This chapter presents a comprehensive study on the thermodynamics of contact angles on general rough, heterogeneous surfaces. Conventionally, contact is defined as the angle formed between a liquid-vapor interface and a liquid-solid interface at the solid-liquid-vapor three-phase contact line. On an ideal solid surface, which is smooth, homogeneous, isotropic, and non-deformable, the contact angle is expressed by the Young equation. The concept of liquid front simplified the thermodynamic treatments of contact angles on rough, heterogeneous surfaces and thus made it possible to model real surfaces. Receding contact angles are poorly reproducible for hydrophilic surfaces but for extremely hydrophobic surfaces, advancing contact angles might have a poor reproducibility. An impurity might cause poor reproducibility for receding contact angles if it is the component with the smallest intrinsic contact angle, but it can make the advancing contact angle. An impurity might not affect contact angle hysteresis if it is the component with an intermediate intrinsic contact angle.

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.

Physical method for the treatment of the surfaces of polyolefinic plastic laminates, polytetrafluoroethylene (PTFE), cardboards and metal sheets such as, particularly, aluminium and tinplate, of any thicknesses and widths, by means of a flame produced by the combustion of a mixture of air-hydrocarbon gas, characterized in that such a mixture is enriched with pure oxygen gas.

Metallized polyethylene terephthalate film produced by first subjecting a surface of the film to a reducing flame, and thereafter depositing on the treated surface a coating of metal, e.g., aluminum, deposited from a vapor of the metal.

This application is a continuation-in-part of our copeuding application Ser. No. 469,317, filed July 2, 1965 now abandoned.

This invention relates to a process for the improvement of the adhesion of vacuum-deposited metal to linear polyester film. More specifically, it relates to the flame treatment of polyethylene terephthalate film to promote the adhesion of vacuum-deposited metal.

Surface treatment of monofilaments of polypropylene (PP), poly (ethylene terephthalate) (PET), and polyamide-6 (PA-6) was carried out by corona discharge. The process was conducted with an inter-electrode distance of 4 mm and treatment time in the range of 10 s to 120 s using a wire-plan system under controlled ambient conditions. The samples, before and after corona, were characterized through contact angle measurements, water absorption, Fourier transform infrared spectroscopy/attenuated total reflectance (FT-IR/ATR), scanning electron microscopy (SEM), and differential scanning calorimetry (DSC). After corona, the PP, PET, and PA-6 samples showed water absorption degrees of 9.4%, 8.5%, and 9.1%, respectively. Meanwhile, their dynamic contact angles reduced by 29.6% (PP), 27.9% (PET), and 18.6% (PA-6), while their corresponding surface energies were 71.1 mJ/m², 77.4 mJ/m², and 75 mJ/m², respectively. The FT-IR/ATR, SEM, and DSC results showed that corona treatment effectively improves the wettability of polymeric surfaces through oxidation and surface morphology alteration, but does not affect the bulk thermal properties.

The interactions of NH₃ and N₂ plasmas with the surfaces of polystyrene (PS) and bisphenol-A polycarbonate (PC) have been studied with X.p.s. and SSIMS. Primary amino groups could be detected at the surfaces of both polymers after treatment with the NH₃ plasma but not with the N₂ plasma, with the aid of derivatization reactions with salicylaldehyde and 5-bromosalicylaldehyde. PC differs in its reactivity from PS with respect to its ease of undergoing chain scission during the plasma treatments, which results in modified structures of low molecular weight at the surface. The surface coverage of primary amino groups on PS after treatment with the NH₃ plasma was determined by means of neutron activation analysis after derivatization of these groups with 5-bromosalicylaldehyde and estimated to be approximately 0.5 amino groups per nm².

An investigation of the surface by XPS photoelectron spectroscopy has shown that the process of production of cast contact lenses based on poly(2-hydroxyethyl methacrylateco-diethyleneglycol methacrylate) is accompanied by mass transfer at the lens-mold boundary. This phenomenon, which impairs the compatibility of the lens during its application, can be considerably suppressed by employing a suitable surface modification of polypropylene molds. The surface treatment consisting in the oxidation of the mold surface by an AC corona discharge in the oxygen atmosphere increased hydrophilicity of the material, thus facilitating separation of the lens from the mold. The results of the XPS study were also confirmed microscopically by employing the SEM method. © 1992 John Wiley & Sons, Inc.
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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.

Process and product-by-process of selectively treating a surface of plastic film to prevent blocking by blanketing the surface with a noble gas and by striking a corona discharge within the noble gas atmosphere, while the other surface of the film is in contact with some other gas or gas composition, such as air.

The technique of inverse gas chromatography (IGC) is used to investigate and compare the surface chemical properties of chlorine dioxide-bleached pulps with peroxide- and ozone-bleached pulps and to study the influence of a latex binder (with dispersant) on the properties of calcium carbonate coating particles. IGC measurements with a series of alkane probes yield the dispersive component of the surface energy of the test solid and show only small differences between the various bleached pulps. The use of acid and base probes shows all pulps tested to be predominantly acidic. The presence of latex binder together with a poly (acrylic acid)/carboxymethyl cellulose dispersant decreases the dispersive component, but increases both the acidic and basic components, of the surface free energy of calcium carbonate.

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 objective of this study was to determine the surface free energy components of aqueous-based cellulose ether films and compare these values with those of other cellulose polymers. 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. The cellulose ethers studied were hydroxypropyl methylcellulose (HPMC), methylcellulose (MC), hydroxypropyl cellulose (HPC) and hydroxyethyl cellulose (HEC). The total surface free energy of these cellulose ethers ranged from 42 to 50 mJ m−². The contribution of the acid–base (AB) component of surface free energy to the total surface free energy of the polymers ranged from 4 to 12%, which was considerably lower than that of cellulose. The cellulose ethers demonstrated near monopolarity and had dominant electron donor (Lewis-base) character. The overall trend in the values of the thermodynamic terms derived from the surface free energy parameters as indicators of hydrophilicity and hydration were in good agreement with the relative bulk solubility and hydration behavior of the polymers. Independent estimates of the AB character of the polymers from work of adhesion terms calculated from the liquid wetting data agreed with those obtained from the surface free energy parameters. 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. Although no direct correlation could be established between the surface free energy parameters and the type of substitution on the cellulose backbone for the cellulose ethers, the values of the terms derived from the LW/AB approach were consistent with those of cellulose and ethylcellulose. 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.

Starting from a comparative assessment of the outstanding works on the ring method (du Noüy) for the determination of the surface tension of liquids and its solutions it is shown that the application of this method to surfactant solutions can lead to substantial errors if one follows conventional conditions. These errors are mainly connected with so far unknown phenomena occurring during the raising of the ring and concerning the influence of the hydrophilic vessel wall above the solution level and the stretching of the solution surface. This is demonstrated quantitatively with surfactant solutions of different kind and concentration. These effects can be explained theoretically very simply by introducing certain assumptions on the behaviour of a surfactant adsorption layer on the inner vessel wall. Conditions leading to the elimination of these errors are given, thus enabling the application of the ring method to the determination of the surface tension of surfactant solutions.

COF groups are formed by electron irradiation of PTFE [poly(tetrafluoroethylene)] powders in air, especially at the surface and in near-surface regions which can be easily hydrolysed to carboxyl groups by air humidity. The application of special additives during irradiation leads to modified micropowders. Fourier transform infrared (FTIR) spectroscopy enables the detection of carboxyl and COF groups. γ-Irradiation of PTFE mainly causes degradation of the polymer; the concentration of carboxyl groups is much lower. Carboxylated micropowders created via radiation treatment retain the essential properties of PTFE. With increasing radiation dose, the increasing concentration of functional groups in the micropowders causes an increase in the surface free energy. This diminishes the strong water and oil repellency of PTFE in such a way that homogeneous incorporation into aqueous and organic liquids or other polymers is possible. So, the special properties of PTFE can be made effective in these media. Modified PTFE micropowders have been successfully tested in many application areas. The aim of our present work was to increase the concentration and vary the nature of functional groups by radiation-chemical methods or chemical conversion of COF groups (polymer-analogous reactions). A highly modified PTFE powder was used to reduce the repellent properties of PTFE diaphragms for application in brine electrolysis. The COF groups of the micropowders were modified by γ-aminopropyltriethoxysilane. The irradiation of FEP [poly(tetrafluoroethylene-co-hexafluoropropylene)] and PFA [poly(tetrafluoroethylene-co-perfluoroalkylvinylether)] yields products which contain a higher content of carboxyl groups than PTFE.

COF groups are formed by electron irradiation of PTFE [poly(tetrafluoroethylene)] powders in air, especially at the surface and in near-surface regions which can be easily hydrolysed to carboxyl groups by air humidity. The application of special additives during irradiation leads to modified micropowders. Fourier transform infrared (FTIR) spectroscopy enables the detection of carboxyl and COF groups. γ-Irradiation of PTFE mainly causes degradation of the polymer; the concentration of carboxyl groups is much lower. Carboxylated micropowders created via radiation treatment retain the essential properties of PTFE. With increasing radiation dose, the increasing concentration of functional groups in the micropowders causes an increase in the surface free energy. This diminishes the strong water and oil repellency of PTFE in such a way that homogeneous incorporation into aqueous and organic liquids or other polymers is possible. So, the special properties of PTFE can be made effective in these media. Modified PTFE micropowders have been successfully tested in many application areas. The aim of our present work was to increase the concentration and vary the nature of functional groups by radiation-chemical methods or chemical conversion of COF groups (polymer-analogous reactions). A highly modified PTFE powder was used to reduce the repellent properties of PTFE diaphragms for application in brine electrolysis. The COF groups of the micropowders were modified by γ-aminopropyltriethoxysilane. The irradiation of FEP [poly(tetrafluoroethylene-co-hexafluoropropylene)] and PFA [poly(tetrafluoroethylene-co-perfluoroalkylvinylether)] yields products which contain a higher content of carboxyl groups than PTFE.

Plasma treatment is one of the methods currently used to obtain polymeric materials with surface properties appropriate to the functionality for which they were designed. However, the effects achieved after surface modification are not always long lasting and involve chemical and physical changes in the outermost layer. In this context, the effects of both argon and oxygen plasma on polylactic acid (PLA) films deposited on titanium were studied to determine which physical and chemical processes occur at the surface, and their duration. Regarding physical surface changes, there were scarcely any differences between both plasmas: roughness was very similar after treatments, root mean square height (Sq) being 10 times higher than the control, without plasma. Water contact angle (WCA) showed that the surface became more hydrophilic after application of the plasma, although hydrophilization was longer lasting in the case of argon treatment.

With regard to chemical changes, it was observed that the argon plasma treatment caused greater fragmentation of the polymer chains, and increased crosslinking between them. ToF-SIMS analysis made it possible to propose mechanisms to explain the formation of the fragments observed.

Two or more chemically dissimilar and non-compatible films may be bonded together to form a composite sheet by simultaneously subjecting them to high voltage electric corona discharge of selected intensity continuously through a critical region of mutual contact of the films. The critical region begins at the point at which the film surfaces to be bonded are not in contact with one another and extends at least to the point where all the films to be bonded are in mutual contact with their adjacent films.

A preferred film suitable for use as a wrapping material and obtained by the process of the invention comprises at least one layer of a polyolefin film and at least one layer of a film containing an acrylonitrile polymer.

The carbon fibers (CFs) reinforced polytetrafluoroethylene (PTFE) composites have been modified using proton irradiation, and the surface energy, hardness and tribological properties have been investigated before and after irradiation. The CFs increased the hardness and the wear resistance. Proton irradiation led to defluorination and carbonization of the CF/PTFE composite surface, and decreased the surface wettability and the surface energy. The irradiation depth was 820 nm from the material surface calculated with SRIM software package. In addition, the wear resistance was improved after proton irradiation. Proton irradiation improved the wear resistance of the composite and induced the material transfer from Cu alloy surface to CF/PTFE. These significant improvements could enable potential applications in aeronautics and smart medical materials.

Modification of polyolefin surfaces is often necessary to achieve improved printability, lamination, etc. Although corona discharge and flame treatments can produce the higher surface energy needed for these applications, the properties of the resulting surfaces are not always optimal. Atmospheric pressure plasma is a surface modification technique that is similar to corona discharge treatment, but with more control, greater uniformity, and higher efficiency. Using an atmospheric pressure plasma unit with a dielectric barrier discharge generated using an asymmetric pulse voltage, the effects of different gases, powers, and linespeeds on polyethylene surface treatment were studied. Our results show that atmospheric pressure plasma can be used to achieve higher long-term wettability, higher surface oxygen and nitrogen, and a greater range of surface chemistries with better robustness versus standard corona treatment. Atomic force microscopy results suggest significant differences in the mechanism of surface functionalization versus etching and ablation depending on the gases used. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 319–331, 1999
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A new method for determining the surface tension of liquids has been derived. This involves the consideration of the advancing and receding contact angles of a liquid drop on a tilted solid surface. The theory has been tested by an improved optical projection technique for a variety of liquid/ solid systems and the results obtained are in agreement with the accepted values. It is shown that the advancing and receding contact angles are characteristic constants of liquid/solid system s and the calculated and measured values of the minimum receding angles are in agreement. The prevailing views of ‘hysteresis’ effects or ‘stationary’ contact angles which have arisen to account for the data available are incorrect and the discordant experimental results reported are due to inadequate technique. The difference between the adhesions corresponding to the advancing and receding angles is ascribed to the work done in removing an adsorbed unimolecular layer. The work done in gcal./mol. in forming this adsorbed layer is in reasonable agreement with that expected from studies in gas/solid systems and the forces involved are van der Waals’. Further, different solids that might be expected to show similar surface structures yield similar values for the work done. The variation in the value of the advancing angle in some liquid/solid systems and its constancy in others is reconciled with the polar character of the solid surface, i.e. it is suggested that short-range forces are involved. It has been found that monolayers of ferric stearate on glass are orientated with their hydrocarbon tails away from the interface in agreement with electron diffraction measurements. It is suggested that the methods may be useful for investigating the structure of monofilms and built-up layers of monofilms.

The present methods of measuring contact angles all require that the solid material be obtainable in some special shape, such as a flat plate or capillary tube. Many surfaces, for example, those of plant materials, occur in irregular forms and must be dealt with in situ, because of the inhomogeneity of the body. The chief value of the method herein described is that its applicability is largely independent of the form of the solid surface. Some of the earliest determinations of contact angles were made from measurements of the dimensions of bubbles and drops. The work has been confined to large drops, but the use of very small drops may be shown to possess several advantages . . .

Ethylene-propylene diene monomer (EPDM) containing dicyclopentadiene (DCPD) and ethylidene norbornene (ENB) as the termonomers, styrene-butadiene rubber (SBR), and acrylonitrile-butadiene rubber (NBR) have been surface-modified by 10% methyl ethyl ketone (MEK) solutions of trimethylol propane triacrylate (TMPTA) at an irradiation dose of 100 kGy. The irradiation dose and TMPTA concentration were optimized using samples treated with 2, 5, 10, 20, and 50% TMPTA and 50, 100, 200, and 500 kGy doses. Two per cent solutions of acrylate rubber having diene, chloro, and epoxy groups at the reactive sites and tripropyleneglycol diacrylate (TPGDA) and tetramethylol methane tetracrylate (TMMT) were also employed as the surface modifiers. The level and nature of the vulcanization system were varied. The modified rubbers were characterized by attenuated total reflection infrared (ATR-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and contact angle measurements. IR and XPS studies confirmed the generation of polar groups such as CO and COC on the surfaces. The contact angles and the surface energy change with the nature of the modifiers, rubbers, diene monomers, the crosslinking system and the level of the curing agent. The total surface energy and the thermodynamic work of adhesion of the different systems have been correlated with the amount and the nature of the polar groups generated.

This paper, as the title underlines, will be focused on flame treatment technology applications, mainly on BOPP substrates.

After an introduction regarding flame chemistry and BOPP surface activation mechanisms, this paper will be focused on unique flame treatment oxidation performances, in comparison with other treatment methods actually used in the market.

Focus will then be moved to the characteristics and advantages of using flame treatment for film surface treatment. In particular, a comparison will be run with other surface treatment technologies (corona surface treatment and atmospheric plasma treatment) in terms of:

• q surface energy after treatment;
• surface oxidation mechanisms and chemical species involved;
• quantity of oxygen on treated surface (oxidation level);
• quality of oxygen on treated surface;
• adhesion;
• printability/print quality.

Typical and new applications of flame treatment will be presented, underlining benefits coming from flame usage for pretreating different types of skins. Finally, the paper will try to make rid of prejudices and misinformation concerning flame treatment process applications, especially to certain kind of webs and substrates.