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

Low-pressure gas plasma treatments were proposed as an alternative to the chemical surface treatments (e.g. halogenation, cyclization) of vulcanized styrene-butadiene (SBR) rubber. The effectiveness of low-pressure oxygen plasmas has been already shown. In this study the influence of the oxygen/nitrogen ratio on the adhesion performance of rubber/polyurethane adhesive joints was considered. Different mixtures of oxygen (20–40 vol%) and nitrogen (80–60 vol%) were used for the plasma treatment of an SBR rubber between 1 and 15 minutes, using a power of 50 watts and a residual pressure of 1 Torr. The modifications produced on the rubber surface by the plasma treatment were assessed using advancing and receding contact angle measurements, ATR-IR spectroscopy and scanning electron microscopy. Adhesion was determined from T-peel tests on plasma treated rubber/polyurethane adhesive joints. The treatment of rubber with oxygen-nitrogen mixture plasmas decreased the advancing and receding contact angle values and increased the T-peel strength (a cohesive failure in the rubber was produced). This increase was due to the partial removal of hydrocarbon moieties from the rubber surface and to the creation of oxygen containing species. The increase in the time of treatment decreased the peel strength and made the locus of failure mainly cohesive in the rubber. The higher the percentage of oxygen in the gas mixture, the greater the degree of oxidation on the rubber surface, the higher the degree of roughness and the more effective the treatment. A minimum percentage of 20 % oxygen in the gas composition was required to achieve good adhesion. Nitrogen plasma produced a different effect than the oxygen-nitrogen mixture plasma due to crosslinking reactions on the treated rubber surface which directed the failure to be cohesive in the adhesive.

In this study, an unvulcanized (thermoplastic) block styrene-butadiene-styrene rubber S0 was treated with argon, oxygen and carbon dioxide plasmas and the surface modifications produced were analyzed. The Ar, CO2 and O2 plasma treatments produced an increase in peel-strength values of S0 rubber/polyurethane adhesive joints due to improved wettability, chemical and morphological modifications. Ar plasma created polar moieties on the S0 rubber surface and a consequent increase of the polar component of the surface energy. On the other hand, CO2 and O2 plasma treatments produced ablation of the oxidized outermost S0 rubber surface. Short plasma treatment times are enough to produce adequate T-peel-strength values and a cohesive failure was obtained in the joint produced with S0 rubber treated with CO2 plasma for 1 min. The increase in the length of treatment or the treatment with the other plasmas did not affect the peelstrength values but different loci of failure in the adhesive joints were obtained.

The forces acting between cellulose surfaces have been studied using the interferometric surface force apparatus. The cellulose surfaces were prepared by Langmuir-Blodgett deposition of trimethylsilyl cellulose (TMSC) onto hydrophobized mica. Prior to measurements, the surfaces were desilylated to obtain pure cellulose. The degree of silylation and the molecular weight of the TMSC both affect the structure of the deposited layer. This was observed from the surface pressure-area isotherm, force versus distance curves, and atomic force microscopy images. The forces between the cellulose surfaces were found to depend on the pH of the solution. In dilute electrolyte solutions, the cellulose film was uncharged and rather compact when the pH of the solution was 6.0. However, when the pH was increased to 7.3, the cellulose film swelled considerably and a long-range steric force was measured. The swelling of the film is interpreted as being due to the dissociation of a few carboxylic acid groups present along the cellulose chain. The forces measured were, however, dominated by steric interactions. The repulsion does not increase substantially when the pH is increased from 7.3 to 9.5. Our results suggest that the pK_a of the acid groups present within the cellulose film is larger than it would be in the bulk aqueous solution.

The Harkins relationship, that the spreading coefficient of an adhesive on a release coating is the difference between the work of adhesion of the materials and the work of cohesion of the adhesive, has been found to apply to a variety of silicone release coatings. The works of adhesion and cohesion were estimated from contact angle data using the Owens and Wendt approach. The prediction of the Harkins relationship is obeyed by almost all the combinations of pressure-sensitive adhesive and release coatings we have examined. Release occurs when the spreading coefficient is negative and does not when it is positive. The main exception to this general spreading coefficient rule is the failure of polytetrafluoroethylene to release polydimethylsiloxane-based pressure-sensitive adhesives. The cause is believed to be roughness of the polytetrafluoroethylene surface.

Corona-treated polyethylene films have been reported to exhibit strong self-adhesion when joined together under conditions of heat and pressure that give no adhesion with untreated films. The present study of this effect has shown that the adhesion is completely destroyed by the application of any hydrogen-bonding liquid to the adhesive joint and that the effects of liquids is completely reversible. Joints allowed to dry recover full strength. These facts together with the results of chemical reactions conducted on the treated film surface have established that the adhesive bond is a hydrogen bond. Corona treatment forms keto groups on the polyethylene chain; these groups enolize and the enolic hydrogens bond with carbonyl groups in the adjacent sheet of film when two sheets are heated together under pressure.

The ability of corona treatment to render polyethylene film self-adherent has been previously reported and the mechanism explained. A similar effect has now been found with corona-treated poly(ethylene terephthalate) film which adheres strongly to itself when joined under conditions of heat and pressure that give no adhesion with untreated film. Poly(ethylene terephthalate) films irradiated with short-wave UV light also become self-adherent. The behavior of the adhesive joints in both cases is the same as that reported for corona-treated polythylene film in that the joint strength is zero in the presence of hydrogen-bonding liquids, but recovers completely if the joint is allowed to dry undisturbed. Chemical and physical tests have shown that the adhesive bond is a hydrogen bond between the hydrogens of phenol groups created by corona or UV irradiation in one surface with carboxyl carbonyl groups in the other surface. Thin-layer chromatography of surface extracts from corona- and UV-treated films has shown the products of treatment to be practically identical for both types of treatment, supporting the conclusion that the mechanism of corona treatment resembles that of greatly accelerated photo-oxidation.

A method for measuring the surface energy of solids and for resolving the surface energy into contributions from dispersion and dipole-hydrogen bonding forces has been developed. It is based on the measurement of contact angles with water and methylene iodide. Good agreement has been obtained with the more laborious γ_c method. Evidence for a finite value of liquid-solid interfacial tension at zero contact angle is presented. The method is especially applicable to the surface characterization of polymers.

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.

The surface of polypropylene (PP) film was oxidized by exposure to a flame fueled by isotopically labeled methane (CD4). The isotopic sensitivity of static secondary ion mass spectrometry (SIMS) was then used to gain new insights into the mechanism of flame treatment. SIMS analysis indicated that much of the oxidation of PP occurring in fuel-lean flames is not deuterated, while for PP treated in fuel-rich flames, some of the affixed oxygen is deuterated. These observations imply that O₂ is the primary source of affixed surface oxygen in fuel-lean flame treatments, but that OH may be a significant source of affixed oxygen in fuel-rich flame treatments. Hydroxyl radicals are primarily responsible for hydrogen abstraction in fuel-lean flames, while H is the primary active gasphase species in fuel-rich flames. SIMS also detected trace quantities of oxidized nitrogen groups affixed to the flame-treated PP.

In this paper are discussed some of the fundamental principles which are relevant to an understanding of the influence that interfacial roughness may have on adhesion. The surface energies of the adhesive, substrate and of the interface between them determine the extent of wetting or spreading at equilibrium. Numerical values for surface energies may be obtained either from contact angle measurements or from analysing force–displacement curves obtained from the surface forces apparatus. The extent to which the relationships, appropriate for plane surfaces, may be modified to take into account interfacial roughness are discussed. For modest extents of roughness, the application of a simple roughness factor may be satisfactory, but this is unrealistic for many of the practical surfaces of relevance to adhesive technology which are very rough, and is ultimately meaningless, if the surface is fractal in nature. Some examples are discussed of published work involving polymer–metal and polymer–polymer adhesion, where the roughness of the interface exerts a significant influence on the adhesion obtained. Roughness over a range of scales from microns to nanometres may strengthen an interface, increasing fracture energy by allowing bulk energy dissipating processes to be activated when the bond is stressed.

The thermodynamic energies associated with conventional wetting, spreading, adhesion, cohesion, and disjoining pressure, as defined in classical equations, are re-examined for their significance in a force field. They are then converted into dimensionless form such that the equilibrium properties of both wetting and spreading all fall on the same line when the dimcnsionless spreading coefficient is plotted as a function of the dimensionless work of adhesion. The effects of a force field such as gravity are examined and it is further shown that spreading is always thickness-dependent, whether in a force field or in a gravity-free field. Non-equilibrium processes such as autophobicity are shown on the same dimensionless plot and indicate clearly that the speed with which the process approaches equilibrium depends on the difference between the initial and equilibrium spreading coefficients. All these processes are expressed in terms of a dimensionless group P_n, the reduced wetting energy, which, when lying between the values of + 1 and -1, equals the cosine of the contact angle, . The implication of this approach to non-equilibrium processes is discussed.

Surface tensions of the n-alkanes and interfacial tensions between the n-alkanes and water have been calculated. The ca1culations use a modified form of the Moelwyn-Hughes' equation for the dispersion interaction between two particles, the integtation method of Hamaker to derive the total interaction across a plane surface, the geometric mean relationship of Good and Girifalco for the interaction of two dissimilar phases, and an assumption that the entropy of surface formation equals the difference between the interaction energy so calculated and the total intern&l energy of surface formation. The calculated surface tensions of the n-alkanes are compared with and agree well with experimentally determined values; also, some of their calculated interfacial-tension, contact-angle, and spreading-coefficient measurements with water all agree with the corresponding experimental values. For other systems, calculations are limited lo the contribution of the dispersion forces to the total interaction of the system.

Surface tensions of the n-alkanes and interfacial tensions between the n-alkanes and water have been calculated. The ca1culations use a modified form of the Moelwyn-Hughes' equation for the dispersion interaction between two particles, the integtation method of Hamaker to derive the total interaction across a plane surface, the geometric mean relationship of Good and Girifalco for the interaction of two dissimilar phases, and an assumption that the entropy of surface formation equals the difference between the interaction energy so calculated and the total intern&l energy of surface formation. The calculated surface tensions of the n-alkanes are compared with and agree well with experimentally determined values; also, some of their calculated interfacial-tension, contact-angle, and spreading-coefficient measurements with water all agree with the corresponding experimental values. For other systems, calculations are limited lo the contribution of the dispersion forces to the total interaction of the system.

This study has characterized the energetics of both the liquid state and the solid state of two commercially available epoxy resins: a DGEBA- and a TGMDA-based epoxy system. The surface properties of the liquid epoxies were evaluated by wetting measurements using a dynamic contact angle analysis (DCA). The Lifshitz-van der Waals components of the surface tension were found to be similar for both epoxy systems, while the acid-base components were found to be slightly different. Two different techniques were used to characterize the cured epoxy surface properties: wetting measurements and vapor adsorption measurements by means of inverse gas chromatography (IGC). The Lifshitz-van der Waals components of the surface energy were observed to be nearly the same for both epoxies, confirming that both resins have the same potential for non-specific interactions, in both liquid and solid states. Evaluations of the acid-base components of the work of adhesion by DCA and the Gibbs free energy change by IGC suggest that both cured epoxies show non-negligible specific interactions with both acidic and basic probes. However, computations of the accepticity and donicity parameters showed that both cured epoxies are predominantly basic, but also possess non-negligible acidity. It is likely that the presence of water on the solid surface contributes to the acidic character of the cured epoxies. The temperature dependence of the liquid surface tension for both epoxy systems was investigated. The same temperature dependence was observed: the surface tension decreased with temperature, following a linear regression. Corrections for viscous-drag effects on the liquid surface tension measurements were also made.