The adhesive interaction between oxygen-plasma-treated, polyacrylonitrile-based, high-tensile-strength carbon fibers and a polycarbonate matrix has been studied. Several models have been used to predict the impact of the plasma treatment process on the strength of adhesion between both jointing partners. These approaches have been the thermodynamic work of adhesion which was calculated from the solid surface tensions, based on the results of contact angle measurements versus test liquids, the contact angle which was directly obtained via polycarbonate melt droplets on single carbon fibers and the zeta (ς)-potential data provided by streaming potential measurements. The results have been compared with the interfacial shear strength determined from the single-fiber fragmentation test. Additionally, the single-fiber tensile strength of the oxygen-plasma-treated carbon fibers was determined.

We confirmed that any physico-chemical method on its own fails to describe exactly the measured adhesion. However, for the investigated system, the conscientious interpretation of the data obtained from wetting measurements, in conjunction with the thermodynamic approach, is sufficient to predict the success of a modification technique which has been applied to one component in order to improve adhesion.

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.

We have subjected polycarbonate (PC), low density polyethylene (LDPE), polystyrene (PS), polypropylene (PP), and Hytrel^® (HY, a thermoplastic elastomer) to atmospheric pressure oxygen plasma treatment for varying amounts of time. Effects of the treatment have been evaluated in terms of the water wetting angle, dynamic friction, scratch resistance, and sliding wear. Although PS, PP, and HY do not undergo significant tribological changes as a result of the interaction with plasma, PC and LDPE show more pronounced and useful effects, such as a lowering of dynamic friction in PC and wear reduction in LDPE. These results can be explained in terms of the changes in chemical structures and increase of hydrophilicity. Based on the effects of oxygen plasma treatment on PC and LDPE, these two polymers have been subjected to longer oxygen plasma treatments and to argon, nitrogen, and air plasmas. Resulting effects on friction and scratch resistance are compared to determine the mechanisms responsible for the various surface behaviors. Chemical surface modification—as represented by changing contact angles—contributes to the tribological responses. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers

This paper describes our investigation of the effects of forced air plasma treatment on polypropylene and polyethylene. The morphology of the treated surfaces has been carefully examined using a variety of tools including optical profiling. The complex surface morphology was observed to change with increasing treatment and varying intensity of the treatment over the surface. Optimum treatment conditions have been deduced using surface energy determinations and can be compared with the morphological changes. Determinations of surface energy, both the polar and non-polar components, have been made after exposure to varying moisture conditions for varying times. Different results are obtained for different environments and from different materials. These results demonstrate that forced air plasma treatment is a highly effective means of increasing the surface energy of polymers, which can be long-lasting, provided the treated surfaces are kept in dry conditions.

Chromic acid solutions were used to oxidatively etch linear (high density) and branched (low density) polyethylene and isotactic polypropylene. Etched surfaces were characterized by surface IR spectroscopy, wettability, electron microscopy and aqueous adhesive bonding (peel test). Polypropylene was found to etch rapidly, but showed little residual chemical or topographical change. The polyethylenes etched more slowly, especially in the case of the linear polymer, but showed large changes in surface chemistry as a result of oxidative attack. Adhesion onto polyolefin films and fabric increased very rapidly during the first few seconds of attack. This increase is interpreted in terms of wettability, topography and cohesive strength of the surface layer. The differences in etch behavior between the polyolefins is interpreted in terms of ease of oxidative attack at branch points, and surface accessibility to the acid.

Polypropylene–nylon 6 10 composites were prepared by the in situ polymerization of the nylon monomers on polypropylene films. The adhesion between the nylon and the polypropylene was markedly improved by a brief corona discharge treatment of the films in nitrogen prior to coating. This improvement was demonstrated by an increase in the peel strength of the nylon coating and a decrease in brittleness of photo-oxidized compesites when corona treatment was used. Adhesive bonding between the nylon and substrate was sufficiently strong to cause cohesive failure in the corona-treated polypropylene. Only interfacial failure was observed at untreated surfaces. These effects were demonstrated by electron microscopy of the surfaces produced in peel tests. The effects of corona treatment on adhesive bonding characteristics of surfaces are discussed in terms of the chemical and physical changes observed in treated surfaces.

The wetting (or dewetting) of a solid by a liquid is an integral part of many important processes such as coating, petroleum recovery, distillation and the handling of liquid fuels in low gravity conditions. Several experiments^1–4 have shown that wetting lines (where liquid, air and solid phases meet) which are straight at slow rates of movement over the solid have a sawtooth shape at sufficiently high speeds. We now offer a quantitative explanation for this phenomenon based on the postulate that, for a given system, there is a maximum rate at which wetting can proceed. The consequences of this interpretation are likely to be important, since, in many practical situations, the aim is to maximise the speed of wetting without entraining the displaced phase.

Wetting is basic to coating. Initially air contacts the solid, and during coating the liquid displaces the air from the moving solid surface so that none is visible in the coated film. Thus, coating is a process of dynamic wetting. For uniform coating, the wetting line must remain straight and advance steadily. At sufficiently high speeds, however, the wetting line becomes segmented and unsteady as a thin air film forms between the solid and liquid. The air film disrupts the uniformity of the coated film, and often air bubbles appear in the coating. Dynamic wetting failure limits coating speed.

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.

Any review on the shape of a liquid droplet on top of a solid surface has to start with the pioneering work by P.S.Laplace and Sir Thomas Young almost two centuries ago [1, 2]. Young and Laplace set out to describe the phenomenon of “capillary action” in which the liquid inside a small capillary tube may rise several centimeters above the liquid outside the tube [3]. To understand this effect, two fundamental equations were derived by Young and Laplace. The first equation, known as the Laplace or Young-Laplace equation [1], relates the curvature at a certain point of the liquid surface to the pressure difference between both sides of the surface, and we consider it next in more detail. The second equation is Young’s equation [2], which relates the contact angle to the surface tensions involved.

A reexamination of previous studies concerning the electrical (‘corona’) discharge treatment of polyethylene and the resulting enhancement of autoadhesion has been carried out. X-ray photoelectron spectroscopic data provide new insight into the phenomenon by showing surface oxidation to result from treatment in ‘inert’ gases. Treatment in hydrogen is an exception and results in no autoadhesion enhancement even though energy input into the film is more efficient than in air. Autoadhesion theories based on electret formation are rejected; those based on hydrogen bonding are largely up-held and shown to be more generally applicable than at first imagined.

Titanium films, 1 μm thick were electron‐beam evaporated onto polyethylene (PE) that had been pretreated in situ by 2 keV Ar⁺ bombardment. A measure of the film adhesion was obtained by measuring the pull strength required to remove the Ti films. A strong dependence of the adhesion on the ion dose was found. The pull strength had a maximum of approximately 20 MPa after a dose of 6×10¹⁴ ions/cm² but decreased for higher ion doses. Without any ion bombardment prior to deposition, the adhesion was very poor with a pull strength of approximately 2 MPa. XPS analysis was used to examine the effect of the ion bombardment on the chemistry of the PE substrate and the Ti/PE interface. Untreated PE samples were contaminated with surface impurities and probably also with low molecular weight hydrocarbons. As the adhesion is maximized, most of the impurities are removed by the ion bombardment. The strong adhesion is suggested to be due to formation of a carbidelike Ti–C interfacial layer, detected by XPS.

Ti films were deposited onto high‐density polyethylene (HDPE) samples by electron‐beam evaporation. Prior to film deposition the samples were in situ pretreated by Ar ion bombardment using a sputter ion gun. The adhesion of the films, determined as the pull strength required for film failure, was measured as a function of ion dose. HDPE substrates processed at two different temperatures were examined. The adhesion of the Ti films to HDPE samples processed at ≊150 °C increased with the ion dose to a steady‐state value corresponding to the cohesive strength of the HDPE substrate. The adhesion to the samples processed at ≊200°C increased to a maximum and then decreased for further ion bombardment to a level of the same order as that for films deposited onto as‐prepared samples. The effects of the ion bombardment upon the HDPE surface chemistry were examined by means of x‐ray photoelectron spectroscopy (XPS). The ion bombardment resulted in dehydrogenation and cross linking of the surface region and for prolonged ion bombardment, a graphitelike surface was obtained. The film/substrate interface as well as the initial Ti film growth were examined by XPS analysis. A chemical interaction which resulted in Ti–C bonds was observed at the interface. The Ti film growth followed a pronounced three‐dimensional growth mode on as‐prepared surfaces whereas the ion bombardment resulted in a change toward a more two‐dimensional growth mode. The difference in adhesion behavior for the two types of HDPE substrates was found to be due to a difference in the amounts of low molecular weight products present within the substrates. The HDPE substrates processed at ≊200°C contained larger amounts of low molecular weight products and also had a lower degree of crystallinity and a less closely packed structure compared to those substrates processed at ≊150°C. This resulted in a segregation of low molecular weight products towards the surface of substrates processed at ∼200 °C. This segregation in turn is suggested to lead to a weak boundary layer, reducing the adhesion to as‐prepared samples and to substrates exposed to a high ion dose.

In this work we modified the surface of polyethylene in order to coat it with highly-fluorinated UV-curable coatings and assure good adhesion between the two polymers. Different methods were investigated, and a successful treatment was the grafting of a monomer containing a group able to dissociate under UV light. The surface modification was assessed by XPS, ATR–FT-IR and AFM analyses. The modified substrate was easily coated with the photocurable fluorinated formulation, and the highly hydrophobic and oleophobic layer formed after irradiation adhered well to the polyethylene substrate.

An expression is derived, from simple statistical thermodynamical considerations, to relate the cohesive energy density (C.E.D.) to intermolecular interaction parameters. From analogous theoretical relations in the literature for the surface tension and the index of refraction together with the derived expression for the C.E.D., we can obtain relations between the C.E.D. on the one hand and the surface tension and the index of refraction, respectively, on the other. These relations are compared with empirical relations in the literature. The exponents of the surface tension and the index of refraction in the empirical relations are different from those in the relations obtained here. The derived relation between C.E.D. and surface tension is shown to be applicable to experimental data with excellent agreement for both organic liquids and polymers. As surface tension measurements are very simple to perform, another main point of interest of the derived relation is knowledge of the solubility parameters of polymers (the square root of the C.E.D.) from critical surface tension measurements without the necessity of solubility and swelling experiments which are often awkward. The relation between the C.E.D. and the index of refraction derived in this paper implies grave theoretical objections to applications in practice.