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1036. Nihlstrand, A., T. Hjertberg, and K. Johansson, “Plasma treatment of polyolefins - influence of material composition, 1: Bulk and surface characterization,” Polymer, 38, 3581-3589, (1997).

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.

1035. Sako, N., T. Matsuoka, and K. Sakaguchi, “Effect of interface on fracture mechanism of GF/PP composites using O2 plasma treatment,” Composite Interfaces, 4, 401-415, (1997).

Polypropylene sheets are treated with oxygen plasma for the interfacial control of GF/PP composites. The interfacial strength between glass fabric and PP resin is estimated by the T-peel test method. The evaluation of T-peel test data is done by both the T-peel strength method and the T-peel amplitude method. The T-peel strength value and T-peel amplitude value were respectively increased to about 50% and 120% compared with each value of non-treated specimens. The T-peel strength relates to the surface energy on the PP-sheet and the T-peel amplitude relates to the fracture pattern of the delamination surface. From SEM observations on the delamination surface, many voids in the space enclosed with fiber bundles are observed in the case of non-treated specimen and no void and fiber bridging are observed on the plasma treated specimens. It is found that interfacial properties between fiber and resin are improved by this plasma process.

1032. Bodio, F., N. Compiegne, L. Kohler, J.J. Pireauz, and R. Cuadano, “Tailoring the SiOx-polypropylene interface through plasma pretreatment: A test case for the acid-base concept,” in 20th Annual Anniversary Meeting, 41-44, Adhesion Society, 1997.

1031. Weitzsacker, C.L., N. Dontula, A. Centeck, M.J. Ricj, and L.T. Drzal, “Utilising x-ray photoelectron spectroscopy to investigate modified polymer surfaces,” in 20th Annual Anniversary Meeting, 641-643, Adhesion Society, 1997.

1029. Friedrich, J., “Plasma treatment of polymers,” Adhasion Kleben & Dichten, 41, 28-33, (1997).

1022. Sullivan, N., M.C. Branch, M. Ulsh, and M. Strobel, “Flame treatment of polyolefin materials: Characterisation of gas phase phenomena,” in 20th Annual Anniversary Meeting Conference Proceedings, 101-103, Adhesion Society, 1997.

984. Nihlstrand, A., T. Hjertberg, and K. Johansson, “Adhesion properties of oxygen plasma-treated polypropylene-based copolymers,” Polymer, 38, 1557-1563, (1997).

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.

983. Xiao, G.Z., “Effects of solvents on the surface properties of oxygen plasma-treated polyethylene and polypropylene films,” J. Adhesion Science and Technology, 11, 655-663, (1997).

The effects of solvents on the surface properties of oxygen plasma-treated polyethylene and polypropylene films have been studied by ESCA, contact angle measurement, and adhesion testing. The results show that oxygen plasma treatment produces some low molecular weight materials (LMWM) on the treated surfaces, which can be removed, to some extent, by solvents. It seems that the LMWM has different solubilities in different solvents. Among the solvents (water, acetone, and 2-propanol) used, acetone has the most significant effect. The removal of LMWM considerably reduces the wettability of the treated materials, but does not impair the adhesion increased by the plasma treatment.

982. Nihlstrand, A., T. Hjertberg, and K. Johansson, “Plasma treatment of polyolefins - influence of material composition, 2: Lacquer adhesion and locus of failure,” Polymer, 38, 3591-3599, (1997).

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.

981. Choi, D.M., C.K. Park, K. Cho, and C.E. Park, “Adhesion improvement of epoxy resin/PE joints by plasma treatment of PE,” Polymer, 38, 6243-6249, (1997).

Low density polyethylene (LDPE) and high density polyethylene (HDPE) were plasma-treated with N2 and O2 plasma. The wettability and polar component of surface free energy of plasma-treated polyethylene were investigated by contact angle measurement. The concentration of functional groups formed by plasma treatment such as hydroxyl and carbonyl groups was measured using attenuated total reflection Fourier transform infrared spectroscopy (ATR FTi.r.). The concentration of polar functional group increased rapidly with 5–10s of plasma treating time and then very slowly after that. The adhesion strength of epoxy resin/plasma-treated polyethylene joints was examined by a 90° peel test. The increase of the adhesion strength was similar to that of concentration of polar functional groups. The higher adhesion strength of epoxy resin/plasma-treated HDPE joints was observed than that of epoxy resin/plasma-treated LDPE joints since HDPE deformed more during the peel tests and had more polar functional groups on the surface.

974. Saito, D., “Surface modification by corona discharge,” Nippon Gomu Kyokaishi, 70, 333-339, (1997).

908. no author cited, “Surface tension of inks and paper; project 2695-26,” Chesapeake Packaging Co., 1997.

550. Rawls, A.S., et al, “Evaluation of surface concentration of additives in LLDPE films,” in ANTEC 97, Society of Plastics Engineers, 1997.

530. Matuana, L.M., J.J. Balatinecz, and C.B. Park, “Evaluation of adhesion between PVC and surface-treated wood veneer laminates,” in ANTEC 97, Society of Plastics Engineers, 1997.

453. Dontula, N., C.L. Weitzsacker, and L.T. Drzal, “Surface activation of polymers using ultraviolet light activation,” in ANTEC 97, Society of Plastics Engineers, 1997.

2397. Grace, J.M., J. Chen, L.J. Gerenser, and D.A. Glocker, “Use of glow discharge treatment to promote adhesion of aqueous coatings to substrate,” U.S. Patent 5582921, Dec 1996.

2078. Koh, S.-K., W.-K. Choi, J.-S. Cho, S.-K. Song, Y.-M. Kim, and H.-J. Jung, “Ar+ ion irradiation in oxygen environment for improving wettability of polymethylmethacrylate,” J. Materials Research, 11, 2933-2939, (Nov 1996).

Ion irradiation with various oxygen flow rates has been carried out to improve the wettability of polymethylmethacrylate (PMMA) to water and to enhance the adhesion between Al and the polymer. Ar+ ion and oxygen ion were irradiated on the polymer, and amounts of ions were changed from 5 × 1014 Ar+/cm2 to 5 × 1016 Ar+/cm2 by a broad ion beam source. Oxygen gas from 0 ml/min to 7 ml/min was flowed near the polymer surface during the ion irradiation, and the energy of ions was changed from 500 eV to 1500 eV. The wetting angle was reduced from 68° to 49° with the Ar+ ion irradiation only at 1 keV energy, to 43° with the oxygen ion irradiation, and dropped to 8° with Ar+ ion irradiation with flowing 4 ml/min oxygen gas near the polymer surface. Changes of wetting angle with oxygen gas and Ar+ ion irradiation were explained by a two-step chemical reaction among polymer matrix, energetic ions, and oxygen gas. The effects of Ar+ ion and oxygen ion irradiation were explained by considering formation of hydrophilic groups due to a reaction between irradiated polymer chain by energetic ion irradiation and blown oxygen gas, and enhanced adhesion between Al and PMMA was explained by the formation of electron acceptor groups in polymer and electron donors in metal, and by the chemical reaction in the interface between irradiated polymer surface and deposited metal.

1205. Comyn, J., L. Mascia, X. G., and B.M. Parker, “Corona-discharge treatment of polyetheretherketone (PEEK) for adhesive bonding,” Intl. J. Adhesion and Adhesives, 16, 301-304, (Nov 1996).

1441. Teltech Resources Network Corp., “Low surface energy substrates present bonding challenges,” Adhesives Age, 39, 38-44, (Oct 1996).

1047. DiGiacomo, J.D., and J. Pezzuto, “Troubleshooting flame plasma surface treating systems-Q&A approach,” in 1996 Polymers, Laminations and Coatings Conference Proceedings, 101-104, TAPPI Press, Oct 1996.

986. Kang, E.T., K.L. Tan, K. Kato, Y. Uyama, and Y. Ikada, “Surface modification and functionalisation of polytetrafluoroethylene films,” Macromolecules, 29, 6872-6879, (Oct 1996).

Argon plasma-pretreated polytetrafluoroethylene (PTFE) films were subjected to further surface modification by near-UV light-induced graft copolymerization with acrylic acid (AAc), sodium salt of styrenesulfonic acid (NaSS), and N,N-dimethylacrylamide (DMAA). The surface compositions and microstructures of the modified films were characterized by angle-resolved X-ray photoelectron spectroscopy (XPS). A stratified surface microstructure with a significantly higher substrate-to-graft chain ratio in the top surface layer than in the subsurface layer was always obtained for PTFE surface with a substantial amount of the hydrophilic graft. The stratified surface microstructure was consistent with the observed hysteresis in advancing and receding water contact angles. The graft yield increased with Ar plasma pretreatment time and monomer concentration. Covalent immobilization of trypsin on the AAc polymer-grafted PTFE films was facilitated by water-soluble carbodiimide (WSC). The effective enzyme activities increased initially with increasing surface concentration of the grafted AAc polymer but became saturated at a moderate AAc polymer concentration. The immobilized enzyme could still retain close to 30% of its original activity. Solution-coating of the polymeric acid-modified PTFE films with the emeraldine (EM) base of polyaniline readily resulted in an interfacial charge transfer interaction and a semiconductive PTFE surface.

302. Ray, A., “Is in-line corona treating necessary?,” Flexo, 21, 56-58, (Oct 1996).

36. Boyle, E., “Taking the measure of surface treatment is a learning process,” Paper Film & Foil Converter, 70, 52-54, (Oct 1996).

5. Bentley, D.J., “How to measure treatment (or, is this trip necessary?),” Paper Film & Foil Converter, 70, 24, (Oct 1996).

1409. Meiners, S., J. Salge, E. Prinz, and F. Forster, “Surface modification of polymer materials by transient gas discharges at atmospheric pressure,” in 5th International Conference on Plasma Surface Engineering, Garmisch-Partenkirchen, Sep 1996 (also in Suraface and Coatings Technology, Jan 1998, Vol. 98, p. 1121-1127).

The treatment of surfaces by corona discharges is a well-established method to improve surface properties. The surface to be treated is moved continuously and is exposed to transient gas discharges, known as microdischarges, in air at atmospheric pressure between electrodes, where at least one electrode is covered with a dielectric barrier. Because of the short duration, only some 10 ns, the current through the microdischarges is predominantly carried by electrons. The ion temperature remains close to room temperature. Owing to these properties such discharges are qualified to treat surfaces which are sensitive to higher temperatures. For a large number of applications this treatment is adequate, but the adhesion of aqueous glues and inks to some plastic materials is insufficient if the surfaces are treated in this way. Furthermore, it is difficult to meet the requirements of surface properties of, for instance, polyolefine film (e.g. surface tension, adhesion). This material is not based on monomers containing chlorine or fluorine and is preferred for ecological reasons. This paper presents the results of experiments which demonstrate that in comparison to a common corona treatment significant improvements in surface properties of plastic materials can be achieved if repetitively generated pulse trains and reactive gases are used instead of air. If, for instance, the microdischarges are established in acetylene, thin films with a thickness of several namometres are formed on surfaces, which increase and stabilize the surface tension up to a level of 72 mN m−1. The state of the art of this new technology is discussed.

1195. Belgacem, M.N., A. Blayo, and A. Gandini, “Surface characterization of polysaccharides, lignins, printing ink pigments, and ink fillers by inverse gas chromatography,” J. Colloid and Interface Science, 182, 431-436, (Sep 1996).

84. Dinelli, B., J.C. Jammet, and K. Kuusipalo, “Interactions between melt nature and pretreatments: key to good adhesion,” TAPPI J., 79, 189-193, (Sep 1996).

4. Bentley, D.J., “Taking the 'magic' and mystery out of treating,” Paper Film & Foil Converter, 70, 24, (Sep 1996).

2148. Coates, D.M., and S.L. Kaplan, “Modification of polymeric material surfaces with plasmas,” http://www.4thstate.com/publications/modofpolyPrint.htm, Aug 1996.

1943. Nakamura, Y., and K. Nakamae, “Adhesion between plasma-treated polypropylene films and thin aluminum films,” J. Adhesion, 59, 75-86, (Aug 1996).

Polypropylene (PP) film was treated with radio-frequency-induced oxygen plasma, followed by the vacuum deposition of aluminum (Al) thin film, and the peel strength of the Al deposited PP film (Al/PP) was examined. The peel strength of plasma-treated PP film varied widely in the range of 6.7 to 157 N/m depending upon the plasma treatment conditions, whereas that of the untreated PP was 5.2 N/m. The peel strength was minimized at oxygen pressure near 13.3 Pa (0.1 Torr), and decreased with increasing discharge power. The peel strength rapidly increased at the initial stage of plasma treatment (∼ several seconds), decreased at the second stage, and slightly increased again at the third stage. A good agreement was found between the peel strength of Al/PP and the amounts of oxygen introduced onto the PP surface at the initial stage. A short-time treatment was very effective to improve the adhesion of Al/PP. At the end of the second stage, a large amount of carbon was detected by XPS on the Al layer of the peeled interface of Al/PP, which gave a minimum peel strength. Cohesive failure of PP film might have occurred. SEM photograph showed that PP surface was etched by oxygen plasma at the thrid stage. These peel behaviors of Al/PP were explained by the chemical and physical changes of the PP surface caused by oxygen plasma treatment: (1) introduction of O-functional groups onto the PP surface at the initial stage, (2) formation of weak booundary layers resulting from the partial scission of PP molecules at the second stage, and (3) plasma etching of the PP surface at the third stage.

310. Sarmadi, M., and F. Denes, “Surface modification of polymers under cold plasma conditions,” TAPPI J., 79, 189-204, (Aug 1996).

2396. Grace, J.M., J. Chen, L.J. Gerenser, and D.A. Glocker, “Use of glow discharge treatment to promote adhesion of aqueous coatings to substrate,” U.S. Patent 5538841, Jul 1996.

988. Miller, J.D., S. Veeramasuneni, J. Drelich, M.R. Yalamanchili, and G. Yamauchi, “Effect of roughness as determined by atomic force microscopy on the wetting properties of PTFE thin films,” Polymer Engineering and Science, 36, 1849-1855, (Jul 1996).

The influence of film roughness on the wetting properties of vacuum-deposited polytetrafluorethylene (PTFE) thin films has been investigated using atomic force microscopy (AFM) and contact angle goniometry. Surface roughness has been characterized by atomic force microscopy in terms of RMS roughness (Rq) and fractal dimensions. A contact angle correlation with surface roughness, as determined by AFM, is evident from these results, which are discussed on the basis of wetting theory. The results also confirm that the high water contact angles (as high as 150°) recently observed at the surface of a new water repulsive coating material (mixture of PTFE and binder) are because of surface roughness. Such measurements clarify the effect of nanometer-size surface asperities on the wetting properties of hydrophobic coating.

989. Strobel, M., M.C. Branch, M. Ulsh, R.S. Kapuan, S. Kirk, and C.S. Lyons, “Flame surface modification of polypropylene film,” J. Adhesion Science and Technology, 10, 515-539, (Jun 1996).

Contact-angle measurements, the ASTM standard wetting test for polyolefin films, and X-ray photoelectron spectroscopy (XPS or ESCA) were used to characterize flame-treated polypropylene (PP) films. Two combustion models, STANJAN and PREMIX, were then used to determine the chemical and physical properties of the flames used to treat the PP films. Both the flame equivalence ratio and the position of the PP film in the flame are important variables in determining the extent of oxidation and improvement in wettability obtained by flame treating. The optimal equivalence ratio for the flame treatment of PP is 0.93, while the optimal luminous flame-to-film distance is 0-2 mm. Modeling of the combustion processes occurring in the flame provides evidence that the extent of treatment correlates closely with the concentrations of H, O, and OH radicals present in the flame. The extent of surface modification of the flame-treated PP does not appear to correlate with either the flame temperature or the concentraion of oxygen molecules. The mechanism of surface oxidation by flame treatment probably involves polymer-radical formation by O and OH, followed by rapid reaction of the polymer radicals with O, OH, and O2.

725. Li, D., and A.W. Neumann, “Wettability and surface tension of particles,” in Applied Surface Thermodynamics, Neumann, A.W., and J.K. Spelt, eds., 509-556, Marcel Dekker, Jun 1996.

The interfacial energetics and wettability of small particles are of technological interest in many areas of applied science. Areas where such phenomena are important include the preparation of stable suspensions of particles (e.g., colour pigments in paints), the adhesion of particles to solid surfaces in various scenarios (e.g., lubrication), the dispersion of particles into a liquid or melt of a polymer, and the modification of particle surface properties through the adsorption of polymeric macromolecules or surfactants. The successful manipulation of the process being considered is largely determined by the physicochemical surface properties of the interacting surface components, and particularly the wettability and the surface (or interfacial) tension of the particles. The complexities of contact angle phenomena and surface tensions were discussed in Chapter 3.

724. Lahooti, S., O.I. del Rio, P. Cheng, and A.W. Neumann, “Axisymmetric drop shape analysis (ADSA),” in Applied Surface Thermodynamics, Neumann, A.W., and J.K. Spelt, eds., 441-508, Marcel Dekker, Jun 1996.

Numerous methodologies have been developed for the measurement of contact angles and surface tensions as outlined in Chapter 8 and Refs. 1-4. Liquid surface tension measurements commonly involve the determination of the height of a meniscus in a capillary, or on a fiber or a plate. Contact angles are most commonly measured by aligning a tangent with the profile of a sessile drop at the point of contact with the solid surface. Other notable methods are the Wilhelmy slide (Chapter 8) and the capillary rise technique (Chapter 9). An overview of such techniques reveals that in most instances a balance must be struck between the simplicity, the accuracy, and the flexibility of the methodology.

723. Kwok, D.Y., D. Li, and A.W. Neumann, “Capillary rise at a vertical plate as a contact angle technique,” in Applied Surface Thermodynamics, Neumann, A.W., and J.K. Spelt, eds., 413-440, Marcel Dekker, Jun 1996.

In the vast majority of contact angle studies in the literature, the method used is direct measurement of sessile drops. Recent developments in image analysis and processing have increased the accuracy and reduced the subjectivity considerably (see Chapter 10). Nevertheless, there are certain limitations which leave room for other techniques. One of the limitations of the classical sessile-drop method is that the camera or imaging device will be focused on the largest meridian section, and hence reflect only the contact angles at the point in which the meridian plane intersects the three-phase line. Surface heterogeneity and/or roughness could well cause variations of the contact angle along the three-phase line. An alternate approach is to infer the contact angle from the drop contact diameter (see Chapter 10). But even on very good solid surfaces, on which such effects are absent, there is a systematic problem with this method: contact angles will change as a function of drop size for drops up to approximately 1 cm diameter. While this dependence can indeed be used to determine line tension (see Chapter 4), this and other similar effects interfere with the interpretation of contact angles in terms of surface energetics (see Chapter 3).

722. Spelt, J.K., and E.I. Vargha-Butler, “Contact angle and liquid surface tension measurements: general procedures and techniques,” in Applied Surface Thermodynamics, Neumann, A.W., and J.K. Spelt, eds., 379-412, Marcel Dekker, Jun 1996.

The accurate measurement of contact angles is essential in many areas of applied surface thermodynamics. As was seen in Chapters 3 and 5, the contact angle provides a unique means of determining solid-vapor and solid-liquid surface tensions. The range of applications of this measurement is remarkable, both as a simple tool to assess, for example, the cleanliness of surfaces, and as a highly sensitive scientific measurement aimed at providing information on the solid surface tension and the physical state of the surface. When first encountered, the measurement of contact angles appears to be quite straightforward. This apparent simplicity is, however, very misleading, and experience has shown that the acquisition of thermodynamically significant contact angles requires painstaking effort. This chapter addresses the many practical issues pertaining to the measurement of contact angles and liquid surface tensions, including the preparation of suitable solid surfaces and measuring liquids.

721. Moy, E., and A.W. Neumann, “Theoretical approaches for estimating solid-liquid interfacial tensions,” in Applied Surface Thermodynamics, Neumann, A.W., and J.K. Spelt, eds., 333-378, Marcel Dekker, Jun 1996.

720. Spelt, J.K., E. Moy, D.Y. Kwok, and A.W. Neumann, “The theory of surface tension components and the equation of state approach,” in Applied Surface Thermodynamics, Neumann, A.W., and J.K. Spelt, eds., 293-332, Marcel Dekker, Jun 1996.

The determination of solid and solid-liquid surface tensions is of importance in a wide range of problems in pure and applied science. There exist, at present, many indirect approaches for obtaining these values because it is not possible to measure directly surface tensions involving a solid phase. These various methods are often in considerable disagreement, both quantitatively and from a theoretical standpoint. The problem persists since most of these approaches have not been tested objectively through the prediction of physical phenomena which could be independently observed and thus used to validate the various theories.

 

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