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1249. Qiu, Y., Y.J. Hwang, C. Zhang, B.L. Bures, and M.G. McCord, “Atmospheric pressure helium + oxygen plasma treatment of ultrahigh modulus polyethylene fibers,” J. Adhesion Science and Technology, 16, 449-457, (2002).

Ultrahigh modulus polyethylene fibers were treated with atmospheric pressure helium + oxygen plasma in a capacitively coupled device at a frequency of 7.5 kHz. The fibers were treated for 0, 0.5, 1, 1.5, and 2 min. The surfaces of the fibers treated with He + O2 plasma were etched and micro-cracks were formed. XPS analysis showed a 65—213% increase in oxygen content on the surfaces of all plasma-treated fibers, except for the 1.5 min group. An increase in the concentration of CSingle BondO and the appearance of CDouble BondO bonds on the surfaces of plasma-treated fibers were observed. In the micro-bond test, He + O2 plasma-treated groups had a 65–104% increase in interfacial shear strength over that of the control. The tensile strength of the fibers was either unchanged or decreased by 10–13% by the plasma treatments.

1248. Qiu, Y., C. Zhang, Y.J. Hwang, B.L. Bures, and M.G. McCord, “The effect of atmospheric pressure helium plasma treatment on the surface and mechanical properties of ultrahigh-modulus polyethylene fibers,” J. Adhesion Science and Technology, 16, 99-107, (2002).

Ultrahigh-modulus polyethylene fibers were treated with atmospheric pressure He plasma on a capacitively coupled device at a frequency of 7.5 kHz and a He partial vapor pressure of 3.43 × 103 Pa. The fibers were treated for 0, 1, and 2 min. Microscopic analysis showed that the surfaces of the fibers treated with He plasma were etched and that the 2-min He plasma-treated group had rougher surfaces than the 1-min He plasma-treated group. XPS analysis showed a 200% increase in the oxygen content and a 200% increase in the concentration of CSingle BondO bonds (from 11.4% to 31%) and the appearance of CDouble BondO bonds (from 0% to 7.6%) on the surface of plasma-treated fibers for the 2-min He plasma-treated group. In the microbond test, the 2-min He plasma-treated group had a 100% increase of interfacial shear strength over that of the control group, while the 1-min He plasma-treated group did not show a significant difference from the control group. The 2-min He plasma-treated group also showed a 14% higher single-fiber tensile strength than the control group.

1233. McCafferty, E., “Acid-base effects in polymer adhesion at metal surfaces,” J. Adhesion Science and Technology, 16, 239-255, (2002).

The Lewis acid-Lewis base properties of various polymers have been determined by measuring the contributions γs + and γS - to the solid surface free energy using the contact angle approach of van Oss, Chaudhury, and Good. A new linear method to solve for γS + and γS - is employed in addition to the usual approach which uses three simultaneous equations. The set of liquid surface tension parameters developed by van Oss, Chaudhury, and Good, and the recent set of values developed by Della Volpe and Siboni are both useful in distinguishing between acidic and basic polymers. The adhesion (peel force) of an acidic pressure-sensitive adhesive is greatest on a basic oxide film. In addition, the adhesion (pull-off force) of the basic polymer poly(methyl methacrylate) is greatest for acidic oxide films. Thus, direct experimental evidence is provided as to the importance of Lewis acid-Lewis base effects in the adhesion of polymers on oxide-covered metals.

1227. Landete-Ruiz, M.D., J.A. Martinez-Diez, M.A. Rodriguez-Perez, A. Miguel, et al, “Improved adhesion of low-density polyethylene/EVA foams using different surface treatments,” J. Adhesion Science and Technology, 16, 1073-1101, (2002).

The adhesion between a polyurethane (PU) adhesive and four foams containing different low-density polyethylene (LDPE)/ethylene vinyl acetate (EVA) blends was improved by using different surface treatments. UV-ozone, corona discharge, and low-pressure oxygen plasma treatments for different times were used to increase the surface energy of the foams. The low-pressure oxygen plasma was the most successful surface treatment to promote the adhesion of the foams. A reduced length of treatment was needed to improve the adhesion of the foams containing higher EVA content. The surface treatments produced a noticeable decrease in contact angle values due mainly to the creation of different carbon–oxygen moieties and to the formation of cracks/heterogeneities on the foams surfaces. After oxygen plasma, removal of non-polar material from EVA surfaces allowed to expose acetate groups which are likely to be important for increasing the adhesion of the foams.

1223. Koh, S.K., J.S. Cho, K.H. Kim, S. Han, and Y.W. Beag, “Altering a polymer surface chemical structure by an ion-assisted reaction,” J. Adhesion Science and Technology, 16, 129-142, (2002).

A new surface modification technique, the so-called ion-assisted reaction (IAR), has been developed; such modification of polymer surfaces offers many industrial applications. The addition of new functional groups on polymer surfaces and permanent hydrophilic polymer surfaces (water contact angle below 30° and surface energy 60-70 mJ/m2) have been accomplished by IAR treatment. The formation of functional groups is significantly dependent on the flow rate of the reactive gas, the irradiating ion dose, and the ion beam energy. Improvements in wettability and surface energy are primarily attributed to the increase of polar characteristics due to the formation of functional groups such as Single Bond(CDouble BondO), Single Bond(CDouble BondO)Single BondOSingle Bond, Single Bond(CSingle BondO)Single Bond, etc. The characteristics of the IAR treatment have been reviewed, with outstanding results regarding the wettability and adhesion of various polymers such as PMMA, PC, PP, PS, PI, PVDF, and PTFE.

1221. Kim, B.K., K.S. Kim, C.E. Park, and C.M. Ryu, “Improvement of wettability and reduction of aging effect by plasma treatment of low-density polyethylene with argon and oxygen mixtures,” J. Adhesion Science and Technology, 16, 509-521, (2002).

To improve the hydrophilicity and reduce the aging effect, argon and oxygen mixtures were employed in the plasma treatment of low-density polyethylene (LDPE). Argon resulted in producing more oxygen ions and radicals in the plasma than only oxygen and forming cross-linked layers on the LDPE surface. Therefore, the water contact angle on plasma-treated LDPE decreased and the oxygen content measured by X-ray photoelectron spectroscopy (XPS) increased with the increase of argon content. The aging effect was also much reduced with the increase of argon content since argon induced cross-linking.

1218. Inagaki, N., K. Narushima, Y. Tsutsui, and Y. Ohyama, “Surface modification and degradation of poly(lactic acid) films by Ar-plasma,” J. Adhesion Science and Technology, 16, 1041-1054, (2002).

Surface modification of poly(lactic acid) (PLA) film surface by Ar-plasma was investigated by contact angle measurements and XPS in order to answer the following two questions. (1) Could the Ar-plasma modify the PLA film surfaces? (2) What chemical reactions occurred on the film surfaces during the Ar-plasma treatment? The Ar-plasma treatment did not lead to hydrophilic modification of the PLA film surface, but to degradation reactions of the PLA film. Poor modification may be due to instability of the carbon radicals formed from CSingle BondO bond scission in the PLA chains by the Ar-plasma.

1213. Green, M.D., F.J. Guild, and R.D. Adams, “Characterisation and comparison of industrially pre-treated homopolymer polypropylene, HF135M,” Intl. J. Adhesion and Adhesives, 22, 81-90, (2002).

The effects of 13 pre-treatments were examined to determine their effect on the surface region of homopolymer polypropylene. Five of the pre-treatments were examined in detail due to excellent joint strengths. They were: corona discharge, flame, fluorination, low-pressure vacuum plasma and atmospheric plasma. The pre-treatments were examined using X-ray photoelectron spectroscopy (XPS), angle resolved XPS (AR-XPS) and atomic force microscopy (AFM), to determine surface chemistry and topography. Of the 13 pre-treatments examined, it was found that the first five all showed the highest surface chemical modification of the pre-treatments studied. It was identified that the surface chemistry, concentration depth and topography varied widely across the five pre-treatments. However, all have been shown to have similar bond strengths with polyurethane adhesives, indicating that a number of significant factors were responsible for bond strength. It is surmised that the depth of the functional group concentration is the determinant joint strength parameter and not the O : C ratio or surface roughness.

1204. Chibowski, E., A. Ontiveros-Ortega, and R. Perea-Carpio, “On the interpretation of contact angle hysteresis,” J. Adhesion Science and Technology, 16, 1367-1404, (2002).

The determination of solid surface free energy is still an open problem. The method proposed by van Oss and coworkers gives scattered values for apolar Lifshitz-van der Waals and polar (Lewis acid-base) electron-donor and electron-acceptor components for the investigated solid. The values of the components depend on the kind of three probe liquids used for their determination. In this paper a new alternative approach employing contact angle hysteresis is offered. It is based on three measurable parameters: advancing and receding contact angles (hysteresis of the contact angle) and the liquid surface tension. The equation obtained allows calculation of total surface free energy for the investigated solid. The equation is tested using some literature values, as well as advancing and receding contact angles measured for six probe liquids on microscope glass slides and poly(methyl methacrylate) PMMA, plates. It was found that for the tested solids thus calculated total surface free energy depended, to some extent, on the liquid used. Also, the surface free energy components of these solids determined by van Oss and coworkers' method and then the total surface free energy calculated from them varied depending on for which liquid-set the advancing contact angles were used for the calculations. However, the average values of the surface free energy, both for glass and PMMA, determined from these two approaches were in an excellent agreement. Therefore, it was concluded that using other condensed phase (liquid), thus determined value of solid surface free energy is an apparent one, because it seemingly depends not only on the kind but also on the strength of interactions operating across the solid/liquid interface, which are different for different liquids.

1194. Banik, I., K.S. Kim, Y.I. Yun, D.H. Kim, C.M. Ryu, and C.E. Park, “Inhibition of aging in plasma-treated high-density polyethylene,” J. Adhesion Science and Technology, 16, 1155-1169, (2002).

The effects of cross-linking and crystallinity on the aging of plasma-treated high-density polyethylene (HDPE) have been investigated. In the case of mixed argon and oxygen, aging has been found to be reduced with an increased amount of argon in the mixture owing to an increased degree of cross-linking. A similar decrease in hydrophobic recovery has been achieved by increasing the crystallinity of HDPE. Diffusion of polar functional groups from the surface into the bulk has been observed to be lowered by both increasing the degree of cross-linking and crystallinity. The samples were analyzed by angle-resolved XPS, contact angle measurements and SEM investigations.

661. Gutowski, W.S., S. Li, L. Russell, C. Filippou, M. Spicer, and P. Hoobin, “Molecular brush concepts in surface engineering of polymers for enhanced adhesion of adhesives and polymeric coatings,” in Adhesive Joints: Formation, Characteristics and Testing, Vol. 2, K.L. Mittal, ed., 3-48, VSP, 2002.

This paper reviews the theoretical principles of macromolecular design of polymer interface/interphase systems for obtaining maximum adhesion. Subsequently, a relatively simple and industry-feasible technology for surface grafting connector molecules is discussed in detail and supported by a range of experimental examples. It is shown, in agreement with contemporary theory, that the use of chemically attached graft chemicals of controlled spatial geometry and chemical functionality enables a significant increase in the strength and fracture energy of the interphase, to the point of cohesive fracture of the substrate, or that of an adjacent medium such as adhesives, paints or elastomers. This occurs even after prolonged exposure of bonded or painted materials to adverse environments such as hot water, thermal shock, UV radiation and other hostile ambients.

405. no author cited, “Standard T698: Determination of wetting tension of polyethylene and polypropylene films and coatings (modified visking analytical technique),” in TAPPI 2002 - 2003 Test Methods, TAPPI Press, 2002.

404. no author cited, “Standard T552: Determination of wetting tension of polyolefin films and coated surfaces via the mayer rod technique,” in TAPPI 2002 - 2003 Test Methods, TAPPI Press, 2002.

2193. Donberg, D., “One new treater, many new benefits,” Paper Film & Foil Converter, 75, 0, (Dec 2001).

1724. no author cited, “Surface free energy of polymers - Optimisation of the determination of polymer surface free energy,” Materials Australia, 33, (Dec 2001).

1385. Tusek, L., M. Nitschke, C. Werner, K. Stana-Kleinschek, V. Ribitsch, “Surface characterization of NH3 plasma treated polyamide 6 foils,” Colloids and Surfaces A: Physicochemical and Engineering Aspects, 195, 81-95, (Dec 2001).

Nitrogen-containing plasmas are widely used to improve wettability, printability, bondability, and biocompatibility of polymer surfaces. Plasma-treatments fed with NH3 give rise to N-functionalities, such as amino ( NH2), imino ( CH NH), cyano ( C N) and others on polymers, plus oxygen-containing groups due to post-plasma atmospheric oxidation. This work deals with NH3 plasma treatment of PA 6 foils and the evaluation of surface modification as a function of treatment time. The introduced functionalities were observed by streaming potential measurements (surface charge), X-ray photoelectron spectroscopy analysis (nature of introduced functionalities), atomic force microscopy (surface topography), and contact angle measurement (assessment of treatment effect). The results show that the introduction of N-containing groups is increasing with longer treatment time only to a certain extent where the negative effect of surface destruction prevails over the positive effect of introduction of functional groups. The treatment causes a shift of the isoelectric point (IEP) toward pH of 6.2 as compared to 4.2 found for the untreated foil. If the treatment time is longer than 1 min the IEP is shifted to lower pH, the number of amino groups on the surface is reduced and the contact angle is increased.

1246. Pijpers, A.P., and R.J. Meier, “Adhesion behaviour of polyproylenes after flame treatment determined by XPS (ESCA) spectral analysis,” J. Electron Spectroscopy and Related Phenomena, 121, 299-313, (Dec 2001).

In a number of automotive applications of polypropylene (PP) good paint adhesion is essential. For industrial applications, the initially poor adhesion properties of PP compounds are often improved by flame treatment, resulting in good paint adhesion on the PP parts. For control purposes, intensive and time consuming paint tests are required. To relate adhesion behaviour with the parameters used in the flame treatment modification, several methods are applied such as simple surface tension tests with inks (wetting tests), contact angle measurements and standard XPS(ESCA) measurements. Unfortunately a good correlation is rarely obtained between these tests and the desired adhesion behaviour under rigid test conditions. Good wetting, for example, is necessary, but is no guarantee for good adhesion. In this paper results are presented on the characterisation of flame treated PP compounds by XPS, as well as the predictive information obtained from the XPS study concerning the paint adhesion behaviour of the modified PP surfaces.

893. Hibbard, D., “Sticky science: new polymer technology makes it easier to paint and glue plastic parts,” Modern Paints & Coatings, 91, 31, (Dec 2001).

887. Veselovsky, R.A., and V.N. Kestelman, Adhesion of Polymers, McGraw-Hill, Dec 2001.

2409. Blose,F., and K. Dippmann, “Corona station for the preliminary processing of a strip material,” U.S. Patent 6320157, Nov 2001.

1929. Leahy, W., V. Barron, M. Buggy, T. Young, A. Mas, F. Schue, T. McCabe, M. Bridge, “Plasma surface treatment of aerospace materials for enhanced adhesive bonding,” J. Adhesion, 77, 215-249, (Nov 2001).

The increased use of polyphenylene sulphide (PPS) and polyetheretherketone based composites for aircraft structures has highlighted the need for reliable methods of bonding these materials to metallic components such as titanium. Both composite and titanium adhesive bonds exhibit poor long-term durability when exposed to hot/wet conditions, aerospace fluids and solvents. As a result, surface treatments are employed to enhance surface energy, surface roughness and alter surface chemistry to provide better long-term durability. In this initial study the adhesive bonding of glass fibre reinforced GFR-PPS and commercially pure titanium was investigated. Prior to bonding, both materials were plasma treated using argon and oxygen gases in a RF discharge. Surface characterisation was carried out to optimise these treatments. Surface energy and wettability were examined using contact angle analysis, surface roughness was examined using scanning electron microscopy and atomic force microscopy, while X-ray photo-electron spectroscopy (XPS) was employed to study the surface chemistry. Bond strengths were determined using lap shear tests. Initial results reveal that these optimum plasma treatments produce a significant increase in bond strength.

1930. Li, L.-H., C. Macosko, G.L. Korba, A.V. Pocius, and M. Tirrell, “Interfacial energy and adhesion between acrylic pressure sensitive adhesives and release coatings,” J. Adhesion, 77, 95-123, (Oct 2001).

The interfacial adhesive behavior between acrylic pressure sensitive adhesive-like networks (PSA-LNs) and poly(vinyl N-alkyl carbamate) release coatings was studied using a contact mechanical method and peel tests. Surface energy and interfacial energy were directly measured in JKR tests using a novel sample construction. The surface energy of the poly(vinyl N-alkyl carbamates) was found to be around 20 mJ/m2. Interfacial energies between PSA-LNs and the release coatings were found to be quite high – between 7 and 24 mJ/m2. Changes in adhesion dynamics were governed by acid-base interactions between the carbamate in the release coating and the acid groups in the PSA-LN. The length of the alkyl chain in the release coating moderated this effect. We also found a correlation between fundamental adhesion energy and peel strength. Examination of this phenomenon provides a basis for understanding the poor storage stability of PSA tapes made using alkyl carbamates and acid-containing PSAs.

697. Jarvis, S.P., “Adhesion on the nanoscale,” in Nano-Surface Chemistry, Rosoff, M., ed., 17-58, Marcel Dekker, Oct 2001.

2212. Nolan, M.D., S. Greig, and N. Jadon, “Corona, ozone and flame treaters for extrusion coating lines,” in 2001 Polymers, Laminations and Coatings Conference Proceedings, TAPPI Press, Sep 2001.

1931. Zenkiewicz, M., “Some effects of corona discharge treatment of biaxially-oriented polypropylene film,” J. Adhesion, 77, 25-41, (Sep 2001).

The effects of the unit corona-treatment energy on the contact angle of various liquids, on the surface free energy, on the extent of oxidation of a surface layer, and on the adhesion of acrylic adhesive were studied using a biaxially-oriented polypropylene (BOPP) film. The surface free energy was determined with the van Oss-Chaudhury-Good (VCG) approach as well as with the wettability method. The extent of oxidation of the surface layer of the corona-treated BOPP film was evaluated with X-ray photoelectron spectroscopy. The adhesion strength of joints between the BOPP film and the acrylic adhesive was measured using the 180°

In the range of the unit corona-treatment energy up to 1.2 kJ/m2, a rapid increase in the surface free energy with the treatment energy is observed. In the range above that value, the surface free energy rises relatively slowly. The extent of oxidation of the surface layer and the adhesion strength of joints between the BOPP film and the acrylic adhesive are approximately in direct proportion to the unit energy of the corona treatment. A five-fold growth of the adhesion strength of the studied joints within the examined range of the treatment energy was found.In the range of the unit corona-treatment energy up to 1.2 kJ/m2, a rapid increase in the surface free energy with the treatment energy is observed. In the range above that value, the surface free energy rises relatively slowly. The extent of oxidation of the surface layer and the adhesion strength of joints between the BOPP film and the acrylic adhesive are approximately in direct proportion to the unit energy of the corona treatment. A five-fold growth of the adhesion strength of the studied joints within the examined range of the treatment energy was found.In the range of the unit corona-treatment energy up to 1.2 kJ/m2, a rapid increase in the surface free energy with the treatment energy is observed. In the range above that value, the surface free energy rises relatively slowly. The extent of oxidation of the surface layer and the adhesion strength of joints between the BOPP film and the acrylic adhesive are approximately in direct proportion to the unit energy of the corona treatment. A five-fold growth of the adhesion strength of the studied joints within the examined range of the treatment energy was found.

1528. Shenton, M.J., and G.C. Stevens, “Surface modification of polymer surfaces: atmospheric plasma versus vacuum plasma treatments,” J. Physics D: Applied Physics, 34, 2761-2768, (Sep 2001).

An atmospheric pressure non-equilibrium plasma (APNEP) has been developed in the UK by EA Technology Ltd and is currently being investigated in collaboration with the University of Surrey. The main focus is the use of atmospheric pressure plasmas to modify the surfaces of commercially important polymers including polyolefins, poly(ethylene terephthalate) and poly(methyl methacrylate). These surface modifications include surface cleaning and degreasing, oxidation, reduction, grafting, cross-linking (carbonization), etching and deposition. When trying to achieve targeted surface engineering, it is vital to gain an understanding of the mechanisms that cause these effects, for example, surface functionalization, adhesion promotion or multi-layer deposition. Hence comparisons between vacuum plasma treated surfaces have also been sought with a view to using the extensive vacuum plasma literature to gain further insight. In this paper, we will introduce the APNEP and compare the key characteristics of the plasma with those of traditional vacuum plasma systems before highlighting some of the surface modifications that can be achieved by using atmospheric plasma. Data from the analysis of treated polymers (by spectroscopy, microscopy and surface energy studies) and from direct measurements of the plasma and afterglow will be presented. Finally, our current understanding of the processes involved will be given, particularly those that are important in downstream surface treatments which take place remote from the plasma source.

1434. Kunz, M., “Surface modification of polymer substrates for improved adhesion of UV-cured systems,” in European Coatings Conference: Adhesion and Performance Enhancement, 115-128, Vincentz Verlag, Sep 2001.

1275. Lei, J., and X. Liao, “Surface graft copolymerization of 2-hyrdoxyethyl methacrylate onto low-density polyethylene film through corona discharge in air,” J. Applied Polymer Science, 81, 2881-2887, (Sep 2001).

The corona discharge technique was explored as a means of forming chemically active sites on a low-density polyethylene (LDPE) film surface. The active species thus prepared at atmospheric pressure in air was exploited to subsequently induce copolymerization of 2-hydroxyethyl methacrylate (HEMA) onto LDPE film in aqueous solution. The results showed that with the corona discharge voltage, reaction temperature, and inhibitor concentration in the reaction solution the grafting degree increased to a maximum and then decreased. As the corona discharge time, reaction time, and HEMA concentration in the reaction solution increased, the grafting degree increased. With reaction conditions of a 5 vol % HEMA concentration, 50°C copolymerization temperature, and a 2.0-h reaction time, the degree of grafting of the LDPE film reached a high value of 158.0 μg/cm2 after treatment for 72 s with a 15-kV voltage at 50 Hz. Some characteristic peaks of the grafted LDPE came into view at 1719 cm−1 on attenuated total reflectance IR spectra (inline imageCDouble BondO in ester groups) and at 531 eV on electron spectroscopy for chemical analysis (ESCA) spectra (O1s). The C1s core level ESCA spectrum of HEMA-grafted LDPE showed two strong peaks at ∼286.6 eV (Single BondCSingle BondOSingle Bond from hydroxyl groups and ester groups) and ∼289.1 eV (ODouble BondCSingle BondOSingle Bond from ester groups), and the C atom ratio in the Single BondCSingle BondOSingle Bond groups and ODouble BondCSingle BondO groups was 2:1. The hydrophilicity of the grafted LDPE film was remarkably improved compared to that of the ungrafted LDPE film. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2881–2887, 2001
https://onlinelibrary.wiley.com/doi/abs/10.1002/app.1738

1040. Shenton, M.J., M.C. Lovell-Hoare, and G.C. Stevens, “Adhesion enhancement of polymer surfaces by atmospheric plasma treatment,” J. Physics D: Applied Physics, 34, 2754-2760, (Sep 2001).

An atmospheric pressure non-equilibrium plasma (APNEP) developed in the UK by EA Technology Ltd is currently being investigated in collaboration with the University of Surrey. Of the many applications of surface modification that can be induced using plasmas, adhesion enhancement is one of the most commercially important. In this paper, we illustrate the use of an atmospheric plasma to enhance the adhesion characteristics of low-density polyethylene (LDPE) and poly(ethylene terephthalate) (PET). The polymers were treated in the remote afterglow region of an atmospheric pressure plasma to avoid the thermal effects that can cause degradation for thermally sensitive materials when placed in direct contact with the plasma. Reactive (oxygen containing) and inert (oxygen free) atmospheric plasmas rapidly impart adhesion enhancement by a factor of two to ten as measured by 180° peel tests. However, extended exposure to the atmospheric plasma does not impart additional adhesion enhancement as the surface is ablated revealing the underlying polymer with poor adhesive characteristics. In contrast, vacuum plasma treated LDPE and PET show increased adhesion with extended plasma treatment. An adhesion enhancement in excess of two to three orders of magnitude was found to be achievable for vacuum plasma treatment times greater than 10 min.

621. Della Volpe, C., and S. Siboni, “The evaluation of electron-donor and electron-acceptor properties and their role in the interaction of solid surfaces with water,” in Water in Biomaterials Surface Science, Morra, M., ed., 183-214, John Wiley & Sons, Sep 2001.

620. Vogler, E.A., “On the origins of water wetting terminology,” in Water in Biomaterials Surface Science, Morra, M., ed., 149-182, John Wiley & Sons, Sep 2001.

1932. Li, L.-H., M. Tirrell, G.A. Korba, and A.V. Pocius, “Surface energy and adhesion studies on acrylic pressure sensitive adhesives,” J. Adhesion, 76, 307-334, (Aug 2001).

The surface energy and adhesion dynamics of pressure sensitive adhesives-like networks (PSA-LNs) as mimics for PSAs were studied using JKR-based contact mechanics and peel tests. Acrylic acid (AA) was co-polymerized with 2-ethyl hexyl acrylate (2-EHA) and 1,6-hexane diol diacrylate (HDDA) to create PSA-LNs. The measured surface energy (27 to 31 mJ/m2) was sensible as surmised from their structure. Acrylic acid content increases the surface energy, threshold adhesion energy and adhesion hysteresis of PSA-LNs. Measurements of adhesion dynamics showed a dependence of adhesion energy to the 0.6–0.8 power of crack speed, depending upon the model chosen for analysis of the data. When compared with actual pressure-sensitive adhesive tape peel tests, the adhesion dynamics data predicted the peel strength. This study shows a direct relationship between threshold adhesion energy, crack propagation mechanics and peel strength measurements.

122. Geitner, W., “Flame treatment effect on OPP,” AIMCAL News, 14, (Aug 2001).

2545. Kropke, S., Y.S. Akishev, and A. Hollander, “Atmospheric pressure DC glow discharge for polymer surface treatment,” Surface and Coatings Technology, 142-144, 512-516, (Jul 2001).

We present a new approach for the surface treatment of polymer films at atmospheric pressure. The DC glow discharge is generated by applying a high voltage between two electrodes which are placed in a channel with a high flux of air. The air flow removes charge carriers from the plasma zone which prevents the formation of sparks. In the almost homogeneous plasma a comparably high electrical power is converted forming a high concentration of active species. The flowing air transports them to the polymer surface. We report the results of the first experiments with this set-up. The influence of various process parameters on the discharge properties is shown. The resulting alterations in the surface structure of the polymers are characterised by XPS and contact angle geometry.

2499. Arefi-Khonsari, F., J. Kurdi, M. Tatoulian, and J. Amouroux, “On plasma processing of polymers and the stability of the surface properties for enhanced adhesion to metals,” Surface and Coatings Technology, 142-144, 437-446, (Jul 2001).

This paper deals with the plasma surface treatment of polymers in a low frequency bell jar reactor with non-symmetrical configuration of electrodes. The highly energetic character of this discharge due to its low excitation frequency and electrode configuration, as well as its small discharge volume makes it a very efficient and fast functionalization process. Amongst the different plasma gases used for the adhesion improvement of polypropylene to aluminum, ammonia has shown to be the most suitable one for this application. Since the NH and NH 2 radicals play an important role in the kinetics of nitrogen incorporation in polymers, mixtures of N 2 and H 2 were also used as possible substitutes for ammonia. The former are more environmentally friendly and easier to handle in industry than ammonia. The efficiency of nitrogen rich mixtures in the case of the second application, i.e. adhesion improvement of copper to fluoropolymers has been compared to that of ammonia which still shows faster nitrogen incorporation. The last part of this paper is devoted to the study of the energetic character of plasmas of mixtures of He+NH 3 by OES and electrical measurements in the whole range of composition of the two gases. The results show that an ammonia percentage ranging from 5 to 10% in plasmas of mixtures of He/NH 3 represents a transition between two different discharge regimes. Plasmas of mixtures of He+2% NH 3 , characterized by highly energetic electrons, ions and probably metastables of helium give rise to enhanced adhesion of PP to aluminum which remains stable with time.

2408. Selwyn, G., I. Henins, S.E. Babayan, and R.F. Hicks, “Large area atmospheric-pressure plasma jet,” U.S. Patent 6262523, Jul 2001.

2031. Lim, H., Y. Lee, S. Han, and J. Cho, “Surface treatment and characterization of PMMA, PHEMA, and PHPMA,” J. Vacuum Science and Technology A, 19, 1490-1496, (Jul 2001).

Poly(methylmethacrylate) (PMMA), poly(2-hydroxyethyl methacrylate (PHEMA), and poly(2-hydroxypropyl methacrylate) (PHPMA) were modified to improve the wettability by two techniques: plasma and plasma source ion implantation. The modified surfaces were characterized to investigate the dependence of the modification and hydrophobic recovery on the polymer structure. The differences obtained under optimal experiment conditions among the polymers were interpreted in terms of their polymer structures including the glass transition temperature. The surface free energy, calculated from the contact angle measurements, revealed that its polar component was a dominant factor in improving the wettability. The PSII treatment created more functional groups on the surface and extensively modified the polymer layer than the plasma treatment.

1933. Lee, L.-H., “The unified Lewis acid-base approach to adhesion and solvation at the liquid-polymer interface,” J. Adhesion, 76, 163-183, (Jul 2001).

We present our unified Lewis acid–base approach to adhesion and solvation at the liquid-polymer interface. This approach is to complement the original methodologies proposed by Fowkes and by van Oss, Chaudhury and Good (VCG). Intermolecular interactions are primarily dominated by dispersion, d, hydrogen bonding, h, and secondarily affected by orientation, o, and induction, i. Generally, the polarization component, p, represents both i and o interactions. Fowkes suggested that the acid–base component, γab, of the surface tension should consist of both h and p interactions. However, VCG proposed that the acid–base components, γab, result solely from hydrogen bonding, γh, that is equivalent to 2(γ+ γ)1/2, where γ+ and γ are the two hydrogen bonding parameters. VCG defined γLW as the Lifshitz-van der Waals component consisting of d, o and i contributions, thus, surface tension, γ, equals γab(VCG)+γLW. Both Fowkes and VCG assumed that the polar interactions for a liquid on a low energy surface are negligible.

Now, we assume otherwise, and we treat the specific acid-base interaction to be hydrogen bonding. In addition, we also take into account the nonspecific polarization, p, interaction in terms of the equilibrium spreading pressure, πe, resulting from the adsorption of a liquid vapor on the polymer surface. Thus, our unified approach uses the dispersion component, γd, of Fowkes, the hydrogen bonding, h, of VCG and the polarization, p, in terms of πe. The difference between the initial (theoretical) and equilibrium (experimental) surface tensions is πe, and others have observed that πe on some polymers is substantial. The determination of several initial surface tensions of polymers by considering the effect of polarization is discussed.

In the Appendix, we shall illustrate that this polar component, πe, is equivalent to the LESR polarity-dipolarity parameter, πe, (represented by the same symbol but in different context) for the solvatochromic treatment. Furthermore, the surface tension components, πd, γ+, γ and πe, are now somewhat comparable with the four parameters in the original Taft-Kamlet relationship, δ, α, B, and πe. Thus, our proposed unified approach may finally help elucidate the long-debated Lewis acid–base theories pertaining to adhesion and solvation of polymers.

956. Novak, I., and S. Florian, “Investigation of hydrophilicity of polyethylene modified by electric discharge in the course of ageing,” J. Materials Science Letters, 20, 1289-1291, (Jul 2001).

Hydrophilicity of polyethylene modified by electric discharge in the course of aging was investigated. The experiments were carried out with the foils of low-density polyethylene (PE) containing additives as well as with additive-free foils. Antiblocking or sliding agents, antioxidants and antistatic agents were used as additives. The results showed that the absence of additives in PE was responsible for the higher degree of modification of PE foils by corona discharge when compared with the polymer containing additives. The value of surface free energy (SFE) found after 30 days of aging of the modified PE foils was lower than the value recommended for inking the printing foils.

888. Beake, B.D., N.J. Brewer, and G.J. Leggett, “Scanning force microscopy of polyester:Surface structure and adhesive properties,” in Advances in Scanning Probe Microscopy of Polymers (Macromolecular Symposia 167), Tsukruk, V.V., and N.D. Spencer, eds., 101-116, Wiley-VCH, Jul 2001.

Scanning force microscopy has been used to characterize the surface structure and properties of poly(ethylene terephthalate) (PET) films. Two types of biaxially oriented film have been studied: one (Melinex O) is free of additives while the other (Mylar D) contains particulate additives at the surface. Contact mode characterization of both materials provide clear images of the polymer surface and (in the case of Mylar D) the additives. Phase images reveal substantial nanoscale morphological detail, including small features thought to be crystallites. To model the adhesive properties of polymer surfaces, mixed self-assembled monolayers containing polar and methyl terminated adsorbates were studied using chemical force microscopy. It was found that the strength of the tip-sample adhesion increased with the fraction of polar terminated adsorbates at the surface when a carboxylic acid terminated tip was employed, while the trend was reversed when a methyl terminated tip was used. Adhesion forces measured for plasma treated PET increased with treatment time, and linearly with the cosine of the water contact angle, illustrating the chemical selectivity of chemical force microscopy. However, friction forces were found to vary in a non-linear fashion, indicating that changes to the polymer surface mechanical properties following treatment were important.

 

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