Improper or inadequate surface treatment is one of the commonest causes of failure in adhesive bonding, but the selection of a good surface treatment can bring marked improvements in the wet durability of adhesive bonds to metals and glasses, and can permit the bonding of otherwise unbondable materials such as polytetrafluoroethylene (ptfe) and the polyolefins. Untreated surfaces may be unsatisfactory for adhesive bonding because they may be contaminated, may lack polar chemical groups or the interface they make with an adhesive may be susceptible to hydrolysis.

The surface chemistry of sheet molded composite (SMC) following interaction with a natural gas/air flame operated under reducing, stoichiometric, and oxidizing conditions has been investigated. The SMC surface chemistry is altered to contain in addition to hydrocarbon, ether, and ester functional groups, carbonyl and a greater carboxyl concentration. The extent of surface oxidation varies with the flame condition in the manner oxidizing ∼ stoichiometric > reducing. Lap shear tests carried out at 82°C (180°F) for coupons bonded with a urethane adhesive did not fail by fiber tear. Surface analysis results indicate failure at an oxidized SMC-adhesive/non-oxidized SMC interface and within the non-oxidized SMC surface.

A summary of recent studies on the corona treatment of films is presented. Chemical functional groups generated by the corona discharge on these films are identified and their effect on ink film wettability and adhesion discussed.

A high-temperature-vulcanized polydimethylsiloxane (PDMS) elastomer has been subjected to corona discharges for different periods of time in dry air. The loss and recovery of hydrophobicity of the surface have been characterized by contact angle measurements. Immediately after exposure to corona discharges, samples showed a low surface hydrophobicity and, on storage in dry air, a continuous increase in hydrophobicity finally approaching the hydrophobicity of the unexposed material. The activation energy of the hydrophobicity recovery was two to four times greater than the activation energy of the diffusivity of low molar mass PDMS in PDMS elastomers, indicating that the diffusivity properties of the oxidized surface layer were different from that of the bulk. PDMS elastomers quenched in liquid nitrogen or subjected to small mechanical deformation ( < 1% strain) after exposure to corona discharges for 1 h or more recovered their hydrophobicity faster than untouched specimens kept under identical conditions. X-ray photoelectron spectroscopy confirmed the early formation of a silica-like surface layer, with a thickness of at least 10–12 nm. The atomic composition of the oxidized surface layer remained essentially unchanged after the first hour of corona discharges. It is suggested that the silica-like surface layer delayed the recovery of hydrophobicity by inhibiting the transport of low molar mass PDMS to the surface. It is also suggested that thermally or purely mechanically induced stresses lead to a cracking of the brittle silica-rich layer and that this in turn facilitates the transport of low molar mass PDMS to the surface and to a more rapid recovery of the hydrophobicity. Data obtained by reflection infrared spectroscopy assessing the outermost micrometer, confirmed the oxidation and the formation of hydroxyl groups at a progressively higher concentration with increasing exposure time of corona discharges.

A method for checking the degree of plasma treatment of an article. The method comprises depositing a substance able to change color as a result of plasma treatment on a carrier, the carrier having pores having an average pore size of 0.2-3 μm, placing the carrier having said substance deposited thereon near the surface of the article, subjecting the substance carrying carrier and the article to plasma treatment, and evaluating the color change that has occurred in the substance.

Measurements have been made of the energy required to break through unit area of polystyrene (PS), polymethylmethacrylate (PMMA), and joints prepared by molding the two polymers in contact. The results were: 1.23 ± 0.5 kJ/m² (PS), 0.46 ± 0.10 kJ/m² (PMMA), and 0.22 ± 0.04 kJ/m² for the bonded joint. Thus, the interface was significantly weaker than either adherend, but surprisingly strong for two incompatible materials. Microscopy and selective dyeing revealed that fracture took place at the interface itself, with no appreciable transfer of material from one side to the other. It is concluded that Van der Waals interactions are sufficient to create relatively strong bonds.

Metallized OPP (oriented polypropylene) film offers exceptional gas and water vapor barrier properties, making it one of the most cost-effective flexible protective packaging materials. Its barrier properties correlate with opacity, which, in turn, de pends on the degree of coverage by the metallization. Minor defects, such as scratches, will generally represent only a small percentage of the total coverage of a package and have a proportionally small effect on the barrier properties of the pack age. The high-energy metal surface is extremely active and will wet well and adhere strongly when clean. In fact, it is so active that it is easily coated with trace amounts of any low energy organic material with which it makes contact. For assurance of consistent wetting and bonding, metallized OPP surfaces should be cleaned in-line, such as by bare-roll corona treatment.

Electron Spectroscopy for Chemical Analysis (ESCA) is generally considered to be a non-destructive analytical technique as compared to e.g., SIMS and Auger spectroscopy. In fact, there have appeared only a few reports in the literature where soft X-ray induced spectral changes were noted. These studies have recently been reviewed by Storp. Several of these studies have been carried out with non-monochromatic X-ray sources which typically expose a sample surface with a flux of high kinetic energy electrons and thermal radiation. As pointed out by Storp, it is not entirely clear whether or not the reported changes can be therefore considered as uniquely caused by X-ray photons. Wheeler and Pepper have published a detailed beam damage study on polytetrafluoroethylene (Teflon) using a non-monochromatic X-ray source. The authors provided convincing evidence that the detected fluorine depletion of the surface is indeed caused by X-rays rather than electron bombardment. We wish to report ESCA experiment on Teflon and several other polymeric materials using a spectrometer with a monochromatic Al Kα X-ray source. Due to the physical separation between source and sample an unambiguous differentiation between X-ray vs. electron induced damage can be obtained.

As demonstrated in Part II of this series of studies, the hydrophobic character of CF₄ plasma-treated Nylon 6 and poly(ethylene terephthalate) (PET) decay with time of water immersion, and the rate of decay can be used as a measure for the surface mobility of (substrate) polymers. The same method of using fluorine-containing moieties introduced by CF₄ plasma treatment as surface labeling is applied to investigate the influence of a thin layer of plasma polymer of methane applied onto the surface of those polymers. An ultrathin layer of plasma polymer provides a barrier to the rotational and diffusional migration of the introduced chemical moieties from the surface into the bulk of the film. The influence of operational parameters of plasma polymerization on the surface dynamic stability are examined by measuring the decay rate constants for (subsequently) CF₄ plasma-treated samples. The rate constant was found to decrease sharply with increasing value of plasma energy input manifested by J/kg monomer, and no decay was observed as the energy input reached a threshold value (about 6.5 GJ/kg for PET, about 7.0 GJ/kg for Nylon 6), indicating that unperturbable surfaces can be created by means of plasma polymerization.

Surface chemical modification of polymer thin films induced by sputter etching was studied by x‐ray photoelectron spectroscopy (XPS) and infrared reflection–absorption spectroscopy (IRRAS). The polymers studied were polystyrene, polypropylene, and poly(ethylene terephthalate) (PET). Oxygen and argon sputter etching of these polymers causes surface oxidation and possibly crosslinking; trends in polymer oxidation can be correlated with the etchant gas, etch power, and initial material properties. For polystyrene and polypropylene, the predominant new functionalities formed are CO and CO groups; the breadth of the infrared absorption bands suggests that many different types of these groups exist. For PET, the predominant damage mechanism is crosslinking, with only a slight degree of oxidation resulting from oxygen sputter etching. This work suggests that the information provided by XPS and IRRAS is highly complimentary and will be useful in future studies of polymer functionalization and derivatization.

The effects of surface modification of polyethylene (PE) and aluminum on the adhesion strength have been investigated. PE was modified by KMnO₄/H₂SO₄ treatment followed by adsorption of different cations, Ca²⁺, Ba²⁺, and Zn²⁺. The aluminum surface was treated with alkali and was also modified by adsorption of titanates. The surfaces were characterized by means of multiple internal reflection (MIR) IR and ESCA. The adhesion strength was measured by the T-peel test. Both ESCA and MIR analyses show the presence of hydroxyl, carbonyl, ester, and carboxyl groups on the KMnO₄/H₂SO₄-treated PE surface. In addition, sulfate and sulfonate groups are present. The sulfonate groups are apparently localized in crevices extending beneath the ESCA sampling depth of 50 A. Vinylidene groups are also present on the surface. Cation adsorption on the oxidized PE surface seems to be determined by the solubility constant of the corresponding sulfate salts and is in the order Ba²⁺ > Ca²⁺ > Zn²⁺. Adsorption of Ca²⁺ and Ba²⁺ increases the relative concentration of oxygen-containing groups on the KMnO₄/H₂SO₄-treated surface. A further increase is seen after annealing. KMnO₄/H₂SO₄ treatment almost doubled the adhesion strength of PE to aluminum. Ca²⁺ adsorption on the surface prior to lamination increased the adhesion strength nearly three times and caused cohesive failure in the T-peel test. However, when Zn²⁺ was adsorbed, the adhesion strength decreased drastically. Alkaline treatment of the aluminum surface had only a minor effect on adhesion. The chemical structure of the adsorbed titanates has a great influence on the adhesion strength.