Most polymeric materials, particularly polyolefins and their derivatives, present a low surface energy which is the cause of their poor wettability and limits processes such as adhesive bonding, painting, or metalizing. Many methods have been developed and used to modify polymer surfaces for improved wetting, including mechanical treatments, wet-chemical treatments with strong acids or bases, and exposure to flames or corona discharge. In this paper the improvement of wetting properties of several polymeric materials widely used in the automotive industry, such as high density polyethylene (HDPE), low density polyethylene (LDPE), polypropylene (PP) and silicone, is studied by means of surface mechanical abrasion using sandpapers of different grain sizes (1000, 180 and 80). Measurements of the surface roughness are performed using a Hommel Tester T8000 device equipped with a diamond stylus, which provides data on the arithmetic average roughness R_a parameter and Abbott–Firestone curve. Variations in the polymers surface energy (SE) are estimated through contact angle measurements using five test liquids of different polarities. Both components of the SE, dispersion (σ^D) and polar (σ^P), as well as total (σ^T) at different conditions of treatment are analyzed using the Owens–Wendt–Rabel–Kaelble (OWRK) method. Morphological changes induced in the surface are analyzed by Scanning Electron Microscopy (SEM). Additionally, measurements of the static friction coefficient (μ_s) are carried out by the standard method ASTM D 1894-08. A slight enhancement in surface wettability is found with the mechanical abrasion pre-treatment from the SE increase. Finally, a higher value of μ_s is achieved for the abraded specimens as the normal force acting onto the system is increased.

In this work a DC plasma reactor was used for deposition of plasma polymerized coating from hexamethyldisiloxane-Ar (35/65%) mixture on polypropylene films. Surface energy parameter have been calculated using Owens-Wendt approaches with the sessile drop method are used to obtain the dispersive γ^D and polar γ^P component of surface free energy. The surface morphology of samples were investigated using scanning electron microscope. Also the chemical properties and wetability of prepared samples were tested using Fourier transform infrared spectroscopy and contact angle measurement, respectively.

Polyethylene terephthalate (PET) plates have been exposed to different nitrogen containing plasmas with the purpose of incorporating nitrogen functional groups on its surface. Results with a dielectric barrier discharge (DBD) at atmospheric pressure and a microwave discharge (MW) at reduced pressure and those using an atom source working under ultrahigh vacuum conditions have been compared for N₂ and mixtures Ar + NH₃ as plasma gases. The functional groups have been monitored by X-ray Photoemission Spectroscopy (XPS). Nondestructive oxygen and carbon depth profiles for the plasma treated and one month aged samples have been determined by means of the nondestructive Tougaard’s method of XPS background analysis. The surface topography of the treated samples has been examined by Atomic Force Microscopy (AFM), while the surface tension has been determined by measuring the static contact angles of water and iodomethane. It has been found that the DBD with a mixture of Ar+NH₃ is the most efficient treatment for nitrogen and amine group functionalization as determined by derivatization by reaction with chlorobenzaldehyde. It is also realized that the nitrogen functional groups do not contribute significantly to the observed increase in surface tension of plasma treated PET.

In this work the influence of the atmospheric pressure plasma treatment on the surface properties of polypropylene (PP) films was investigated. The film samples were modified by atmospheric pressure plasma treatment by diffuse coplanar surface barrier discharge (DCSBD) using ambient air as working gas. The contact angle measurement, the test pen method, atomic force microscopy (AFM) and attenuated total reflection technique Fourier transformed infrared spectroscopy (ATR-FTIR) were applied to analyze the changes of the surface of the polymer film. In all experiments, the contact angle of the treated polypropylene samples decreased and the surface energy of the samples increased in comparison with the plasma untreated samples. The proper surface energy for printing using solvent-based inks was detected by all the samples. There were not observed any significant changes in mechanical properties of the films after plasma treatment by measuring their tear parameters.

The objective of this paper was to understand the effects of plasma activation, and thus influence of the surface energy and chemistry changes on offset print quality. Pigment coated and surface sized papers were treated with corona and atmospheric plasma in pilot and laboratory scales. The surface energy and surface chemistry changes were evaluated by contact angle and X-ray photoelectron spectroscopy (XPS). Offset printing was performed in laboratory scale with an IGT unit with predampening and in a pilot scale sheet-fed offset printing press. In addition, the ink setting rate was measured using an ink on paper tack tester. Plasma activation increased the surface energy of the papers. Furthermore, the polarity of the paper surface increased due to formed polar oxygen containing molecular groups. Due to differences in treatment times laboratory scale plasma treatment formed mainly carboxyl and ester groups, whereas pilot scale treatment induced mainly alcohol, ethers, aldehydes and/or ketones on paper surfaces. Printing evaluation showed that plasma activation influences both ink and water absorption properties. According to print tack results plasma activation led to faster ink-setting. With hydrophobic surface-sized paper plasma activation influenced the ink transfer, print gloss and density by changing dampening water absorption properties. The difference in surface chemistry with laboratory scale plasma treated samples was also reflected in the print quality properties. SEM imaging showed that too intense plasma

Four types of contact angles (receding, most stable, advancing, and “static”) were measured by two independent laboratories for a large number of solid surfaces, spanning a large range of surface tensions. It is shown that the most stable contact angle, which is theoretically required for calculating the Young contact angle, is a practical, useful tool for wettability characterization of solid surfaces. In addition, it is shown that the experimentally measured most stable contact angle may not always be approximated by an average angle calculated from the advancing and receding contact angles. The “static"” CA is shown in many cases to be very different from the most stable one. The measured contact angles were used for calculating the surface tensions of the solid samples by five methods. Meaningful differences exist among the surface tensions calculated using four previously known methods (Owens-Wendt, Wu, acid-base, and equation of state). A recently developed, Gibbsian-based correlation between interfacial tensions and individual surface tensions was used to calculate the surface tensions of the solid surfaces from the most stable contact angle of water. This calculation yielded in most cases higher values than calculated with the other four methods. On the basis of some low surface energy samples, the higher values appear to be justified.

There are many current and emerging wetting and adhesion issues which require an additional surface processing to enhance interfacial surface properties. Materials which are non-polar, such as polymers, have low surface energy and therefore typically require surface treatment to promote wetting of inks and coating. One way of increasing surface energy and reactivity is to bombard a polymer surface with atmospheric plasma. When the ionized gas is discharged on the polymer, effects of ablation, crosslinking and activation are produced on its surface. In this paper we will analyse the role of plasma and its use in increasing the surface energy to achieve wettability and improve adhesion of polymeric surfaces.

Blown film processors, large and small, have limited resources in both capital and manpower to devote to optimizing their productivity. Yet avenues of improvement are open for even the most over-extended organization. And some of the most effective modifications cost little more than a small change in equipment orientation or procedures. A key aspect of optimizing a blown film layout is line footprint and determining how to minimize footprint and maximize output with each integral piece of equipment on the line. Multiple surface treatment systems are integral to every blown film line and can control product quality and line efficiencies. The objective of this work is to present best practices of blown film manufacturers ranging from multinationals to small privately owned operations relative to the most effective surface treatment system designs, their roll coverings, optimum power density settings, alternative treatment technologies, troubleshooting protocols, and model line layouts that optimize production output.

An atmospheric pressure oxygen and helium plasma was used to activate the surface of poly(methyl methacrylate) (PMMA). The plasma physics and chemistry was investigated by numerical modeling. It was shown that as the electron density of the plasma increased from 3 × 10¹⁰ to 1 × 10¹² cm⁻³, the concentration of O atoms and metastable oxygen molecules (¹Δ_g) in the afterglow increased from 6 × 10¹⁵ to 1 × 10¹⁷ cm⁻³. Exposing PMMA to the afterglow for times between 0 and 30 s led to a 35° ± 3° decrease in water contact angle, and a ten-fold increase in bond strength to several adhesives. X-ray photoelectron spectroscopy of the polymer revealed that after treatment, the surface carbon attributable to the methyl pendant groups decreased 5%, while that due to carboxyl acid groups increased 7%. The numerical modeling of the afterglow and experimental results indicate that oxygen atoms generated in the plasma oxidize the polymer chains.

In this work, an experimental investigation of fluorine gas (F₂) plasma treatment of polypropylene (PP) film reveals the evolution of PP fluorination. Surface analysis of fluorinated PP surfaces describes a surface modification process that is initially quite rapid but slows sharply as the fluorination progresses. The fluorination reaction occurs more rapidly at the PP film surface and evidence of a treatment gradient is seen in the ESCA sampling depth of 10 nm. The increasingly fluorinated surface becomes less reactive to the plasma chemistry and develops a fully fluorinated, cross-linked surface layer that eventually extends the full ESCA sampling depth.

A theory, based on the presence of an adsorbed film in the vicinity of the triple contact line, provides a molecular interpretation of intrinsic hysteresis during the measurement of static contact angles. Static contact angles are measured by placing a sessile drop on top of a flat solid surface. If the solid surface has not been previously in contact with a vapor phase saturated with the molecules of the liquid phase, the solid surface is free of adsorbed liquid molecules. In the absence of an adsorbed film, molecular forces configure an advancing contact angle larger than the static contact angle. After some time, due to an evaporation/adsorption process, the interface of the drop coexists with an adsorbed film of liquid molecules as part of the equilibrium configuration, denoted as the static contact angle. This equilibrium configuration is metastable because the droplet has a larger vapor pressure than the surrounding flat film. As the drop evaporates, the vapor/liquid interface contracts and the apparent contact line moves towards the center of the drop. During this process, the film left behind is thicker than the adsorbed film and molecular attraction results in a receding contact angle, smaller than the equilibrium contact angle.

An experimental investigation of the surface modification of polytetrafluoroethylene (PTFE) by an Ar and Ar/O₂ plasma created with an atmospheric-pressure radio frequency (r.f.) torch is presented here. The surfaces were analyzed by atomic force microscopy (AFM), XPS and water contact angle (WCA) to get an insight of the surface morphology and chemistry. An increase of roughness is observed with the Ar/O₂ plasma treatment. The WCA analysis shows that these surfaces are more hydrophobic than pristine PTFE; a contact angle of 135° was measured. When a PTFE surface is treated by Ar plasma, no roughening or significant change of the surface morphology and chemistry of PTFE was observed. The effects of the Ar and O₂ fluxes on the PTFE surface treatment were analyzed, as well as the effect of the power and treatment time. The plasma phase was also analyzed by optical emission spectroscopy, and some correlations with the treatment efficiency of the plasma are made. The chemistry on the surface is finally discussed and the competition between etching and re-deposition chemical reactions on the surface is proposed as a possible explanation of the results. Copyright © 2010 John Wiley & Sons, Ltd. https://analyticalsciencejournals.onlinelibrary.wiley.com/doi/10.1002/sia.3384

This paper aims to provide an exhaustive and comprehensive overview on flame treatment as a valuable technique for improving the surface properties of polymers, especially polyolefins. It starts with a brief historical excursus on the origin of flame treatment, and the second section deals with the major fundamentals of flame chemistry, with a special focus on the combustion process and mechanism of surface activation. The most important parameters influencing the extent of the oxidation reaction along with relevant practical notes are discussed in the third section. The concluding section outlines how the most significant features of flame treatment can be profitably used to improve the wettability and adhesion properties of polyolefin surfaces, especially from the perspective of developing novel composite solutions such as polyolefins/bio-based coating pairs intended for many different applications.

In this paper, a dielectric barrier discharge operating in nitrogen at atmospheric pressure has been used to improve the surface hydrophilic property of polypropylene (PP) non-woven fabric. The changes in the hydrophilic property of the modified PP samples are investigated by the contact angle measurements and the variation of water contact angle is obtained as a function of the energy density; micrographs of the PP before and after plasma treatment are observed by scanning electron microscopy (SEM) and the chemical composition of the PP surface before and after plasma treatment is also analyzed by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The results show that the surface hydrophilic property of the PP samples is greatly improved with plasma treatment for a few seconds, as evidenced by the fact that the contact angle of the treated PP samples significantly decreases after plasma treatment. The analysis of SEM shows that the surface roughness of the treated PP samples increases due to bonding and etching in plasma processing. The analyses of FTIR and the C1s peak in the high-resolution XPS indicate that oxygen-containing and nitrogen-containing polar functional groups are introduced into PP surface in plasma processing. It can be concluded that the surface hydrophilic property of the modified PP samples has been obviously improved due to the introduction of oxygen-containing and nitrogen-containing polar groups and the increase of the surface roughness on the PP surface.

Atmospheric pressure gas discharge plasmas, especially those operated at energy non-equilibrium and low gas temperatures, have recently become a subject of great interest for a wide variety of technologies including surface treatment and thin-film deposition. A driving force for these developments is the avoidance of expensive equipment required for competing vacuum-based plasma technologies. Although there are many applications where non-equilibrium (cold) plasma at atmospheric and higher pressures represents a substantial advantage, there are also a number of applications where low-pressure plasmas simply cannot be replaced due to specific properties and limitations of the atmospheric plasma and related equipment. In this critical review, the primary principles and characteristics of the cold atmospheric plasma and differences from vacuum-based plasma processes are described and discussed to provide a better understanding of the capabilities and limits of emerging atmospheric plasma technologies.

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.

Measurement of contact angles on super hydrophobic surfaces by conventional methods can produce ambiguous results. Experimental difficulties in constructing tangent lines, gravitational distortion or erroneous assumptions regarding the extent of spreading can lead to underestimation of contact angles. Three models were used to estimate drop shape and perceived contact angles on completely nonwetting super hydrophobic surfaces. One of the models employed the classic numerical solutions from Bashforth and Adams. Additionally, two approximate models were derived as part of this work. All three showed significant distortion of microliter-sized drops and similar trends in perceived contact angles. Liquid drops of several microliters are traditionally used in sessile contact angle measurements. Drops of this size are expected to and indeed undergo significant flattening on super hydrophobic surfaces, even if the wetting interactions are minimal. The distortion is more pronounced if the liquid has a lesser surface tension or greater density. For surfaces that are completely nonwetting, underestimation of contact angles can be tens of degrees. Our modeling efforts suggest that accurate contact angle measurements on super hydrophobic surfaces would require very small sessile drops, on the order of hundreds of picoliters.

The surface of polyimide (PI) films before/after plasma surface treatment using a remote-type modified dielectric barrier discharge was investigated to improve the adhesion between the PI substrate and the metal thin film. Among the plasma treatments of the PI substrate surface using various gas mixtures, the surface treated with the N-2/He/SF6/O-2 plasma showed the lowest contact angle value due to the high C=O bondings formed on the PI surface, while that treated with N-2/He/SF6 showed the highest contact angle value due to the high C-F-x chemical bondings on the PI surface. Specifically, when the O-2 gas flow was varied from 0 to 2.0 slm in the N-2(40 slm)/He(1 slm)/SF6(1.2 slm)/O-2 (x slm) gas composition, the lowest contact angle value of about 9.3 degrees was obtained at an O-2 gas flow of 0.9 slm. And it was due to the high content of oxygen radicals in the plasma, which leads to the formation of the highest C=O bondings on the PI surface. When the interfacial adhesion strength between the Ag film and PI substrate was measured after the treatment with N-2(40 slm)/He(1 slm)/SF6(1.2 slm)/O-2(0.9 slm) followed by the deposition of Ag, a peel strength of 111 gf/mm was observed, which is close to the adhesion strength between a metal and the PI treated by a low pressure plasma.

Surface layer of com. polylactide (PLA) was modified with corona discharges and studied for contact angle (H2O, CH2J2) and the geometric structure (at. force microscopy). The surface free energy was caled, by using Owens-Wendt equation. The treatment resulted in a decrease in the contact angle and an Increase in the surface free energy of the PLA film.

A basic and affordable experimental apparatus is described that measures the static contact angle of a liquid drop in contact with a solid. The image of the drop is made with a simple digital camera by taking a picture that is magnified by an optical lens. The profile of the drop is then processed with ImageJ free software. The ImageJ contact angle plugin detects the edge of the drop and fits its profile to a circle or an ellipse. The tangent to the triple line contact is calculated and drawn by the ImageJ software, thus, returning the value of the contact angle with acute precision on the measurement.