Study On Flame Retardancy Of Wood Plastic Based HDPE Composites

As a sustainable green material, the wood plastic composites(WPC)are widely usednowadays. However the further application is restricted due to its flammability. Therefore, it isimportant to study on the flame retardancy of the WPC.In this paper, the flame-retardant mechanism, application of major flame retardants wereintroduced and a low toxicity, less harmful and good effect of trinity intrumescent flame retardant(IFR) was synthesized. The effects of the IFR content and added methods on flame retardancy ofwood flour based highdensity polyethylene composites (HDPE-Wood) were studied. Forcomparison, flame retarded WPC were also prepared with decabromodiphenyl oxide (DBDPO)and antimonous oxide (Sb₂O₃). The flame retardancy and mechanical properties of flameretarded WPC were studied by thermalgravimereic analysis (TG), limited oxygen index (LOI),vertical firing test.In this paper, the main research conclusions are as follows:1. The flame retardants synthesized with two different methods, which have a good flameretardantcy effect. IFR-a which had the best expansion performance was synthesized byphosphoric acid, pentaerythritol and aniline, the molar ratio was2:1:1, reaction temperature was100℃and reaction time was6h. IFR-b was synthesized by phosphoric acid, pentaerythritol andaniline, the molar ratio was2:1:2, reaction temperature was100℃and reaction time was6h.According to the char yield test, the char layer of IFR-a had lots of small holes, whereas the charlayer of IFR-b was thick and compact. It is expected that the mechanisms of the flame retardantswere different. From the TG test, it is suggested that the IFR-b had the better thermal stabilitythan IFR-a.2. Poplar thin board treated by IFR-a solution was also studied. It is clear that the soakingtemperature was the crucial factor. By orthogonal experiment the best wood fire-retardanttreatment conditions were found: soaking temperature was80℃, IFR contration was8%, soakingtime was3h. The LOI of the sample10made according to the optimal treatment conditions canreach as high as46.7%.3. It could be observed that there was no significantly influence on the thermal stabilitywhen WPC treated by different methods. Compared with nonflame retarded WPC, the woodflour thermal decomposition of flame retarded WPC will occur in advance, while the mass loss ofHDPE will decrease. The WPC made with the wood flour treated by IFR solution had the lessflame retardancy than the WPC made with the IFR filled directly, whereas the former WPC hadthe better mechanical properties. 4. With the increase of IFR content, the surface of WPC expansion became bigger after0burning, as well as the char layer became more dense and stable. As mentioned above, it wasfound that the flame retardancy was better. When added40g IFR into200g WPC, the verticalfiring rating can achieve FV-2and no dripings; when added60g IFR into200g WPC, the verticalfiring rating can reach FV-0, the LOI was28.2%.5. It is showed that there was no significantly influence on flame retardancy when theDBDPO added to the WPC alone. The flame retardancy and mechanical properties will improveas the added of Sb₂O₃. The WPC will have the best flame retardancy when DBDPO and Sb₂O₃have the weight ratio of3:1²:1.