Experiment Investigation Of Homogeneous Dielectric Barrier Discharge At Atmospheric Pressure And The Surface Modification Of Polypropylene Non-woven Fabric

The atmospheric pressure homogeneous dielectric barriec discharge(HDBD) has been a hot point of plasma application reseach in recent years because of its various nice features, such as the uniform dicharge,the suitable power density,to prevent from injurying the surface of the workpiece,low energy consumption,low pollution(dry treatment),no requirement for vacuum system,low cost,and it can be used on production line,and so on.In this paper,the generation,machanics and application of the atmospheric pressure HDBD are investigated experimentally.The main research results are as following:1.The atmospheric He HDBD with multiple current peaks(MCP) was investigated systematically The research results showed the narrower gas gap,the higher applied voltage and the lower driving frequency are advantage for the formation of MCP.The applied voltage needed for the first breakdown gradually decreases and the amplitude of the current pulses quasi-monotonically decreases with the increase of the applied voltage, the decrease of the gas gap and the decrease of the driving frequency in per half cycle of the applied voltage.Secondly,the breakdown voltage for each current pulse is different. The breakdown voltage of the next current pulse is always affected by the previous current pulse in per half cycle of the applied voltage.Thirdly,the glow and Townsend discharge modes can be coexcitence in a MCP discharge sequence.The discharge pulses tend to convert from glow to Townsend discharge mode when increasing the applied voltage,decreasing the gas gap and reducing driving frequency respectively.Fourthly, the accumulated charges on the dielectric plate after the discharge extinguishes in previous half cycle is the prerequisite for the formation of the MCP discharge,while the uneven radial charges distribution can promote the development of the MCP discharge. And the memory voltage caused by the accumulated charges on the dielectric barrier promotes the discharge at the beginning and restrains the discharge at the following stage in a MCP discharge sequence.Fifthly,in the case of persistent HDBD in atmospheric helium,the number of the current pulse in per half of the applied voltage gradually increases with the increase of the content of the nitrogen,oxygen or carbon dioxide and finally transits to filament discharge.2.The effects of impedance mathching and ultraviolet(UV) pre-ionization from UV lamp for atmospheric N₂ and air dielectric barrier discharge(DBD) were experimentally investigated.The research results showed the discharge transits from filamentary discharge to homogeneous discharge in atmospheric N₂ when the gas gap is 3 mm after inserting the impedance matching network between the power supply and the plasma reactor or using the UV lamp irradiation.However,for atmospheric air DBD,the discharge does not transit from filamentary to homogeneous discharge although the gas gap is decreased to 1 mm after using the UV lamp irradiation;but the peak-to-peak threshold value of the applied voltage has a drop of different degree for certain gas gap and driving frequency.Moreover,after the discharge from filamentary to homogeneous discharge using the impedance matching,when the driving frequency and the gas gap are fixed,the discharge current and power increase very slowly if the discharge area does not bespread the entire electrode;but the disharge current and power increase linearly if the discharge area bespreadeds the entire electrode.However,when the applied voltage and the gas gap are fixed,there are a difference between the optimal driving frequency obtained by the experiment and the simulation result offered by Chen.We think the parameters of matching net should be adjusted according the experiment circumstance when we apply the formulas of Chen.3.The dynamics behaviors of the atmospheric He and Ar MCP discharge and the atmospheric N₂ HDBD were experimentally investigated.The research results show the discharge mode of HDBD at atmospheric pressure can be judged according to the differential conductivity of the current-voltage relationship in process of the increase of the discharge current;the discharge is glow discharge mode if the current-voltage relationship is shown to be negative differential conductivity;however,the discharge is Townsend discharge mode if it presents positive differential conductivity.Secondly,the three-dimensional trajactory of the MCP discharge in atmospheric helium shows a limited cycle with convolutions and undergos a series of bifurcation process;however,the three-dimensional trajectory of atmospheric N₂ HDBD is the limited cycle having not any convolution and any bifurcation process.Thirdly,the first ionization coefficient of working gas plays a very important role in defining the discharge mode of atmospheric HDBD and the transition of the discharge mode.For the gas with the higher first ionization coefficient,especially for helium,the dielectric plates with very high relative permittivity can lead to the drop of the dynamics stability of atmospheric HDBD.4.The surface treatment of polypropylene non-woven fabric(PPNWF) using atmospheric DBD plasma was preliminarily investigated by experiment.The research results showed that the hydrophilicity of PPNWF is considerably improved as long as the short time (several seconds) plasma treatment.The further measurements and analysis of X-ray Photoelectron Spectroscopy,Fourier Transform Infrared Reflection Spectroscopy,and Scanning Electron Microscope showed that the atmospheric N₂ DBD plasma has the function of dehydrogen;meanwhile a mass of oxygen- or nitrogen-containing function groups,which are mainly amide group,carboxyl group,hydroxyl group and amine salt radical,are introduced into the molecular chain of the PPNWF surface,and there exist some physical processes such as adhesion,etching,and fracture on the fabric surface which lead to the increase of the fabric surface roughness after the PPNWF is treated by the atmospheric N₂ DBD plasma.These physical and chemical processes lead to the improvement of the surface hydrophilicity of PPNWF;but the hydrophilicity has the time effect when the PPNWF samples are exposed in ambient air.In addition,when the plasma treatment time is fixed,the surface water contact angle of PPNWF sharply decreases and then reaches saturation with the increase of the peak-to-peak value of the aplied voltage.Therefore,it is necesarry to select the proper value of the applied voltage. Moreover,when a spot of O₂ is added in atmospheric N₂,the shorter plasma treatment time is not advantage for improving the hydrophilicity of PPNWF;while the longer plasma treatment time is advantage for it.On the contrary,when a spot of O₂ is added in atmospheric He,the shorter plasma treatment time is advantage for improving the hydrophilicity of PPNWF;while the longer plasma treatment time is not advantage for it. However,whether a spot of CO₂ is included in atmospheric N₂ or He,the CO₂ is not advantage for improving the hydrophilicity of PPNWF.