Studies On The Electrical/Flame-Retardant Propreties Of Graphene/HDPE Nanocomposites

Although plastic is widely used in electronic packaging application due to its high electrical insulation, its applications are very limited owing to the low flash point and the static discharge may cause a fire, which will bring some huge potential security problems.To meet the extended application fields,extensive efforts have been in progress to modify antistatic properties and flame retardant performance. In this work, maleic anhydride (MA-HDPE) and High density polyethylene (HDPE) are matrixes, raphite and polyethyleneimine (PEI) function of reduction graphene oxide (PEI-RGO) are as conductive fillers, and brominated polystyrene (BPS) is as a flame retardant filler.And electrically conductive and flame-retardant composites are prepared by different matrixes and different fillers.The contents of this subject consist of the following parts:1. Research of PEI reduced and modified GO. Firstly, natural graphite sheets were oxidized via Hummers method to introduce oxygen-containing functional groups on their surfaces, and then graphene oxide (GO) was obtained. GO was reduced by polyethyleneimine (PEI) subsequently.The massive amine groups can not only occur amide reaction with carbonyl groups of GO but also take place nucleophilic addition with its epoxy groups.PEI was grafted on the surface of GO by fassitance of covalent bonds, then the hybrid are further reduced by hydrazine hydrate to get PEI-GO conductive filler. Experimental results suggest that PEI is grafted well on the surface of GO leading to the improvement of thermalstability of GO, in addition,the layer distance of GO was increased, which leads to the good dispersion of PEI-RGO in HDPE;after further reduce by hydrazine hydrate,the thermal stability and electrical conductivity are further improved.2. Research of electrical conductive Properties. The effect of different matrixes (MA-HDPE and HDPE) and conductive fillers (graphite and PEI-RGO) on the conductive properties of the composites was studied to fabricate high-performance conductive composite materials. Studies have shown that graphite has a bad dispersion in HDPE matrix and the conductivity of the composite with 15 wt% of graphite is just 10'5 S/m, and the mechanical property declines with the increase of graphite content. In terms of MA-HDPE/RGO composite fabricated by solution method, PEI-RGO has a good dispersion in the matrix to endow the composite with a lower percolation threshold (<0.5 wt%) and the conductivity can reach to 0.0233 S/m when the content of filler is 2 wt%; What's more, the addition of PEI-RGO hasn't caused the decrease of the mechanical property and thermal stability of the composites due to the cohesion of the filler and matrix. Compared with MA-HDPE/RGO, HDPE/RGO has a lower conductivity and it can be 2.78×10-7 S/m with a 2.0 wt% content of filler, which is in the static category; the conductivity is much higher than that of HDPE/graphite and it has no obvious negative effect on the mechanical property and thermal stability of the composite.3. Study on flame retardant properties. Although halogen-containing flame retardants can efficiently improve the flame retardant properties of the material, the combustion process releases large amounts of smoke and toxic gases, which will pollute the environment. Therefore, we selected a new environmentally friendly halogen flame retardant, Brominated Polystyrene, to improve the flame retardant properties of the material. Studies have shown that only when the content of BPS reaches 25 wt% in the MA-HDPE /RGO/BPS prepared by solution method with poor compatibility with the matrix of the BPS, can the composites achieve the vertical burning grade of UL-94 V-0, and due to the poor compatibility.According to the excluded volume theory, the conductive percolation threshold of PEI-RGO in the composite material further decrease. Besides, when the mass fraction of RGO and BPS comes to 1.5 wt% and 25wt% respectively, the conductivity of composite materials reaches 1.07×10-5 S/m, which is greatly higher than that of MA-HDPE/1.5 wt% RGO (4.3×10-6 S/m), causing the mechanical properties and thermal stability of composite materials to slightly decline concomitantly.