The present invention provides a method of modifying the surface of a polymeric substrate, e.g., to improve the wettability of the polymer film surface and/or alter the reactivity of the surface of the substrate by further oxidation, comprising exposing the substrate to a flame. The flame is supported by a fuel and oxidizer mixture that includes an effective amount, for modifying the polymeric substrate, of at least one oxygen-containing compound that functions as a fuel substitute. Oxygen comprises between about 10 and 50 atomic percent of the compound. Large increases in the ASTM wetting test over that reported with conventional flame-treating processes, have been observed in films treated according to this invention. In addition, significant increases in polymer film surface oxidation levels have been observed.

Cold plasma treatments of polymers, dry processes, allow either the elaboration of hydrophilic or hydrophobic surfaces. For example, a poly(propylene) film treated in nitrogen plasma shows a surface having a hydrophilic and basic character since amino groups are attached onto the surface during the treatment. The treatment induces an increase of the surface tension of the polymeric material, which may be sometimes destroyed by an aging effect. For the treatment of poly(propylene) in nitrogen plasma, the aging is mostly due to a motion of attached groups from the surface to the bulk of the material and some oxidation of radicals formed during plasma treatment. The surface radicals formed and used for a post-reaction such as grafting are characterized in terms of chemical nature, density and reactivity.

The surface modification of synthetic fiber fabrics via corona discharge treatment and subsequent graft polymerization was investigated. Polyethylene (PE) nonwoven fabric and polyamide-6 (PA-6) nonwoven fabric were used as base fabrics. Acrylic acid (AAc) was graft polymerized onto the fabrics via corona discharge pre-treatment. The grafted amounts of PAAc were dependent on the grafting time, that of PA-6 being higher than that of PE. It was confirmed that the surface of the fibers constructing the fabric was fully covered with PAAc after the 20 min reaction. The surface of the PAAc grafted fabrics was characterized by X-ray photoelectron spectroscopy. The leakage of electrostatic charge from the fabric was determined and the dyeability was studied with methylene blue. The period of time in which the charge potential attenuated to 1/2 of the initial potential decreased drastically by grafting with PAAc. The grafted amount was enough for dyeing the entire fabrics.

Poly(vinylamine) (PVAm) was grafted on a poly(ethylene) (PE) film surface via the surface graft polymerization of N-vinylformamide (NVF) and N-vinylacetamide (NVA) and the subsequent hydrolysis of those grafted polymers. The surface was characterized by X-ray photoelectron spectroscopy (XPS), contact angle, moisture absorption, and the leakage of electrostatic charge from the films. PNVF and PNVA were introduced onto the surface of the PE film successfully, in spite of the fact that the initiator for polymerization was a peroxide group. The grafted amounts of PNVF and PNVA were dependent on the grafting time. A PVAm-grafted surface was obtained via the hydrolysis of the grafted PNVF. The grafted-PNVA was not hydrolyzed under mild hydrolysis. The obtained PVAm-grafted surface appeared to be useful for various applications, such as protein immobilization or chemical modification. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 1583–1587, 1999
https://onlinelibrary.wiley.com/doi/abs/10.1002/%28SICI%291097-4628%2819990620%2972%3A12%3C1583%3A%3AAID-APP11%3E3.0.CO%3B2-0

This paper contains a brief overview on the recent developments of corona charging of polymers, with emphasis on the current corona triode. This latter method, which has been successfully applied to several types of polymer, is a legacy from Prof. Bernhard Gross' work in São Carlos, Brazil. Following a short introduction to corona charging, the experimental setups are described, especially with regard to the advantages in the constant current method. A few examples are given of the use of the constant current corona triode in the investigation of electrical properties of nonpolar and ferroeleectric polymers. The application of corona charging to pole nonlinear optic (NLO) polymers is discussed, including the perspectives for the constant current charging method for the NLO field.

The surface of poly(ethylene terephthalate) (PET) film was modified by low-temperature plasma with O₂, N₂, He, Ar, H₂, and CH₄ gases, respectively. After being treated by low-temperature plasma, their surface wettability and chemical composition were investigated by means of electron spectroscopy for chemical analysis (ESCA) and contact angle measurement. The result shows that the surface wettability of PET can be improved by low-temperature plasma, and the effect of the modification is due mainly to the kind of the gases. Mainly because of the contribution of hydrogen bonding force γ[STACK]^c_S[ENDSTACK], the surface wettability of PET treated with O₂, N₂, He, and Ar plasma for a short time (3 min) increase sharply, and the surface wettability is also improved by H₂ plasma treatment; but the CH₄ plasma treatment does not improve the wettability of PET. ESCA shows that the effect of wettability of PET is tightly related to the presence of polar functional groups that reside in the outermost surface layer of PET. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 1327–1333, 1999
https://onlinelibrary.wiley.com/doi/abs/10.1002/%28SICI%291097-4628%2819990606%2972%3A10%3C1327%3A%3AAID-APP13%3E3.0.CO%3B2-0

The aim of this publication is to describe an industrial application of the oxyfluorination process to polymer webs. Controlled oxyfluorination of polymer surfaces is a solventless, highly efficient and cost-effective technique of surface modification. The adhesive properties of oxyfluorinated polypropylene films are largely improved so that a variety of solventand water-based printing inks used in contact printing technology can be used. We have confirmed that, in many cases, the necessity to employ an expensive top-coating process that uses acrylic primers to optimise the film printability, can be avoided. The oxyfluorination process with its long lasting effect is a competitive alternative to the simple corona discharge treatment. The oxyfluorination ALKOR' SURFOX process can be described as an environmentally responsible technology that delivers a broad range of products possessing many exceptional surface properties.

The change in adhesive properties of discharge plasma-modified biaxially oriented polypropylene was not very strong. Very low changes were detected in free surface energy (FSE) values; more intensive was the decrease in the polar contribution to FSE, polar fraction and the mechanical work of adhesion to polyvinyl acetate. After 30 days of aging of the biaxially oriented polypropylene foils, the measured value of FSE was suitable for printing. It has been determined that the correlation between mechanical adhesion work to polyvinyl acetate and polar fraction of polypropylene modified by discharge plasma is linear.

Continued innovations in the polymer industry have made polymer surface modification methods a subject of intense research. The importance and necessity of surface modification of plastics are explained, and the advantages of physical surface treatments over the less-sophisticated chemical methods are outlined. Currently available physical surface modification methods for food packaging polymers are reviewed from the food packaging perspective. These physical surface modification methods include flame, corona discharge, UV, gamma-ray, electron beam, ion beam, plasma, and laser treatments. The principle of operation of each method is briefly described, and the advantages and disadvantages of each technique are cited. The extent to which each of these methods can produce the specific modifications desired is discussed. Furthermore, the effects of each treatment on barrier, mechanical, and adhesion properties of food packaging polymers are also examined. Finally, an overview of economic aspects of sophisticated surface modification techniques, including ion beam, plasma, and laser treatments, is presented.

Atmospheric pressure non-equilibrium plasma (APNEP) has been developed in the UK by EA Technology Ltd and is currently being investigated in a joint project with the University of Surrey. APNEP has been used to induce surface modification changes on commodity polymers such as high density polyethylene (HDPE), low density polyethylene (LDPE), polypropylene (PP), poly(ethylene terephthalate) (PET) and poly(methyl methacrylate) (PMMA).

A stable atmospheric pressure glow discharge can be formed with a variety of gases, (e.g., nitrogen, air, argon and helium). In all cases, the plasmas are capable of inducing surface modification of commodity polymers in the near-field and remote afterglow regions. However, as APNEP can have a significant thermal component, care must be taken to avoid thermal decomposition of the polymers.

This study has used differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) to investigate the thermally induced transitions and thermal decomposition behaviour of commercial polymers. The DSC measurements give melting points, heats of fusion and crystallinities. TGA has been used to measure the onset of thermal degradation in both air and nitrogen atmospheres. In parallel with these experiments, temperature profiles of the downstream region of APNEP have been recorded. As a result, positioning of samples and residence times to avoid thermal damage to the substrates can now be achieved.

Advancing and receding contact angles of four organic liquids and water were measured on a variety of polymer surfaces and silicon wafers using an inclinable plane. Contact angles varied widely from liquid to liquid and from surface to surface. Surface roughness was relatively unimportant. Instead, the contact angles seemed to be more closely tied to the chemical nature of the surfaces. In general, contact angles increased with the liquid surface tension and decreased with the surface tension of the solid. Several definitions were used to calculate contact angle hysteresis from the experimental data. Although hysteresis is usually considered an extensive property, we found that on a given surface a wide range of liquids gave a unique value of reduced hysteresis. Apparently, reduced hysteresis represents an intrinsic parameter describing liquid–solid interactions.

The first part of the contribution deals with the interfacial tension, σ, of phase‐separated polymer solutions in single or mixed solvents and of binary polymer blends as a function of the relative distance to the critical temperature of the system, special attention being paid to the possibilities of theoretical prediction. Two methods are discussed in more detail. One is based on a realistic description of the Gibbs energy of mixing as a function of composition, the second correlates σ with the length of the measured tie line. The second part is devoted to another aspect, namely the effects of additives on the interfacial tension between the coexisting phases of demixed polymer solutions and between highly incompatible polymers. In the former case, it is demonstrated that an addition of a thermodynamically good solvent is normally associated with a reduction in σ; however, adding a high‐molecular‐weight compound which is incompatible with the dissolved polymer leads to an increase in σ. The interfacial tension between incompatible homopolymers is efficiently reduced by block copolymers consisting of monomeric units which are either identical with or different from those of the homopolymers; in contrast to theoretical expectation, the molecular architecture of the additives seems to be of minor importance only. Random copolymers which are insoluble in the homopolymers can also efficiently reduce the interfacial tension.

A brief review of the surface tension of polymer liquids is presented. A strong emphasis is placed on recent measurements of surface tensions of homologous liquid series up to high-molecular-weight polymers, and the thermodynamic liquid properties of these same homologous series obtained from sources such as pressure-volume-temperature (PVT) data. The accuracy and limitations of the thermodynamic information which are used as input to many of the theories applied to the surface properties of polymer molecules are discussed. By scaling the surface tension data using a true measure of the cohesive energy density of the liquid state, we can clearly observe the entropic contribution to the surface tension caused by the conformational restriction of a large molecule at the liquid-vapor interface. The scaling implies the existence of a corresponding states principle for both polymer liquids and for low-molecular-weight liquids. The ramifications of the existence of a corresponding states principle for the surface tension of polymer melts are discussed. One consequence of the corresponding states principle is that it allows us to use surface tension measurements to compute the cohesive energy density of polymer melts using PVT data.

Polycarbonate (PC) and poly(vinylidene fluoride) (PVDF) are two immiscible polymers which form two‐phase blends with weak interfacial adhesion and high interfacial tension. This situation may be changed by the addition of poly(methyl methacrylate) (PMMA), which concentrates preferably in the PVDF‐rich phase, but also at the PVDF/PC interface. The interfacial activity of PMMA was estimated by the measurement of the interfacial adhesion and interfacial tension in relation to the PMMA content in the PVDF/PC blends. The interfacial adhesion between PC and homogeneous PVDF/PMMA blends of various compositions was measured by the dual cantilever beam technique. The imbedded fiber retraction method was used for the measurement of the interfacial tension. A very beneficial effect was observed when PVDF was premixed with PMMA amounts increasing up to ca. 35 wt.‐%. Beyond that content, the improvement tends to level off.

Several thermoplastic (technical, engineering, and high-performance) polymers were characterized using contact angle and electrokinetic measurements. From the measured contact angles of various test liquids on polymers, we calculated the solid surface tensions using the different approaches to determine them and compared the results. Zeta (ζ)-potential measurements gave information about the swelling behavior of the polymers in water, the surface chemistry, and the interactions with dissolved potassium and chloride ions. All investigated polymers displayed an acidic surface character. Comparing the results obtained from the ζ-potential measurements with the acid-parameter of the surface tension γ⁺ calculated from the measured “static” contact angles using the van Oss, Good, and Chaudhury approach revealed the same tendency. The correctness of the acid–base approach regarding the “overall” chemical surface character could be shown. However, it seems that the basic parameter γ⁻ obtained from the acid–base is greatly overestimated.

The chemical and morphological stabilities of polymer segments in the near-surface layer were investigated by spectroscopic methods such as X-ray photoelectron spectroscopy and near-edge X-ray absorption fine structure spectroscopy. Model studies were undertaken with Langmuir–Blodgett films, self-assembled monolayers and oligomer films. For thin polymer layers (30 to 500 nm), the changes in molecular-weight distributions of some polymers were investigated systematically by size exclusion chromatography, matrix-assisted laser desorption/ionization–time-of-flight mass spectrometry and thermal-field flow fractionation for oxygen- and helium-plasma exposures. The polymer surfaces were found to be relatively stable at exposure to an oxygen low-pressure plasma up to ca. 2 s. This is important information to get maximum adhesion to metals in composites. In correlation to their redox potentials, potassium, aluminium and chromium react with oxygen functional groups at the polymer/metal interface. In a dedicated study, chromium was found to attack aromatic rings and form different reaction products.

Polypropylene (PP) was exposed to various fluorine-gas mixtures and the fluorinated PP surfaces were characterised by means of X-ray photoelectron spectroscopy, Rutherford backscattering, attenuated total reflectance infrared spectroscopy, solid–liquid contact angles and thermogravimetric analysis. The surface wettability and surface tensions of PP, as functions of fluorination and oxyfluorination times, were also determined and discussed.

Surface fluorination is an interesting method of rendering surfaces more acceptable to adhesion. The adhesive properties of fluorinated and oxyfluorinated propylene surfaces, using epoxy, polyester and epoxy vinyl ester adhesives, are described. Lap shear tests were carried out to determine the strength of the adhesive joints.

Apparatus capable of sustained glow discharge at atmospheric pressure mounted along the web path in a web coating machine ahead of the point of coating application, for glow discharge treatment of the surface of a polymeric web shortly before coating. Latencies of treatment (the time between treatment and coating) approaching zero are possible, minimizing or preventing loss of treatment effect and maximizing adherence of a coated layer to the web surface. Elimination of one or more conventional subbing adhesion layers on the web surface is possible in some applications.

The surface free energy parameters of ethylcellulose (EC) films were determined using the Lifshitz-van der Waals/acid-base approach and the influence of plasticizers on their surface energetics was assessed. Films were prepared by dip-coating glass slides in organic solvents containing EC and the advancing angles of drops of pure liquids on the EC films were measured with a contact angle goniometer using the captive drop technique. EC has lower surface free energy than cellulose. The acid-base (AB) term made only a slight contribution to the total surface free energy and the surfaces exhibited predominantly monopolar electron-donicity. The addition of plasticizer (dibutyl sebacate or dibutyl phthalate) resulted in a small decrease in the total surface free energy. The effects of film forming variables, including solvent system, concentration and post-formation treatment (annealing), on the surface free energy parameters of EC films were also investigated. These data were then used to analyze how the surface energetics affect the interaction of the EC films with other surfaces based on interfacial tension, work of adhesion and spreading coefficient calculations. Lifshitz-van der Waals (LW) interactions provided the major contribution to the work of adhesion for EC with all of the solid substrates analyzed. However, the AB interactions contributed significantly to the work of adhesion for EC with 'bipolar' substrates and to the spreading coefficients of EC over substrates. The consideration of work of adhesion and spreading coefficient based on surface free energy parameters may have potential use in evaluating factors affecting film adhesion and, furthermore, in optimizing pharmaceutical film coating processes.

A process for corona treating a polymer is described. The process involves exposing at least one surface of an article comprising a polymeric material selected from the group consisting of fluoropolymers, polycarbonates, and polyimides to a corona discharge in an atmosphere containing nitrogen and about 0.01 to about 10 percent of an additional gas selected from the group consisting of hydrogen, ammonia and mixtures thereof.

Contact angles can be of great value; however, making meaningful contact angle measurements and interpreting those measurements is complex. For years, researchers have addressed a wide variety of issues concerning contact angles. Some questions have been qualitatively answered; others remain open. In this paper, we focus on three issues which are particularly important for the measurement and use of contact angles: the appropriate definitions and use of macroscopic and microscopic contact angles, a brief survey of the length scales relevant to phenomena controlling contact angles, and the role of vibrations in determining contact angles. We emphasize contact angle issues relevant to heterogeneous surfaces, specifically, ambient surfaces prevalent in nature and industry.