Study of a 'T'-type peel test on a metal/polymer/metal sheet sandwich

This paper describes the specific 'T'-type peel mode in the case of a metal/polymer/metal sheet sandwich and gives experimental results on the influence of plastic deformation in the metallic substrates on the peel energy. We propose an experimental method of carefully determining the peel energy of a metal-polymer interface in a sandwich structure. Based on the mechanical properties of the stainless steel substrates and the maximum curvature of the metallic sheet measured experimentally during the peel test, several expressions for the clastoplastic deformation energy of the metal substrates are given. It is noteworthy that the curvature of the metal substrate layers depends not only on the mechanical properties of the material, but also on the work necessary to overcome the interfacial or cohesive forces. It is shown that even for thin metallic substrates (0.1 mm thick stainless steel), the work absorbed by the deformation represents roughly 50% of the total measured energy. During peeling the same specimen at different rates, the propagation peel force is higher or lower than the initiation force depending on the previous curvature of the metal sheets.     

Polymer/clay aerogel‐based glass fabric laminates

Laminates of polymer/clay aerogels and glass fabric sheets were prepared with varying epoxy adhesion application levels. A poly(amide‐imide) and an epoxy (1,4‐butanediol diglycidyl ether/2,6‐diaminopyridine) were chosen as the two “foam core” polymers; both single‐layered and double‐layered glass fiber laminates were investigated. The adhesion between polymer clay aerogels and glass fibers was quantified using the T‐peel method. The peel strength properties were found to increase as adhesive loading increased up to an optimal value, after which peel strength declines. Flexural and compressive testing of the laminates was also performed as a way of measuring mechanical strength. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Adhesion and Crosslinking in Epoxy Resin/Steel Assemblies

A novel technique has been employed to investigate the development of interfacial bonding between steel and epoxy resins. Whereas such systems are usually rigid, precluding use of the very informative peel test, we have used spring steel as a flexible adherend and peeled this from the (relatively) rigid crosslinked polymers. Peel energy has been assessed for 180° and 90° tests, using a cylindrical former to limit irreversible deformation of the steel. Cure cycles for the resins DGEBA/DDA and DGEBA/DDS have been studied using DSC, and results exploited in such a way that peel tests could be effected on assemblies for which the total degree of polymer crosslinking was standardised, yet polymer/steel contact time during crosslinking was varied. The degree of potential reactivity of the polymers with respect to the steel was thus controlled. It was found, for both polymers, that measured adhesion energy was an approximately linear function of the fraction of crosslinking agent that reacted whilst epoxy/steel contact was maintained. Master curves for the two systems have been plotted, irrespective of cure conditions, the DGEBA/DDS system presenting better adhesion. Although no direct evidence of type and/or number of interfacial bonds is presently available, a simple argument suggests that chemical reactions occurring at ca. 1% of available surface sites may markedly improve adhesion.     

Effect of Deformation-induced Residual Stress on Peel Strength of Polymer Laminated Sheet Metal

The adhesion between adhesively bonded polymer film and a metallic sheet substrate in a polymer laminated sheet metal (PLSM) subjected to large deformation, such as in a forming process, is influenced by two deformation-induced factors. These are (i) evolution of surface roughness of metallic substrate with applied strain and (ii) development of residual stress in the polymer adherend (polymer film with a thin uniform adhesive layer on one side) arising from significant differences in the deformation behavior of metal and polymeric components. A new experimental methodology was devised in this study to decouple the effects of substrate surface roughness and residual stress on interfacial peel strength (IPS) of uniaxially deformed PLSMs. This methodology was based on 180° peel testing of PLSM specimens prepared under two different lamination conditions, one involving systematic pre-straining in uniaxial tension of the metallic substrate prior to laminations and the other involving post-lamination pre-straining of the PLSM. The role of pre-strain and peel test speed, for the above laminations conditions, were critically analyzed for their effect on IPS of two differently tailored PLSM systems. The IPS results were attributed to the effect of deformation-induced residual stress and metallic surface roughness. The analysis suggests that IPS is strongly dependent upon the residual stress induced by uniaxial deformation but only marginally on substrate surface roughness depending upon the constituents (film and adhesive) of the adherend. The magnitude of pre-strain was inversely and non-linearly related to IPS for both deformed PLSMs. Peel test speed, on the other hand, showed a more complex behavior in terms of IPS for the two PLSM systems.     

An FT-IR Study on Interfacial Interactions in Ethylene Copolymers/Aluminium Laminates in Relation to Adhesion Properties

The effect of three different functional groups in ethylene copolymers on the adhesion with aluminium was studied. The interface in polymer/metal laminates was analyzed by FT-IR, and the adhesion mechanism for each functional group was evaluated. Laminate samples were prepared by solution casting or by hotpressing polymeric film onto the aluminium substrate. In the latter case, the interface was exposed by solvent extraction. The interfacial structures developed by the different copolymers were correlated to the mechanical strength of hotpressed laminates, which was measured by a peel test. The polymer surfaces were further characterized by contact angle measurements.

Polar functional groups, carboxylic acid and butyl ester in hotpressed laminates were found to form Lewis acid/base interactions with the aluminium oxide. The strength of the interfacial interactions was correlated to the concentration and acidity/basicity of the group, the acid group being the most efficient. A silane functional group provided strong adhesion to the laminates at a much lower concentration than the polar groups. Silanols as well as Al-O-Si linkages were detected at the polymer/aluminium interface.     

An FT-IR Study on Interfacial Interactions in Ethylene Copolymers/Aluminium Laminates in Relation to Adhesion Properties

The effect of three different functional groups in ethylene copolymers on the adhesion with aluminium was studied. The interface in polymer/metal laminates was analyzed by FT-IR, and the adhesion mechanism for each functional group was evaluated. Laminate samples were prepared by solution casting or by hotpressing polymeric film onto the aluminium substrate. In the latter case, the interface was exposed by solvent extraction. The interfacial structures developed by the different copolymers were correlated to the mechanical strength of hotpressed laminates, which was measured by a peel test. The polymer surfaces were further characterized by contact angle measurements.

Polar functional groups, carboxylic acid and butyl ester in hotpressed laminates were found to form Lewis acid/base interactions with the aluminium oxide. The strength of the interfacial interactions was correlated to the concentration and acidity/basicity of the group, the acid group being the most efficient. A silane functional group provided strong adhesion to the laminates at a much lower concentration than the polar groups. Silanols as well as Al-O-Si linkages were detected at the polymer/aluminium interface.     

A study of the adhesion between steel and an ethylene-acrylic acid-acrylate terpolymer

The interfacial interaction of an ethylene-acrylic acid-t-butyl acrylate (EAA) terpolymer with metals (mild steel) has been studied by spectroscopic techniques (XPS, AES, and IR), SEM, and mechanical testing. Using peel tests it was shown that the copolymerization of small quantities of acrylic acid and t-butyl acrylate with ethylene induces polymer/metal adhesion values rather higher than in plain polyethylene. The fracture surfaces were analyzed by XPS, AES, and SEM. It was shown that the fracture is cohesive and occurs within the polymer. Some specimens were aged under various conditions. In this case, the failure was located at the polymer/metal interface. In fact, SEM, XPS, and AES did not show the presence of polymer on the metal surface. Iron corrosion is then considered responsible for the failure of the joint. Since a thin layer of metal oxide covers the surface of mild steel, so to understand the polymer/ metal interfacial interaction better, IR spectroscopy was performed on polymer/metal oxide (goethite and hematite) composites. It was shown that the carboxyl groups of the polymer react with hydroxyl groups present at the metal surface. Adsorption isotherms of the polymer on iron oxides were also obtained, showing remarkable EAA terpolymer chemisorption, while there was no evidence of bonding between iron oxides and plain polyethylene.     

Significance of Peel Test Speed on Interface Strength in Cohesive Zone Modeling

The analysis of the experimental peel test data for obtaining the adhesion fracture energy of an adhesively laminated polymer to the sheet metal surface is considered. The experimental results of the 180° peel test on two types of polymer laminated sheet metal at three different peel speeds are analyzed by two methodological approaches in cohesive zone modeling. These approaches are linear-elastic stiffness approach and critical maximum stress approach. Comparing the results of these two approaches reveals the significance of the peel test speed on the interface strength determination for cohesive zone modeling. It is concluded that a “reference” peel speed may exist at which the interface strength is equal to the yield strength of the peel arm material. A constitutive equation has been proposed which relates the interface strength to the peel test velocity by using the reference peel speed and its corresponding peel arm yield strength.     

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.     

Improvement in the adhesion between copper metal and polyimide substrate by plasma polymer deposition of cyano compounds onto polyimide

The surface modification of Kapton film by means of plasma polymer deposition is discussed from the viewpoint of improving the adhesion between copper metal and Kapton film substrate. Plasma polymers of AN (acrylonitrile) and FN (fumaronitrile) were used for the surface modification, and the adhesion between the copper metal and the plasma polymer-coated Kapton film was evaluated by the T-peel strength measurement. The surfaces of peeled layers were analyzed by X-ray photoelectron spectroscopy (XPS) and the failure mode is discussed. The plasma polymer deposition of AN and FN shows an effective improvement in the adhesion between the copper metal and Kapton film; in particular, the AN plasma polymer deposition increased the peel strength 4.3 times. Failure occurred mainly in the Kapton film, and the adhesion between the AN plasma polymer and the Kapton film and that between the copper metal and the AN plasma polymer were found to be quite strong.     

Predictions of micromechanics models for interfacial/interphase parameters in polymer/metal nanocomposites

In this paper, the polymer-metal interfacial/interphase parameters (PMIP) in polymer/metal nanocomposites are studied by modeling the mechanical properties. In this regard, the experimental results of yield strength, Young's modulus and elongation at break can be compared with the micromechanical models to evaluate the PMIP. The good agreement obtained between the experimental data of samples and the predictions confirms the applicability of models for polymer/metal nanocomposites. Many calculated parameters show the existence of a strong interphase in the reported samples. It is concluded that the fine morphology of nanoparticles and the strong interaction/adhesion at the polymer-metal interface can produce the significant PMIP in the polymer/metal nanocomposites.     

Influence of vibrations on interface delamination in metal–polymer composites

The main objective of this work was the study of vibration effects on the viscoelastic coating protecting the steel layer in a metal–polymer composite, with simulated conditions of the transportation of food containers. Mechanical resonance tests in metal–polymer [electrolytic chromium-coated steel–poly(ethylene terephthalate) (PET)] sheets were performed to generate vibration conditions to induce structural modifications in the viscoelastic layer covering the surface of the plates. Consequently, schematic representations of the areas affected by these modifications were made. The modified structures were later analyzed by electron microscopy to detect and evaluate alterations in the morphology of the material. In addition, vibrational Raman spectroscopy analyses were performed to assess the chemical and structural changes on the protective PET at the metal–polymer interface level. The results of this study are expected to provide basic information on the mechanisms and nature of the delamination processes taking place in metal–polymer laminates employed in food-container applications. These damages have previously been detected in some food containers made of PET materials. The study of these damages can lead to the improvement of current composites or the development of higher quality materials. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Complex-induced coupling effect: adhesion of some polymers to copper metal promoted by benzimidazole

Improved adhesion of a polymer with polar functional groups to copper has been achieved by pretreating the copper surface with benzimidazole solution. The adhesion strength was found to increase by two to three times. The coupling mechanism and interfacial structure of the copper-polymer composite have been investigated by X-ray photoelectron and Fourier transform infrared relection-absorption spectroscopies. We found that benzimidazole reacted with copper metal in the presence of oxygen to form benzimidazolato copper(+1), which covered the surface in the form of a thin polymeric layer. As the surface was exposed to air, some of the cuprous cations were oxidized to cupric ions. When poly(vinylpyridine) was coated onto the pretreated surface, the nitrogen atoms of the side groups of the polymer chains co-ordinated to the cupric cation to form interfacial bonding connecting the polymer to the copper metal.     

Relationship between interfacial phenomena and viscoelastic behavior of laminated materials

A literature review shows that the main arguments used to describe viscoelastic behavior of polymer composites are the existence of an interphase and/or physico-chemical matrix-reinforcement interactions. The purpose of this investigation was to study the influence of both of these parameters on the viscoelastic behavior of a sandwich structure. Using a theoretical approach of the mechanical coupling between phases in laminate composites, the interphase influence is shown to be negligible. In order to understand the influence of an interphase on viscoelastic features of laminates, some metal/polymer/metal laminates were processed under various conditions to obtain different degrees of metal/polymer adhesion. Dynamic mechanical spectroscopy tests reveal that both the amplitude of the main loss factor peak and the low temperature apparent modulus increase with the adhesion. Finite elements calculations show that discontinuities of displacements at the metal/polymer interface explain the loss peak changes. The continuity of displacements is ensured only from a threshold value of the peel energy.     

Effect of surface roughness on interlaminar peel and shear strength of CFRP/Mg laminates

In this study, grit blasting with different abrasive particle sizes was carried out on magnesium alloy sheets, then the carbon fiber reinforced polymer (CFRP)/magnesium alloys laminates were prepared using a hot-press process. The surface characteristics of magnesium alloy, and the interlaminar strength of CFRP/Mg laminates were examined, in order to investigate comprehensively the effect of surface roughness on interlaminar strength of laminates under peel and shear loading conditions. The results show that the rougher surface significantly improves the peel strength of laminates, while the shear strength of laminates increases only slightly with increasing surface roughness. Hence, the rougher surface exhibits a good overall interlaminar strength under peel and shear loading when compared to the smoother surfaces.     

Analysis of the Molecular Structure at the PPS/Copper Interphase and its Role in Adhesion

X-ray photoelectron spectroscopy (XPS) was used to examine the interfacial chemistry in polyphenylene sulfide (PPS)/copper bonded laminates. Several surface pretreatments were studied including a simple methanol wash, two acid etches, thermal oxidation and chemical oxidation. Peel test analysis showed poor adhesion to the methanol-washed and acid-etched foils, giving a peel strength of only 3-5 g/mm. XPS analysis of the failure surfaces revealed a large amount of inorganic sulfide at the interface with reduction of the copper oxide. Chemical oxidation using an alkaline potassium persulfate solution gave a matt-black surface consisting of primarily cupric oxide. These samples showed improved adhesion and XPS analysis of the failure surfaces revealed fracture through a mixed PPS/cuprous oxide layer. A simple thermal oxidation yielded a cuprous oxide surface layer and laminates bonded to these surfaces showed a more than ten-fold increase in peel strength. XPS analysis of the failure surfaces showed much lower amounts of interfacial copper sulfide and it was postulated that excess sulfide at the interface was responsible for the poor adhesion observed for other pretreatments.     

Effects of corona treatment on composite formation. Adhesion between incompatible polymers

Polypropylene–nylon 6 10 composites were prepared by the in situ polymerization of the nylon monomers on polypropylene films. The adhesion between the nylon and the polypropylene was markedly improved by a brief corona discharge treatment of the films in nitrogen prior to coating. This improvement was demonstrated by an increase in the peel strength of the nylon coating and a decrease in brittleness of photo-oxidized compesites when corona treatment was used. Adhesive bonding between the nylon and substrate was sufficiently strong to cause cohesive failure in the corona-treated polypropylene. Only interfacial failure was observed at untreated surfaces. These effects were demonstrated by electron microscopy of the surfaces produced in peel tests. The effects of corona treatment on adhesive bonding characteristics of surfaces are discussed in terms of the chemical and physical changes observed in treated surfaces.     

Surface modification of plasma‐pretreated high density polyethylene films by graft copolymerization for adhesion improvement with evaporated copper

Surface modification of Ar plasma‐pretreated high density polyethylene (HDPE) film via UV‐induced graft copolymerization with glycidyl methacrylate (GMA) and 2‐hydroxyethylacrylate (HEA) was carried out to improve the adhesion with evaporated copper. The surface compositions of the modified HDPE surfaces were characterized by X‐ray photoelectron spectroscopy (XPS). The adhesion strengths of evaporated copper with the graft‐copolymerized HDPE films were affected by the Ar plasma pretreatment time, the monomer concentration used for graft copolymerization, and the graft concentration. Post‐treatments, such as plasma post‐treatments after graft copolymerization and thermal treatment (curing) after metalization, further enhanced the adhesion strength of the Cu/HDPE laminates. The T‐type peel strengths of the laminates involving the graft‐modified and plasma posttreated HDPE films were greater than 15 N/cm. The enhanced adhesion strength resulted from the strong affinity of the graft chains for Cu and the fact that the graft chains were covalently tethered on the HDPE surface. XPS characterization of the delaminated surfaces of the Cu/HDPE laminates revealed that the failure mode of the laminates with T‐peel adhesion strengths greater than 5 N/cm was cohesive in nature.     

The level of matrix-filler interfacial adhesion in metal and polymer nanocomposites reinforced with carbon nanotubes

In this paper, the interfacial adhesion between metal matrix and carbon nanotubes (CNTs) is determined in various metal/CNT nanocomposites by several models. The models apply the experimental data to calculate the interfacial parameters. A good correlation is acquired between theoretical and experimental results which validates the current analysis. The calculated parameters reveal the formation of a perfect adhesion at the interface between the metal matrix and CNT in all reported samples. In addition, the calculations are compared with similar results for polymer nanocomposites which show a stronger adhesion at metal–CNT interface in comparison to polymer–filler interfacial adhesion in polymer nanocomposites.