Adhesion in Polymer/Steel Sandwiches

Polymer/steel sandwiches are able to reduce the nuisance due to vibrations and noise in automotive applications, for example. Thin layers of polymer are inserted between two metal sheets. The deformation of the polymer is responsible for the damping properties of the sandwiches and, therefore, the viscoelastic behavior of the polymer is of major importance. However, adhesion between the two materials is also required. The polymer studied in the present work is a copolymer of ethylene and vinyl acetate (EVA) containing 28 wt% of vinyl acetate grafted with maleic anhydride (1 wt%). A wedge test is used to measure the interfacial strength and the durability of the adhesive bond. The influence of the surface treatment of the steel substrate on the adhesive behavior and the effect of water has been studied. FTIR surface analysis after cleavage helped us to identify the nature of the interfacial bonds.     

Adhesion in Polymer/Steel Sandwiches

Polymer/steel sandwiches are able to reduce the nuisance due to vibrations and noise in automotive applications, for example. Thin layers of polymer are inserted between two metal sheets. The deformation of the polymer is responsible for the damping properties of the sandwiches and, therefore, the viscoelastic behavior of the polymer is of major importance. However, adhesion between the two materials is also required. The polymer studied in the present work is a copolymer of ethylene and vinyl acetate (EVA) containing 28 wt% of vinyl acetate grafted with maleic anhydride (1 wt%). A wedge test is used to measure the interfacial strength and the durability of the adhesive bond. The influence of the surface treatment of the steel substrate on the adhesive behavior and the effect of water has been studied. FTIR surface analysis after cleavage helped us to identify the nature of the interfacial bonds.     

The relationship between the strength of an adhesive bond and the thermodynamic properties of its components

Maximum stability of any system is achieved when its free energy is minimum, in accordance with the second law of thermodynamics. Considering the adhesive bond as a thermodynamic system, it is proposed that the minimum interfacial energy coincides with (1) the maximum strength, and (2) the maximum durability, understood as bond resistance to degradation under environmental attack. The thermodynamic properties of bond components which play a key role in promoting conditions for maximum strength of adhesion have been identified. The general pattern of the relationship: STRENGTH = function (interfacial energy and related parameters), has been developed based on experimental data covering a variety of adhesives and substrates such as metals (steel and aluminium), plastics, ceramics and glass fibre composites. The influence of adhesion promoters (eg, silanes) has also been considered.

It is shown that conditions for maximum strength coincide with the minimum interfacial energy of the system, acquired when the ratio of the surface energy of the substrate, γ₁, to that of the cured adhesive, γ₂ (ie, a = γ₁/γ₂), has a specific value denoted a_MIN. Systems with energy ratios a a_MIN were found to have engineering utility, because the strength deficiency for a >a_MIN was found to be significantly less than for a MIN.     

Effect of Surface Energetics of Substrates on Adhesion Characteristics of Poly (p-xylylenes)

In investigating the effect of the surface energetics of substrate materials on the adhesion characteristics of poly(p-xylylene) and poly(chloro-p-xylylene) by the “Scotch Tape” method, it was found that if the substrates had not been preconditioned (treated with argon or a methane plasma), the adhesion was poor. The characteristics of water resistant adhesion that were observed when coated substrates were boiled in 0.9% sodium chloride solution were found to vary from excellent (when the polymer did not peel from the substrate after three cycles of 8 hours of boiling and 16 hours at room temperature) to poor (when the polymer peeled off almost immediately). It was noticed that water resistant adhesion depends on the hydrophobicity of the substrate material (the greater the hydrophobicity, the greater the adhesion) and is not related to the dry adhesive strength of poly(p-xylylene). The oxygen glow discharge treatment of the substrates decreased both the dry and wet adhesive strength of the polymer. The effect of the argon glow discharge treatment depended on the surface energetics of the substrate, and the methane glow discharge treatment increased both the dry and wet adhesive strength of the polymer. These preconditioning processes are discussed in terms of the sputtering of the material from the wall of the reactor in contact with the plasma and the deposition of the plasma polymer of the sputtered material on the substrate surface.     

Effect of Surface Energetics of Substrates on Adhesion Characteristics of Poly (p-xylylenes)

In investigating the effect of the surface energetics of substrate materials on the adhesion characteristics of poly(p-xylylene) and poly(chloro-p-xylylene) by the “Scotch Tape” method, it was found that if the substrates had not been preconditioned (treated with argon or a methane plasma), the adhesion was poor. The characteristics of water resistant adhesion that were observed when coated substrates were boiled in 0.9% sodium chloride solution were found to vary from excellent (when the polymer did not peel from the substrate after three cycles of 8 hours of boiling and 16 hours at room temperature) to poor (when the polymer peeled off almost immediately). It was noticed that water resistant adhesion depends on the hydrophobicity of the substrate material (the greater the hydrophobicity, the greater the adhesion) and is not related to the dry adhesive strength of poly(p-xylylene). The oxygen glow discharge treatment of the substrates decreased both the dry and wet adhesive strength of the polymer. The effect of the argon glow discharge treatment depended on the surface energetics of the substrate, and the methane glow discharge treatment increased both the dry and wet adhesive strength of the polymer. These preconditioning processes are discussed in terms of the sputtering of the material from the wall of the reactor in contact with the plasma and the deposition of the plasma polymer of the sputtered material on the substrate surface.     

Influence of corona treatment on adhesion and mechanical properties in metal/polymer/metal systems

The effect of corona treatment (CT) on the adhesion at the metal–polymer interface was studied. Metal/polymer/metal laminates were manufactured by the laboratory roll‐bonding process with preliminary corona surface treatment of the polymer core: a polyethylene and polypropylene sheet as well as steel sheet. It was treated with corona discharge to increase its surface energy and the adhesion to metal, an austenitic steel. The adhesion, which was measured by T‐peel and shear tests, was increased by 43% of crack peel and 22% of mean peel resistance respectively, after 120 s CT. On the basis of scanning electron spectroscopy observations, improvements in the adhesive properties were attributed to the change in the interfacial morphology. In mechanical tests, yield and tensile strengths were strongly influenced by CT, indicating that these laminates were sensitive to interfacial phenomena. However, elongation at rupture of the composites was found to be unchanged. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.     

Role of Sn on the adhesion in Cu–Sn alloy-coated steel–rubber interface

Cu–Sn coatings with varying Sn content were deposited on steel substrate by immersion route and the effect of variation of Sn content and the substrate roughness on the interfacial adhesion strength of Cu–Sn-coated steel substrates vulcanized with styrene butadiene rubber were investigated. The surface roughness of the coatings did not vary compared to pristine steel substrate with change in Sn weight% in the coatings. The coated surfaces exhibited bare spots or deep trough as micro-discontinuities in the coatings, where formation of Fe₂O₃ was evident from SEM-EDS, AES, and XPS analysis. Microstructural study of the coating cross-section and coating-substrate interface by transmission electron microscopy of cross-sectioned samples revealed inadequate penetration of coating inside these troughs. Peel test carried out on the Cu–Sn-coated steel–rubber joints showed mixed mode i.e. adhesive and cohesive mode of interfacial fracture irrespective of the coating composition. The peel test further indicated higher interfacial adhesion strength for Cu–Sn-coated samples than pure Cu-coated samples, with an optimum adhesion strength for the coatings containing 3–4?wt.% Sn.     

Interfacial Adhesion of Polyamide 66 Fibres to an Aqueous Polyurethane–Acrylic Hybrid Polymer Adhesive

In this work, the interfacial adhesion between a polyamide 66 fibre, and an aqueous polyurethane–acrylic hybrid polymer adhesive was investigated. Silane and air plasma treatments were introduced to modify the surface of the polyamide 66 fibre. The surface chemistry was characterised using X-ray photoelectron spectroscopy (XPS). There were more oxygen-containing functional groups, –OH or –COOH, introduced by air plasma and silane treatments on the surface of polyamide fibre to increase its chemical activity. The microbond test was used to measure the interfacial shear strength (IFSS) between the waterborne polyurethane–acrylic hybrid polymer adhesive and a polyamide fibre. It has been found that air plasma and silane surface treatments can be used to improve interfacial adhesion. IFSS at 8.7 and 5.9 MPa, respectively, were higher than that of the control, 5.0 MPa. After water immersion at 50°C for 48 h, IFSS dropped to 7.0 MPa for air plasma-treated specimen and to 4.4 and 4.1 MPa for silanised and control specimens, respectively. Air plasma surface treatment is more effective than silane treatment to improve the interface adhesion in the polymer fibre–polymer composite.     

Surface energy, surface topography and adhesion

In this paper are discussed some of the fundamental principles which are relevant to an understanding of the influence that interfacial roughness may have on adhesion. The surface energies of the adhesive, substrate and of the interface between them determine the extent of wetting or spreading at equilibrium. Numerical values for surface energies may be obtained either from contact angle measurements or from analysing force–displacement curves obtained from the surface forces apparatus. The extent to which the relationships, appropriate for plane surfaces, may be modified to take into account interfacial roughness are discussed. For modest extents of roughness, the application of a simple roughness factor may be satisfactory, but this is unrealistic for many of the practical surfaces of relevance to adhesive technology which are very rough, and is ultimately meaningless, if the surface is fractal in nature. Some examples are discussed of published work involving polymer–metal and polymer–polymer adhesion, where the roughness of the interface exerts a significant influence on the adhesion obtained. Roughness over a range of scales from microns to nanometres may strengthen an interface, increasing fracture energy by allowing bulk energy dissipating processes to be activated when the bond is stressed.     

Adhesion of polymer coils to a solid surface: influence of the depletion effect

The specific properties of polymer coils are often disregarded in theories of adhesion, but polymer properties are essential for the strength of the adhesive bond. Polymer coils are repelled entropically from impenetrable surfaces. This causes the depletion effect and creates a layer of reduced concentration right at the interface. To bond a polymer coil to a substrate, it must be forced actively towards the interface, driven by the gaining of adsorption energy. The adsorption of specific groups in the (co)polymer, which interact with 'polar' sites on the substrate, must be used to suppress the depletion. Adsorption diminishes the effective distance between the surface and the adhesive polymer. The balance between adsorption and depletion (rather than the effect of polar groups or pretreatments on the work of adhesion as such) is the most important chemical possibility of affecting adhesion. The strength of the bond between polymeric materials and solid surfaces varies as H^-3, with the effective distance H between the polymer and substrate. Therefore, it changes by an order of magnitude when the polymer adhesive is pulled towards the substrate by adsorption.     

Influence de l'epaisseur de l'adhésif et du vieillissement sur les propriétés mécaniques dynamiques d'un assemblage: Adhésif structural/acier inoxydable

Dynamic mechanical properties of bounded joints—stainless steel/epoxy adhesive—are investigated as a function of the thickness of the adhesive and aging conditions. The viscoelastic properties of the bounded joints have been investigated by Dynamic Thermo Mechanical Analysis (DTMA). The glass transition temperature (T_g) showed a dependence on both the chemical/electrochemical pretreatments of the substrate and the thickness of the adhesive in the bounded joint. The crosslinking density in the adhesive thus seemed more important in the interfacial region than in adhesion bulk. The water uptake induces a plasticization of the adhesive and a decrease in T_g. The most stable bounded joints were obtained by carrying out sulfochromic acid anodization as a pretreatment step. The most important stability of the bounded joints was obtained with the sulfochromic anodization of the substrate.     

Adhesion between polymer substrates and plasma films from tetramethylsilane and tetramethyltin by glow discharge polymerization

Adhesion between various polymer substrates and plasma films, which had been prepared from either tetramethylsilane or tetramethyltin by glow discharge polymerization and deposited on the surface of the polymer, was evaluated by the Scotch tape test and by lap-shear strength. It was found that the plasma films exhibited fairly good adhesion to the polymer substrates (with the exception of polypropylene). The position where failure occurred was determined by X-ray fluorescence analysis, scanning electron microscopy and energy diffractive X-ray analysis. This position was at an inner layer of the plasma film (cohesive failure of plasma film), within the polymer substrate (material failure of polymer) or at the interface between polymer substrate and plasma film (adhesive failure) depending upon the polymer substrate. These results indicate an important aspect of durability of surface modification by glow discharge polymerization.     

Cathodic disbondment resistance with reactive ethylene terpolymer blends

Adhesion to metallic substrates can be improved through the addition of polar functional groups, which bond with surface groups on the metal substrate. Additionally, polar interactions have been shown to increase adhesive strength even in wet environments (such as in the case for cathodic protection). A polymer blend is proposed as a coating material to provide adequate protection against the diffusion of moisture and air to the metallic surface along with superior adhesion even in the presence of wet and corrosive environments to resist cathodic disbondment. A reactive ethylene terpolymer (RET) of ethylene/n-butyl acrylate/glycidyl methacrylate (E/nBA/GMA) was compounded with HDPE to develop a potential coating material. The HDPE component offers high chemical and moisture resistance to permeation, while the RET component provides the material with high polarity and reactivity, which enhances adhesion to the substrates to be coated. The introduction of the reactive ethylene terpolymer decreases the magnitude of cathodic disbondment area of polyethylene coatings. After applying a cathodic potential to the coating substrate, the adhesive strength was observed to remain the same for silane-pretreated steel dollies. Without silane pretreatment, post-CD adhesive loss resembles that of the open circuit “wet” condition. EDAX data in conjunction with oxygen and water vapor transmission rates suggest an initial stage of disbondment where interfacial oxide is dissolved resulting in the delamination of coating around the initial defect. This initial disbondment zone acts like a moving crack tip creating larger areas of disbondment where interfacial bonds are degraded by the ingress of moisture and ions along the interface.     

Cathodic disbondment resistance with reactive ethylene terpolymer blends

Adhesion to metallic substrates can be improved through the addition of polar functional groups, which bond with surface groups on the metal substrate. Additionally, polar interactions have been shown to increase adhesive strength even in wet environments (such as in the case for cathodic protection). A polymer blend is proposed as a coating material to provide adequate protection against the diffusion of moisture and air to the metallic surface along with superior adhesion even in the presence of wet and corrosive environments to resist cathodic disbondment. A reactive ethylene terpolymer (RET) of ethylene/n-butyl acrylate/glycidyl methacrylate (E/nBA/GMA) was compounded with HDPE to develop a potential coating material. The HDPE component offers high chemical and moisture resistance to permeation, while the RET component provides the material with high polarity and reactivity, which enhances adhesion to the substrates to be coated. The introduction of the reactive ethylene terpolymer decreases the magnitude of cathodic disbondment area of polyethylene coatings. After applying a cathodic potential to the coating substrate, the adhesive strength was observed to remain the same for silane-pretreated steel dollies. Without silane pretreatment, post-CD adhesive loss resembles that of the open circuit “wet” condition. EDAX data in conjunction with oxygen and water vapor transmission rates suggest an initial stage of disbondment where interfacial oxide is dissolved resulting in the delamination of coating around the initial defect. This initial disbondment zone acts like a moving crack tip creating larger areas of disbondment where interfacial bonds are degraded by the ingress of moisture and ions along the interface.     

Modification of high‐performance polymer composite through high‐energy radiation and low‐pressure plasma for aerospace and space applications

In this investigation, attempts are made to modify a high‐performance polymer such as polybenzimidazole (PBI) (service temperature ranges from ?260°C to +400°C) through high‐energy radiation and low‐pressure plasma to prepare composite with the same polymer. The PBI composites are prepared using an ultrahigh temperature resistant epoxy adhesive to join the two polymer sheets. The service temperature of this adhesive ranges from ?260°C to +370°C, and in addition, this adhesive has excellent resistance to most acids, alkalis, solvents, corrosive agents, radiation, and fire, making it extremely useful for aerospace and space applications. Prior to preparing the composite, the surface of the PBI is ultrasonically cleaned by acetone followed by its modification through high‐energy radiation for 6 h in the pool of a SLOWPOKE‐2 (safe low power critical experiment) nuclear reactor, which produces a mixed field of thermal and epithermal neutrons, energetic electrons, and protons, and γ‐rays, with a dose rate of 37 kGy/h and low‐pressure plasma through 13.56 MHz RF glow discharge for 120 s at 100 W of power using nitrogen as process gas, to essentially increase the surface energy of the polymer, leading to substantial improvement of its adhesion characteristics. Prior to joining, the polymer surfaces are characterized by estimating surface energy and electron spectroscopy for chemical analysis (ESCA). To determine the joint strength, tensile lap shear tests are performed according to ASTM D 5868–95 standard. Another set of experiments is carried out by exposing the low‐pressure plasma‐modified polymer joint under the SLOWPOKE‐2 nuclear for 6 h. Considerable increase in the joint strength is observed, when the polymer surface is modified by either high‐energy radiation or low‐pressure plasma. There is further significant increase in joint strength, when the polymer surface is first modified by low‐pressure plasma followed by exposing the joint under high‐energy radiation. To simulate with spatial conditions, the joints are exposed to cryogenic (?196°C) and high temperatures (+300°C) for 100 h. Then, tensile lap shear tests are carried out to determine the effects of these environments on the joint strength. It is observed that when these polymeric joints are exposed to these climatic conditions, the joints could retain their strength of about 95% of that of joints tested under ambient conditions. Finally, to understand the behavior of ultrahigh temperature resistant epoxy adhesive bonding of PBI, the fractured surfaces of the joints are examined by scanning electron microscope. It is observed that there is considerable interfacial failure in the case of unmodified polymer‐to‐polymer joint whereas surface‐modified polymer essentially fails cohesively within the adhesive. Therefore, this high‐performance polymer composite could be highly useful for structural applications in space and aerospace. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1959–1967, 2006     

Pressure-sensitive adhesion in the blends of poly(N-vinyl pyrrolidone) and poly(ethylene glycol) of disparate chain lengths

Adhesive behavior in blends of high molecular weight poly(N-vinyl pyrrolidone (PVP) with a short-chain, liquid poly(ethylene glycol) (PEG) has been studied using a 180° peel test as a function of PVP-PEG composition and water vapor sorption. Hydrophilic pressure-sensitive adhesives are keenly needed in various fields of contemporary industry and medicine, and the PVP-PEG blends, pressure-sensitive adhesion has been established to appear within a narrow composition range, in the vicinity of 36 wt% PEG, and it is affected by the blend hydration. Both plasticizers, PEG and water, behave as tackifiers (enhancers of adhesion) in the blends with glassy PVP. However, PEP alone is shown to account for the occurrence of adhesion, and the tackifying effect of PEG is appreciably stronger than that of sorbed water. Blend hydration enhances adhesion for the systems that exhibit an apparently adhesive type of debonding from a standard substrate (at PEG content less than 36 wt%), but the same amounts of sorbed water are also capable of depressign adhesion in the PEG-overloaded blends, where a cohesive mechanism of adhesive joint failure is typical. The PVP-PEG blend with 36% PEG couples both the adhesive and cohesive mechanisms of bond rupture (i.e., the fibrillation of adhesive polymer under debonding force and predominantly adhesive locus of failure). Blend hydration effect on adhesion has been found to be reversible. The micromechanics of adhesive joint failure for PVP-PEG hydrogels involves the fibrillation of adhesive polymer, followed by fibrils stretching and fracturing as their elongation attains 1000-1500%. Peel force to rupture the adhesive bond of PVP-PEG blends increases with increasing size of the tensile deformation zone, increasing cohesive strength of the material, and increasing tensile compliance of the material, obeying the well-known Kaelble equation, derived originally for conventional rubbery pressure-sensitive adhesives. The major deformation mode upon peeling the PVP-PEG adhesive from a standard substrate is extension, and direct correlations have been established between the composition behaviour of peel strength and that of the total work of viscoelastic strain to break the PVP-PEG films under uniaxial drawing. As a result of strong interfacial interaction with the PET backing film, the PVP-PEG adhesive has a heterogeneous two-layer structure, where different layers demonstrate dissimilar adhesive characteristics.     

PRESSURE-SENSITIVE ADHESION IN THE BLENDS OF POLY(N-VINYL PYRROLIDONE) AND POLY(ETHYLENE GLYCOL) OF DISPARATE CHAIN LENGTHS

Adhesive behavior in blends of high molecular weight poly(N-vinyl pyrrolidone (PVP) with a short-chain, liquid poly(ethylene glycol) (PEG) has been studied using a 180° peel test as a function of PVP-PEG composition and water vapor sorption. Hydrophilic pressure-sensitive adhesives are keenly needed in various fields of contemporary industry and medicine, and the PVP-PEG blends, pressure-sensitive adhesion has been established to appear within a narrow composition range, in the vicinity of 36 wt% PEG, and it is affected by the blend hydration. Both plasticizers, PEG and water, behave as tackifiers (enhancers of adhesion) in the blends with glassy PVP. However, PEP alone is shown to account for the occurrence of adhesion, and the tackifying effect of PEG is appreciably stronger than that of sorbed water. Blend hydration enhances adhesion for the systems that exhibit an apparently adhesive type of debonding from a standard substrate (at PEG content less than 36 wt%), but the same amounts of sorbed water are also capable of depressign adhesion in the PEG-overloaded blends, where a cohesive mechanism of adhesive joint failure is typical. The PVP-PEG blend with 36% PEG couples both the adhesive and cohesive mechanisms of bond rupture (i.e., the fibrillation of adhesive polymer under debonding force and predominantly adhesive locus of failure). Blend hydration effect on adhesion has been found to be reversible. The micromechanics of adhesive joint failure for PVP-PEG hydrogels involves the fibrillation of adhesive polymer, followed by fibrils stretching and fracturing as their elongation attains 1000-1500%. Peel force to rupture the adhesive bond of PVP-PEG blends increases with increasing size of the tensile deformation zone, increasing cohesive strength of the material, and increasing tensile compliance of the material, obeying the well-known Kaelble equation, derived originally for conventional rubbery pressure-sensitive adhesives. The major deformation mode upon peeling the PVP-PEG adhesive from a standard substrate is extension, and direct correlations have been established between the composition behaviour of peel strength and that of the total work of viscoelastic strain to break the PVP-PEG films under uniaxial drawing. As a result of strong interfacial interaction with the PET backing film, the PVP-PEG adhesive has a heterogeneous two-layer structure, where different layers demonstrate dissimilar adhesive characteristics.     

Improvement of the resistance to water of an adhesive joint between polymers and aluminium by using thin adhesion layers

The influence of a thin adhesive layer (AL) of a polymer on the wet adhesion of an epoxy coating on an aluminium substrate has been studied by the peel and tape test method. It is shown that thin layers considerably improve the stability of adhesive joints in the presence of water. The mechanism of this improvement and the mechanical properties required for such thin layers are discussed. Some experimental evidence for improved wet adhesion of polymer binders to an aluminium support is presented and the mechanism explained. These results on interfacial processes contribute to a better understanding of the mechanism of adhesion.     

Strength Loss Mechanisms for Adhesive Bonds to Electroplated Zinc and Cold Rolled Steel Substrates Subjected to Moist Environments

Mechanisms of strength toss which affect the durability of epoxy adhesive bonds in moist environments were investigated for electroplated zinc and cold rolled steel substrates. Activation energies for adhesion loss, formation of corrosion product on the substrate surface, and moisture diffusion in the adhesive were determined experimentally. For cold rolled steel substrates, the activation energy for adhesion loss was identical, within experimental error, to the measured activation energy for moisture diffusion in the adhesive. Both of these values were substantially less (=40%) than the activation energy for formation of corrosion product. This confirms the previous results of Gledhill and Kinloch (J. Adhesion 6, 315 (1974)), who attributed strength loss to thermodynamic instability of the adhesive/substrate interface due to the presence of moisture. In contrast, for electroplated zinc substrates, activation energies for adhesion loss and corrosion product formation were essentially equal, and were both significantly higher than that for moisture diffusion. Consequently, it was concluded that corrosion of the electroplated zinc layer was responsible for bond strength loss. Formation of corrosion product in the bond was not, therefore, a post-failure phenomenon as was the case for cold rolled steel.     

Surface structures and adhesion enhancement of poly(tetrafluoroethylene) films after modification by graft copolymerization with glycidyl methacrylate

Surface modifications of Ar plasma-pretreated poly(tetrafluoroethylene) (PTFE) film were carried out via near-UV light-induced graft copolymerization with glycidyl methacrylate (GMA). The structure and chemical composition of the copolymer surface and interface were studied by angle-resolved X-ray photoelectron spectroscopy (XPS). For PTFE substrate with a substantial amount of grafting, the grafted GMA polymer penetrates or becomes partially submerged beneath a thin surface layer of dense substrate chains to form a stratified surface microstructure. The concentration of the surface-grafted GMA polymer increases with the plasma pretreatment time, the near-UV light illumination time, and the monomer concentration. The GMA graft copolymerized PTFE surfaces adhere strongly to one another when brought into direct contact and cured (i) in the presence of a diamine alone or (ii) in the presence of an epoxy adhesive (epoxy resin plus diamine curing agent). In the presence of diamine alone, failure occurs in the interfacial region. For epoxy adhesive-promoted adhesion, the failure mode is cohesive, i.e. it takes place in the bulk of one of the delaminated PTFE films. The lap shear strengths in both cases increase with the amount of surface-grafted epoxide polymer. The development of the adhesion strength depends on the concentration of the surface graft, the microstructure of the graft copolymerized PTFE surface, the interfacial reactions, and the nature of the bonding agent.