| Due to lightweight, high strength, corrosion resistance and other advantages, it is a trend to use fiber reinforced polymer composites (FRP) as power plant chimney instead of traditional materials. However, composites have two objective problems: high insulation and inflammability. Ihe former may result in electrostatic discharge (EDS) phenomenon; sparks created would threaten the security of constructors or ignite inflammable materials. Therefore, the studies of electrostatic protection and flame retardancy are necessary.The electrical resistivity of composites can be decreased by the addition of conductive fillers, and graphite ones were considered more suitable to the research subject through comprehensive comparison. Then some influencing factors were discussed, inculding the content of graphite, coupling agent and process mode, as well as the proportion and orientation of fiber reinforcement. In addition, it studied the dependence between resistivity and temperature, the curve repeatability with heating multiple times, and the resistivity stability as time went by on the premise of constant temperature. On the basis of experiment, the paper analysed the mechansims that control conductivity of composites doped graphite, then Monte Carlo model and Flory model were set up to predict the electrical properties of composites. The aim of electrostatic protection mainly was to avoid or reduce EDS effect, but not to change the flammable characteristic of resin matrix. In order to make it up to flame retardant standards, appropriate organophosphorus compound, such as TMP and APP, need to be added, and it was also an effective treatment that the versatile resin was repalced by flame retardant resin510C. And the main conclusions were:1The resin doped graphite could appear precolation phenomenon whose threshold was about5Wt%. When graphite content was more than10Wt%, the electrical resistivity tended to stabilize, about106Ω·cm. Silane coupling agent KH-151would decrease the resisitivity, and it was better to deal with graphite by pretreatment with1/80KH-151; oppositely, fiber would increase the resistivity, and small angle contributed to higher conductivity.2The composites doped with graphite could show PTC effect whose quickly-changed temperature was about90℃, but no obvious NTC effect. PTC effect was influenced primarily by the coefficient of thermal expansion, and resisitivity-temperature properties appeared repeatable when resistivity-time properties of fiber reinforced composites stable.3It found that electrostatic protection of composits doped graphite was mainly realized through comprehensive role of conductive channel and tunnel effect by analysing conductive mechanism. Flory model was more significant than Monte Carlo model to predict electric properties, and its precolation threshold was18.8Vol%which was greater slightly than experimental value15.3Vol%. The maximum error between theoretical curve and measured one was about8.82%.4The oxygen index (OI) of411resin matrix doped10Wt%graphite was optimum, about21%. And it would reach up to27%by adding additionally20Wt%TMP or APP, whereas the mechanical performance be degraded to some degree. OI of flame retardant resin(510C) was aobut25%, and its corresponding fiber reinforced composites could be above27%generally, even parts as high as29~30%by doping appropriate graphite. So fiber skeleton fixed carbon layer well, meanwhile, it prevented effectively mechannical performance from degrading.As a result, utilize1-3layer fiber cloth to reinforce510C doped10-12Wt%graphite. The resisitivity of composites was within the limite of electrostatic protection, about106~107.5Ω·cm, and resisitivity-temperature properties proved repeatable when resisitivity-time properties stable. Moreover, fiber reinforced composites belonged to flame retardant materials, and its oxygen index was in the range of29~30%. Beyond that, the retention rate of flexural strength was more than90%. In conclusion, the composites could achieve experimental purpose, as well as keep the mechanical properties well. |
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