Experimental investigation on environmental degradation of automotive mixed-adhesive joints

In this paper, environmental strength degradation of 180 different adhesive single lap joints (SLJ), including mono-adhesive Araldite 2015, mono-adhesive Araldite AV138, and a mixed-adhesive of Araldite 2015 and Araldite AV138 subjected to moist conditions are experimentally studied. Four different moist conditions, i.e. dry, 75.3, 84.2 RH% and immersion in tap water, have been taken into consideration and the specimens are tested after exposing to these environments at room temperature for 0, 35, 80 and 270 days. The specimens have been tested in two different strain rate, i.e. 1 mm/min and 100 mm/min. The results reveal that although, in a dry environment, mixed-adhesive joints have higher failure loads in comparison to mono-adhesive SLJs, in a moist environment, they have the highest reduction in static failure load with regard to the mono-adhesive ones. Moreover, despite the finally brittle trend in failure load, mixed-adhesives manifest a behavior very similar to ductile mono-adhesives regarding elongation. Analytical predictions of failure load are also consistent with the experimental observations in dry condition.     

Design of functionally graded joints using a polyurethane-based adhesive with varying amounts of acrylate

Adhesives with graded properties along the bondline are being developed to increase the strength of adhesively bonded joints. Efforts to do this in the past have resulted in mixed results. Two adhesive parameters need to be considered: the geometry of the gradation and the material properties of the adhesive at different gradation levels. In order to consider both of these aspects, a computational model was created to aid in not only the design of adhesive gradations but also judge whether a specific adhesive gradation method will be able to result in strength increases. In this study, the model was introduced and compared with published results. A new adhesive gradation system was created by using a polyurethane-based adhesive with varying amounts of acrylate, and a numerical analysis was performed to determine the potential advantages of the adhesive gradation.     

Polybutylene terephthalate modified with dimer acid methyl ester derived from fatty acid methyl esters and its use as a hot-melt adhesive

A series of polyester copolymers was synthesized via melt polycondensation of dimethyl terephthalate (DMT), dimethyl isophthalate (DMI), and 1,4-butanediol (BDO) with dimer acid methyl ester (DAME) monomers, previously prepared by the Diels–Alder reaction of fatty acid methyl esters (FAMEs). We obtained copolymers with the desired composition and a high molar mass characterized by ¹H NMR, FT-IR, and SEC. The relationship among the composition, thermal behavior, mechanical properties, and adhesion properties of these copolymers was examined, demonstrating that the DAME-modified copolymers could be substituted for HMA applications and are comparable to petroleum-based commercial products. As a result, these polyesters could offer improved sustainability and performance and may be good candidates for hot-melt adhesive materials. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48474.     

Quantitative wood–adhesive penetration with X-ray computed tomography

Micro X-ray computed tomography (XCT) was used to analyze the 3D adhesive penetration behavior of different wood–adhesive bondlines. Three adhesives, a phenol formaldehyde (PF), a polymeric diphenylmethane diisocyanate (pMDI), and a hybrid polyvinyl acetate (PVA), all tagged with iodine for enhanced X-ray attenuation, were used to prepare single-bondline laminates in two softwoods, Douglas-fir and loblolly pine, and one hardwood, a hybrid polar. Adhesive penetration depth was measured with two separate calculations, and results were compared with 2D fluorescent micrographs. A total of 54 XCT scans were collected, representing six replicates of each treatment type; each replicate, however, consisted of approximately 1500 individual, cross-section slices stacked along the specimen length. As these adhesives were highly modified, the presented results do not indicate typical behavior for their broader adhesive classes. Still, clear penetration differences were observed between each adhesive type, and between wood species bonded with both the PF and pMDI adhesives. Furthermore, penetration results depended on the calculation method used. Two adhesive types with noticeably different resin distributions in the cured bondline, showed relatively similar penetration depths when calculated with a traditional effective penetration equation. However, when the same data was calculated with a weighted penetration calculation, which accounts for both adhesive area and depth, the results appeared to better represent the different distributions depicted in the photomicrographs and tomograms. Additionally, individual replicate comparisons showed variation due to specimen anatomy, not easily observed or interpreted from 2D images. Finally, 3D views of segmented 3D adhesive phases offered unique, in-situ views of the cured adhesive structures. In particular, voids formed by CO₂ bubbles generated during pMDI cure were clearly visible in penetrated columns of the solidified adhesive.     

Effects of different segments in polyurethane on the performance of sand stabilization

Synthetic polymers have recently drawn increasing attention to chemical sand stabilization (CSS). The relationship between the molecular structure and the fixing effect, however, is rarely reported aside from the performance. In this article, different segments of waterborne polyurethane dispersions (PUDs) are discussed with respect to their influence on stabilizing sand. We prepared five PUDs by controlling parameters including the diisocyanate-to-polyol ratio (R) and the molecular weight and characterized them with Fourier transform infrared spectroscopy and laser particle analysis. The unconfined compressive strength (UCS), a key criterion in CSS, was used to evaluate the performance of the PUDs. We found that a bigger R gave the polyurethane (PU) film a higher strength than the smaller R but did not do the same to the sand mold. This indicated that homogeneity was a primary property of the sand mold. Taking the details of the crushed sand molds and the PU films into account, we concluded that the soft segments played a major role in the homogeneity. Force analysis showed that four modes of breaking occurred at the interface of the sand and cured PU. We concluded that whereas the hard segments in PU determined the ceiling of the UCS, the soft segments determined the floor by benefiting adsorption. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47267.     

Assessment of hyperelastic material models for the application of adhesive point-fixings between glass and metal

For the investigation of adhesive point-fixings a computationally demanding finite element model is required. The accuracy of the numerical results depends highly on the validity of the used material models, which describe the deformation behaviour of the adhesive. The material models are derived from curve-fitting the mathematical expressions to experimental data mostly derived from uniaxial and equibiaxial experiments. In literature the suitability of the used material models is determined by comparing the numerical results from the same uniaxial and equibiaxial experiments to the experimental results. In contrast, in this contribution, the material models are validated by two additional validation experiments, i.e. an adhesive point-fixing loaded in uniaxial tension and an adhesive point-fixing loaded in a combination of tension and shear.After comparison of the numerical and experimental displacements, it appears that the material models that are calibrated by shear tests or by a combination of shear tests yield the best results. In addition, most numerical load-displacement curves have an almost linear gradient at small strains. Such behaviour is also demonstrated in the experimental measurements of the deformation.     

Investigation of interfacial debonding between steel wire and adhesive resin

Plastic pipes reinforced by cross helically wound steel wire (PSPs) have been widely used in the transportation of petroleum, natural gas, municipal water, and so on. With the applications of PSPs in high‐temperature and high‐pressure environments, the problem of PSP joints has begun to appear. The bulging failure of PSP joints is the main failure mode, and steel–polymer interfacial debonding is the major factor causing bulging failure. Thus, it is crucial to understand the failure criterion of steel–polymer interfacial debonding. In this study, pull‐out tests were carried out at different temperatures and loading rates. A finite element (FE) model was developed on the basis of the cohesive element. We proposed that the key parameter for the bugling failure of PSPs was the shear stress of the steel–polymer interface. We assumed that when the shear stress exceeded the shear strength, this led to the degradation of the interface. By iteratively presetting the shear strength and calculation of the FE model, the FE results were verified with experimental results. We found that the shear stress of the front part of the FE model first reached its peak value; its interface began to degrade, and then, the shear stress decreased. The peak value of the shear stress moved toward the end part of the FE model, and the shear strength could be obtained. Finally, the effects of the temperature and failure time on the shear strength were investigated. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45064.     

Predicting Shear Adhesion of Water-Based Pressure-Sensitive Adhesives via Transient Rheological Measurements

The relation between shear holding power and pressure-sensitive adhesive (PSA) rheological properties is investigated. Two constitutive models of PSA rheology, i.e., Newtonian and Power Law, are considered and experimentally tested for their ability to predict shear holding power. A Power Law model is found to be suitable for this purpose and is used to predict shear holding power with dynamic viscosity and steady shear viscosity measured by means of a transient creep experiment. Dynamic viscosity is shown to fail in predicting shear adhesion of high-viscosity PSA, whereas steady shear produces good agreement. It is demonstrated that the Cox-Merz rule does not hold for high-viscosity PSAs, explaining the need for steady shear viscosity data in modeling shear holding power.     

A New Methodology to Evaluate the Cure of Resin-Impregnated Paper for HPL

This paper presents a study on the curing conditions of several resin-impregnated papers and its impact on the performance of HPL (high-pressure decorative laminate). A new methodology for evaluating the bond strength development between the different layers of a HPL(overlay, decorative, and kraft papers) was developed using ABES (Automated Bonding Evaluation System) equipment. The proposed method can be applied to the study of the curing step of the different impregnated paper and the development of bonds between them (overlay paper on decorative paper, decorative paper on kraft paper, and kraft paper on kraft paper) trying to simulate the hot-pressing of an industrial HPL. This will permit to establish a more adapted temperature gradient in hot-press in order to achieve the same curing rate for all layers and provide a good final overall product quality.     

Morphology and mechanical properties of dual‐curable epoxyacrylate hybrid composites

A dual‐curable epoxyacrylate (EA) oligomer with one epoxide group and one vinyl group at each end was synthesized for the application as adhesive sealant in the liquid crystal display panels. However, after UV and thermal cure, the EA resin was brittle with a poor resistance to crack initiation and propagation. Liquid rubbers with different functional end groups were thus tried as toughening agents for the EA resin. Among all the rubber‐toughened EAs, the EA‐V5A5 added with vinyl‐terminated and amino‐terminated butadiene‐acrylonitrile copolymers (VTBN and ATBN) each at 5 phr had the highest fracture toughness, tensile strength, and elongation at break but a lower initial modulus. To raise the modulus, submicron‐sized silica particles (∼170 nm) with surface vinyl functional groups were further added to the EA‐V5A5 to prepare the hybrid composites. Because of interfacial chemical bonding provided by the surface vinyl functional groups, both modulus and fracture toughness were increased by adding silica particles, without any appreciable decrease in extensibility. For the hybrid composite at 20 phr silica particles, the initial modulus, fracture toughness, and fracture energy were raised by 10.3, 100, and 267%, respectively, when compared to the neat epoxyacrylate. Owing to their strong interfacial bonding, the increase of fracture toughness was mainly due to the crack deflection and bifurcation on silica particles, in addition to the rubber particle bridging and tearing as evidenced by SEM pictures on the fracture surface. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41820.