Dielectric Barrier Discharge Plasma Process Research Articles

Influence of dielectric barrier discharge plasma processing in the volatile compounds and aroma of cashew apple juice

Cashew apple juice is a popular beverage in several parts of the world due to its unique fruity aroma. However, the high styrene concentration contributes to an undesirable balsamic note. To address this issue, cold plasma technology was proposed to alter the juice's volatile compounds, thereby improving its flavor. This study has evaluated the effects of cold plasma on the volatile compounds and aroma of cashew apple juice. The research was conducted by applying dielectric barrier discharge plasma to the juice, varying the frequency (50–1000 Hz) and processing times (5–20 min) while keeping a constant voltage (18 kV). The plasma treatment induced noteworthy changes in the volatile compounds of the juice. Specifically, there was a significant decrease in volatile organic acids (73%) and an increase in aldehydes (52%), alcohols (67%), and short-chain esters (11%). Plasma induced the internal scission of fatty acids and esters, which resulted in the formation of short-chain esters and aldehydes. Further processing has oxidized the aldehydes, generating alcohols and isomerized short-chain esters, which generate branched esters. Cold plasma, however, did not significantly reduce the styrene concentration and could not mitigate the off-flavor caused by this compound.

Dielectric Barrier Discharge Plasma Processing and Sr-Doped ZnO/CNT Photocatalyst Decoration of Cotton Fabrics for Self-Cleaning Application.

Nonthermal plasma processing is a chemical-free and environmentally friendly technique to enhance the self-cleaning activity of nanoparticle-coated cotton fabrics. In this research, Sr-doped ZnO/carbon nanotube (CNT) photocatalysts, namely, S10ZC2, S15ZC2, and S20ZC2 with different Sr doping concentrations, were synthesized using the sol-gel method and coated on plasma-functionalized fabric to perform the self-cleaning tests. The fabrics were treated with dielectric barrier discharge plasma in an open environment for 3 min to achieve a stable coating of nanoparticles. The energy band gap of the photocatalyst decreased with an increase in the level of Sr doping. The band gap of S10ZC2, S15ZC2, and S20ZC2 photocatalysts was estimated to be 2.85, 2.78, and 2.5 eV, respectively. The hexagonal wurtzite structure of ZnO was observed on the fabric surface composited with CNTs and Sr. The S20ZC2 photocatalyst showed better homogeneity and photocatalytic response on the fabric when compared with S10ZC2- and S15ZC2-coated fabrics. The S20ZC2 photocatalyst showed 89% dye degradation efficiency after 4 h of light exposure in methylene blue solution, followed by S15ZC2 (84%) and S10ZC2 (80%) photocatalysts.

Degradation of diazinon by dielectric barrier discharge plasma

Pesticides are chemical compounds widely used in crop pest control, ensuring high productivity and product quality control. However, pesticides are toxic and can be bioaccumulative, and their excessive use causes environmental and health impacts. In this study, the potential of atmospheric cold plasma to degrade diazinon present in water was investigated. For the degradation process, a dielectric barrier discharge (DBD) plasma system was used to process diazinon at a varying voltage (10, 15, and 20 kV), excitation frequency (200, 400, 600, 800, and 1000 Hz), and exposure time (10, 20, and 30 min). The concentration of diazinon and the identification of the by-products were analyzed by gas chromatography coupled to mass spectrum (GC-MS). DBD plasma processing efficiently degraded diazinon, reaching a maximum degradation of 9.44 ± 0.09 mg/L, sufficient to bring diazinon-contaminated waters to safe levels. Analysis of variance indicated that increasing voltage and treatment time and low plasma excitation frequencies increased diazinon degradation. Two parallel degradation routes were proposed for diazinon degradation by cold plasma consisting of an oxidative desulphurization route and a hydrolytic route followed by a ring-opening reaction.

Responses of Rice Seed Quality to Large-Scale Atmospheric Nonthermal Plasmas

Atmospheric nonthermal plasma (ANTP) is used for various biological applications including seed quality improvements in crop production. However, the underlying mechanisms of plasma-induced seed action are not fully explained and operating large-scale ANTP on seeds is highly challenging. Two large-scale ANTPs, streamer corona plasma (SCP) and dielectric barrier discharge (DBD) plasma, were used to enhance rice seed vigor through surface modification and functionalization. The SCP and DBD plasma were conducted under the same power source and applied to rice seeds to modify their surface from being highly hydrophobic to being highly hydrophilic, as defined by the apparent contact angle measurement. The results show that SCP requires less treatment time (~ 2 min) for surface activation than the DBD plasma process (~ 10 min). Both plasma-treated seeds showed higher seed vigor than non-treated seeds. For 50% of the viable seeds to emerge, the SCP-treated seeds took on average about 62 h., while the untreated rice seeds took around 72 h. The germination percentage of all conditions is ~ 92% which is a typical proportion of good seed quality. The microstructure of the rice seed surface suggests that the bombardment of highly energetic ions and the reaction of reactive oxygen and nitrogen species on the seed surface cause morphological changes via surface etching and functionalization without any adverse effects on seed nutrition.Graphical abstract

Comparing impacts of dielectric barrier discharge plasma and electron beam irradiation processing on characteristics of Tartary buckwheat whole flour

Dielectric barrier discharge (DBD) plasma, lower and higher dose electron beam irradiation (EBI) are used widely in food processing. In this research, impacts of DBD plasma and EBI processing on characteristics of Tartary buckwheat whole flour were investigated in the range of parameters used most often in food industry. Cross section, small granule and reaggregation of fragments appeared after processing as well as higher values of L*, a* and WI. DBD plasma processing altered the short range crystal structure and hydrogen-containing groups, increasing oil/water absorption and freeze-thaw stability. DBD plasma and EBI processing had a mostly positive effect on hydration properties at 50 to 70 °C, with contrast to a reduction effect at higher temperature. DBD plasma and EBI processing will not affect the nutrients content indeed. TPC, TFC and antioxidant activity increased significantly after EBI processing (≤ 10 kGy) with few free radicals generated. Industrial relevanceDBD plasma and EBI processing are widely used for flour in food industry, with limited focus on physicochemical properties promotion and antioxidant activity protection. This research indicates that DBD plasma processing can affect the properties of Tartary buckwheat whole flour (TBF) significantly, but it shows negative damage to bioactive compounds and antioxidant activity. EBI processing (≤ 10 kGy) can improve physicochemical properties of TBF, which is given slightly higher TPC, TFC and antioxidant activity simultaneously. Both of DBD plasma and EBI processing are safe methods that can improve processing characteristics of the flour, while lower dose EBI processing is more suitable for development of Tartary buckwheat and functional food industry with protection to bioactive compounds and antioxidant activity.

The reaction characteristics of NO and SO2 in the dielectric barrier discharge plasma process

Many factors affect the reaction characteristics of nitrogen oxides and SO2 in a dielectric barrier discharge reactor. Changing the SO2 initial concentration, oxygen content and water vapor content to study the reaction mechanism of NO and SO2 in the dielectric barrier discharge plasma process has been conducted. It was shown that the initial concentration of SO2 varied in a larger scope has little effect on the reaction characteristics of NO and SO2 in the N2/SO2/NO system. Increasing the water vapor content in the N2/NO/SO2/HO system would reduce the concentration of SO2 significantly in the flue gas, and the influence on SO2 is more obvious than on NO. Then, the influence of oxygen on the reaction characteristics of SO2 is not obvious, increasing the O2 concentration in the N2/NO/SO2/O2 system, the changed of SO2 concentration is less than 10%. But the adding of O2 affects the reaction of NO in the dielectric barrier discharge process obviously, it can promote the conversion of NO2 and other NOx, at the same time, the generation of NO was also being accelerated under certain conditions. By analyzing the reaction mechanism, it was found that the activated radicals produced in the dielectric barrier discharge process concerned SO2 reaction mainly OH, while related the reaction of NO, the O and N play an important role. Through the experiment and analysis, it was also deduced that there are oxidation and reduction reactions existed at the same time, also the generation and removal of NO occurred simultaneously.

Enhanced 4-FP removal with MnFe2O4 catalysts under dielectric barrier discharge plasma: Economical synthesis, catalytic performance and degradation mechanism

The dielectric barrier discharge plasma (DBDP) process has received extensive attention for the removal of organic contaminants from water. A novel microwave-assisted hydrothermal method was used to easily and rapidly synthesize MnFe2O4 catalysts. Based on the DBDP process, MnFe2O4 can enhance 4-fluorophenol (4-FP) abatement from 44.15% to 58.78% through the catalysis within 18 min. Then, the adjunction of O3 generated by discharge can further boost 4-FP degradation to 94.94%. After the whole optimization process is complete, the associated pseudo-first-order reaction kinetic constant and energy efficiency were enhanced from 0.0327 to 0.1536 min−1 and 2067.13 mg kW h−1 to 4444.75 mg kW h−1, respectively. With the help of the condition, blank and radical capture experiments, the catalytic performance caused by MnFe2O4 and O3 was attributed to the joint action of Fenton-like reactions, photocatalysis (ultraviolet, UV), photoassisted Fenton reactions and O3 catalysis. The overall downward trend of the possible intermediate toxicities indicated that the DBDP/MnFe2O4/O3 process can effectively remove and mineralize 4-FP without the generation of more toxic intermediates. In addition, during the 5 cycles, MnFe2O4 can maintain excellent recovery, efficiency and durability. In summary, the coupling of discharge plasma and MnFe2O4 sheds new light on catalysis for wastewater treatment.

Removal of 4-fluorophenol by dielectric barrier discharge plasma in three different structures: Comparison, optimization and mechanism

The performance comparison, optimization and mechanism of dielectric barrier discharge (DBD) plasma were conducted in three different structures through the abatement of 4-fluorophenol (4-FP) in water. Specifically, based on parallel plate structure (device 1), solution circulation (device 2) and coaxial cylindrical structure (device 3) increased the 4-FP removal rate at 30 min from 14.85% to 17.00% and 94.85%, respectively. The adjunction of O3 produced by DBD plasma through aeration on the basis of device 3 can further enhance 4-FP degradation to ~100% at the end of 18 min. Through the comparative analysis of the performance of the three devices under different experimental conditions, the 4-FP removal improvement was attributed to the combined enhancement of absolute contact area, mass transfer effect and discharge intensity. This study provides specific data references for the efficiency difference and related mechanism of different devices under DBD plasma process.

High-efficient removal of tetrabromobisphenol A in aqueous by dielectric barrier discharge: Performance and degradation pathways

Brominated flame retardants are widely used in fire protection area, but also bring great threats to ecological environment and human health. In this study, the potential of brominated flame retardant removal in wastewater by dielectric barrier discharge (DBD) plasma was investigated, with Tetrabromobisphenol A (TBBPA) as a model pollutant. The experimental results showed that TBBPA could be effectively removed by the DBD plasma oxidation. Almost all of the TBBPA in wastewater could be successfully decomposed within 15 min’s oxidation treatment, and the decomposition process fitted well with the pseudo-first-order kinetic model. Relatively lower TBBPA initial concentration favored its decomposition; and the effect of solution pH value on the oxidation process was negligible in the selected pH range. Electron paramagnetic resonance analysis showed that O2–, OH, and 1O2 were produced in the DBD plasma process; and O2– was the main reactive species for TBBPA decomposition, OH and 1O2 also played important roles. The molecular structure of TBBPA was effectively destroyed, and some byproducts including bisphenol A, and dibromophenol were generated. The possible decomposition pathways for TBBPA degradation were proposed. Furthermore, the acute toxicity and bioaccumulation factor of intermediate byproducts were alleviated via the analysis of Toxicity Estimation Software Tool.

Dimethyl phthalate contaminated soil remediation by dielectric barrier discharge: Performance and residual toxicity

Phthalates, as additives in the plastic production process, were able to enter the soil, causing huge risks to soil environment and human health. The potential of phthalates elimination in soil using dielectric barrier discharge (DBD) plasma was evaluated, with dimethyl phthalate (DMP) as a model pollutant. The experimental results demonstrated that DMP in soil could be decomposed by the DBD plasma oxidation. DMP concentration was reduced from 200 mg kg−1 to 87 mg kg−1 after 60 min’s DBD plasma oxidation, and its decomposition process fitted well with the first-order kinetics. Soil moisture was an important parameter affecting DMP decomposition in soil. Lower initial concentration was beneficial for DMP degradation. Analysis on types and action ranges of reactive oxygen species participating in DMP decomposition demonstrated that oxygen-containing species and electron played crucial roles. DMP molecular structure was destroyed in the DBD plasma processing, and phthalic acid monomethyl ester, phthalic acid, acetic acid, and oxalic acid were detected as the main intermediates. DBD plasma oxidation decreased the toxicity of DMP to seed germination and growth. Germination rate of wheat seed and activity of root system both increased, while free radical damage to cell membrane was significantly alleviated after 60 min’s DBD plasma oxidation.

Improvement of wheat seed vitality by dielectric barrier discharge plasma treatment.

Influences of discharge voltage on wheat seed vitality were investigated in a dielectric barrier discharge (DBD) plasma system at atmospheric pressure and temperature. Six different treatments were designed, and their discharge voltages were 0.0, 9.0, 11.0, 13.0, 15.0, and 17.0 kV, respectively. Fifty seeds were exposed to the DBD plasma atmosphere with an air flow rate of 1.5 L min-1 for 4 min in each treatment, and then the DBD plasma-treated seeds were prepared for germination in several Petri dishes. Each treatment was repeated three times. Germination indexes, growth indexes, surface topography, water uptake, permeability, and α-amylase activity were measured. DBD plasma treatment at appropriate energy levels had positive effects on wheat seed germination and seedling growth. The germination potential, germination index, and vigor index significantly increased by 31.4%, 13.9%, and 54.6% after DBD treatment at 11.0 kV, respectively, in comparison to the control. Shoot length, root length, dry weight, and fresh weight also significantly increased after the DBD plasma treatment. The seed coat was softened and cracks were observed, systematization of the protein was strengthened, and amount of free starch grain increased after the DBD plasma treatment. Water uptake, relative electroconductivity, soluble protein, and α-amylase activity of the wheat seed were also significantly improved after the DBD plasma treatment. Roles of active species and ultraviolet radiation generated in the DBD plasma process in wheat seed germination and seedling growth are proposed. Bioelectromagnetics. 39:120-131, 2018. © 2017 Wiley Periodicals, Inc.

악취물질인 유기산 제거를 위한 DBD 플라즈마 촉매 복합공정의 적용

Abstract Odor control technology include absorption, adsorption, incineration and biological treatments. But, most of processes have some problems such as secondary organic acids discharge at the final odor treatment facility. In order to solve the problems for effective treatment of organic acids in odor, it is necessary to develop a new type advanced odor control technology. Some of the technology are plasma only process and plasma hybrid process as key process of the advanced technology. In this study, odor removal performance was compared DBD(Dielectric Barrier Discharge)plasma process with PCHP(plasma catalysis hybrid process) by gaseous ammonia, formaldehyde and acetic acid. Plasma only process by acetic acid obtained higher treatment efficiency above 90%, and PCHP reached its efficiency up to 96%. Acetic acid is relatively easy pollutant to control its concentration other than sulfur and nitrogen odor compounds, because it has tendency to react with water quickly. To test of the performance of DBD plasma process by applied voltage, the tests were conducted to find the dependence of experimental conditions of the applied voltage at 13 kV and 15 kV separately. With an applied voltage at 15 kV, the treatment efficiency was achieved to more higher than 13 kV from 83% to 99% on ammonia, formaldehyde and acetic acid. It seems to the odor treatment efficiency depends on the applied voltage, temperature, humidity and chemical bonding of odors.

Visualization of In Situ Oxidation Process Between Plasma and Liquid Phase in Two Dielectric Barrier Discharge Plasma Reactors Using Planar Laser Induced Fluorescence Technique

Cold atmospheric plasma is considered to be a promising approach for decontamination purposes, e.g. dyeing water decoloration. In order to better understand the complex mechanism of the plasma physics coupled with the plasma chemistry involved in the interaction of the polluted water with the discharge plasma, a novel approach was proposed to study the in situ oxidation process between the plasma and liquid phase in two dielectric barrier discharge (DBD) plasma reactors with different bottom shape (concave vs. plane), by using the planar laser induced fluorescence technique to visualize the process dynamics. Rhodamine B was employed as the tracer dye, which was gradually decomposed by the combined effect of the chemically active radicals (OH, O, H2O2, etc.) as well as the intense UV radiation in the DBD plasma process. The results showed that the DBD plasma filaments induced certain fluctuation on the Rhodamine B liquid layer, which accordingly intensified the mass transfer to a large extent thus accelerated the oxidation process. The comparison of the measured concentration fields in the two DBD plasma reactors illustrated that the DBD reactor #1 with concave bottom showed higher oxidation efficiency than the DBD reactor #2 with plane bottom. Additionally, the experiments demonstrated that the oxidation efficiency in the DBD plasma water treatment was much better than that in the reactor with pure oxidation by ozone gas, which can be further improved by injecting the additional oxygen gas bubbles into the liquid phase in the plasma reactor.

Degradation of gaseous dioxin-like compounds with dielectric barrier discharges

Developing effective technologies to reduce dioxin emissions has become an important issue in the research and industrial fields. In this study, a dioxin-containing gas stream generating system was applied to evaluate the effectiveness of dielectric barrier discharge (DBD) plasma technology for the destruction of dioxin-like compounds. The results indicate that the destruction efficiencies of dioxin-like compounds achieved with DBD plasma strongly depend on the composition of the simulated gas stream. As the DBD plasma is operated with the simulated gas stream containing 20% water vapor, around 74% PCDDs and 89% PCDFs can be destroyed by DBD plasma. UV, electrons, and OH radicals are generated via the DBD plasma process and react with the dioxin-like compounds in the gas stream. Dechlorination via UV and electrons and decomposition via OH radicals occur at the same time and significantly increase the destruction efficiency of PCDD/Fs in the presence of oxygen and water vapor. Additionally, the total toxicity destruction of dioxin-like compounds with the input energy of 1 kJ increases from 1.47 to 3.06 ng-TEQ WHO as the water vapor is incorporated into the gas stream.

Development of dielectric barrier discharge plasma processing apparatus for mass spectrometry and thin film deposition

Cost effective and a very simple dielectric barrier discharge plasma processing apparatus for thin film deposition and mass spectroscopic analysis of organic gas mixture has been described. The interesting features of the apparatus are the construction of the dielectric electrodes made of aluminum oxide or alumina (Al(2)O(3)) and glass and the generation of high ignition voltage from the spark plug transformer taken from car. Metal capacitor is introduced in between ground and oscilloscope to measure the executing power during the discharge and the average electron density in the plasma region. The organic polymer films have been deposited on Si (100) substrate using several organic gas compositions. The experimental setup provides a unique drainage system from the reaction chamber controlled by a membrane pump to suck out and remove the poisonous gases or residuals (cyanogens, H-CN, CH(x)NH(2), etc.) which have been produced during the discharge of CH(4)N(2) mixture.

Temperature dependent evolution of the local electronic structure of atmospheric plasma treated carbon nanotubes: Near edge x-ray absorption fine structure study

Near edge x-ray absorption fine structure (NEXAFS) spectroscopy has been employed to obtain the temperature dependent evolution of the electronic structure of acid treated carbon nanotubes, which were further modified by dielectric barrier discharge plasma processing in an ammonia atmosphere. The NEXAFS studies were performed from room temperature up to 900°C. The presence of oxygen and nitrogen containing functional groups was observed in C K edge, N K edge, and O K edge NEXAFS spectra of the multiwalled carbon nanotubes. The N K edge spectra revealed three types of π* features, the source of which was decisively identified by their temperature dependent evolution. It was established that these features are attributed to pyridinelike, NO, and graphitelike structures, respectively. The O K edge indicated that both carbonyl (CO), π*(CO), and ether C–O–C, σ*(CO), functionalities were present. Upon heating in a vacuum to 900°C the π*(CO) resonances disappeared while the σ*(CO) resonances were still present confirming their higher thermal stability. Heating did not produce a significant change in the π* feature of the C K edge spectrum indicating that the tabular structure of the nanotubes is essentially preserved following the thermal decomposition of the functional groups on the nanotube surface.

Preparation of N-doped TiO2 photocatalyst by atmospheric pressure plasma process for VOCs decomposition under UV and visible light sources

The nitrogen doped (N-doped) titanium dioxide (TiO2) photocatalyst was prepared by the atmospheric-pressure plasma-enhanced nanoparticles synthesis (APPENS) process operated under normal temperature, i.e. the dielectric barrier discharge plasma process. The N2 carrier gas is dissociated in the AC powered nonthermal plasma environment and subsequently doped into the TiO2 photocatalyst that was capable of being induced by visible light sources. The APPENS process for producing N-doped TiO2 showed a higher film deposition rate in the range of 60–94 nm/min while consuming less power (<100 W) as compared to other plasma processes reported in literatures. And the photocatalytic activity of the N-doped TiO2 photocatalyst was higher than the commercial ST01 and P25 photocatalysts in terms of toluene removals in a continuous flow reactor. The XPS measurement data indicated that the active N doping states exhibited N 1s binding energies were centered at 400 and 402 eV instead of the TiN binding at 396 eV commonly observed in the literature. The light absorption in the visible light range for N-doped TiO2 was also confirmed by a clear red shift of the UV-visible spectra.

Dielectric barrier discharge (DBD) processing of PMMA surface: Optimization of operational parameters

This paper reported the effects that the key dielectric barrier discharge (DBD) operating parameters, discharge power, processing speed, processing duration and electrode configurations, have on producing wettability changes and on uniformity in the PMMA surface region. The results obtained indicate that DBD plasma processing is an effective method for the controlled surface modification of PMMA. Relatively short exposures to the atmospheric pressure discharge produces significant wettability changes at the PMMA surface, as indicted by pronounced reductions in the water contact angle measured. It was observed that the wettability of the resultant surface shows no significant differences in respect to sites in orientation parallel (L-direction) or perpendicular (T-direction) to the electrode long axis. However, the resultant surface shown higher standard deviation (S.D.) of contact angle in T-direction than that in L-direction. Analysis of the role of each of the operating parameters concerned shows that they have a selective effectiveness with respect to resultant surface modification in terms of uniformity of modification and wettability. The number of treatment cycles and the discharge power used were found to have the most significant effects on the homogeneity of the resultant PMMA surface changes in L- and T-orientation, respectively. The number of treatment cycles was found to be the dominant factor (at significance level of 0.05) in respect of water contact angle changes at the processed PMMA surface in both orientations. The driven metal electrodes (stainless steel or aluminium) were apparently superior to the driven dielectric electrode (ceramic or quartz) configurations. The grounded electrode in each case was a silicone rubber-covered aluminium plate. The nature and scale of the surface changes that originate from the various processing conditions employed have been considered so as to determine the optimum treatment conditions in respect of processing outcomes, properties and any orientation dependence. It was revealed that higher processing speeds and longer processing durations are key for uniformity along the electrode axial orientation within the test range employed, while lower processing speeds and short exposure durations are key considerations, in the corresponding perpendicular orientation. In general, longer processing durations (low processing speeds and a high number of treatment cycles) and higher plasma powers induced greater changes in the surface wettability of the PMMA, as demonstrated by the observed water contact angles. This behaviour is taken to indicate that different combinations of DBD operating parameters and electrodes produce discharge conditions that can result in different plasma chemical processes in respect of uniformity, treatment efficiency and orientation dependence. The comparison of the processing outcomes between PMMA and PET revealed that the operating parameters have the similar selective effectiveness on both polymers, indicating the obtained results may be used as a general guidance in controllable surface processing by DBD technique.

Uniformity analysis of dielectric barrier discharge (DBD) processed polyethylene terephthalate (PET) surface

A dielectric barrier discharge (DBD) plasma, operating in air at atmospheric pressure, has been used to induce changes in the surface properties of polyethylene terephthalate (PET) films. The effects that the key DBD operating parameters: discharge power, processing speed, processing duration, and electrode configurations, have on producing wettability changes in the PET surface region have been investigated. The approach taken involves the application of an Taguchi experimental design and robust analysis methodology. The various data sets obtained from these analyses have been used to studies the effect of the operating parameters on the surface uniformity and efficiency of the said treatment. In general, the results obtained indicate that DBD plasma processing is an effective method for the controlled surface modification of PET. Relatively short exposures to the atmospheric pressure discharge produces significant wettability changes at the polymer film surface, as indicted by pronounced reductions in the water contact angle measured. It was observed that the wettability of the resultant surface shows no significant differences in respect to orientation parallel (L-direction) or perpendicular (T-direction) to the electrode long axis. However, there was significant differences between the data obtained from these two orientations. Analysis of the role of each of the operating parameters concerned shows that they have a selective effectiveness with respect to resultant surface modification in terms of uniformity of modification and wettability. The number of treatment cycles and the electrode configuration used were found to have the most significant effects on the homogeneity of the resultant PET surface changes in L- and T-orientation, respectively. On the other hand, the applied power showed no significant role in this regard. The number of treatment cycles was found to be the dominant factor (at significance level of 0.05) in respect of water contact angle changes at the processed PET surface in both orientations. The driven metal electrodes (stainless steel or aluminium) were apparently superior to the driven dielectric electrode (ceramic or quartz) configurations. The grounded electrode in each case was a silicon rubber-covered aluminium plate (see later). The nature and scale of the surface changes that originate from the various processing conditions employed have been considered so as to determine the optimum treatment conditions in respect of processing outcomes, properties and any orientation dependence. Thus, it was revealed that higher processing speeds and longer processing durations are key for uniformity along the electrode axial orientation, while lower processing speeds and short exposure durations are key considerations, in the corresponding perpendicular orientation. In general, longer processing durations (low processing speeds and a high number of treatment cycles) and higher plasma powers induced greater changes in the surface wettability of the PET, as demonstrated by the observed water contact angles. This behaviour is taken to indicate that different combinations of DBD operating parameters and electrodes produce discharge conditions that can result in different plasma chemical processes in respect of uniformity, treatment efficiency and orientation dependence.

Statistical analysis of the effect of dielectric barrier discharge (DBD) operating parameters on the surface processing of poly(methylmethacrylate) film

A dielectric barrier discharge (DBD) plasma, operating in air at atmospheric pressure, has been used to induce changes in the surface properties of poly(methylmethacrylate) (PMMA) films. The relative effects that key DBD operating parameters, specifically: discharge power, electrode gap and duration of exposure have on producing chemical and microstructural changes in the polymer surface region have been investigated. The approach taken involves the application of an orthogonal array experimental design and statistical analysis methodology. The various data sets obtained from these analyses have been used to develop an equation in which induced changes in the surface properties of the DBD modified PMMA films are expressed in terms of the effectiveness of the various processing parameters in producing them. In general, the results obtained clearly indicate that DBD plasma processing is an effective method for the controlled surface modification of PMMA. Relatively short exposures to the atmospheric pressure discharge produces a significant amount of oxygen incorporation at the surface as indicted by a pronounced reduction in water contact angle. Analysis of the role of each of the operating parameters concerned shows that they do indeed have selective effectiveness for inducing resultant surface modification. Duration of exposure to the DBD plasma, expressed here as the number of treatment cycles at a given speed of specimen transit through the electrode gap, was found to play a major role in decreasing the surface wettability of PMMA. Conversely, the magnitude of the discharge power was not a significant parameter in this regard. In contrast, the value of the applied power played the dominant role in achieving the observed enrichment of the surface oxygen abundance, as measured by XPS, with the duration of exposure to the discharge playing a secondary role in this case. The nature and scale of the induced surface changes that originate from the various processing conditions employed have been further considered to determine if an interrelationship exists between them. Non-parametric data analysis indicates that no significant correlation exists between the observed changes in measured polymer wettability and the attendant surface oxygen enrichment. This result suggests that the increase in surface wettability caused by DBD processing, as manifested in a reduced contact angle, is not merely attributable to changes in the surface chemistry. As such, it is postulated that changes in the surface microstructure may also contribute to this change in surface wettability.