Miscibility and adhesive properties of EVA‐based hot‐melt adhesives. II. Peel strength

A series of ethylene vinyl acetate copolymers (EVA) were blended with some tackifier resins that were made from wood extracts, and possible relations between their miscibility and properties as hot‐melt adhesives (HMA) were investigated. From our previous report on miscibility of various EVA‐based HMAs, we chose some blends that represent some of the typical miscibility types and investigated their peel strengths. When the blends were miscible at testing temperatures, the temperature at which the maximum value of peel strength was recorded tended to move toward higher temperature as tackifier content of blends increased. This result corresponds to the storage modulus of the blends whose curves tended to move toward higher temperature as tackifier content of blends increased when blend components were miscible as well as their maximum values of tan δ, or glass transition temperatures. It was characteristic for peel strength that there existed second peaks on peel strengths curves at ～ 100°C, which adhesive tensile strengths for the blends did not have. In terms of relationship between miscibility and HMA performances, we suggest that there are several factors other than miscibility that affect absolute values of peel strength more directly than miscibility; this idea has to be investigated further in the a future study. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 726–735, 2002     

钢/塑复合管用热熔胶的制备与性能研究

以PE(聚乙烯)接枝母料、线性低密度聚乙烯(LLDPE)为主要原料,石油树脂为增黏树脂,苯乙烯-乙烯-丁二烯-苯乙烯嵌段共聚物(SEBS)为改性剂,采用单因素试验法优选出制备钢/塑复合管用HMA(热熔胶)的最佳配方。结果表明:增黏树脂的引入能明显提高HMA的剥离强度和熔体指数,并且胶接层的破坏形式为内聚破坏;SEBS类弹性体的引入能显著提高HMA的剥离强度,但熔体指数明显降低,而且胶接层的破坏形式是黏附破坏;当m(PE接枝母料)∶m(LLDPE)∶m(石油树脂)∶m(SEBS)=30∶45∶15∶10时,HMA的综合性能相对最好,其剥离强度为397 N/cm、熔体指数为2.3 g/10 min且胶接层的破坏形式是内聚破坏。     

粗糙度对彩色涂层与基体间附着力的影响

研究粗糙度对基体和涂层之间的附着力的影响,其一,是因为基体表面的凸凹不平导致漆膜在其上附着时产生互相咬合的现象,增大了附着力;另外,基体表面粗糙度越大其真实表面积越大,在基体表面发生腐蚀时腐蚀产物不易扩散,因此涂层附着力不易下降。     

粘合衬用热熔胶全细粉的制备及性能研究

采用“溶涨”粉化法对聚酰胺热熔胶进行制粉 ,通过优化粉化条件 ,制得细粉 (通过 2 0 0目 )达 90 %以上。同深冷粉碎法相比 ,细粉收率高 ,胶粉的应用性能与其相当     

光/湿双固化聚氨酯热熔胶的制备与性能研究

以多元醇、异氰酸酯、含羟基丙烯酸酯和光引发剂等为原料,制备了PET(聚酯)基材粘接用光/湿双固化PU(聚氨酯)-PUA(聚氨酯丙烯酸酯)型反应性HMA(热熔胶)。研究结果表明:该HMA中同时含有可光固化基团(C=C)和可湿固化基团(-NCO);当n(C=C)∶n(-NCO)=20∶80、w(复合光引发剂)=1.5%~2.0%和引入甲基丙烯酸羟乙酯(HEMA)时,相应HMA具有较高的初始强度和最终强度;光/湿双固化HMA的透明度高于湿固化HMA,说明UV固化是增加光/湿双固化HMA透明度的主要原因。     

Metal alkoxide primers in the adhesive bonding of mild steel

The effects of metal alkoxide type and relative humidity on the durability of alkoxide-primed, adhesively bonded steel wedge crack specimens have been determined. Aluminum tri-secbutoxide, aluminum tri-tert-butoxide, tetrabutyl orthosilicate, and titanium(IV ) butoxide were used as alkoxide primers. Grit-blasted, acetone-rinsed mild steel adherends were the substrates bonded with epoxy and polyethersulfone. The two aluminum alkoxides significantly enhanced the durability of the adhesively bonded steel, while the titanium alkoxide showed no improvement in durability over a nonprimed control. The silicon alkoxide-primed samples gave an intermediate response. The failure plane in the adhesively bonded samples varied with the relative humidity during the priming process.     

Evaluation of mechanical and laser surface pre-treatments on the strength of adhesive bonded steel joints for the automotive industry

Recent research efforts in the automotive industry have been focused on the integration of high-strength steels within lightweight vehicles by using improved joining techniques. The present work falls in this subject area and is focused on the analysis of adhesive bonded dual-phase steel/epoxy joints for the automotive industry. Two quasi-static loadcases were considered, i.e. single-lap and T-peel tests, and various surface preparation strategies were evaluated. In particular, the mating surfaces were pre-treated by using pulsed laser irradiation with a fiber laser (1064 nm) and comparisons were made with degreasing and sand blasting. Moreover, the effects of bondline thickness and adhesive type were also assessed. To this aim, two epoxy adhesives with fairly different mechanical behavior (i.e. strain hardening versus elasto-plastic) were deployed for joints fabrication. Finally, T-peel tests were also carried out after sample cycling under controlled high humidity and temperature (i.e. accelerated aging). The obtained results highlighted the beneficial effect of laser irradiation on the joints’ mechanical behavior under both static and hydrothermal loadings.     

Effect of adhesive thickness and surface roughness on the shear strength of aluminium one-component polyurethane adhesive single-lap joints for automotive applications

Adhesively bonded technology is now widely accepted as a valuable tool in mechanical design, allowing the production of connections with a very good strength‐to‐weight ratio. The bonding may be made between metal–metal, metal–composite or composite–composite. In the automotive industry, elastomeric adhesives such as polyurethanes are used in structural applications such as windshield bonding because they present important advantages in terms of damping, impact, fatigue and safety, which are critical factors. For efficient designs of adhesively bonded structures, the knowledge of the relationship between substrates and the adhesive layer is essential. The aim of this work, via an experimental study, is to carry out and quantify the various variables affecting the strength of single-lap joints (SLJs), especially the effect of the surface preparation and adhesive thickness. Aluminium SLJs were fabricated and tested to assess the adhesive performance in a joint. The effect of the bondline thickness on the lap-shear strength of the adhesives was studied. A decrease in surface roughness was found to increase the shear strength of the SLJs. Experimental results showed that rougher surfaces have less wettability which is coherent with shear strength tests. However, increasing the adhesive thickness decreased the shear strength of SLJs. Indeed, a numerical model was developed to search the impact of increasing adhesive thickness on the interface of the adherend.     

Investigation of the relationship between statistical characteristics of substrate surface roughness and the strength of adhesive joints

The relationship between statistical characteristics of butadiene styrene rubber (BSR) surface roughness and shear strength of adhesive joints has been investigated. The assumption of stationary normal distribution of coordinates of surface points was made to determine the statistical characteristics of surface roughness. The profile length above the selected level l ₁ (u) was introduced as a new surface roughness parameter to characterize adhesive penetration depth. The validity of simulated l ₁ (u) value was verified experimentally. A good correlation between experimental and calculated results was found. A relationship between adhesive penetration depth and the bonding pressure during adhesive joint preparation was also obtained. The dependences among lap shear joint strength, bonding pressure and roughness characteristic l ₁ (u) were determined.     

Modification of stainless steel surface hydrophobicity by silver nanoparticles: strategies to prevent bacterial adhesion in the food processing

The ability of silver nanoparticles to modify the thermodynamic characteristics of stainless steel surfaces in order to reduce the adhesion process and thereby inhibit biofilm formation was evaluated. We observed that silver nanoparticles were able to decrease the contact angle of stainless steel from 73.20° when conditioned with water to 12.10° making the surface more hydrophilic. Thus, the thermodynamics of adhesion for all the evaluated bacteria was more unfavorable when the stainless steel surfaces were conditioned with the nanoparticles. Regarding the bacteria, Staphylococcus aureus was the most hydrophilic (p?<?0.05) followed for Escherichia coli, Pseudomonas aeruginosa, and Listeria innocua. Thereby, the silver nanoparticles demonstrated efficiency in inhibiting theoretical adhesion by altering the surface hydrophobicity that can potentially hamper cellular adhesion and prevent biofilm formation.     

Effect of the concentration of the sizing agent on the carbon fibers surface and interface properties of its composites

The effect of the concentration of the sizing agent on performances of carbon fiber and carbon fiber composites has been investigated. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) were applied to characterize carbon fiber surface topographies. At the same time, the single fiber strengths and Weibull distribution were also studied. The interlaminar shear strength and hygrothermal ageing test have been used to study the effect of fiber coatings on the interface of the composites. The analysis of the results shows that the sizing level is essential for improving the surface of carbon fibers and its composite performance. Different concentrations of the sizing agent have different contributions to the wetting performance of carbon fibers. Among the three concentrations of sizing agent studied (1 wt %, 1.5 wt %, and 2 wt %), the optimal sizing level is 1.5 wt %. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci 125:425–432, 2011     

The effect of moisture and temperature on the properties of an epoxide-polyamide adhesive in relation to its performance in single lap joints

A template cutting technique has been used to prepare dumb-bell shaped specimens of the epoxide-polyamide adhesive FM 1000, and their mechanical properties have been examined as a function of water exposure, testing speed, and temperature. The glass transition temperature of the wet adhesive has also been examined. Strengths of single lap joints bonded with the adhesive have been measured after exposure to warm moist air for up to 2500 hours. Strengths of wet and dry joints have been compared over a wide temperature range. The results show that the weakening effect which water has is due to plasticization of the adhesive, and that the rate of weakening depends on water diffusion within the adhesive layer.     

The effect of fluorination on the surface characteristics and adhesive properties of polyethylene and polypropylene

Polyethylene and polypropylene have been treated with fluorine/nitrogen or fluorine/oxygen/nitrogen mixtures at atmospheric pressure. Changes in surface chemistry and topography as well as depth of fluorination have been examined using Fourier transform infra-red analysis, X-ray photoelectron spectroscopy (X.p.s.), atomic force microscopy (AFM) and ellipsometry. Even very short exposure times caused a large substitution of the hydrogen atoms by fluorine. No change in surface topography was noticed at magnifications of up to 5000 times with the scanning electron microscope (SEM), but AFM showed that fluorination led to an increase of microroughness. The influence of fluorine or fluorine/oxygen concentration, as well as time of treatment and time of storage before adhesive bonding, on adhesion of polypropylene to steel was investigated with a bending peel test. Significant improvement in peel strength was already achieved with minor fluorination intensity. Increase of fluorination intensity did not lead to further improvement in peel strength. Analysis of the fracture surfaces was carried out with the SEM and by energy dispersive X-ray spectroscopy and X.p.s. The findings showed that the samples failed cohesively in the polymer or directly beneath the fluorinated layer. A model to describe the formation of specific interactions between substrate and adhesive is suggested.     

On the importance of specific interface area in clay nanocomposites of PMMA filled with synthetic nano-mica

In clay nanocomposites, the specific interface area is the key factor determining potential improvements of properties. Nevertheless, in most systematic studies of nanocomposites little emphasis is put on assuring and characterizing dispersion quality. To probe the influence of dispersion quality, we compare nanocomposites filled with two layered silicates which were made by melt compounding and solution blending, respectively. Poly(methyl methacrylate) (PMMA) is chosen here as a thermoplastic model matrix which was compounded with a synthetic nano-mica (O-hect) and commercial Bentone with typical diameters of 5–7 μm and <300 nm, respectively.     

On the thermodynamic functions of gas-solid adsorption and liquid-solid immersion,and their relation to adhesion,contact angle and surface tension

The thermodynamic functions of gas-solid adsorption and liquid-solid immersion are summarized on a literature basis. For adsorption, the isosteric and calorimetric methods are compared; for immersion, the Gibbs free energy of adhesion as a function of relative pressure is introduced.The thermodynamic functions reported are enthalpy, Gibbs free energy and entropy of adsorption, immersion and adhesion. All the formulae given contain only those values that result from adsorption, immersion, contact angle or surface tension of the liquids measurements.Interrelations between the thermodynamic functions of adsorption, immersion and adhesion are also given. They permit cross checks and substitution of measurements, e.g., of immersion for adsorption measurement.Typical values are reported and plots of some thermodynamic functions versus coverage are discussed with respect to height and decrease of the powder-adsorptive interaction with layer thickness.     

Effect of CNT dispersion methods on the strength and fracture mechanism of interface in epoxy adhesive/Al joints

The tensile and shear strengths of adhesively bonded aluminum (Al) joints were inspected in the presence of amino functionalized multi-wall carbon nanotubes (MWCNTs). Tensile and shear tests were carried out using butt and lap-shear joints. The main goal was to compare the effects of dispersion methods of functionalized-CNT into epoxy on the mechanical performances and failure mechanisms of Al joints. Two different types of dispersion procedures, distributing CNT in the hardener (HH method) and distributing CNT in the resin (RR method), were applied. To identify the failure mechanisms, the morphology of fracture surfaces were analyzed using scanning electron microscopy (SEM). Comparing two dispersion methods against one another ascertained that following the RR method for dispersing CNTs in the adhesive displayed larger shear strength, while applying HH method offered fairly greater tensile strength. Moreover, dispersing CNTs in the resin induced more uniform dispersion of CNTs as compared to distributing nanofillers in the hardener. Following RR method, CNTs good dispersion as well as the presence of effective crack growth dissipating mechanisms, increased the shear strength of CNT reinforced adhesive joint. Incorporating CNTs using HH approach encouraged the plastic void formation of epoxy around the agglomerated CNTs, and as a consequence, promoted the plastic deformation under tension.     

气相白炭黑的比表面积与表面特性对硅橡胶补强效果的影响

探讨了气相白炭黑的比表面积和表面特性对硅橡胶力学性能的影响,同时采用扫描电镜和溶胀法分别研究了不同表面特性白炭黑补强硅橡胶的拉伸断面形貌和交联密度。结果表明：随着疏水性白炭黑比表面积的增加,硅橡胶拉伸强度和断裂伸长率增加;对比发现,疏水性白炭黑的补强效果优于亲水性白炭黑,这是由于疏水性白炭黑在橡胶基体中分散更加均匀,而且疏水性白炭黑补强硅橡胶的交联密度更大。     

Cyclic voltammetric behaviour and some surface characteristics of the lead electrode in aqueous HCL solutions

The positive linear sweep voltammograms of lead were investigated in 0.01–2.00 M aqueous HCl solutions. The results revealed the occurrence of one anodic current peak as the result of formation of a thin PbCl₂ surface layer. Intensive study of the electrochemical behaviour of the lead electrode in 1.00 M HCl solution was carried out by cyclic voltammetry. The results indicated that the formation of PbCl₂ is a reversible process controlled by diffusion of Cl^? ions to the electrode surface. Controlling the voltammetric conditions enabled the building up of a relatively thick and porous PbCl₂ layer that could resist rupture or breakdown. In addition, the electrode surface products were examined by scanning electron microscopy and X-ray diffractometry. The morphology of the as-formed PbCl₂ layers showed a primitive dependence on the voltammetric conditions. X-ray diffraction analysis proved that only PbCl₂ was formed on the electrode surface and no other products could be detected.     

On the durability of rubber/metal bonds in seawater

A study of the durability of rubber/metal bonds in seawater is described, using natural rubber, polychloroprene and acrylonitrile rubber bonded to carbon steel or titanium. Results are presented on the effect of water absorption by rubber on the elastic modulus, fatigue crack growth rate, peel energy and areas of interfacial failure of three different test-piece designs. It has been discovered that, although in electrochemically inert conditions rubber/metal bonds proved highly durable, in conditions of increased electrochemical activity bond failure occurs at relatively rapid rates. Thin encapsulating layers of rubber were found to be highly effective in preventing corrosion of steel or bond failure, and seawater exposure had in general no seriously adverse effect on the rubber itself.     

DEIS evaluation of the relative effective surface area of AISI 304 stainless steel dissolution process in conditions of intergranular corrosion

The results presented in this paper contribute further information concerning examinations of AISI 304 stainless steel dissolution process in conditions of proceeding intergranular corrosion (IG) which have been determined on the basis of dynamic electrochemical impedance spectroscopy (DEIS) measurements. For the first time changes of the relative effective surface area versus time of AISI 304 stainless steel dissolution process in conditions of proceeding intergranular corrosion (IG) in 0.5 M H₂SO₄ + 0.01 M KSCN solution within the range of reactivation polarization scan have been demonstrated. The assessment of the effective surface area of the investigated process was based on approximation to theory of iron dissolution in sulfuric acid medium according to the shape of instantaneous impedance spectra recorded by means of DEIS technique. As a result, it was possible to evaluate that initially changes of the employed equivalent circuit parameters are not only caused by the changes of the relative effective surface area but also by the changes of the AISI 304 SS dissolution process kinetics. Further progress of the examined process implied that changes of the equivalent circuit parameters are only affected by the changes of the relative effective surface area during proceeding IG. Moreover, it was found that the character of changes of the relative effective surface area in conditions of proceeding IG can be described by exponential function.