Oxidative activation of resinous wood surfaces by a corona treatment to improve adhesive bonding was studied. It was found that the wettability of the veneers, including hardwoods, softwoods, and tropical woods increased with an increase in the degree of treatment, and the gluability increased rapidly after the initial mild treatment. To elucidate the nature of any chemical change occurring on the wood surface, the dyeing examination of the wood and its components with Schiff's reagent was made, and the results showed a higher dyeing ability for corona-treated samples compared to untreated ones, indicating that aldehyde groups increased by the corona treatment. The treatment affected the alcohol-benzene extractives, and oxidized them to produce aldehyde groups. Especially, the neutral fraction in the extractives was significantly affected. On the other hand, negligible chemical effects of the treatment on the surface modification of the wood's main components were seen. Both the untreated and corona-treated samples adsorbed basic dye to the same extent of coloration. Thus, no measurable carboxyl groups increased on the surface of the samples. It seems that an increase in the wettability of corona-treated wood veneers resulted mainly from the oxidation of the high hydrophobic surface layer of neutral fraction substances in the extractives, and from the reduction in their hydrophobicity. © 1993 John Wiley & Sons, Inc.
https://onlinelibrary.wiley.com/doi/abs/10.1002/app.1993.070490714

Wetting involves the interaction of a liquid with a solid. It can be the spreading of a liquid over a surface, the penetration of a liquid into a porous medium, or the displacement of one liquid by another. It can help to characterize surfaces and to determine solid/liquid interactions. Wettability is most often described by a sessile or resting drop. A schematic diagram is shown in Fig. 1. The contact angle (6) is a measure of wettability. A low contact angle means high wettability and a high contact angle means poor wettability. Zero contact angles are possible but they are always less than 180.(The highest commonly observed angle, mercury on glass, has been reported to be as high as 148 [1].) Systems having more than one stable contact angle are said to show contact-angle hysteresis.

The fiber/epoxy resin adhesion increases after plasma treatment on ultrahigh molecular weight polyethylene (UHMW-PE) fibers. The surface modification of UHMW-PE monofilaments was studied using a combination of techniques: contact-angle measurements, SEM, and pullout tests. The results may be summarized as follows: Infiuenced by different plasma parameters and draw ratios of the monofilaments, the adhesion increases by at least four times by plasma treatment. Failure in the pullout tests involve rupture within a treated monofilament and the skin of it was peeled off; the degree of peeling-off is affected by different plasma treatment conditions and draw ratios of the monofilaments. There is only a slight decrease in the surface energy of the treated monofilaments with aging time. Ways of combining plasma etching with other chemical treatments to further improve the fiber/resin adhesion have also been studied. © 1993 John Wiley & Sons, Inc.
https://onlinelibrary.wiley.com/doi/abs/10.1002/app.1993.070471116

This article reviews theoretical and practical aspects of electrical discharge plasma treatment for automotive parts at atmospheric pressure. Paints and bonding compounds adhere poorly to polyolefins because of their intrinsic non-polar chemical structure. Therefore, these materials require pretreatment before bonding and finishing to improve their adhesive properties. The electrical discharge plasma treatment at atmospheric pressure offers several advantages to automotive suppliers, such as the high treatment level, its repeatability and cost effectiveness, versatility of in-line processing, and the environmentally-safe nature of the process. Despite its increasing use, industry standards for surface treatment of plastic pa* have not been developed.

An apparatus and method are provided for surface treating the inside surfaces of hollow or three dimensional plastic objects. While the invention will be described with respect to plastic objects, it will be understood that other objects having a high dielectric strength, such as ceramics, cardboard, paper and wood, may be similarly treated. The surface treating is effected by selectively directing a high voltage plasma field to a selected interior surface of the object to enhance adhesion of various glues, inks and the like. The plasma field is generated in the interior of a tunnel directed into an opening of the hollow portion of the object to be treated. A specially designed electrode is supported from the opening to direct in a controlled manner the field to the selected interior area of the object to be treated. The electrode is supported from a high dielectric shield covering a central area of the opening to direct the plasma field around the shield to a laterally extending electrode below the shield. The electrode is supported from the shield by a conductive rod and is fashioned to extend in a spaced relation to the interior of the object to provide a proper energy level in the plasma to the area to be treated. A plurality of electrodes may be utilized to treat separate and selected interior areas of the object.

Untreated aluminium and aluminium hydrated for 60 s in boiling water have been extrusion-coated with low-density polyethylene (LDPE). The hydration transforms the oxide surface into a porous oxyhydroxide, known as pseudoboehmite. LDPE samples with different melt indices (4.5, 7.5, and 15) were used, which influence the ability to penetrate into the pores. Compared with untreated aluminium, a superior peel strength was obtained for the laminates with hydrated aluminium. In almost all cases, the peel strength for the laminates with hydrated aluminium could not be measured, due to rupture in the polymer film. This improvement is suggested to be due to stronger acid-base interactions, increased contact surface, and mechanical keying into the porous surface. The obtained peel strength and analysis by means of scanning electron microscopy indicated that the polymer with the highest melt index or lowest melt viscosity had the greatest ability to penetrate into the formed pores. After ageing up to 12 weeks in solutions with 1% and 3% acetic acid, the peel strength dropped rapidly for the untreated Al laminates, but remained constant for the hydrated Al laminates. This is explained by the fact that, besides the improved adhesion, the hydrated oxide prevents corrosive attack.

Asymmetric poly(vinyl alcohol) (PVA) membranes were prepared by the phase inversion technique, and crosslinked with glutaraldehyde. The degree of crosslinking of the membrane was controlled by varying the crosslinking conditions. The effects of the degree of crosslinking on the swelling characteristics, contact angles, critical surface tensions, and pervaporation characteristics were examined. A method for the evaluation of the degree of crosslinking, which needs only the gluaraldehyde concentration of the crosslinking solution to be measured after the crosslinking reaction, is proposed, and was found useful. The degree of swelling of PVA membrane for water decreases abruptly as the degree of crosslinking increases. However, the degree of swelling for ethanol is nearly independent of the degree of crosslinking. The critical surface tension of the membrane increases more or less within the range of 37.0–40.0 dyn cm⁻¹ with increasing degree of crosslinking below 30%. But, it is nearly constant at 40.5 dyn cm⁻¹ above 30%. The wetting behavior of the membrane may not be greatly affected by the degree of crosslinking. The selectivity factor and permeate flux of the membrane in the pervaporation of the ethanol-water mixture of 95 wt% ethanol concentration decrease similarly with increasing degree of crosslinking. The pervaporation characteristics seem to be closely related to the swelling behavior. The degree of crosslinking is an important variable for swelling behavior and pervaporation characteristics.

The virtues of chemical inertness and low surface energy which make polytetrafluoroethylene (PTFE) a valuable engineering polymer also account for the difficulty in achieving structural adhesive bonds. While plasma surface treatment has proven to be the most effective means of maximizing strength and permanence of adhesive bonds with the most inert of engineering polymers, a simple plasma treatment has proven elusive for PTFE. The following studies evaluate two very different plasma processes, activation and deposition, as a means to achieve reliable and high-strength structural adhesive bonds. Sodium naphthalene-etched PTFE is used as a control. Presented are ESCA data which support a theory that improvement is limited by a weakened boundary layer of the PTFE.