Investigating tensile behaviour of toughened epoxy paste adhesives using circumferentially notched cylindrical bulk specimens

Toughened epoxy adhesives are frequently used to bond metals and polymer-matrix composite materials in many structural applications. The mechanical properties of adhesives are often characterised by testing either bulk adhesive specimens or bonded joints (i.e. in-situ form). In this paper, cylindrical bulk specimens with circumferential notches were manufactured and tested to investigate the tensile behaviour of an epoxy paste adhesive toughened with hollow glass microspheres. Bulk specimens were manufactured from the paste adhesive using injection moulding. Tensile tests were conducted for strain-rate and stress triaxiality effects by varying displacement rates and notch radii, respectively. Fracture surfaces were examined using optical and scanning electron microscopy to identify failure mechanisms. The results obtained from the toughened paste adhesive indicate that strain-rate and stress triaxiality influence its tensile fracture behaviour.     

Facile fabrication of superhydrophobic polyimide/polytetrafluoroethylene composite coatings with high water adhesion

A facile casting method was used to fabricate superhydrophobic polyimide/polytetrafluoroethylene composite coatings with high water adhesion. The water contact angles of the composite coatings were larger than 150 °, expressing superhydrophobic property. But water droplets pinned tightly on the composite coating, even if it was upside down. The X‐ray photoelectron spectrum analysis indicated that polyimide and polytetrafluoroethylene coexisted in the resulting coating. The observation with scanning electron microscopy showed that the composite coating formed lotus‐like structure with many spherical polyimide papillae randomly bonding on the surface. But the tops of the polyimide papillae were not covered by lance‐shaped Teflon fibres, forming an inhomogenous and discontinuous surface structure. This special surface chemical distribution and lotus‐like structure combined to contribute to the high adhesive superhydrophobicity. This simple method may greatly extend the application range of high adhesive superhydrophobic surfaces in microcontrollable and microfluidic application. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42810.     

Viscous behaviour of Bi2O3–B2O3–ZnO glass composites with ceramic fillers

Abstract

Variation in the viscous flow behaviour, nature and extent of glass fluidity in glass/filler composites are addressed with respect to various factors such as filler type, content, size, density and migration distance. The characterisation of a glass (Bi₂O₃–B₂O₃–ZnO) composite consisting of two different fillers (cordierite and willemite) was determined using hot stage microscopy, a differential scanning calorimeter and a flow button test. The microstructure was analysed using a scanning electron microscope. The apparent viscosity of the glass composites increased on increasing concentration and density of the filler. The variation in the viscosity is due to the diffusion of the glass matrix through channels in the cordierite filler of the composite. Based on the calculated migration distance of the filler in the glass matrix, the present work suggests that the interfacial behaviour and the density of the filler play a significant role in determining the viscous flow of the glass composites.     

Effects of solid substrate on structure and properties of casting waterborne polyurethane/carboxymethylchitin films

We prepared two series of semiinterpenetrating polymer network (semi-IPN) films from cross-linked waterborne polyurethane (WPU) and carboxymethylchitin (CMCH) in the aqueous solution on the glass and Teflon as the hydrophilic and hydrophobic substrates, respectively, by casting method. The chemical compositions, structure and morphologies of the films were examined by attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) and scanning electron microscopy (SEM). The miscibility, thermal stability and mechanical properties of the films were investigated by density measurement, dynamic mechanical analysis (DMA), ultraviolet (UV) spectroscopy, thermogravimetric analysis (TGA), tensile testing and solvent swelling testing. The results revealed that the semi-IPN films exhibited good miscibility when CMCH content was lower than 35 and 65 wt% for the films prepared on the glass and Teflon, respectively, resulting in higher light transmittance, thermal stability and tensile strength than the WPU film. Interestingly, the films prepared with the Teflon as the substrate possessed better miscibility and higher storage modulus, thermal stability, tensile strength and solvent-resistance than that with the glass as the substrate over the entire composition range studied here. This difference can be attributed that a strong intermolecular interaction occurred between WPU and CMCH to form a dense architecture, owing to that two kinds of macromolecules all were repulsed from the Teflon surface and forced to concentrate into inner surface. It has been confirmed that the hydrophility and hydrophobility of the solid substrate significantly influenced the structures and properties of the casting films, and using Teflon solid substrate can more effectively improve the miscibility and properties of the semi-IPN materials with hydrophilic character than glass one. We proposed a model describing the formation of WPU/CMCH semi-IPN films cast on the hydrophilic and hydrophobic substrates to illustrate the different structures of two types of films.     

Laser and furnace pyrolyzed organosilazane-based glass/ZrO2 composite coating system—A comparison

The laser pyrolysis of a ceramic coating system composed of an organosilazane (Durazane 1800) with monoclinic ZrO₂ and glass particles as fillers was investigated. The samples were produced by spray coating on pre-treated stainless steel substrates and subsequently pyrolyzed by Nd:YV0₄ laser radiation (λ =1064 nm). The interaction of laser radiation with the polysilazane-based glass/ZrO₂ coating system led to formation of semi-crystalline dense coatings with a thickness up to 20 μm in a short time.Laser pyrolyzed ceramic coatings were characterized and compared with furnace pyrolyzed coatings. The microstructure of the coatings was investigated by scanning electron microscopy (SEM). Additionally the corrosion resistance and mechanical properties, such as hardness, adhesive strength and the tribological behaviour have been investigated. Ceramic coatings generated by laser pyrolysis showing promising mechanical properties, a super-hydrophobic surface as well as a high corrosion resistance.     

Mode-I adhesive fracture energy of carbon fibre composite joints with nanoreinforced epoxy adhesives

The effect of the addition of carbon nanoreinforcements to an epoxy adhesive on the strength and toughness of carbon fibre/epoxy composite joints was studied. The laminate surfaces, treated with peel ply, were characterised by profilometry, image analysis and wettability. The mechanical properties of the joints were determined by lap shear testing and double cantilever beam testing. The fracture mechanisms were studied by scanning electron microscopy.The addition of carbon nanofibres and carbon nanotubes caused an increase in the mode-I adhesive fracture energy, G_IC, of the joints while their lap shear strengths remained approximately constant. This improvement in the fracture behaviour was attributed to the occurrence of toughening mechanisms when carbon nanoreinforcements were added to the epoxy adhesive. Additionally, the use of carbon nanotubes improved the interfacial strength between the adhesive and the substrate, changing the crack growth behaviour and the macroscopic failure mode.     

Toughening epoxy adhesives with multi-walled carbon nanotubes

In this paper, the effect of adding multi-walled carbon nanotubes (MWCNTs) with an outer diameter of less than 8 nm to an epoxy adhesive was studied on the adhesive fracture resistance and damage behaviour. The fracture energies of the neat and toughened adhesives were measured by testing double-cantilever beam specimens. Moreover, a cohesive zone model (CZM) was used to numerically study the effect of MWCNTs on the damage behaviour of the toughened adhesives. The maximum improvement of 58.4% in the adhesive fracture energy was obtained when the adhesive was toughened with 0.3 wt% of MWCNTs. The fracture surfaces were analysed using the scanning electron microscopy (SEM) technique. It was found that the presence of MWCNTs in the toughened adhesives caused rougher fracture surfaces. Moreover, some fracture mechanisms including nanotube pull-out and de-bonding were observed in the fracture surfaces. The numerical analyses showed that the damage process zone length was also influenced by MWCNTs. The longest damage process zone was obtained for the toughened adhesive with 0.3 wt% of MWCNTs.     

A Reliable Method to Measure the Adhesive Force with a Tiny Amount of Adhesive Material

A new method is proposed and developed to measure adhesive forces by use of the force-distance curve of a micro cantilever with an extremely small amount of testing material such as adhesive proteins. The contact area should be well-controlled at a reasonable value. Even though the area is desired to be as small as possible, a contact region of several micrometers by several micrometers is adopted in order to avoid obtaining meaningless measured values and uncertainty in the contact areas. An AFM cantilever is used after having been modified with a micro glass bead to enlarge the contact area for adhesion. A glass plate with micro-scale circular patterns is fabricated from a glass wafer by micro-machining processes in order to control precisely the contact area in adhesion tests. In the proposed method the adhesive materials are directly applied to the bead attached at the AFM cantilever before it is applied on the top area of the truncated cone on the fabricated glass plate. The developed method is applied to measure the adhesive forces of Cell-Tak® (which is a commercial extracted mussel adhesive) and recombinant Mgfp-5 (which is a recombinant mussel adhesive protein) and the statistical credibility of the measured adhesive force data is enormously improved as a result.     

A Reliable Method to Measure the Adhesive Force with a Tiny Amount of Adhesive Material

A new method is proposed and developed to measure adhesive forces by use of the force-distance curve of a micro cantilever with an extremely small amount of testing material such as adhesive proteins. The contact area should be well-controlled at a reasonable value. Even though the area is desired to be as small as possible, a contact region of several micrometers by several micrometers is adopted in order to avoid obtaining meaningless measured values and uncertainty in the contact areas. An AFM cantilever is used after having been modified with a micro glass bead to enlarge the contact area for adhesion. A glass plate with micro-scale circular patterns is fabricated from a glass wafer by micro-machining processes in order to control precisely the contact area in adhesion tests. In the proposed method the adhesive materials are directly applied to the bead attached at the AFM cantilever before it is applied on the top area of the truncated cone on the fabricated glass plate. The developed method is applied to measure the adhesive forces of Cell-Tak® (which is a commercial extracted mussel adhesive) and recombinant Mgfp-5 (which is a recombinant mussel adhesive protein) and the statistical credibility of the measured adhesive force data is enormously improved as a result.     

Effects of interfacial adhesion on microdamage and rheological behaviour of glass bead filled nylon 6

Model composites consisting of glass beads dispersed in a matrix of nylon 6 with different degrees of interfacial adhesion were prepared. The effects of interfacial adhesion on damage generation in the glass bead filled nylon 6 were studied by acoustic emission monitoring and scanning electron microscopy, and the critical damage stress was measured. Improvement of the interfacial adhesion enhanced the tensile strength of the composite. The melt rheological behaviour of the glass bead filled nylon 6 was also investigated. It was found that the interfacial adhesion strength significantly affected the rheological behaviour of the glass bead filled nylon 6.     

Preadhesion laser surface treatment of polycarbonate and polyetherimide

The effects of carbon dioxide (10.6 μm) and argon fluoride excimer (193 nm) lasers as preadhesion surface treatments for polycarbonate and polyetherimide were studied. Single lap shear specimens bonded with a flexible polyurethane adhesive were utilized to investigate the effect of the various laser treatments on final shear properties and mode of failure. Experimental results based on mechanical properties, scanning electron microscopy and Fourier transform infra-red have indicated that the excimer laser is more effective than the carbon dioxide laser with respect to shear properties and the level of adhesion obtained with the thermoplastic adherends and polyurethane adhesive studied. Polycarbonate with its lower glass transition temperature T_g was affected by the carbon dioxide laser to a higher extent than the higher T_g polyetherimide. Furthermore, polycarbonate exhibited enhanced shear properties and a higher level of chemical modification following excimer laser irradiation compared to polyetherimide.     

About the Realistic Porosity of Porous Glasses

Nitrogen adsorption, mercury intrusion, scanning electron microscopy and small-angle X-ray scattering have been used to determine the texture properties of a selected mesoporous glass. The glass has been prepared by a combined acid and alkaline leaching treatment of a phase separated sodium-borosilicate initial glass. Residues of silica gel, remaining in the pores of the investigated glass after the treatment with alkaline solution, lead to differences in the results of the standard characterization techniques nitrogen adsorption and mercury intrusion.In order to explain these differences, small-angle scattering experiments in combination with scanning electron microscopy have been performed.Here, a well-defined range order L 60 nm has been selected and a 50% porosity results. The behaviour of the second derivative of the small-angle scattering correlation function has been checked by the use of the linear simulation model.     

Modification of glass surfaces adhesion properties by atmospheric pressure plasma torch

This work is focused in the surface modification of glass samples by an atmospheric pressure plasma torch (APPT), with the aim of properly characterizing every chemical surface modification which could contribute to the assessment of reliable adhesive bonding with polyurethane, silicone, epoxy and cyanoacrylate adhesives.Characterization of glass surfaces both pristine and plasma treated is achieved by surface energy determination through contact angle measurements, Fourier transform infrared spectroscopy in attenuated total multiple reflection mode (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and surface roughness determination. Moreover, the hydrophobic recovery processes suffered by the samples throughout a period of 30 days of storage after APPT treatment is evaluated. Finally, adherence tests are carried out following the ASTM D4541 standard. Results show an increased surface energy with treatment, which partially recovered its initial value with aging. For the adhesive bonding, only the polyurethane shows an improvement on resistance among all the tested adhesive fluids. It is possible to conclude a cleaning, etching and activation effects on the glass surfaces after plasma treatment, with a change in the locus of failure from adhesive to cohesive in some cases, and a reduction in data standard deviation.     

Polyvinylpyrrolidone adhesion layer for increased uniformity and optical transmittance of silica nanoparticle antireflective coatings

The uniformity of silica nanoparticle antireflective coatings deposited from aqueous solutions on glass substrates is limited by the high surface tension and low evaporation rate of water. In this work, thin films of polyvinylpyrrolidone (PVP) were utilized as an adhesion layer to increase the uniformity and optical transmittance of silica nanoparticle coatings. The increase in adhesive force caused by the presence of the PVP layer was measured using atomic force microscopy (AFM). The micro- and nanoscale uniformities of silica nanoparticle films with and without PVP adhesion layers were characterized using scanning electron microscopy and AFM. It was found that a thin PVP adhesion layer provides the adhesion required to form uniform films of silica nanoparticles. Solar weighted transmittance of 97.6% over a wavelength range of 330–1000 nm was achieved with soda-lime glass substrates coated on both sides.     

Elastomer‐modified epoxy/amine systems in a resin transfer moulding process

The effect of the elastomer structure on toughening highly crosslinked epoxy systems in a resin transfer moulding process (RTM) was investigated. Two kinds of elastomers containing carboxyl functionalized groups were used: (1) a reactive liquid elastomer based on carboxyl‐terminated butadiene‐acrylonitrile copolymer (CTBN), (2) a preformed core‐shell rubber (CSR). The introduction of CTBN rubber caused the modification in the glass transition temperature due to the miscibility in the epoxy matrix, whereas CSR particles did not. During cure, these elastomers affected the morphological, rheological and dielectric behaviour of epoxy/amine systems. A blend of 5% CTBN and 5% CSR exhibited a bimodal distribution of rubber particle sizes (analyzed by transmission electron microscopy) whereas scanning electron microscopy showed the glass fibre‐matrix cohesion in fracture surfaces. A semi‐empirical model was used (developed by Castro‐Macosko for describing chemorheological behaviour of epoxy/amine systems for the RTM process). The increase in viscosity and the reduction in ion conductivity were the two key parameters to monitor the cure process. The presence of rubber affected the rheological behaviour involving initial viscosity and gel point. The investigation of temperatures, pressures and ionic conductivities in various glass fibre layers was conducted to control the front flow filling and the cure reaction. The introduction of rubber modified the inflexion area of the cured rubber–epoxy blends by changing the cure rate. Copyright © 2004 Society of Chemical Industry     

Effect of pH on distribution and adhesion of Staphylococcus aureus to glass

The adhesion of Staphylococcus aureus ATCC 25923 to glass at different pH values was investigated using scanning electron microscopy (SEM) and image analysis with the Mathlab^® program. The images obtained by SEM show that the adhesion behaviour of Staphylococcus aureus ATCC 25923 depends on the pH of the suspending medium. At highly acidic (pH 2, pH 3) and alkaline pH, the cells deposited in aggregate forms, while at pH 5 the aggregation phenomenon was absent. The quantitative adhesion (number of adhering cells to glass surface) showed that cells adhered strongly in the pH range 4 to 6 and weakly at highly acidic (pH 2, pH 3) and alkaline pH. Moreover, the surface properties of the cells were characterized by the microbial adhesion to solvents (MATS) method. A good correlation was obtained between physicochemical properties (hydrophobicity or electron donor electron acceptor character) of Staphylococcus aureus ATCC 25923 and the number of adhering cells to glass. These results show that the adhesion of Staphylococcus aureus ATCC 25923 to glass is controlled by both acid–base and hydrophobic interactions.     

Skin permeation of buflomedil form adhesive matrix patches

The main objective of this research work was to fabricate and evaluate adhesive matrix-type transdermal patches of buflomedil hydrochloride, employing different ratios of pressure sensitive adhesives (PSAs) by solvent casting technique. The adhesive matrix-type transdermal patches were evaluated by their in vitro physicochemical properties such as thickness, moisture content, weight variation, drug content uniformity, etc. The effects of PSAs ratio, drug loading, and concentration of permeation enhancer were evaluated thoroughly. Ex vivo skin permeation studies with kinetic modeling of adhesive matrix patches were systematically evaluated. Based on the above observations, the best optimized buflomedil hydrochloride-loaded adhesive matrix-type transdermal patch was further characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction study, and differential scanning calorimetry analyses. Drug containing adhesive matrix patches showed sustained release property without showing any incompatibility in adhesive matrix system. Hence, adhesive matrix-type transdermal patches of buflomedil hydrochloride can be used as a potential carrier for sustained transdermal delivery of hydrophilic drugs like buflomedil hydrochloride.     

Atmospheric pressure plasma surface modification of titanium for high temperature adhesive bonding

In this investigation surface treatment of titanium is carried out by plasma ion implantation under atmospheric pressure plasma in order to increase the adhesive bond strength. Prior to the plasma treatment, titanium surfaces were mechanically treated by sand blasting. It is observed that the contact angle of de-ionized water decreases with the grit blast treatment time. Optical microscopy and scanning electron microscopic (SEM) analysis of untreated and atmospheric plasma treated titanium are carried out to examine the surface characteristics. A substantial improvement in the surface energy of titanium is observed after the atmospheric pressure plasma treatment. The surface energy increases with increasing exposure time of atmospheric pressure plasma. The optimized time of plasma treatment suggested in this investigation results in maximum adhesive bond strength of the titanium. Unmodified and surface modified titanium sheets by atmospheric pressure plasma were adhesively bonded by high temperature resistant polyimide adhesive. The glass transition temperature of this adhesive is 310 °C and these adhesively bonded joints were cured at high temperature. A substantial improvement in adhesive bond strength was observed after atmospheric pressure plasma treatment.     

Adhesion Characteristics of Carbon Black Embedded Glass/Epoxy Composite

The surface of glass/epoxy composite material was embedded with carbon black which was dispersed in methyl ethyl ketone (MEK) during the curing process to enhance the adhesion strength of the glass/epoxy composite structure. The morphological effect of the carbon black on the surface of composite was observed using scanning electron microscopy (SEM) and atomic force microscopy (AFM). Quantitative chemical bonding analysis with X-ray photoelectron spectroscopy (XPS) was also performed to observe chemical bonding states on the surface. The lap shear strength of the glass/epoxy composite adhesive joints where composite adherends were embedded with carbon black was investigated with respect to the type and amount of embedment. Also, the tensile properties of the carbon black embedded glass/epoxy composites were measured to observe the mechanical degradation of the composite due to the MEK. The surface free energies of carbon black embedded composites were determined from the van Oss–Chaudhury–Good equation to correlate the lap shear strength of the adhesive joints with the surface free energies of composite adherends. From the experimental results, it was found that the carbon black embedment of the composite adherend improved much the bond strength due to the increased surface roughness on nano-scale as well as increased surface free energy.     

The Effect of Cure Conditions on a Rubber-Modified Epoxy Adhesive

The effect of cure conditions on the mechanical properties of a piperidine-cured, rubber-modified epoxy is described. The results obtained reveal that variations in cure conditions (temperature and time) have a pronounced influence on the mechanical behaviour, in particular the fracture energy obtained in both bulk and adhesive joint form. Techniques such as dynamic mechanical spectroscopy and scanning electron microscopy have been employed in an attempt to explain the trends.