o optimize the effects of some discharge parameters on the surface wettability of polypropylene (PP) in atmospheric pressure dielectric barrier discharge, a surface modification model is created based on statistical theory and orthogonal experimental design method. Contact angle measurements, atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) are used to study the changes in the surface wettability, surface topology and chemical compositions of the samples. The results show that surface wettability has been improved due to roughness increasing and the introduction of oxygen-containing functional groups. High-resolution XPS of C1s peak deconvolution indicates that the types and contents of oxidized functional groups are different in different discharge conditions or plasma energy. Moreover, the model analysis reveals that it has better predictive ability, and different discharge parameters has selective influence on water contact angle and surface O atom percentage.

Air plasma treatment at low pressure was applied to modify the surface of a cellulose film with the aim to improve its wettability, dyeability and adhesion properties. The contact angles of different polar liquids on the treated films show an exponential decay with treatment time at a given power; the power–time reciprocity is followed. The calculated surface tension values exponentially rise to the same maximum value with a decrease of the polar fraction. ATR-FTIR analyses suggest that a cellulose dehydration takes place rather than a surface oxidation. The plasma treatment improves also the cellophane dyeability with typical dyes for cellulose fibers: the results of dye uptake follow the same trend as the surface energy. The bond strength of lap joints of cellophane with LLDPE film shows a strong improvement of the adhesion depending on the duration and the power of treatment. The whole results are consistent with ablation effects like those observed with air corona treatment rather than oxygen plasma.

To many people, plasma is a laboratory curiosity or limited in scale. Few know that plasma is a commercial process used daily in the treatment of fabrics, non-woven webs and film. This paper reviews applications and processes used to modify materials up to 60 in. in width in a roll-to-roll plasma system. The applications are quite varied. Sometimes, the process is simply to change the surface energy, while at other times, far more sophisticated processes, such as plasma-enhanced chemical vapor deposition (PECVD) processes, are employed to provide a chemical barrier or alter the tribological properties. As will be seen in this review presentation, plasma is extremely versatile and applicable to high-volume web applications.

Atmospheric pressure N₂ cold plasmas are generated with a torch-type generator using 60-Hz AC power. High flow rate N₂ gas is injected into the plasma generator and high voltage of about 2 kV is introduced into the power electrode through transformer. Discharge characteristics of N₂ cold plasma, such as current–voltage profile, gas temperature and radial species in plasma, are measured. As one possible application, the N₂ cold plasma is used to modify the surface of polymer, especially polypropylene, for adhesion improvement. Power dissipation in discharge has the maximum value at optimal power electrode position, z=3 mm, which lead to the generation of more energetic electrons capable of creating N₂* and N₂⁺ excited states in plasmas effectively. These excited species can induce high population of oxygen and nitrogen atoms on polymer surface through creation of polymer excited states. Maximum bonding strength about 10.5 MPa is obtained at optimal power electrode position.

In this paper, polyester (PET) and polypropylene (PP) films are modified by a dielectric barrier discharge in air, helium and argon at medium pressure (5.0 kPa). The plasma-modified surfaces are characterized by contact angle measurements and X-ray photoelectron spectroscopy (XPS) as a function of energy density. The polymer films, modified in air, helium and argon, show a remarkable increase in hydrophilicity due to the implantation of oxygen-containing groups, such as C–O, O–CO and CO. Atomic oxygen, OH radicals, UV photons and ions, present in the discharge, create radicals at the polymer surfaces, which are able to react with oxygen species, resulting in the formation of oxygen-containing functionalities on the polymer surfaces. It is shown that an air plasma is more efficient in implanting oxygen functionalities than an argon plasma, which is more efficient than a helium plasma. In an air plasma, most of the created radicals at the polymer surface will quickly react with an oxygen particle, resulting in an efficient implantation of oxygen functionalities. However, in an argon and helium plasma, the created radicals can react with an oxygen particle, but can also recombine with each other resulting in the formation of an oxidized cross-linked structure. This cross-linking process will inhibit the implantation of oxygen, resulting in a lower efficiency. In argon plasma, more ions are present to create radicals, therefore, more radicals are able to react with oxygen species. This can explain the higher efficiency of an argon plasma compared to a helium plasma.

Parallel plates dielectric barrier discharge (DBD) at atmospheric pressure has been investigated to modify and functionalize the surface of different polymer substrates, e.g. polyolefins, poly(ethylene terephtalate), polyamide, in order to enhance their hydrophilic properties. Surface properties have been altered to meet the requirements of specific applications by introducing the appropriate functionalities through the use of either acetic acid or ethyl acetate. The coatings have been characterized through wettability measurements, labeling coupled with X-Ray photoelectron spectroscopy, and IR spectroscopy.

In the present work three common polyolefins: high density polyethylene (HDPE), low density polyethylene (LDPE) and polypropylene (PP) have been treated with an atmospheric pressure air plasma torch (APPT) in order to improve their wettability properties. The variations in surface energy (γ_s), as well as the durability of the treatment are determined by means of contact angle measurements for different aging times after plasma exposure (up to 270 days) using five test liquids which cover a wide range of polarities. The introduction of new polar moieties (carbonyl, amine or hydroxyl) is confirmed by Fourier transform infrared spectroscopy in attenuated total multiple reflection mode (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS). Furthermore, scanning electron microscopy (SEM) provides information on the morphological changes and variation on surface roughness, revealing that smoother, lamellar and semispheric micrometric structures are created on the LDPE, HDPE and PP surfaces, respectively. Results show that APPT treatment enhances both the total and polar components of the γ_s under study, with an unprecedent stability (> 8 months) in time.

The peel strength of aluminium to polypropylene and poly(tetrafluoroethylene) was determined in dependence on the type and the concentration of functional groups on the polymer surface. For this purpose the polymer surface was equipped with monotype functional groups. The first method to produce monotype functionalized surfaces was an introduction of O functional groups using an oxygen plasma treatment and converting these groups to OH groups applying a wet chemical reduction. In result of this two-step treatment the hydroxyl group concentration at the polymer surface could be increased from 3–4 to 10–14 OH groups/100 C atoms. The second method consists in the deposition of a 150 nm adhesion-promoting layer of plasmapolymers or copolymers onto the polymer surface using the pulsed plasma technique. For that purpose functional groups carrying monomers as allyl alcohol, allylamine and acrylic acid were used. Applying the plasma-initiated copolymerization and using neutral “monomers” like ethylene or butadiene the concentration of the functional groups was varied.

A correlation of peel strength with the ability of forming chemical interactions between Al atoms and functional groups was found: COOH > OH >> NH₂ > H(CH₂–CH₂).

In this work particular attention has been paid to the aging behavior of biaxially oriented polypropylene (BOPP) film surfaces modified with the acrylic acid (AAc) corona discharge treatment previously reported. Three different corona energies of 15.3, 38.2 and 76.4 kJ/m² were studied. The surface properties of treated films during 90 days of aging were compared with those of normal air-corona treated films prepared with the same corona energies. The surface chemical compositions of aged films were analyzed by curve-fitting of the ATR-FTIR spectra. The wettabilities of all aged films were monitored by water contact angle and surface free energy measurements. The change of surface topology of air- and AAc-corona treated films was investigated at 1 day, 7 days and 90 days of aging using the technique. In addition, the surface adhesions of aged films were determined with the T-peeling test. The results showed that the amount of polar functional groups on the surface of aged films had changed. However, the aged films of the AAc-corona treated films still showed greater wettability than did the air-corona treated films and could retain high surface hydrophilicity for more than 90 days of aging under ambient condition. The surface topology of both types of aged films changed after aging from a globular structure to a flatter surface, due to mobility of the deposited polymer layer. The AAc-corona treated films showed rougher surfaces due to the influence of poly(acrylic acid) deposition and they could retain the improved surface wettability despite the change in surface topography. The adhesion peel forces of aged films decreased slightly due to the topological changes. A mechanism for the change in surface topography and in chemical functionality of each type of aged film is proposed.

In this work, air dielectric barrier discharge (DBD) operating at the line frequency (60 Hz) or at frequency of 17 kHz was used to improve the wetting properties of polypropylene (PP). The changes in the surface hydrophilicity were investigated by contact angle measurements. The plasma-induced chemical modifications of PP surface were studied by X-ray photoelectron spectroscopy (XPS) and Fourier-transformed infrared spectroscopy (FTIR). The polymer surface morphology and roughness before and after the DBD treatment were analyzed by atomic force microscopy (AFM). To compare the plasma treatment effect at different frequencies the variation of the contact angle is presented as a function of the deposited energy density. The results show that both DBD treatments leaded to formation of water-soluble low molecular weight oxidized material (LMWOM), which agglomerated into small mounts on the surface producing a complex globular structure. However, the 60 Hz DBD process produced higher amount of LMWOM on the PP surface comparing to the 17 kHz plasma treatment with the same energy dose. The hydrophilic LMWOM is weakly bounded to the surface and can be easily removed by polar solvents. After washing the DBD-treated samples in de-ionized water their surface roughness and oxygen content were reduced and the PP partially recovered its original wetting characteristics. This suggested that oxidation also occurred at deeper and more permanent levels of the PP samples. Comparing both DBD processes the 17 kHz treatment was found to be more efficient in introducing oxygen moieties on the surface and also in improving the PP wetting properties.

After the atmospheric pressure plasma treatment of polypropylene (PP) film surface, we measured the contact angle of the surface by using polar solvent (water) and nonpolar solvent (diiodomethane). We also calculated the surface free energy of PP film by using the measured values of contact angles. And then we analyzed the change of the contact angle and surface free energy with respect to the conditions of atmospheric pressure plasma treatment. Upon each condition of atmospheric pressure plasma treatment, the contact angle and surface free energy showed optimum value or leveled off. Through AFM analysis, we also observed the change of surface morphology and roughness before and after plasma treatment. The surface roughness of PP film showed the highest value when the plasma treatment time was 90 s. Finally, we analyzed the change of chemical compositions on the PP film surface through XPS. As the result of analysis, we observed that polar functional groups, such as –CO, –C=O, and –COO were introduced on the PP film surface after atmospheric pressure plasma treatment.

In this work, the surface modifications of various polymer films due to helium–oxygen dielectric barrier discharge (DBD) exposure operating under atmospheric pressure are reported. The polymer films studied include ultra high molecular weight polyethylene, polyamide, polytetrafluoroethylene and polyimide. Experimental results reveal increased hydrophilicity and surface energy of the plasma exposed polymers. This is attributed to the presence of oxygen containing groups grafted onto the surface during plasma treatment, as confirmed by X-ray photoelectron spectroscopy (XPS) analysis. Scanning electron microscopy (SEM) data show the appearance of micro depressions, the size of which depends on the chemical structure and the treatment time, suggesting that mild etching occurs in a predicted fashion. Most importantly, this uniform modification occurs within a few seconds of exposure, time comparable to continuous on-line industrial processing.

Without any preprocessing, polyester fabric has a lower ability to hold on water and inks due to the smooth morphology and chemistry property of polyester fibers. Therefore, patterns directly printed with pigment inks have poor color yields and bleed easily. Plasma surface treatment of polyester fabrics was carried out in composite atmosphere with air and 10% Ar under different experimental conditions. After plasma treatment the samples were printed with pigment inks. The results show that surface-modified polyester fabrics exhibited enhanced color yields and excellent pattern sharpness. SEM and XPS analyses indicated that this improved color performance was mainly contributed by not only the etching effect but also oxygen-containing polar groups induced onto fiber surfaces through plasma treatment. Thereby the surface modification of polyester fabrics using air/Ar plasma offers a potential way to fabric pretreatment for pigment inkjet printing with the advantages of environmental friendly and energy saving over traditional pretreatment methods.

In this work, polyamide (Nylon 6) fibers and films were treated under atmospheric pressure glow discharges (APGD) and the effects on the morphology and chemistry of the material were studied. The fibers were plasma treated with N ₂ , C ₂ H ₂ in He for (0.6–9.6) s at a frequency of 90 kHz, leading to the functionalization of the surface through the addition of new reactive chemical groups such as –COOH and –OH and changing the energy, chemical composition and wettability of the surface.Surface characteristics were examined via contact angle measurements, XPS, and SEM. Wettability tests revealed the improvement of the hydrophilic character of the surface as the water contact angle measured after the plasma treatments significantly decreased. The corresponding changes of the total surface energy were evaluated with a dynamic contact angle analysis system revealing a significant increase due to the exposure that can be mainly attributed to the increase of its polar component. Preliminary XPS results show a significant increase in oxygen content with the addition of carboxylic and hydroxylic groups and a decrease in the carbon content of the surface. Most importantly, the plasma modified nylon fibers and films exhibit a stable wetting behavior, even for weeks after being treated, suggesting that it is a promising technique to minimize aging phenomena.

In this work, the acrylic acid (AAc)-corona discharge was carried out on biaxially oriented polypropylene (BOPP) films by introducing AAc vapor into the corona region of a normal corona treater. Three different corona energies of 15.3, 38.2 and 76.4 kJ/m² were studied. Surface properties of treated films were compared with those of air-corona treated films prepared with the same corona energies. The change in chemical composition on the film surface was characterized by curve-fitting of the ATR-FTIR spectra. The wettability of treated films, before and after aging in different environments, was observed by water contact angle and surface free energy. The surface morphology of air- and AAc-corona treated films was investigated using SEM and AFM techniques. Adhesion of the treated films to some other substrate was determined with the T-peeling test. It was found that the hydrophilicity of all treated films increased with increasing corona energy. AAc-corona treated films showed greater wettability than did the air-corona treated films and could retain the surface hydrophilicity for more than 90 days of aging under ambient conditions. The surface morphology of BOPP films changed after corona treatment into a globular structure. The AAc-corona treated films showed rougher surfaces due to surface oxidation and polymer formation, whereas, air-corona treated films displayed a similar structure but of smaller size due to the formation of low molecular weight oxidized materials (LMWOM) arising from the degradation of BOPP films. AAc-corona treated films showed greater peel strength than did the air-corona treated films.

Plasma treatment is often used to modify the surface properties of polymer films, since it offers numerous advantages over the conventional surface modification techniques. However, plasma-treated polymer films have a tendency to revert back to the untreated state (aging process). Therefore, the stability of plasma-induced changes on polymer surfaces over a desired period of time is a very important issue. The objective of this study is to examine the effect of storage conditions (relative humidity and temperature) on the aging behavior in air of plasma-treated low density polyethylene (LDPE) films. Plasma treatment is performed using a dielectric barrier discharge (DBD) operating in different argon/water vapor mixtures at medium pressure (5.0 kPa). Results show that the aging process can be suppressed by storing the plasma-modified LDPE films at low temperature and by decreasing the relative humidity of the surrounding air. Adding water vapor in the plasma discharge has a positive influence on the aging process: lower plateau WCA values are found for plasmas containing a higher water vapor concentration and it takes a longer time to reach these plateau values. In this paper, it is also shown that storage first at a lower temperature and then aging at a higher temperature is not able to slow down the aging effect.

Polymers/metal laminates are often used to improve physical and mechanical properties, especially those required in building applications. A flat aluminum composite panel (ACP) consisted mainly of two thin metal sheets usually made of aluminum (Al) and a non-metal core, such as polyethylene (PE). The lack of adhesion associated with the low wettability of PE is a serious problem. An eco-friendly, dry, non-destructive corona treatment technique can be applied to solve this problem. In this work, the use of a corona treatment to enhance the adhesion properties of linear low-density polyethylene (LLDPE) was studied. The changes in surface and adhesion properties were thoroughly analyzed using various analytical techniques and methods to obtain the optimal parameters for corona discharge using contact angle measurements, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and atomic force microscopy (AFM). AFM force adhesion measurements were used to analyze the effect of the corona treatment on the adhesion enhancement of LLDPE, and the peel tests confirmed a significant increase in peel resistance in the LLDPE/Al laminate. A synergy effect from using the corona treatment in combination with an ethylene acrylic acid dispersion primer was observed.

A Nylon-6,6 film has been treated using an atmospheric pressure air dielectric barrier discharge (DBD). The resultant surface modifications were studied using X-ray photoelectron spectroscopy (XPS), contact angle measurement and secondary ion mass spectrometry (SIMS). The surface oxidation arising in the DBD discharge was found to arise in two stages: in the first stage, the creation of the carbon sites singly bonded to oxygen is dominant, the second stage leads to further conversion of such lightly oxidised carbons to those more heavily oxidised. The marked increase found in the hydrophilicity of the surface post-treatment is in the main believed to be associated with the earlier outcome. Partial recovery of the surface contact angle values is found for the treated samples following extended storage in ambient air. The final contact angle obtained for the treated samples was ∼50°, still reduced significantly from that of 83.5° for the untreated material.

A uniform and smooth transfer of stresses across the polymer matrix/fiber interface is enhanced when adhesion between the matrix and fiber surface is optimized. In the absence of covalent bonds matching the Hansen solubility (cohesion) parameters (HSP) of the fiber surface with the HSP of a matrix polymer assures maximum physical adhesion to transfer loads uniformly. Plasma treatment of ultra-high-molecular-weight (UHMWPE) fibers is shown to significantly increase the amount of oxygen in the surface. There are two distinct types of surfaces in both the plasma treated and the untreated UHMWPE fibers. One type is typical of polyethylene (PE) polymers while the other is characteristic of the oxygenated surface at much higher values of HSP. The oxygenated surface of the plasma treated fibers has the HSP δ_D, δ_P, and δ_H equal to 16.5, 15.3, and 8.2, compared to the pure PE surface with HSP at 18.0, 1.2, and 1.4, all in MPa^½. The dispersion parameter has been lowered somewhat by the plasma treatment, while the polar and parameters are much higher. The HSP methodology predicts enhanced adhesion is possible by skillful use of anhydride and nitrile functional groups in matrix or tie polymers to promote compatibility in the system.