Bio-Based Epoxy Adhesives with Lignin-Based Aromatic Monophenols Replacing Bisphenol A

A bio-epoxy surface adhesive for adherence of the metal component species to glass substrate with desirable adhesion strength, converted controlled removal upon request, and bio-based resource inclusion was developed. For the development of resin, three different lignin-based aromatic monophenols, guaiacol, cresol, and vanillin, were used in the chemical epoxidation reaction with epichlorohydrin. The forming transformation process was studied by viscoelasticity, in situ FTIR monitoring, and Raman. Unlike other hydroxyl phenyls, guaiacol showed successful epoxide production, and stability at room temperature. Optimization of epoxide synthesis was conducted by varying NaOH concentration or reaction time. The obtained product was characterized by nuclear magnetic resonance and viscosity measurements. For the production of adhesive, environmentally problematic bisphenol A (BPA) epoxy was partially substituted with the environmentally acceptable, optimized guaiacol-based epoxy at 20, 50, and 80 wt.%. Mechanics, rheological properties, and the possibility of adhered phase de-application were assessed on the bio-substitutes and compared to commercially available polyepoxides or polyurethanes. Considering our aim, the sample composed of 80 wt.% bio-based epoxy/20 wt.% BPA thermoset was demonstrated to be the most suitable among those analyzed, as it was characterized by low BPA, desired boundary area and recoverability using a 10 wt.% acetic acid solution under ultrasound.

Mechanical Properties of Transparent Epoxy Adhesives for Glass Structures

Adhesive connections are commonly used in many industries as automotive, aerospace, electronics and also in civil engineering. Adhesives in civil engineering are used for non-load bearing structures but nowadays are requirements for using adhesive also for load- bearing structures especially for glass structures. Silicones are mostly used adhesives in civil engineering, they have good resistance to external environment but their lower strength and lower stiffness does not meet requirements for many applications. For this reason, are better semi-rigid or rigid adhesives but there is a lack of information about them. The paper is focused on experimental testing of transparent adhesive connection glass to glass. Four epoxy adhesives were chosen for double lap shear joint. Specimen were exposed to shear test until failure. Shear force and displacement were measured during test. Shear stress, elongation at break, shear modulus and failure mode were obtained from the tests. Only one epoxy adhesive had low adhesion to glass. Specimen with this adhesive had the lowest shear strength. Other three adhesives showed good adhesion to glass and had shear strength 6.5 times higher. Failure mode of specimen with these adhesives was always breaking of the glass.

Recent Advances on Thermally Conductive Adhesive in Electronic Packaging: A Review

The application of epoxy adhesive is widespread in electronic packaging. Epoxy adhesives can be integrated with various types of nanoparticles for enhancing thermal conductivity. The joints with thermally conductive adhesive (TCA) are preferred for research and advances in thermal management. Many studies have been conducted to increase the thermal conductivity of epoxy-based TCAs by conductive fillers. This paper reviews and summarizes recent advances of these available fillers in TCAs that contribute to electronic packaging. It also covers the challenges of using the filler as a nano-composite. Moreover, the review reveals a broad scope for future research, particularly on thermal management by nanoparticles and improving bonding strength in electronic packaging.

SEMINAL DEVELOPMENTS IN THE DURABILITY AND DAMAGE TOLERANCE ASSESSMENT OF BONDED JOINTS

Structural adhesives are widely used for joining composite components in many industries and crack growth in such materials is far more likely to occur when they are subjected to repeated cyclic loading than to monotonic loading. Whilst the Hartman- Schijve equation for fatigue crack growth (FCG) has been shown to hold for cohesive crack growth in adhesives under Mode I, Mode II and Mixed-Mode I/II loading, little attention has been paid to its ability to capture the effects of the thickness of the adhesive layer. The present paper examines the growth of fatigue cracks, that occurs cohesively through the adhesive layer, in two toughened epoxy adhesives typical of those used in the automotive and the aerospace industries. Firstly, it is established that when the crack growth rate, da/dN, curves are expressed as a function of Δ√G, or ΔG, where G is the energy release-rate, then the crack growth curves are a function of the thickness of the adhesive layer. It is then shown that this dependency vanishes when da/dN is expressed as a function of the crack-driving force, Δκ, as defined by the Hartman-Schijve equation. Therefore, it is suggested that the parameter Δκ appears to be a valid similitude parameter.