture morphology,flame retardant properties, mechanical properties, melt flow rate and flame retardancy mechanism of HDPE/rIFR composites. The main results and conclusions were summarized as follows:(1) We synthesized Pentaerythritol phosphate ester (PEDP) on the basis of Phosphoric acid and pentaerythritol with the mole ratio 2.5:1. Then the Reactive-type intumescent flame retardant(rIFR) was gotten with 47.52% of carbon residue and 56.5% of yield with the mole ratio of PEDP/MA/MUF-AM=1:1:1.(2) The initial decomposition temperature of rIFR was 220℃, and the decomposition temperature range of rIFR also covered the pyrolysis temperature range of HDPE, so rIFR well matched with HDPE.(3) There was chemical connection between rIFR and HDPE matrix, which improved the compatibility of two phases.(4) LOI of HDPE/rIFR composite materials increased with the content of rIFR increasing, the horizontal buring rate continuously decreased.When the content of rIFR increased from 0% to 30wt%,LOI of composites incresed from 18.5% to 24.5%, and horizontal buring rate reduced from 33.6mm/min to 21mm/min;The flame retanrdant properties of composites slightly reduced after surface treatment for rIFR,and the effect of the content of coupling agent wasn’t evident for flame-retardant properties of HDPE/rIFR.(5) The tensile yield strength(TYS) of HDPE/rIFR had no obvious viration with the content of rIFR increasing,flexural modulus(FM) of composites increased, notched izod impact strength(NIIS)of composites gradually decreased, when the content of rIFR was 30wt%,the FM got to 1.40 times that of pure HDPE, and TYS and NIIS were 104% and 71% respectively that of pure HDPE; However, after surfacial modification of rIFR by siloxane coupling agent,the NIIS of composites had maximum value which was maintained 95% that of pure HDPE when the content of coupling angent reached 2.5wt% of rIFR, and the TYS and FM got to 1.04 and 1.40 times respectively that of pure HDPE.(6) HDPE/rIFR can form intumescent carbon layer during the process of burning, however, because the char layer wasn’t thick and solid,heat and flammable volatiles could easily penetrate the char layer into the flame zone, this caused HDPE/rIFR composites had limited flame retardancy.
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