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.

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.

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.

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

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.

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.

We compare two surface treatments of biaxially-oriented polypropylene (BOPP), which are carried out in the same dielectric barrier discharge (DBD) apparatus, namely air corona, and N₂ atmospheric pressure glow discharge (APGD). Changes in the surface energy and chemistry are investigated by contact angle measurements, by X-ray photoelectron spectroscopy (XPS) and by attenuated total reflectance infrared spectroscopy (ATR-FTIR). It is shown that N₂ APGD treatment leads to a higher surface energy than air corona treatment, and to the formation of mostly amine, amide, and hydroxyl functional groups at the polypropylene surface. Finally, hydrophobic recovery of the treated film is studied; for both treatment types, the increased surface energy is found to decay in a similar manner with increasing storage time after treatment.

The increasing use of polymeric materials in high technological fields, such as automotive, has forced the need to overcome some of their limitations by means of innovative processing. In the automobile industry a complex and critical process is used in order to enhance both wettability and adhesive properties of polypropylene bumper surfaces. Cold plasma treatment represents an efficient, clean and economic alternative to activate polymeric surfaces.

The present work deals with air cold plasma treatment of polypropylene surfaces. Particularly, the influence of AC electrical discharge cold plasma parameters on wettability and adhesion of polymeric surfaces was studied. Also, the nature of the relationship between wettability and adhesion was investigated. Owing to the complexity of plasma–workpiece interaction, an experimental approach was followed. A set of process variables (voltage, time and air flow rate) was identified and used to conduct some experimental tests on the basis of design of experiment techniques. The experimental results show that the proposed plasma process may considerably increase polypropylene wettability and adhesion properties. These outcomes represent the first step in trying to optimise the polymeric adhesion by means of this non-conventional manufacturing process.

Tetrafluoroethylene–hexafluoropropylene (FEP) copolymer sheets were modified by remote H₂, N₂, O₂, and Ar plasmas, and the effects of the modification on adhesion between FEP sheets and copper metal were investigated. The four plasmas were able to modify the FEP surfaces' hydrophilicity. Defluorination and oxidation reactions on the FEP surfaces occurred with exposure to the plasma. The hydrophilic modification by H₂ plasma was best, followed by modification by O₂, Ar, and N₂ plasmas. The surface modification of FEP by all four remote plasmas was effective in improving adhesion with copper metal. The peel strength order of the FEP/Cu adhesive joints was H₂ plasma > Ar plasma > N₂ plasma > O₂ plasma. Mild surface modification is important for the adhesion improvement of FEP with Cu metal. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1258–1267, 2002
https://onlinelibrary.wiley.com/doi/10.1002/app.2293

We demonstrate that stable microwave-coupled atmospheric pressure nonequilibrium plasmas (APNEPs) can be formed under a wide variety of gas and flow-rate conditions. Furthermore, these plasmas can be effectively used to remove surface contamination and chemically modify polymer surfaces. These chemical changes, generally oxidation and crosslinking, enhance the surface properties of the materials such as surface energy. Comparisons between vacuum plasma and atmospheric plasma treatment strongly indicate that much of the vacuum-plasma literature is pertinent to APNEP, thereby providing assistance with understanding the nature of APNEP-induced reactions. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 95–109, 2002
https://onlinelibrary.wiley.com/doi/abs/10.1002/pola.10056

Glycerol monostearate (GMS) can serve as an anti-fogging agent by increasing the hydrophilic nature of a film surface. In this study, blends of GMS and LLDPE were extruded into film and the GMS was allowed to migrate to the surface over time. The surface was characterized by measuring the static water contact angle, which was then used to calculate the surface free energy of the film. Results showed that the equilibrium wettability of the film deviated dramatically from that of neat LLDPE when the GMS concentrations were greater than about 1900 ppm. Time-dependent studies demonstrated that the rate of surface-energy change was significantly influenced by the GMS concentration.

In this work, the effect of corona discharge treatment on surface properties of polyimide film was investigated in terms of FT-IR(Fourier Transform-IR), XPS(X-ray Photoelectron Spectroscopy) and contact angles. And the adhesion characteristics of the film were studied in peel strengths of polyimide coatings. As a result, polyimide surfaces treated by corona discharge led to an increase of oxygen-containing functional groups or polar component of the surface free energy, resulting in improving the adhesion characteristics of the polyimide/copper foil. However, the surface energy of the film was decreased as the aging time increased. These results could be discussed in the formation of surface functional groups or deterioration of reactive sites of polyimde film in the presence of corona treatment with aging time.

X-ray photoelectron spectroscopy (XPS) and contact angle measurements were used to characterize the surface modification and possible production of low molecular weight reaction products on biaxially oriented polypropylene (BOPP) and on low density polyethylene (LDPE) films treated by atmospheric pressure glow discharge (APGD) in pure nitrogen and by air corona. We have observed that surface degradation is more pronounced for air corona treatments in the case of both polymers.

Polyamide 12 (PA12) films have been modified by CF₄ and CF₄+H₂ (50/50 v/v) microwave plasma with different treatment times. The surface modifications have been followed versus plasma exposure duration by water contact angle measurements and atomic force microscopy (AFM) Pervaporation measurements were carried out to characterize the effects of these plasma treatments on water transport through PA12 films. From these measurements, water permeability was determined for each duration time of treatment. The efficiency of these plasma treatments in reduced permeability is compared. For both plasma treatments (CF₄ and CF₄+H₂), the analysis of the experimental data shows an increase and then a decrease of the permeability coefficient P with treatment durations. These observations are related with the evolution of the surface versus treatment time. From all these experimental results, it is clearly shown that the barrier effect to water in plasma-treated layers of PA12 is improved significantly, especially with CF₄.

Adhesion between polymeric phases like adhesives and plastic surfaces is critical in many technological and industrial applications. In the last decades much progress has been made to understand the impact of the surface properties of both phases on the adhesive strength between them. These surface properties influence processes like wetting, molecular adsorption and inter-diffusion which determine how an interface develops into an interphase after the two materials have been brought into contact. Ultimately, the properties of this interphase determine the overall adhesion strength of an assembly. In this paper important parameters in the adhesion process will be reviewed, including methods to engineer these parameters in order to attain adhesion strengths ranging from complete release to irreversible bonding.

We report on the surface modification of Sylgard-184 poly(dimethyl siloxane) (PDMS) networks by ultraviolet (UV) radiation and ultraviolet/ozone (UVO) treatment. The effects of the UV light wavelength and ambient conditions on the surface properties of Sylgard-184 are probed using a battery of experimental probes, including static contact angle measurements, Fourier transform infrared spectroscopy, near-edge X-ray absorption fine structure, and X-ray reflectivity. Our results reveal that when exposed to UV, the PDMS macromolecules in the surface region of Sylgard-184 undergo chain scission, involving both the main chain backbone and the side groups. The radicals formed during this process recombine and form a network whose wetting properties are similar to those of a UV-modified model PDMS. In contrast to the UV radiation, the UVO treatment causes very significant changes in the surface and near-surface structure of Sylgard-184. Specifically, the molecular oxygen and ozone created during the UVO process interact with the UV-modified specimen. As a result of these interactions, the surface of the sample contains a large number of hydrophilic (mainly –OH) groups. In addition, the material density within the first ≈5 nm reaches about 50% of that of pure silica. A major conclusion that can be drawn from the results and analysis described in this work is that the presence of the silica fillers in Sylgard-184 does not alter the surface properties of the UVO- and UV-modified Sylgard-184.

The low temperature plasma produced by a surface barrier discharge generated in nitrogen at atmospheric pressure has been used for the treatment of polyester nonwoven (PET NW) fabrics. Surface modifications of three types of PET NW with different square weights (25, 50 and 80 g/m(2)) have been investigated. To determine the treated PET NW hydrophilicity, the strike-through time was measured. The optimum treatment time acceptable for technological applications was looked out with respect to the ageing phenomena. The obtained results show significant improvement in the wettability of PET NW. The effect of increasing wettability is considerably reduced with the increase of material square weight. The method has the potential to be suitable for industrial technologies, especially for thin materials.

Preliminary results are presented on hydrophilization, grafting, and metal plating of PP nonwovens using novel types of atmospheric-pressure low-temperature plasma sources, namely the "Surface Discharge Induced Plasma Chemical Processing" source and the plasma source based on a coplanar diffuse surface discharge. The plasma sources generate a thin (~ 0.3 mm) surface layer of plasma and are capable of meeting the basic on-line production requirements for surface activation and permanent hydrophilization of light-weight nonwovens.

The effect of energy of corona discharge treatment (CDT) on the physico-chemistry of the surface of a polyester film was investigated systematically using a number of complementary surface analytical techniques: contact angle analysis, x-ray photoelectron spectroscopy, time-of-flight secondary ion mass spectrometry and atomic force microscopy. The energy of treatment can be controlled by either varying the speed of the treatment with constant power input or by varying the power of the treatment with constant speed. The changes in surface energy, surface chemistry and surface morphology of poly(ethylene terephthalate) (PET) induced by these two modes of CDT have been investigated.

The surface energy and the polar contribution of the film increased with increasing energy of corona. Phenolic-OH, carbonyl and carboxylic acid (HOC=O) have been identified as the functional groups incorporated onto the surface. Low-molecular-weight oxidized materials were observed in the form of a globular morphology on the surface of the film. By washing the film in methanol–water prior to surface analysis, it was shown that the oxygen content at the surface of the film decreased and the globular morphology was removed.

Differences in the surface energy of corona-treated PET films have been observed under similar corona energy conditions, depending on whether the sample was treated with constant speed or constant power. However, the total surface oxygen content was found to be similar at low-energy treatments. When the high-resolution C 1s XPS spectrum was peak fitted, the relative concentrations of functional groups introduced and other changes to the original polymer structure were shown to be independent of the mode of treatment.

These observations may be explained because although the total energy transferred from the power source to the PET under the conditions of ‘constant power, variable speed’ and ‘variable power, constant speed’ is theoretically the same, these experimental conditions are not interchangeable. At constant power, the concentration of active species, radiation and dielectric breakdowns in the discharge are independent of speed. However, in the case of constant speed, the concentration of active species, radiation and dielectric breakdown increase with increasing power, resulting in a different surface energy between the two sets of samples. However, because the composition of the active species will not change, the functional groups on the surface of the film will be the same across comparable energy levels, independent of mode of treatment. Copyright © 2002 John Wiley & Sons, Ltd.
https://analyticalsciencejournals.onlinelibrary.wiley.com/doi/abs/10.1002/sia.1429

This paper reviews the background to the theory of Lewis acid-base (AB) interactions in adhesion, adsorption, wetting and mixing of polymers and other materials (pigments, fillers, fibres, etc.). These specific materials interactions require the revision of old concepts («polar» interactions) and the development of new analytical techniques and methodologies. Four of the most currently used techniques to characterize AB interactions are described: contact angle measurements, inverse gas chromatography. X-ray photoelectron spectroscopy, and atomic force microscopy.

The relative importance of atmospheric negative ions in corona formation and breakdown in a radial electric field has been investigated, with special reference to effects occurring at an insulating surface of a cycloaliphatic polyurethane with dolomite filler. The inception times, corona charge, light emission (by UV photography) and sparkover voltages under lightning impulses have been recorded under natural atmospheric conditions and under the influence of negative ions introduced from an auxiliary corona. The presence of excess negative ions on the surface is shown to increase both the charge injected and the mean radius of the corona, attributable to an augmentation of streamer discharges. In similar experiments in air, the excess ions cause a transition to a `glow' discharge. Effects of negative ions on sparkover are not significant on the insulator surface, but they cause a small increase in air. Comparisons between the two cases lead to the conclusion that the most important effect of the ions on the surface is to provide `seed' electrons for streamer propagation, following ion detachment in the field of advancing streamer tips.

Recently, a number of authors have been rearranging the various combinations and permutations of the different apolar and polar liquids with which contact angles can be measured on polar surfaces and in so doing have arrived at bizarre results. The rational order and procedures to be followed in the determination of the apolar and polar surface tension properties of polar materials, according to the van Oss-Chaudhury-Good components and parameters of the approach, are reiterated.

Total surface free energy, γ_S ^TOT, for several solids (glass, PMMA, duralumin, steel and cadmium) was calculated from the surface free energy components: apolar Lifshitz–van der Waals, γ_S ^LW, and acid–base electron–donor, γ_S ^-, and electron–acceptor, γ_S ⁺. Using van Oss and coworkers' approach (Lifshitz–van der Waals/acid–base (LWAB) approach), the components were determined from advancing contact angles of the following probe liquids: water, glycerol, formamide, diiodomethane, ethylene glycol, 1-bromonaphthalene and dimethyl sulfoxide. Moreover, receding contact angles were also measured for the probe liquids, and then applying the contact angle hysteresis (CAH) approach very recently proposed by Chibowski, the total surface free energy for these solids was calculated. Although the thus determined total surface free energy for a particular solid was expected to depend on the combination of three probe liquids used (LWAB approach), as well as on the kind of the liquid used (CAH approach), surprisingly the average values of the surface free energy from the two approaches agreed very well. The results obtained indicate that both approaches can deliver some useful information about the surface free energy of a solid.

Ultrahigh modulus polyethylene fibers were treated with atmospheric pressure helium + oxygen plasma in a capacitively coupled device at a frequency of 7.5 kHz. The fibers were treated for 0, 0.5, 1, 1.5, and 2 min. The surfaces of the fibers treated with He + O₂ plasma were etched and micro-cracks were formed. XPS analysis showed a 65—213% increase in oxygen content on the surfaces of all plasma-treated fibers, except for the 1.5 min group. An increase in the concentration of CO and the appearance of CO bonds on the surfaces of plasma-treated fibers were observed. In the micro-bond test, He + O2 plasma-treated groups had a 65–104% increase in interfacial shear strength over that of the control. The tensile strength of the fibers was either unchanged or decreased by 10–13% by the plasma treatments.

Ultrahigh-modulus polyethylene fibers were treated with atmospheric pressure He plasma on a capacitively coupled device at a frequency of 7.5 kHz and a He partial vapor pressure of 3.43 × 10³ Pa. The fibers were treated for 0, 1, and 2 min. Microscopic analysis showed that the surfaces of the fibers treated with He plasma were etched and that the 2-min He plasma-treated group had rougher surfaces than the 1-min He plasma-treated group. XPS analysis showed a 200% increase in the oxygen content and a 200% increase in the concentration of CO bonds (from 11.4% to 31%) and the appearance of CO bonds (from 0% to 7.6%) on the surface of plasma-treated fibers for the 2-min He plasma-treated group. In the microbond test, the 2-min He plasma-treated group had a 100% increase of interfacial shear strength over that of the control group, while the 1-min He plasma-treated group did not show a significant difference from the control group. The 2-min He plasma-treated group also showed a 14% higher single-fiber tensile strength than the control group.