Through the controlled use of selected pretreatments, significant improvements to adhesion levels can be realised. Pretreatment options include chemical activation, corona discharge treatment, plasma-induced modifications and grafting. Using such methods, adhesion levels that render substrates fit for the intended purpose can be achieved. Such improvements can be realised without compromising the inherent properties of the materials being treated. Various approaches are considered as is the nature of the adhesion process. Several reasonably recent examples of the use of surface activation are presented.

The interactions between CO₂ plasma, less degrading than O₂ plasma, and polymeric surfaces are studied. CO₂ discharge and the relationships between the density of plasma reactive species are analyzed by optical emission spectroscopy and mass spectrometry. The optical emission spectrum was identified and five principal systems of carbon monoxide were assigned: the 4th and 3rd positive systems, Angstrom and 3A systems. Other systems dealing with ionized species CO⁺ ₂ and CO⁺ were also found. Mass spectrometry showed that the carbon monoxide and atomic oxygen were created through CO₂ dissociation by electronic impact. The detected molecular oxygen coming from the atomic oxygen recombination was associated with the power. The study of plasma/polymer interface showed the consumption of ionized species, the appearance of atomic hydrogen due to methyl groups transformation into exomethylene groups onto the polypropylene surface, and a degradation mechanism dependent on atomic oxygen density in the plasma phase.

Corona discharge treatment (CDT) is a surface modification technique commonly used to treat plastic films prior to adhesive bonding, printing with inks, lamination to other films and other coating applications. In this study, the treatment conditions are, in energy terms, representative of those used in industrial and laboratory coating applications.

The physicochemistry of the surface of untreated and corona-discharge-treated biaxially oriented polypropylene (BOPP) film was investigated using a number of complementary surface analytical techniques: contact angle analysis; x-ray photoelectron spectroscopy (XPS); atomic force microscopy (AFM). This report describes the surface energetics, chemical functionality and morphology of polypropylene film before and after CDT. Both AFM and XPS were utilized, along with washing experiments, to investigate the presence of a weak boundary layer.

The surface energy was found, as expected, to increase with increasing energy of the corona. The functional groups incorporated onto the surface have been identified as hydroxyl [COH], peroxy [COO], carbonyl [CO], ester [COCO], carboxylic acid [HOCO] and carbonate [OC(O)O]. These groups are present in varying relative concentrations, depending on the energy of the corona utilized.

The morphology of the film changed after CDT. Initially, a fibrillar crystalline structure was observed, whereas after CDT a globular morphology became apparent. These globular features were attributed to low-molecular-weight oxidized material (LMWOM) created by CDT. The roughness of the film was not found to increase under the corona conditions employed.

Formation of LMWOM was found to be independent of treatment energy. However, two mechanisms have been suggested for its formation, dependent on the energy of treatment: below a threshold energy of ∼4 kJ m⁻², oxidation and scission of the inherent low-molecular-weight boundary layer present on polyolefin films is the dominant means for the formation of LMWOM; above 4 kJ m⁻², oxidation and scission of the polymer backbone is the main process.

This work provides a comprehensive reference around CDT of polypropylene film for industrial applications, while also informing how the optimal level of treatment can be determined. In the case of adhesion of silicones, it would be expected that optimal adhesion would be obtained where the maximum amount of oxygen incorporated was in a water-insoluble form. Copyright © 2002 John Wiley & Sons, Ltd.
https://analyticalsciencejournals.onlinelibrary.wiley.com/doi/abs/10.1002/sia.1217

Modification of the surface properties of a polypropylene (PP) film using an air dielectric barrier discharge has been studied using atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and contact angle measurement. The atmospheric pressure air discharge is found to modify the PP surface in both morphology and composition, as expressed in the following outcomes: the spherulitic features of the surface of the pristine PP film change into randomly-shaped surface protrusions, with the surface roughness increasing as the processing time is extended; heavily oxidized carbon species are found on the plasma-processed surface and the contact angle is also reduced dramatically from 93.7° for the untreated surface to 53.8° post-treatment. After long-term storage in ambient air, the much lowered surface contact angle of the processed PP film is found to in part recover. Effective plasma-induced chemical etching appears to equilibrate after 25% of the surface carbon is oxidized. The CH₃ functionalities in the PP are believed to be oxidized preferentially by the air discharge plasma.

Oxygen plasma treatment was used to change the hydrophobic polysulfone ultrafiltration membrane to the hydrophilic membrane. The contact angle of water decreased with increasing the oxygen plasma treated time of polysulfone membrane and was saturated with 20 s of oxygen plasma treated time. Functional groups introduced by oxygen plasma treatment were examined using X-ray photoelectron spectroscopy (XPS) and zeta potential of oxygen plasma treated polysulfone membrane was measured using electrophoretic light scattering (ELS) spectrometer. O/C ratio increased from 33 to 50% and isoelectric point (IEP) of membrane surface increased from pH 3 to 4.5. For oxygen plasma treated polysulfone membrane, the flow rates of pure water and gelatin solution increased at all pH range and plasma treated membranes showed less fouling at membrane surface. The mechanisms of reduced fouling and improved cleaning efficiency of oxygen plasma treated polysulfone membrane were also studied.

The purpose of this work was to investigate the influence of a low-pressure, low-frequency ammonia plasma treatment on the wettability of polypropylene (PP) thin films and its consequences on the adhesion properties of such treated films to thermally evaporated aluminium coatings. The wettability was determined by contact angle measurements while the adherence was evaluated by a U-Peel test especially suited to thin flexible substrates with thin metallic layers. Furthermore, an image processing system was used to measure the percentage of the peeled-off metal. Measurements carried out on NH₃ plasma-treated PP films revealed a sharp increase in the wettability and in the adhesion properties for treatment times as short as 1 s. Electron-induced X-ray emission spectroscopy and X-ray photoelectron spectroscopy showed the formation of new chemical bonds at Al/NH₃ plasma-treated PP film interfaces. The new types of bonds have been characterized by well-defined chemical states (C–NH_x, CO–NH, Al–N–C) in the N 1s (and C 1s) spectra. The interfacial complexes Al–N–C and Al–N–CO are formed by the NH₃ plasma treatment which creates at the PP surface active sites (N(C–NH_x) and N(CO–NH)) which react with the evaporated aluminium atoms. These interfacial bonds play an important role in the enhancement of the metal/polymer adhesion.

The surface of polyether ether ketone (PEEK) films was modified using plasma treatment, corona, or surface etching to improve their adhesion with regard to glued copper foils and copper layers generated by physical vapor deposition. After the pretreatments, surface chemical analysis was performed by X-ray photoelectron spectroscopy (XPS). The wetting behavior was qualitatively investigated by contact angle measurements. Surface topography was monitored by laser scanning microscopy (LSM). After coating, the adhesion strength of the copper layer was measured by a peel force test. Plasma treatment, corona discharge, or etching lead to a significant increase in adhesion. This increase is caused by a change in surface topography as well as by the incorporation of polar groups into the surface.

High density polyethylene sheets 2 mm thick were flame treated to modify the surface properties. Sheets treated using a flame with air to gas (methane) ratio ∼ 10:1 at different distances between the inner cone tip of the flame and the polymer surface were investigated. Grafting of selected monomers as maleic anhydride, acrylamide and glycidyl methacrylate was attempted by flame treatment of sheets covered with a monomer layer. Good grafting results were obtained with acrylamide and maleic anhydride. The surface temperature-time dependence during the flame treatment was measured with a high resolution thermocouple. Scanning Electron Microscopy (SEM) allowed evidencing a modified thickness of about 120 μ. The chemical surface modification was studied by X ray Photoelectron Spectroscopy (XPS) and Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFT). The hydroxyl, carbonyl and carboxyl content was measured after derivatization with reagents containing an elemental tag to facilitate XPS analysis of surface functional groups. In comparison to the untreated polyethylene, wetting tension and contact angle of the flamed materials showed a strong variation. This variation was almost independent of the distance between the flame and the polymer surface. Adhesion between treated polyethylene and a polyurethane adhesive was determined using T-peel test measurements. High adhesion levels were found with flame treated polyethylene at 5 mm distance. XPS results indicate that when adhesion is high, the hydroxyl is in excess compared to the other measured functions, i.e. carbonyl and carboxyl species.

Electrons produced in atmospheric pressure corona discharges are used for a variety of beneficial purposes including the destruction of gaseous contaminants, and surface treatment. In other applications, such as electrostatic precipitators and photocopiers, unintended reactions such as ozone production and deposition of silicon dioxide are detrimental. In both situations, a kinetic description of the electron distribution in the corona plasma is required to quantify the chemical processes. In this paper, the electron density and energy distributions are numerically determined for a positive dc corona discharge along a wire. The electron density distribution is obtained from the 1-D charge carrier continuity equations and Maxwell's equation. The non-Maxwellian electron kinetic energy distribution is determined from the Boltzmann equation. The effects of wire size (10-1000 μm) and current density (0.1–100 μA/cm of wire) on number density and energy distribution of electrons are presented. With increasing current, the electron density increases, but the thickness of the plasma and the electron energy distribution are not affected. Smaller electrodes produce thinner plasmas and fewer, but more energetic electrons, than larger wires. The effect of electrode size on the electron-impact chemical reaction rate is illustrated by the rates of dissociation and ionization of oxygen and nitrogen.

The common measurement of the contact angle is performed in conditions not corresponding to true equilibrium states and gives non-equilibrium values, the advancing and receding contact angles. To solve this problem, a very simple experimental device, based on the Wilhelmy experiment, is proposed in the present paper. It is able to transfer mechanical energy to the three-phase system in a controlled way through a simple loudspeaker; the analysis of some common surfaces is made through this method showing as a new stable minimum of the surface free energy can be attained, independent on the initial conditions and corresponding to a value of the contact angle intermediate between the advancing and receding ones. A comparison is developed with literature results on heterogeneous and rough surfaces, some ‘first-order’-approximation equations proposed in the literature are examined and compared with the new results. A simple but useful theoretical treatment is also compared with the experimental results to allow a more detailed, although qualitative-level, analysis. An important consequence with respect to the calculations of solid surface free energies is indicated.

A treater system includes a conductive roller electrode that supports a moving web that is to be treated. One or more active electrode assemblies mounted to support headers have a pair of active electrodes that are positioned to treat one surface of the web as the web passes over the roller electrode. Air or a gas/gas mixture can be selectively piped to a chamber adjacent the active electrodes and diffused along the length of the discharge surfaces to allow the treater to operate in three distinct modes: corona, chemical corona and atmospheric plasma. The active electrodes are cooled by passing air into and through tubular bodies of the active electrodes.

The acid-base theory of surfaces, as proposed by van Oss, Chaudhury and Good, comнmonly suffers from a series of problems (apparent too high basicity of surfaces, results depending on the choice of liquid triplets, etc.). These problems can be solved if and only if a great attention is paid to the mathematical properties of the equations on which the theory is based. Two of these problems are analysed in detail in the present paper: the choice of the acid-base scale using water as a reference, and the use of the 'equilibrium' contact angle instead of the adнvancing contact angle.

The effects of 1, 2, 3, 4-tetrahydronaphthalene (tetralin) solvent and ammonia plasma treatments on surface characteristics and adhesion of ultra-high-strength polyethylene (UHSPE) fiнbers to epoxy resin were studied. Spectra™ 1000 (UHSPE) fibers were treated with either tetralin solvent or in combination with ammonia plasma, under various conditions. The changes in the fiber surface topography were characterized using scanning electron microscopy (SEM). Dynamic wetнtability measurements were made using the Wilhelmy technique. The fiber/epoxy resin interfacial shear strength (IFSS) was evaluated by the single fiber pull-out test. The fiber surfaces after the pull-out test were characterized by SEM. The SEM photomicrographs and wettability data showed that the surface roughness of the fibers increased after the tetralin solvent treatment and the fiber surface became more polar after the ammonia plasma treatment. The IFSS results indicated that combined tetralin and ammonia plasma treatments resulted in significant improvement in the adheнsion strength of UHSPE fibers with epoxy resin. This is attributed to the chemical, mechanical and topographical changes of the fibers resulting from the treatments.

The two methods used for contact angle determination in this study are based on liquid porosimetry (LP). The LP measures volumes of different size pores when the liquid advances and then when the liquid drains from a porous structure. The LP provides pore volume distribution (PVD) and numerous other pore structure characteristics. The experimental data for this study were obtained with an automated TRI/Autoporosimeterо. The first method for contact angle measurement uses two liquids. One liquid has a known contact angle with the sample solid and the second is the liquid of interest. A comparison of the capillary pressures in different size pores for the two liquids provides the contact angle data for different size pores in the sample.

Recently receding contact angles have increasingly attracted attention in studies of wetting phenomena. The difference between the advancing and receding contact angles of the same liqнid on the same solid surface is termed 'contact angle hysteresis'. The hysteresis is usually ascribed to the solid surface roughness and/or its chemical heterogeneity. These possible mechanisms of the hysteresis appearance do not exclude another interpretation of the receding contact angle origin (E. Chibowski et al., in: Surfactants in Solution, A.K. Chattopadhyay and K.L. Mittal (Eds.), pp. 31-53, Marcel Dekker, 1996). In this approach, the presence of liquid film behind the drop is considered to be the cause for the ovbserved hysteresis, except, of course, for cases of rough and/or macro-chemically heterogeneous solid surfaces. In this paper, a new approach is presented and then verified using experimental advancing and receding contact angles taken from the literature. This approach allows an evaluation of the total surface free energy of a solid if the advancing and receding contact angles for a probe liquid are known. It does not require values of the solid surface free energy components for estimation of the value of total surface free energy.

The objective of this study was to determine the surface free energy components of celнlulose ethers films. The surface free energy parameters were calculated from the contact angles of sessile drops of apolar and polar liquids on cellulose ether films cast on glass slides using the Lifshitz-van der Waals/acid-base (LW/AB) approach according to the method of van Oss, Chaudhury and Good (Chem. Rev. 88, 927-941, 1988). The cellulose ethers studied were hydroxypropyl methylcellulose (HPMC), methylcellulose (MC), hydroxypropylcellulose (HPC) and hydroxyethylcellulose (HEC) and ethylcellulose (EC). The total surface free energy of these cellulose ethers ranged from 29-50 mJ/m2. The overall trend in the values of the thermodynamic terms derived from the surface free energy parameters as indicators of hydrophilicity was in good agreement with the relaнtive bulk solubility and hydration behavior of the polymers. Calculation of the work of adhesion with substrates of varying surface free energy parameters indicated that acid-base interactions made a major contribution to the total work of adhesion between cellulose ethers and bipolar surfaces. Changes in surface free energy as a result of the presence of plasticizer or change in solvent compoнsition for EC films were resolvable with the LW/AB approach. Although no direct correlation could be established between the surface free energy parameters and the type of substitution on the celluнlose backbone for the cellulose ethers, the values of the terms derived from the LW/AB approach were consistent with those of cellulose. The LW/AB approach provides a reasonably consistent method for estimating the surface properties of cellulose ethers and the resulting surface free energy parameters are shown to relate to the interfacial properties of the polymers.

The behavior of a silicone sealant during its application, from its extrusion from the carнtridge to the completion of the joint, has been identified as a key feature for professional applicators. This feature called “ease of use’* is very complex and includes many different criteria such as the ease of extrusion and joint smoothing, the aesthetic of surface finish, the stringing, and the action of a tooling aid (aqueous solution of surfactant) during the smoothing operation. Several of these criteнria seem directly linked to surface properties of the uncured sealant. In an attempt to translate these subjective properties into quantitative measurements in the laboratory and to understand the underнlying parameters that can be used to control these features, the surface energy of uncured sealants was measured using the solid-liquid contact angle technique. The surface energy data were further correlated with ratings collected from professional applicators with regards to ease-of-use criteria. A correlation was also built between the contact angle values obtained with various tooling aid soluнtions against the surface of the sealant and the ease of smoothing obtained by using these tooling aids at the application stage. The evolution of the contact angle of a water droplet at the surface of uncured sealant with time provided some insights in the understanding of the migration and/or reнorientation of polar entities from the sealant bulk to the sealant surface.

The surface energies of poly (methyl methacrylate), polycarbonate and poly (tetrafluoroethylene) which have been exposed to UV radiation in an ambient ozone-air atmosphere have been elucidated from surface tension and contact angle data using these test liquids: ethylene glycol, formamide, glycerol, methylene iodide and water. Comparisons of surface energy values obtained using Kaelble’s two-liquid method, Good’s three-liquid method and Neumann’s macroscopic apнproach are reported. It is tentatively suggested that atmospheric moisture may play a role in producнing discordant values since the test liquids ethylene glycol, formamide and glycerol are highly hyнgroscopic in nature. It has been demonstrated that UV/ozone irradiation produces changes in surface roughness. Poly (tetrafluoroethylene) shows three distinct regions: first, where at low irradiation times the surface roughness is enhanced and following this, the roughness decreases before increasнing finally to a terminal value. The behavior is somewhat similar for polycarbonate although the dramatic increase in roughness exhibited by poly (tetrafluoroethylene) is absent. The roughness characteristics are quite different for poly (methyl methacrylate) where a large change in roughness is observed at only one specific irradiation time. Thus presently it is not possible to predict surface roughness changes for a particular polymer and more studies on the morphological changes occurнring at different surfaces are being carried out.

The water base adhesion promotor for polypropylene comprises: a grafted polypropylene chloride, which includes a polypropylene chloride moiety and a maleic anhydride moiety as bonded thereto, and which has a chlorine content of 15-25 weight % and a maleic anhydride moiety content of 1-5 weight %; an amine-neutralized water-soluble resin; a wettability-improving agent; and water; and is characterized by having: a combination ratio of 25-90 weight % as of the grafted polypropylene chloride to the total of the grafted polypropylene chloride and the amine-neutralized water-soluble resin; a combination ratio of 2.5-6.0 weight % as of the wettability-improving agent to the entirety of the promotor; and a solid content of 2-10 weight % of the entirety of the promotor. The method for coating to polypropylene materials comprises: a pretreatment step in which the polypropylene material is beforehand cleaned and then the above water base adhesion promotor is applied, and then dried; and a coating step in which a paint is coated to the material after the pretreatment step.

The liquid state of matter plays a very important role in everyday life, and the liquid surface has a dominant role in many phenomena. In fact, about 70% of the surface of Earth is covered by water. The most fundamental characteristic of liquid surfaces is that they tend to contract to the smallest surface area to achieve the lowest free energy. Whereas gases have no definite shape or volume, completely filling a vessel of any size containing them, liquids have no definite shape but do have a definite volume, which means that a portion of the liquid takes the shape of that part of a vessel containing it and occupies a definite volume, with the free surface plane except for capillary effects where it is in contact with the vessel. This is evident in rain drops and soap films, in addition to many other systems that will be mentioned later. The cohesion forces present in liquids and solids and the condensation of vapors to liquid state indicate the presence of much larger intermolecular forces than the gravity forces. Furthermore, the dynamics of molecules at interfaces are important in a variety of areas, such as biochemistry, electrochemistry, and chromatography. The degree of sharpness of a liquid surface has been the subject of much discussion in the literature.

Novel types of non-thermal plasma sources at atmospheric pressure based on multi-pin DC (direct current) diffusive glow discharge and AC (alternative current) streamer barrier corona have been elaborated and tested successfully for cold surface treatment of polymer films [polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET),] and polyester fabric. Results on physical properties ofdischarges mentioned and output energy characteristics of new plasma sources as well as data on after-treatment changes in wettability of films and fabrics are presented. The main goal of this study was to find out the experimental conditions for gas discharge and surface processing to achieve a remarkable wettability change for a short treatment time.

The changes of contact angle (θ) and surface free energy (γS) under low-temperature air plasma in the polymers of different chemical structure and polarity (polyethylene, PE; polypropylene, PP; poly(ethylene terephtalate), PET and poly(methyl methacrylate), PMMA) pointed out to the greater effect of short-time plasma action (5–15 s) on these parameters as compared to longer times of exposure.

The non-reversion effect of θ changes caused by plasma in PE and PP suggests that the oxidation processes mainly decide about values in nonpolar polymers. The significantly greater θ changes in PE than those in PP indicate that the side groups present in the main chains impede oxidation of such a polymer by plasma.

The reversion of θ changes in PET and in PMMA, and return of these values to almost the initial ones after 10 min storage proves that the main reason for θ changes in polar polymers is a certain alteration of the chain conformation.

These changes, taking place after longer plasma treatment, suggest that the side ester groups in PMMA retard the above-mentioned conformational transformations. Then, in both kinds of polymers (polar and nonpolar) the structure of macrochain decides about the efficiency of reaction caused by plasma, and at the same time the side groups retard not only the oxidation processes but the conformational changes as well.

The rf power was modulated (discharge on-time of 10 μs and discharge off-time of 50–500 μs), for pulsed argon (Ar) and oxygen (O₂) plasmas used to irradiate PET film surfaces to modify the film surfaces. From data regarding the contact angle for the modified PET film surfaces and chemical analyses with XPS, effects of the rf power modulation on the surface modification are discussed. The pulsed Ar and O₂ plasmas are effective in modification of the PET film surface. There is no difference in the contact angle between the pulsed plasma and the continuous plasma. Furthermore, the pulsed Ar plasma is advantageous in formation of hydroxyl groups on the PET film surfaces. The rf power modulation has a possibility to modify into peculiar surfaces. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2845–2852, 2002
https://onlinelibrary.wiley.com/doi/abs/10.1002/app.10865

The wet adhesion of water borne acrylic dispersions is a crucial factor on the performance of outdoor coatings on wood. Pine sapwood was treated with several methods for surface activation to increase the wet adhesion of water borne acrylic dispersions. The wet adhesion was measured by pull-off tests as well as with a modified cross-cut test. Atmospheric plasma, corona treatment and fluorination increased the wet adhesion of the coating which is attributed to the increasing polar portion of the surface free energy. Other ways of improving the wet adhesion are the addition of promotors, the use of primers and organisational improvements.