The effects of intense pulsed high power ion beam (HPIB) treatment of ultra-high strength polyethylene (UHSPE) fibers on the fiber/epoxy resin interface strength were studied. For this study, argon ions were used to treat Spectra^™ 1000 (UHSPE) fibers in vacuum. Chemical and topographical changes of the fiber surfaces were characterized using Fourier transform infrared spectroscopy in attenuated total reflectance mode (FTIR-ATR), X-ray photoelectron spectroscopy (XPS), dynamic wettability measurements, and scanning electron microscopy (SEM). The fiber/epoxy resin interfacial shear strength (IFSS) was evaluated by the single fiber pull-out test. The FTIR-ATR and XPS data indicate that oxygen was incorporated onto the fiber surface as a result of the HPIB treatment. The wettability data indicate that the fibers became more polar after HPIB treatment and also more wettable. Although the total surface energy increased only slightly after treatment, the dispersive component decreased significantly while the acid-base component increased by a similar amount. SEM photomicrographs revealed that the surface roughness of the fibers increased following the HPIB treatment. The single fiber pull-out test results indicate that HPIB treatment significantly improved the IFSS of UHSPE fibers with epoxy resin. This enhancement in IFSS is attributed to increased roughness of the fiber surface resulting in mechanical bonding and in increased interface area, increased polar nature and wettability, and an improvement in the acid-base component of the surface energy after the HPIB treatment.

Ultra-high strength polyethylene fibers were treated with excimer laser and high power ion beams (HPIB) to enhance their adhesion to epoxy resins. Laser treatments were carried out in air, argon, and helium environments and HPIB treatments were carried in vacuum. The effects of these treatments on the surface topography and chemistry were characterized using several techniques. It can be seen from the results that both laser and HPIB treatments increased the fiber surface roughness as well as the surface polarity. HPIB treated fibers had a characteristic bumpy surface while the laser treated fibers had deeper striations or a rougher surface. Although the total surface energy did not change after the treatments, the acid-base component increased significantly and the dispersive component decreased by almost the same amount. After the treatments the fiber-epoxy interfacial shear strength (IFSS) increased between 200 to 300%. This enhancement is attributed to the increased roughness of the fiber surface and increased specific interface area, increased polar nature and wettability, as well as improvement in the acid-base component of the surface energy.

An equation of state is developed which allows the surface tension of a low-energy solid to be determined from a single contact angle formed by a liquid which is chemically inert with respect to the solid and whose liquid surface tension is known. The equation of state is obtained using two independent methods. In the first one, similar arguments to those in previous papers are used; however, the qualitative argument, based on the general appearance of plots, is replaced by computer curve fitting and statistical analysis. The second method, which has not been employed heretofore, treats the solid surface tension as an adjustable parameter. Molecular arguments in conjunction with the interaction parameter Φ are used to eliminate poor choices of the solid surface tension. The results are in excellent agreement with the first method.

The range of validity of the equation of state and practical points in its application are discussed.

A technique is described for performing temperature scanning measurements of the surface tension of polymer solutions. Measurements on solutions of a high molecular weight and a low molecular weight monodisperse polystyrene in tetralin, decalin, and n-hexadecane are reported. Whereas previous investigations of other physical properties of polystyrene solutions had revealed only one anomaly, at about 50°C in some cases and at about 70–80°C in others, the curves presented here show two anomalies, near 45°C and 70°C, respectively. These anomalies are tentatively attributed to conformational changes of the polymer chains.

A theoretical treatment of the effect of surface heterogeneity on contact angles is given, by means of a model employing the capillary rise of a liquid in contact with a stripwise heterogeneous surface. Local contortions of the liquid-vapor surface are postulated to conform to an assumed periodic shape of the three-phase line. A minimum of free energy is found in a configuration in which Young's equation is obeyed locally. When the width of the strips is below some value of the order of 0.1 μ, the amplitude of the periodic contortion of the three-phase line is less than about 10 A, which is operationally indistinguishable from a straight line. Extension of this model is made to a patchwise heterogeneous surface, and a mechanism for hysteresis is developed. For patches smaller than about 0.1 μ, it is shown that heterogeneity should make a negligible contribution to hysteresis.

The previous chapter was largely theoretical, in that it dealt with the interpretation of contact angle results in terms of solid surface energies. It also delved into the question of how the structure of a solid surface affects the contact angle that a liquid forms on the solid. The level of structure considered there included features that are not macroscopically observed, such as microheterogeneities, or minute peaks, pits, hills, and grooves in various geometries. Their existence may be inferred from certain observations, such as contact angle hysteresis, and sometimes they can be observed directly, e.g., with the optical or electron microscope.

The critical surface tension γ_c of polyvinyl butyral has been measured with polyhydric alcohols and halogenated hydrocarbons. Despite variations in polymer composition (residual OH content) and modes of preparation, γ_c is found to be 24–25 dynes/cm. with the former class of liquids. The —CH₃ groups appears to predominate over —CH₂, ether oxygen, and OH groups present. Steric effect may account for this biasing of the γ_c values toward the lowest surface energy group present. Fowkes' relation based on dispersion force interactions only is found to fit the data reasonably well. Comparative data on polyethylene are also presented.

Copper films evaporated on argon-oxygen plasma-treated poly(phenylene-vinylene) films have been studied by scratch test, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The adhesion of the metallic film to the polymer substrate was greatly enhanced after treatment and found to increase with the treatment time. SEM observation of the treated samples revealed that the morphology of the polymer surface was gradually changed with the treatment time as compared with that of the bare polymer film. On the other hand, XPS analysis of the polymer-metal interface showed that the bonding between carbon, oxygen and copper were subsequently modified as compared with those obtained in untreated samples. The high adhesion strength observed on these substrates was related to the modification in the surface morphology on the one hand and to the formation of new compounds at the polymer-metal interface on the other. The nature of the interfacial layer and its influence on the adhesion of the copper layer was discussed by comparing the results with those obtained in poly(phenylene-vinylene) (PPV)-Al systems.

The exposure of a polymer to ozone in the presence of ultraviolet light (UV/ozone) is a simple and effective way to improve the wettability of the surface. Using atomic force microscopy (AFM) we were able to examine the changes in morphology and the increase in the adhesion force at the surface of biaxially oriented polypropylene (PP) films after treatment with UV/ozone. It is clearly shown by atomic force microscopy (AFM) that UV/ozone treatment modified the original, fine, fiber-like structure to one displaying the formation of mounds or droplets. These droplets are most likely comprised of short chains of oxidized polymer or low-molecular weight oxidized materials (LMWOM). The size of the mounds increased with increasing treatment time. More interestingly, lateral force imaging AFM were capable of distinguishing these mounds from the surrounding surface, indicating that the mounds were formed on aggregation of the loose LMWOM during the UV/ozone treatment, while the surrounding surface was covered by bound moderately oxidized materials. The adhesion force was estimated from measurements made on the amount of force required to retract the tip from the surface after the two had made contact. A clear increase in adhesion force was observed on the modified PP film surface, which indicates an increase in the surface energy. We have demonstrated that mechanical scratching can alter the surface morphology and increase the surface energy of a polymer on a micrometer scale. The mechanically-scratched areas are more susceptible to modification than the surrounding unscratched surface when exposed to UV/ozone.

The degree of roughness and the linear direction of the abrasion process operated over the adherend surface are two important design factors for the adhesive joint. Thus, in the first part of this study, the surface roughness was varied by means of different grades of abrasive paper and its effect on the joint strength was studied. An investigation involving changing the linear direction with respect to the loading direction was also carried out. These experiments were done to determine the effectiveness of the abrasion process for the pretreatment of the adherend. A significant increase in joint strength was found for the abrasion treatment. However, it was shown that different linear directions did not have any significant effect on the joint strength. In the second part of this study, thermodynamic analysis of the bonding of dissimilar polymeric materials using different adhesives in terms of their surface tension, critical surface tension, and joint strength was carried out. The aim of the study was to determine the thermodynamic criteria for maximum joint strength in bonding dissimilar materials. The results showed that the joint strength was dictated by the adherend with the lower critical surface tension. Maximum joint strength for bonding dissimilar materials is attained when the surface tension of the adhesive used is close to that of the adherend with the lower critical surface tension.

Injection-moulded plates of four commercial thermoplastic polyolefins (TPOs) were subjected to oxygen plasma treatment. The modified surfaces were analyzed by water contact angle measurements and X-ray photoelectron spectroscopy (XPS), and the adhesion properties of the plates were evaluated by a 90 peel test after being lacquered with a two-component polyurethane lacquer. The study included treatments in two different plasma reactors operating at different frequencies. The influence of certain processing parameters, such as discharge power, flow rate and gas pressure, was investigated, as was that of frequency (using the same reactor). While the results revealed that oxygen plasma treatment indeed led to improved wettability, the degree of surface modification was not highly affected by changes in the processing conditions. In contrast, there was a great effect on the lacquer adhesion, in particular by changes in discharge power and gas pressure. The results also showed that the TPOs were sensitive in different ways towards changes in the processing conditions. It was also found that, regardless of the absolute peel force, the failures occurred in the substrate at some distance below the oxidized layer. These observations were attributed to a VUV-induced formation of radicals which, in the case of polypropylenebased materials, predominantly lead to^-scissions. As secondary radicals have a higher tendency to form crosslinks that can compensate for chain scission reactions, the difference in the sensitivity of the TPOs was proposed to be related to the amount and distribution of ethylene in the materials.

The adhesion properties achieved after oxygen plasma treatments of ten polypropylene (PP) and thermoplastic polyolefin (TPO) materials of different compositions were studied. It is shown that the adhesion between a polyurethane (PUR) lacquer and plasma-treated materials was strongly influenced by the plasma treatment conditions and the chemical composition of the materials. Generally, a low power-to-gas pressure (P/G) ratio during the plasma treatment and a high ethylene content, preferably in the form of blocks, and/or the presence of double bonds in the matrix, are favourable for adhesion properties. Moreover, the TPOs were less sensitive towards the plasma treatment conditions than the corresponding PPs. The properties and the type of rubber may also be important for the adhesion properties. Furthermore, it was shown by X-ray photoelectron spectroscopy (X.p.s.) and Fourier transform infrared (FTi.r.) spectroscopy (using the attenuated total reflectance (ATR) technique) that all failures—even the apparently interfacial failures—were located in the substrate, below the oxidized surface layer, the only difference being the depth of failure. The fracture surfaces of samples showing low peel forces generally had a more PP-like composition than fracture surfaces that were clearly cohesive in the substrate. This observation offers evidence that the lacquer adhesion is determined by the extent to which chain scission reactions occur in the near-surface region of the substrate during the plasma treatment. © 1997 Elsevier Science Ltd.

Injection-moulded plates of four polypropylene-based copolymers with ethylene or an unconjugated diene as the comonomer were subjected to oxygen plasma treatments. The main objective was to investigate how the degree of wettability and the adhesion properties were influenced by the type and amount of comonomer and by selected plasma parameters. The change in wettability was monitored by static water contact angle measurements and the adhesion between plasma-treated polypropylene plates and a two-component polyurethane lacquer was evaluated by a 90° peel test. No significant difference in the degree of wettability depending on material composition or treatment conditions could be observed. However, the lacquer adhesion was shown to be a function of both material composition and discharge power, while the influence of gas pressure was less clear. For all procssing conditions used, the lacquer adhesion was distinctly improved as the diene content was increased. An increasing extent of crosslinking reactions combined with a reduction in the number of main chain scissions are proposed to account for the observed results.

Injection-moulded plates of ten polypropylene (PP) and thermoplastic polyolefin (TPO) materials with varying material composition (different type of rubber, varying degree of ethylene etc.) were characterized before and after oxygen plasma treatments. Untreated materials were studied by means of differential scanning calorimetry (d.s.c.), size exclusion chromatography (s.e.c.), Fourier-transform infrared spectroscopy (FTi.r.), attenuated total reflectance (ATR) and transmission measurements, and the effect of plasma treatment conditions was followed by X-ray photoelectron spectroscopy (X.p.s.) and contact angle measurements. S.e.c. analysis revealed only minor variations among the materials, while the d.s.c. and FTi.r. experiments confirmed that the differences were to be expected as a result of the variation in material composition. The FTi.r.-ATR results showed that all samples had a gradient in material composition. The materials were generally more rich in PP in the topmost ∼ 200 nm than in the first ∼800 nm, and a lesser extent of ethylene modification and/or rubber was observed in the topmost ∼ 200 nm. It was also shown that the degree of surface crystallinity was normally greater at ∼ 800 nm than at ∼ 200 nm, and that a higher mould temperature led to a higher degree of surface crystallinity. The water contact angles and the atomic composition showed that the materials were more oxidized after plasma treatment at high power-to-gas pressure (P/G) ratios than at low ratios. Moreover, the dependence on material composition was weak for samples that were plasma-treated at low P/G ratios whereas the materials that were least ethylene-modified were less oxidized than the others at high P/G ratios. © 1997 Elsevier Science Ltd.

The polymers PET, PA6, PVDF, HD-PE, and PP are activated by a commercially available plasma jet system at atmospheric pressure to improve adhesive bondability. The adhesion properties of the activated surfaces are evaluated by lap shear tests. The results are correlated with the surface properties that are investigated by XPS, AFM, and contact angle measurements. In addition the influence of operational parameters of the plasma treatment is studied. The activated samples exhibit a substantially increased bonding strength. The improvement can be related to an increase of oxygen concentration, and to changes of the topology of the substrate surface induced by the thermal component of the plasma. The most influential parameters in the plasma treatment are the distance between substrate and nozzle exit and the treatment time.