ABSTRACTS

The following is a list of the abstracts for papers which will be presented in the SECOND INTERNATIONAL SYMPOSIUM ON ADHESIVES: SYNTHESIS, CHARACTERIZATION AND APPLICATIONS The listing is alphabetical by presenting author. This list is updated continually to add abstracts as they become available and make appropriate corrections. This list may be conveniently searched by using the editor provided with most popular browsers (e.g. Microsoft Explorer, Netscape, ... etc.)

Modeling of Cathodic Debonding of Elastomer-to-Metal Adhesive Bonds

The deleterious effect of galvanic activity on the durability of rubber-to-metal adhesive bonds is investigated. The generation of hydroxyl ions at the elastomer/metal bondline due to an imposed voltage (current) is shown to be detrimental for cathodically exposed adhesively bonded structures. Bond weakening was found to be caused by alkali attack on the primer-metal oxide interface and was found to be governed by a diffusion-controlled degradation process. The independent accelerating parameters contributing to weakening were identified as temperature and the imposed current density (through the applied voltage). An Arrhenius relationship was shown to model the effect of temperature quite well. For a given electrolyte and metal substrate, the effect of voltage is accounted for through an exponential relationship that relates the voltages to the corresponding current densities. A model that takes advantage of these relationships was developed and was utilized to fit the experimentally collected accelerated debond data. The model accounts for the delay times as well as weakening rates. This model may be used as a first-order durability predictor for similar adhesively bonded systems upon exposure to cathodic environments.

The Effect of Ageing on Foamability of Phenol-formaldehyde Plywood Glue

The changes in plywood bonding adhesive systems, for example, gluing with foamable adhesive, has reduced the amount of the needed glue and thereby lowered the production costs. [1-3] At the moment several mills in the USA use foamable phenol-formaldehyde for making plywood. In Finland, so far only one plywood mill uses foamable phenol-formaldehyde glue for plywood production, but the number of mills will increase in the future.

The glue lot may be done in advance for the manufacturing purposes. Depending on the working schedules the glue mixtures may be let to stand over the weekend. After the standing period, the glue should still be usable for making plywood. This study was done to determine the effect of ageing on the foaming of the glue mixture. The experiments were done with two different foaming agents; spray dried blood and sodium lauryl sulphate. A glue lot was foamed after several different time periods; these were 0 h, 1 h, 3 h, 24 h, 48 h, 72 h and 6 days. Viscosities, as well as densities and surface tensions were measured from the unfoamed glue mixture. Densities and surface tensions were determined from the foamed glue. The results were encouraging. In both cases, the mixed glue lots stayed usable for six days. In fact, it was observed that the glue needed some time to stand in order to get the best foaming results.

1. Maloney, T.M., The family of wood composite materials, Forest Prod. J., 46 (1996) 2, p. 19-26.

2. Sellers, T. Jr., Miller, G. D. and Nieh, W. L.-S., Evaluation of three fillers in PF adhesive used to bond intermediate moisture content plywood: glueline durability and knife wear, Forest Prod. J., 40 (1990) 10, p. 23-28.

3. Spelter, H. and Sleet, G., Potential reductions in plywood manufacturing costs resulting from improvement technology, Forest Prod. J., 39 (1989) 1, p. 8-15.

Characteristics of Adhesed Multi-layered Gels and Texturized Fruits

A simple way of achieving different textures and tastes in the same bite is to construct a food product made up of different layers. Multi-layered hydrocolloid-based foods are important in the framework of foods of the future. The compressive force-deformation relationships of multi-layered hydrocolloid gels composed of different combinations of water-soluble, edible polymers and gelled texturized fruits adhesed via three different gluing techniques were calculated from those of the individual layers. The gluing techniques consisted of: pouring hot hydrocolloid solution on a gelled layer, using melted agar as a glue between already gelled layers, or simultaneously pouring pre-gelled hydrocolloid solutions. The modelšs applicability to a given gel system was demonstrated, suggesting a very convenient tool for analyzing and predicting the compressive behavior of any number of food arrays with different layer combinations. The adhesive-bond strength between different adhered edible gel layers was determined by peel and tensile-bond tests. Adhesive strength was influenced by polymer concentration and type, roughness of the layer interface and heat-maintaining capacities of the poured gel layers. Jelly-food-type preparations assembled according to the described methodologies can be produced as multi-layered arrays, with excellent adhesiveness between participating gel layers.

1) Laboratoire des Matériaux Macromoléculaires - UMR CNRS 5627, Institut National des Sciences Appliquées, 20 ave Albert Einstein - 69621 Villeurbanne Cedex, FRANCE

2) DOW Deutschland Inc., D77836 Rheinmuster, GERMANY

3) CERDATO, ATOFINA - 27470 Serquigny, FRANCE

4) Laboratoire Matière Molle et Chimie, UMR ESPCI-CNRS-ATOFINA,

10 rue Vauquelin - 75231 Paris Cedex 05, FRANCE

A New Class of Nanostructured Epoxies

The reinforcing strategies of epoxy thermosets rely on the control of the phase separation between the additive (reactive rubbers or thermoplastics) and the growing thermoset polymer. Initially the additive is soluble in the thermoset precursors. The reduction of entropy due to the polymerization induces the expulsion of the additive from the matrix often well before the gel point. The resulting macrophase separation affects the performances of the material, reliable tools for finely tuning the morphology of such systems are thus clearly desirable. Here, we present a strategy based upon the self-assembly process of blends of epoxy systems and ABC triblock copolymers. It relies on the strong affinity between PMMA and epoxy thermosets. Thanks to a new synthesis route ABC block copolymers with a PMMA block can be produced, namely Poly(Styrene-b-1,4 Butadiene-b-Methyl methacrylate), SBM. Polystyrene and polybutadiene are not soluble in the epoxy precursors at room temperature. Thus, in the reactive system a regular network of SB domains is generated by the self organization process. This nanostructure is governed by thermodynamics, the size and geometry of the dispersed domains are controlled by the concentration and the ratio of the blocks lengths. The domain size is of the order of magnitude of the chain length, ranging typically from 10 to 30 nanometers. What controls the blend's morphology throughout the curing process of the thermoset was one topic on which we focused our interest. The affinity between PMMA and the growing epoxy network was shown to be crucial. Nanostructured thermosets have been obtained. These supramolecular architectures yield significant toughness improvements while preserving the optical transparency of the material. The reinforcing mechanisms are not yet fully understood : it is intriguing to induce significant toughening with elastomer domains smaller than 30 nanometers in diameter. Besides being epoxy tougheners, SBM can broaden the scope of applications of thermosets due to specific rheological behaviors. Thanks to the self assembly process taking place in the blend of the SBM block copolymers with the epoxy thermosets precursors, the reactive solvent can be turned into a reactive gel or solid (before curing). This physical gelation is induced by the microphase separation and is thus thermoreversible. At relatively moderate loadings of block copolymers the reactive blend behaves like a thermoplastic material, with adjustable tackiness, and an elongation at break at room temperature that exceeds 500%. These results evidence that SBM block copolymers open a broad area for designing new class of thermoset materials.

Combinatorial Test Methods for Polymer Adhesion

Although commercial adhesives and issues of adhesion have existed for decades, the scientific community only has a basic understanding of how adhesion works. We know that adhesion depends on a myriad of variables including such parameters as temperature, surface energy, mechanical properties, and thickness. The problem is that the number of possible combinations of different conditions that control adhesion is exhaustively large. Consequently, it is difficult, using existing experimental methods, to explore all of these possibilities to gain a fundamental understanding of adhesion. We have developed a test method that allows the data from as much as 1600 different tests to be efficiently collected within the same time that it takes to complete a single conventional test (approximately 15 minutes). The test can also be used to quickly answer questions like the one posed above. Essentially, we can create a library of the different materials, and within a single test, determine what materials will stick to a given tape. Our initial experiments have focused on efficiently determining the effect of temperature, nanometer changes in thickness and surface energy on the adhesion of glassy polymers and in validating the technique. These studies will play a significant role in the design of high-tech materials such as for electronic packaging where the adhesion of nano-thin polymer films is critical.

1) Faculty of Engineering and Surveying, University of Southern Queensland, West street, Queensland, Toowoomba, 4350, AUSTRALIA.

2) Industrial Research Institute, Swinburne (IRIS), Swinburne University of Technology (SUT), Henry Street, Hawthorn, VIC 3122, AUSTRALIA.

Curing Adhesives using Variable Frequency Microwaves (VFM) Facilities

Microwave processing of adhesives is a relatively new technology alternative that provides new approaches for enhancing material properties as well as economic advantages through energy savings and accelerated product development. Alternative in the sense that most adhesives are normally cured in ambient conditions or in ovens. However, the most commonly used facilities for microwave processing of materials operate on fixed frequency microwaves (FFM), e.g., 2.45 GHz. This paper presents a review of microwave technologies, processing methods and industrial applications, using variable frequency microwave (VFM) facilities. The technique offers rapid, uniform and selective heating over a large volume at a high energy coupling efficiency. This is accomplished using a preselected bandwidth sweeping around a central frequency by employing tunable frequency sources. Successful applications of these modern facilities include finding out the optimum cavity conditions of one glass fibre reinforced thermoplastic matrix composites and three types of adhesives, e.g., two-part five-minute Araldite, and the joining of the above-mentioned composite material with, or without, primers. Finding out the optimum cavity conditions of a material has helped identify the best frequency range to process the material using microwave energy and by means of the VFM facility. Microwave energy has been used to rapidly cure several types of two-part epoxy based adhesives, e.g., Araldite. Bond strengths obtained using variable frequency microwave (VFM) techniques are compared with adhesive joints cured in fixed frequency microwave (FFM) conditions.

^# To whom all correspondence should be addressed.

New Silicone Hybrid Materials Having High Adhesion and Chemical Resistance for Electronic Applications

The objective of our work is to develop new silicone hybrids to meet increasing demand for high adhesion and harsh fluid resistance in electronic packaging industry. Compared to traditional silicones with limited strength variations, a new family of Pt-catalyzed heat curable silicone hybrids from soft gels, tough elastomers to rigid materials with hardness range covering Shore 00, A and D, have been developed based on National Starch and Chemical Company's proprietary silicon hydrocarbon resin. This paper focuses on the new semi-rigid and rigid hybrids (with hardness range of Shore A and D, respectively). The technology capabilities are demonstrated using three typical products. These materials combine the benefits of both high strength and inherent toughness. They deliver high adhesion to a variety of electronic materials including silicon die, ceramics, metals and engineering plastics; and also display good resistance to a broad range of fluids such as fuels, oils, acids and salt solution. Therefore, they are suitable for use as adhesives for packaging electronic and optical components used in harsh environment, particularly in automotive applications. Compared to epoxy and polyurethane technologies, these silicone hybrids offer high temperature resistance, high purity and environmental-friendly solutions.

Practical Adhesion and Residual Stresses : Ultimate Parameters Versus Critical Strain Energy Release Rate

Epoxy-diamine liquid prepolymers are extensively applied onto metallic substrates and cured to obtain painted materials or adhesive bonded structures. Overall performances (including practical adhesion and durability) of paints and adhesive joints depend on the nature of both the substrate (and its surface treatment) and the epoxy-diamine prepolymer (and its curing conditions). Indeed, the behavior of such systems depends on the created interphase between the organic layer and the substrate [1,2]. Moreover, intrinsic and thermal residual stresses are developed within painted or bonded systems. When residual stresses are higher than the organic layer/substrate adhesion, buckling, blistering, debonding may occur leading to a catastrophic drop of their performances. Practical adhesion can be evaluated with either ultimate parameters (Fmax or Dmax) or the critical strain energy release rate. Using the three point flexure test (ISO 14679-1997), it was possible to observe that for the same epoxy-diamine/metallic substrate system, the ultimate load decreases while residual stresses increase when the liquid/solid duration time increases. Ultimate loads and residual stresses depend on the metallic surface treatment. For such systems, the critical strain energy release rate which take into account the residual stress profile and the Young's modulus gradient [3] remains quite constant whatever may be the metallic surface treatment. These variations will be discussed and correlate to the formation mechanisms of the interphase. Then, the increase of residual stresses can be associated to the size increase of the chelate crystals.

[1] S. Bentadjine, A.A. Roche and J. Bouchet, Adhesion Aspects of Thin Films, Vol.1, pp.239-260, Ed. K.L. Mittal, VSP 2001.

[2] S. Bentadjine, R. Petiaud, A.A. Roche and V. Massardier, Polymer, 42 (2001) 6271-6282.

[3] J. Bouchet, A.A. Roche, E. Jacquelin and G.W. Scherer, Adhesion Aspects of Thin Films, Vol.1, pp.217-237, Ed. K.L. Mittal, VSP 2001.

1) Institute of Polymer Research, Hohe Straße 6, D-01069 Dresden, GERMANY

2) Technical University of Chemnitz, Department of Polymer Chemistry, Straße der Nationen 62, D-09111 Chemnitz, GERMANY

Silanol Groups as Reactive Anchor for Polymers - Synthetic Ways to Novel Hybrid Materials -

Hybrids form a new class of materials allowing to combine advanced properties of inorganic metal oxides and synthetic polymers. Several synthetic routes have been developed to produce such novel hybrids. The advanced properties of the new materials are mainly determined by the structure formation between the participating components and the controlled surface reactivity. Electrokinetic measurements carried out in combination with modern surface sensitive analytical techniques like photoelectron spectroscopy (XPS) open up the chance to get information on surface properties. In addition, the knowledge on the reactive behaviour of the hybrid surfaces allows to develop strategies for further surface modification and functionalization reactions.

We used three synthetic concepts to generate hybrid particles where the inorganic phase forms a core covered by the polymer layer. The description of the initial step of the cationic polymerization of vinyl monomers onto silica by means of electrokinetics will be taken as an excellent example to demonstrate the suitability of these methods for the development of synthetic strategies. XPS and microelectrophoresis have been used to investigate the surface structure and reactivity of the formed hybrid particles.

Reactive polymers like polyepoxides were also used to coat silica and alumina. The hybrid particles show surface properties quite different from the ones of graft-polymerized hybrid particles. During secondary reactions aldehyde, amino, and carboxyl groups were introduced in the hybrid surface. Changes in the surface functionality were shown by electrokinetic experiments.

The third species of hybrid particles were made from silica and polyelectrolytes. Partially hydrolyzed poly(vinyl formamide)s containing poly(vinyl amine) sequences were adsorbed onto silica particles. Electrokinetic experiments and potentiometric titrations show rather a weak interaction between the polyelectrolyte molecules and the silica surface. In contrast, hybrids produced via the other synthetic routes show a covalent bonding of the polymers onto the inorganic particle surface.

1) Pennsylvania State University, Materials Science and Engineering, University Park, PA 16802.

Peel Testing and Crack Propagation in Adhesively Bonded Ti/carbon Fiber-Epoxy Composite Panels

Floating roller peel tests were performed at Penn State University on bonded laminate panels. The composite panels were comprised of Ti-6Al-4V alloy sheet, AF-191 structural adhesive, and laminated 8551-7 carbon fiber epoxy composite. Peel force (measured load/specimen width) is a function of fracture energy in the adhesive/composite and plasticity in the titanium adherend. Factors including test methodology, specimen geometry, and sample fabrication led to variations in peel force. Large variations in adhesive thickness were identified as a primary cause of the variation in the data. Changes in adhesive thickness led to changes in the types of fracture that occurred during the peel test. Three different types of crack formation and propagation were identified. After testing, the amount of damage in the composite was measured. Comparison of the peel force with a normalized damage parameter for the composite/adhesive shows that peel force increases with increasing damage parameter. The changes in adhesive thickness also led to changes in test geometry at the point of adherend detachment. This geometry change caused the extent of plastic deformation in the detached titanium strip to vary throughout the test. Recommendations for reducing peel force variability are made.

Manufacture of Medium-Density Fiberboard (MDF) from Laccase-Treated HTMP Fibers

Abstract - High-temperature defibration of wood at preheating temperatures of 171-202°C generates low-molecular weight lignin fragments in the fibers, rendering the fibers reactive toward laccase-catalyzed oxidation. The amount of low-molecular weight lignin in fibers and lignin reactivity toward laccase increase with an increase in defibration temperature. Most of the reactive material can be removed from the fibers by neutral water extraction. The laccase-catalyzed oxidation of easily accessible phenolic hydroxyl groups, located in the low-molecular weight lignin fraction and on the fiber surfaces, results in the formation of phenoxy radicals in the fibers. Dry-process 12-mm thick medium-density fiberboards (MDF) of high mechanical strength can be made from hardwood or softwood HTMP fibers treated with laccase in the refiner blowline without synthetic resins or long laccase incubation times. The bonding mechanism is believed to be largely associated with interaction of phenoxy radicals on adjacent fibers, resulting in interfiber covalent bonding. The internal bond strength (IB) and thickness swell properties of the boards improve as defibration temperature increases. The improvement of board properties correlates with radical formation in the fibers on laccase treatment in water suspension. Differences in the chemical composition of fiber surfaces do not account for the different fiber reactivities during oxidation with laccase and properties of MDF boards bonded with laccase.