Bio-adhesives from soy protein concentrate and montmorillonite: Rheological and thermal behaviour

The incorporation of different amounts of montmorillonite (MMT) to soy protein concentrate (SPC) was used to improve the performance of the bio-nano-adhesive obtained. X-Ray diffraction, rheology, thermogravimetric analysis and scanning electronic microscopy were carried out to characterize the adhesives, and dry and wet strength was used to determine the adhesion strength. In the rheological measurement, the incorporation of up to 3 wt% of MMT did not modify the consistency index values of the SPC, while an increase in the flow consistency index for higher concentrations can be observed due to a strong interaction between MMT and the protein. Besides, the flow point values increase four times with respect to the value obtained for SPC alone. The decomposition temperature of SPC increases with the addition of MMT, which provides a tortuous pathway that obstructs the diffusion of volatile products out of the bio-nano-adhesive. Further addition beyond 5 wt% led to the formation of agglomerates, as verified by SEM. Moreover, the roughness of the fractured surface of the matrix can explain the decrease of the net adhesion of the nano-particles to the SPC suspensions.     

Ohmic contacts to polycrystalline 3C–SiC films for extreme environment microdevices

Ohmic contact characteristics were studied under the surface treatments of poly 3C–SiC films heteroepitaxially grown on SiO₂/Si wafers by APCVD. The poly 3C–SiC surface was polished to remove submicron-sized roughness and to get flat and smooth surface using chemical–mechanical polishing (CMP) process. However, some scratching marks on the poly 3C–SiC have remained surface due to the mechanical defect of CMP process. To remove a part of subsurface damage and scratching marks, the polished surface was oxidized by wet-oxidation furnace and it has been etched by diluted HF solution. Titanium tungsten (TiW) thin film was deposited on the surface treated poly 3C–SiC using circular transmission line model as a metallization process and it was annealed through the rapid temperature annealing (RTA) process to improve interfacial adhesion. The contact resistivity of the treated 3C–SiC surface was measured as the lowest 1.2 × 10⁻⁵ Ω cm³ at 900 °C for 45 s.     

Morphological studies on the adhesion mechanism of pressure-sensitive adhesives

The breaking process of the thin film of pressure-sensitive adhesives which are blends of natural rubber and the pentaerythritol ester of hydrogenated rosin and its surface structure after peeling off have been studied by electron microscopy. The dynamic observation of breaking process of the adhesives during the peeling has also been done by optical microscopy. The fibril structure with diameter of 50-100 Å was observed under the breaking process of the thin film and on the surface after peeling off the adhesive tape consisting of 40-60 wt % of resin. The previously proposed mechanism of adhesion which is based on the dynamic behaviors of fibrils and easy flow regions in the adhesives is confirmed by the electron microscopic observation.     

Chemical solution deposition of pure and Gd-doped ceria thin films: Structural,morphological and optical properties

High quality smooth, uniform and crack-free ceria and gadolinium doped ceria (GDC) thin films were prepared on Si and Si/YSZ substrates by chemical solution deposition. The thermal behavior of Gd-Ce-O precursor was investigated by TG-DSC measurements. The phase purity and structure of deposited films were evaluated using X-ray diffraction (XRD) analysis and Raman spectroscopy. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were employed for the estimation of surface morphological features. Oxidation state of Ce ions in fabricated films was analyzed by X-ray photoelectron spectroscopy (XPS). Optical properties were evaluated by diffuse reflectance UV–vis spectrometry. Thickness of the films can be controlled by applying a certain number of spin coating cycles. A linear relation between the thickness of the films and the number of deposited layers was observed. The single-layer thickness was determined to be approximately 20 nm. The influence of annealing temperature and Gd content on the film structure, morphology and optical properties was studied and discussed. The dependence of an optical band gap as a function of grain size was demonstrated.     

Fumaric Acid as a Promoter of Adhesion in Vulcanized Synthetic Rubbers

The addition of dicarboxylic acids to polyurethane adhesives, to improve their adhesion to vulcanized synthetic rubbers, may cause the degradation over time of the adhesives. To avoid the degradation of polyurethane adhesives, this study proposes a surface treatment on vulcanized synthetic rubbers with carboxylic acid solutions instead of adding them to the adhesives. In all the styrene-butadiene rubbers studied, a great improvement in adhesion to polyurethane adhesives has been obtained. The nature of the solvent used to disperse the fumaric acid over the surface, as well as the nature of the rubber, determined the effectiveness of the surface treatment. The use of fumaric acid solutions provided optimum results when the surface of the rubber was slightly roughened. The increase in the adhesion properties of styrene-butadiene rubbers, treated with fumaric acid, has been attributed to an increase in the degree of the surface roughness and to an enhancement in the surface energy (due to the elimination of abhesive substances on the surface of the rubber and to the formation of C-O groups by surface oxidation). The effectiveness of the surface treatment on rubbers with fumaric acid in the adhesion of styrene-butadiene rubbers has been compared with those produced by other common treatments, such as halogenation and roughening. In general, T-peel strengths obtained in the rubbers treated with fumaric acid were similar to those obtained through halogenation and were always higher than those obtained through roughening. Therefore, surface treatment of styrene-butadiene rubbers with fumaric acid can be considered as an alternative method to chemical treatments currently used, especially in the footwear industry.     

Electrochemical and surface analytical study of vinyl-triethoxy silane films on iron after exposure to air

One of the applications of silanes is to improve adhesion of organic coatings to metals. In this work, films of vinyl-triethoxy silane (VTES) on iron (Fe/VTES system) were used to study the effect of exposure to air on protective properties and on chemical transformations of silane films. After exposure to air for up to 12 days, impedance measurements were made in 0.01 M Na₂HPO₄, and surface analysis was carried out with AES, XPS and FTIR. Exposure to air resulted in an increase of charge transfer resistance of Fe/VTES, and led to chemical changes involving growth of iron oxides at the Fe/VTES interface, formation of SiO₂ and related species, formation of polysiloxanes and polymerisation of vinyl groups. These transformations include hydrolysis and probably also photochemical reactions with the participation of free radicals (formation of SiO₂ and polymerisation). Identified products can contribute to the improved protectiveness by enhancing the barrier properties and by inhibition of corrosion. It is suggested that apart from improving adhesion, silanes play an important role also by protecting against corrosion.     

Improvement of adhesion and paint ability of EVA copolymers with different vinyl acetate contents by treatment with UV-ozone

The surface modifications produced by UV-ozone treatment of two ethylene-vinyl acetate (EVA) copolymers containing 12 and 20 wt% vinyl acetate (EVA12 and EVA20 respectively) were studied. The treatment with UV-ozone improved the wettability of both EVAs due to the creation of new carbon–oxygen moieties. The extent of these modifications increased with increasing length of the treatment and the modifications produced in EVA20 were produced for shorter lengths of treatment. The UV-ozone treatment also created roughness and heterogeneities on the EVA surfaces. Whereas roughness formation prevailed on the UV-ozone treated EVA12, important ablation was dominant on the treated EVA20. T-peel strength values in joints made with polychloroprene adhesive increased when the EVAs were treated with UV-ozone. Short length of UV-ozone treatment (1 min) produced higher T-peel strength in joints made with EVA20 whereas higher T-peel strength values in joints made with EVA12 were obtained after treatment for 5–7.5 min in which a cohesive failure into a weak boundary layer on the treated EVA surface was found. Furthermore, the adhesion of UV-ozone treated EVA20 to acrylic paint increased. Finally, the ageing resistance of the treated EVA/polychloroprene adhesive joints was good and the surface modifications on the UV-ozone treated EVAs lasted for 24 h after treatment at least.     

Experimental investigation into the effect of DC glow discharge pretreatment of HDPE on tensile lap shear strength

The present investigation aims to optimise the process parameters of DC glow discharge treatment through air in terms of discharge power and time of exposure for attaining best adhesive joint of high-density polyethylene (HDPE) to mild steel. The as- received and DC glow discharge exposed HDPE surfaces have been characterised by energy dispersive spectra (EDS). It is observed that with increasing power level up to 13 W, tensile lap shear strength of adhesive (Araldite AY 105) joint of HDPE to mild steel increases and then decreases. At 13 W power level, joint strength increases up to 120 s of exposure and then decreases. At the optimised condition for the surface modification, the effect of two different adhesives Araldite AY 105 and Araldite 2011 on the strength of polymer to mild steel, polymer to polymer and mild steel to mild steel joints have been examined. It is observed that tensile lap shear strength of HDPE–HDPE joint and HDPE–mild steel joint does not change with the change of adhesive and this could be possible as initiation of fracture takes place from subsurface layer of the polymer. This is confirmed by studies under optical microscopy and EDS, which shows when the polymer has been modified by exposure under glow discharge the failure is observed to initiate from subsurface layer of the HDPE, then within the adhesive cohesively and thereafter in the mild steel to adhesive interface.     

Water-based adhesive formulations for rubber to metal bonding developed by statistical design of experiments

Waterborne adhesives for rubber to metal bonding have been available since 1990. However, published information about their formulation has been limited, as proprietary restrictions are exercised by companies. As a consequence, the way these adhesives interact with substrates has not been studied extensively. With the aim of investigating the effect the components of a waterborne adhesive have on rubber to metal bonding, fractional factorial and surface response methodologies of design of experiments were employed in this study. Twenty six formulations were prepared with a polychloroprene latex as the adhesive polymer. Viscosity, wettability and non-volatile solids content were measured with each liquid adhesive, while the mechanical strength was evaluated by applying a tensile mechanical stress over cured solid adhesive films. Adhesion properties were evaluated by using a single lap-shear test on metal to metal joints and a pull-out test on rubber to metal joints. The results showed that the components with the largest relative influence on cohesive and adhesives forces were tackifier resin, silicon dioxide and polychloroprene latex type. In order to better understand the contributions of these variables, mathematical models correlating them with the response variables were obtained. This study is valuable in explaining how, through statistical methods, a waterborne adhesive for rubber to metal bonding can be formulated with a reasonably low number of experiments.     

Adhesion properties of lactic acid based hot melt adhesives and their storage stability in different packaging applications

Adhesion properties and the stability during the use life of the package for two biodegradable hot melt adhesives were evaluated. Adhesives were based on poly (L-lactide) (PLLA) and poly(-caprolactone) (PCL) with molar ratio 81:19. One sample was stabilized by end-capping the terminal hydroxyl groups with acetic anhydride. The other sample was unmodified. Reference adhesive that was used in the studies, was a conventional non-biodegradable hot melt adhesive based on poly(ethylene-co-vinylacetate) (EVA).

Materials, which were bonded with these hot melt adhesives, were typical biodegradable packaging materials: a pigment-coated cardboard, a similar cardboard extrusion laminated with film type PLLA and an uncoated cardboard. The storage stabilities of the copolyester films and bonded structures were monitored during an eight week period at room (23°C) and at low (−18°C) temperatures.

Changes in molecular weight and crystallinity of the copolyesters were measured with gel permeation chromatography (GPC) and differential scanning calorimetry (DSC), respectively. Mechanical strength of the adhesive bonds was measured by a tensile testing instrument. Fracture surfaces of the adhesive bonds were subjected to microscopic studies.

Initial adhesion properties of the copolyesters were similar to those of EVA and better in case of PLLA-laminated cardboard. Both biodegradable copolyester samples degraded during the studied period; however, end-capping of the copolymer retarded this degradation rate.     

Effects of nitrogen plasma treatment of pressure-sensitive adhesive layer surfaces on their peel adhesion behavior

The influence of the surface modification of pressure-sensitive adhesive tapes on their adhesion behavior has been investigated. PBA [poly(butyl acrylate)] and PIB [poly(isobutylene)] adhesives were chosen as pressure-sensitive adhesives and nitrogen plasma was used for the surface modification of the adhesives. The peel force of PBA or PIB adhesive/stainless steel joints was evaluated. The nitrogen plasma treatment showed large effects on the adhesion behavior of both the PBA and the PIB adhesives. The peel force for the PBA adhesive/stainless steel joint decreased by 57 times as a result of the nitrogen plasma treatment and that for the PIB adhesive/stainless steel joint increased by 2.2 times. There are essential differences in the modification reactions caused by the nitrogen plasma between the PBA and PIB adhesives. For the PBA adhesive, cross-linking reactions occurred among the PBA polymer chains and the surface was hardened. For the PIB adhesive, degradation reactions occurred and products with a low molecular weight were formed on the surface. These differences are due to the different responses of the PBA and PIB adhesives towards the nitrogen plasma. The mechanism of the changes in adhesion behavior caused by the nitrogen plasma is discussed.     

Adhesion performance and surface characteristics of low surface energy psas fluorinated by UV polymerization

Acrylic pressure sensitive adhesives (PSAs) have a range of applications in industry, such as medical products, aircraft, space shuttles, electrical devices, optical products, and automobiles, etc. In this study, acrylic PSAs with fluorinated groups were synthesized using 2,2,2‐trifluoroethyl methacrylate (TFMA) under UV radiation. The surface properties and adhesion strength were measured. The results showed that the addition of TFMA reduced the surface energy of the PSAs and improved the adhesion strength. POLYM. ENG. SCI., 2013. © 2013 Society of Plastics Engineers     

Characterization of waterborne polyurethane adhesives containing different amounts of ionic groups

Waterborne polyurethane adhesives are an interesting alternative to the current solvent-based polyurethane adhesives used in footwear industry. In this study, different aqueous polyurethane dispersions were prepared by using the prepolymer mixing process. The ionic groups content in the polyurethane ionomer structure was varied by changing the amount (5 and 8 wt% (with respect to the prepolymer weight) of the internal emulsifier—dimethylolpropionic acid (DMPA). The decrease in the DMPA content slightly increased the particle size in number due to the decrease in both the hydrophilicity of the polyurethane ionomer, and the electrolytic stability of the aqueous polyurethane dispersion. Furthermore, the lower the DMPA amount, the lower the hard segment content in the ionomer and the higher the crystallinity of the polyurethane; however, the resistance to flow under temperature (i.e. thermoplasticity) was reduced. The resistance to thermal degradation of the polyurethane ionomer increased by decreasing the DMPA content due to the lower hard segment content. Finally, high initial adhesive strength was obtained and the adhesion to PVC increased as the DMPA content in the polyurethane ionomer decreased.     

The role of interfacial interactions and loss function of model adhesives on their adhesion to glass

The measurement of adhesion and the evaluation of influencing factors are of great scientific and technological importance. There are two distinct viewpoints on adhesion: (i) surface chemistry, and (ii) fracture mechanics. For elucidation of the relative importance of mechanical properties in the bonding of adhesives, the strength of adhesion between model adhesives and glass plates was measured by the wedge cleavage (WC) test method. Copolymers of methyl methacrylate (MMA) with n-butyl acrylate (nBA) and methyl methacrylate with styrene (S) were prepared as model adhesives. The results show that in MMA-nBA copolymers, by increasing the amount of nBA, both the loss function and the adhesion energy of the adhesives increase. However, by increasing the amount of nBA above a certain level, the adhesion strength begins to decrease. In this situation, the cohesive strength of the adhesive dominates the failure mechanism. On the other hand, a decrease in adhesion was expected upon increasing the amount of styrene in the poly(styrene-co-methyl methacrylate) adhesive, because methyl methacrylate, an interactive monomer with glass, is replaced by a non-interacting styrene monomer, while the loss function of the adhesive is almost constant. But our practical adhesion measurement technique was not sensitive enough to detect this adhesion loss.     

Fabrication of surface-treated BN/ETDS composites for enhanced thermal and mechanical properties

The ceramic/polymer composites based on epoxy-terminated dimethylsiloxane (ETDS) and boron nitride (BN) were prepared for use as thermal interface materials (TIMs). 250 µm-sized BN was used as a filler to achieve high-thermal-conductivity composites. To improve the interfacial adhesion between the BN particles and the ETDS matrix, the surface of BN particles were modified with silica via the sol–gel method with tetraethyl orthosilicate (TEOS). The interfacial adhesion properties of the composites were determined by the surface free energy of the particles using a contact angle test. The surface-modified BN/ETDS composites exhibited thermal conductivities ranging from 0.2 W/m K to 3.1 W/m K, exceeding those of raw BN/ETDS composites at the same weight fractions. Agari׳s model was used to analyze the measured thermal conductivity as a function of the SiO₂-BN concentration. Moreover, the storage modulus of the BN/ETDS composites was found to increase with surface modification of the BN particles.     

Morphology and optical analysis of defect levels in ultrasonically-sprayed zinc tin oxide thin films

We prepared zinc-doped tin oxide (ZTO) films of various concentrations of zinc using the ultrasonic spray pyrolysis technique. The surface morphology and roughness were studied by Field-Emission Scanning Electron Microscope and atomic force microscope. Systematic x-ray diffraction (XRD) measurements revealed that all films have tetragonal rutile structure and mixed preferred orientation along the (200) and (110) planes. The proper substitution of zinc ions into tin sites and the absence of any secondary phase in the films were proved by the analysis of the x-ray photoelectron spectroscopy (XPS) measurements. The detailed analysis of the optical absorption spectra revealed the presence of four direct optical transitions within the energy range 3.8–5.1 eV. The defect levels of the neutral and double-ionized oxygen vacancy states were determined within the energy bandgap by the comprehensive analysis of the photoluminescence spectra. The existence of high concentration of oxygen vacancies is supported by the XPS results. The observed transitions were used to sketch the band diagram of ZTO films.     

Synthetic aspects and characterization of polypropylene-silica nanocomposites prepared via solid-state modification and sol-gel reactions

A new route is developed by combining solid-state modification (SSM) by grafting vinyl triethoxysilane (VTES) with a sol-gel method to prepare PP/silica nanocomposites with varying degree of adhesion between filler and matrix. VTES was grafted via SSM in porous PP particles. Bulk polymerization under similar experimental conditions as in SSM resulted in homopolymerization of VTES. However, SEC and NMR experiments showed that VTES was grafted as a single monomeric unit in the amorphous phase of PP with the possibility of VTES-polymer grafting during SSM. Silica-like nano-particles were synthesized in-situ by the sol-gel method. Magic-angle spinning (MAS) ²⁹Si NMR spectra showed that the chemical building blocks of the silica-like clusters are of Q³ and Q⁴ type. MAS ²⁹Si NMR and FT-IR spectroscopy showed that the grafted VTES becomes part of the in-situ formed silica particles. No decrease in molecular weight of PP was observed, indicating that chain scission is marginal compared to melt modification. The morphology of the nanocomposites as observed by ATR-FTIR microscopy showed a uniform dispersion of grafted VTES as well as in-situ formed silica. TEM and SEM demonstrated that the in-situ formed silica particles are nearly spherical and have sizes in the range of 50-100 nm.     

Adhesion properties of soy protein adhesives enhanced by biomass lignin

Soy protein adhesives have great potential as sustainable eco-friendly adhesives. However, low adhesion under wet conditions hinders its applications. The objective of this research was to enhance the water resistance of soy protein adhesives. The focus of this research was to understand the effect of protein to lignin ratio and lignin particle size i.e. large (35.66 μm), medium (19.13 μm), and small (10.26 μm) on the adhesion performance of soy protein adhesives as well as to characterize its rheological and thermal properties. Results showed that the lignin particle size and the protein to lignin ratio greatly affected the adhesion performance of soy protein adhesives. The addition of lignin slightly increased the viscosity, spreadability, and thermostability of soy protein adhesives. The wet strength of soy protein adhesives increased as lignin particle size decreased. Soy protein mixed with small size lignin at a protein to lignin ratio of 10:2 (w/w) at 12% concentration presented the lowest contact angle and the highest wet adhesion strength of 4.66 MPa., which is 53.3% higher than that of 10% pure soy protein adhesive. The improvements in adhesion performance and physicochemical properties of soy protein adhesives by lignin were ascribed to the interactions between protein and lignin. Lignin with smaller particle size increased the wet shear strength of soy protein adhesives because a larger surface area of lignin was available to interact with the protein.     

Studies on preparation and properties of vinyltriethoxysilane‐grafted styrene‐butadiene rubber

Graft polymerization of vinyltriethoxysilane (VTES) onto styrene‐butadiene rubber (SBR) was carried out in latex using benzoic peroxide (BPO) as an initiator. The concentration of VTES effecting on vulcanization characteristics, mechanical properties and thermal properties of VTES‐grafted SBR (SBR‐g‐VTES) were investigated. The grafting of VTES onto SBR and its pre‐crosslinking were confirmed by attenuated total teflectance‐Fourier transform infrared reflectance and proton nuclear magnetic resonance. The mechanism of graft polymerization was studied. The results revealed that the minimum torque, optimum cure time, tensile strength, thermal decomposition temperature, and glass transition temperature (T_g) all increased with the increasing concentration of VTES. But the grafting efficiency of VTES, rate of vulcanization, and elongation at break of the SBR‐g‐VTES decreased. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Shear strength of adhesively bonded polyolefins with minimal surface preparation

Interest in polyethylene and polypropylene bonding has increased in the last years. However, adhesive joints with adherends which are of low surface energy and which are chemically inert present several difficulties. Generally, their high degree of chemical resistance to solvents and dissimilar solubility parameters limit the usefulness of solvent bonding as a viable assembly technique. One successful approach to adhesive bonding of these materials involves proper selection of surface pre-treatment prior to bonding. With the correct pre-treatment it is possible to glue these materials with one or more of several adhesives required by the applications involved. A second approach is the use of adhesives without surface pre-treatment, such as hot melts, high tack pressure-sensitive adhesives, solvent-based specialty adhesives and, more recently, structural acrylic adhesives as such 3M DP-8005^® and Loctite 3030^®.In this paper, the shear strengths of two acrylic adhesives were evaluated using the lap shear test method ASTM D3163 and the block shear test method ASTM D4501. Two different industrial polyolefins (polyethylene and polypropylene) were used for adherends. However, the focus of this study was to measure the shear strength of polyethylene joints with acrylic adhesives. The effect of abrasion was also studied. Some test specimens were manually abraded using 180 and 320 grade abrasive paper. An additional goal of this work was to examine the effect of temperature and moisture on mechanical strength of adhesive joints.