Influence of adhesive types on bonding defects and adhesion performance of glass substrates

Adhesive-bonded glass substrates are widely used in construction, automotive, and aerospace. However, such materials have long faced the challenge of weak adhesion due to defects. Herein, comprehension of the formation mechanism of bonding defects and their influence on adhesion performance was considered crucial for the optimization of bonded glass structures. In this work, multiple measurements methods were conducted to investigate the bonding defects of polyurethane (PU) adhesive and epoxy adhesive (EP) on glass substrates and explore the mechanism of bond defect formation and its effect on bond performance. Compared with EP, which had a fast curing rate, the selected PU presented a relatively high curing degree and a long curing cycle. The experimental results indicated that PU adhesive with an appropriate viscosity can facilitate glass penetration and diffusion. Surface and interfacial defects at various curing stages were observed via scanning electron microscopy (SEM) and three-dimensional profilometry. Energy dispersive spectroscopy (EDS) and thermogravimetric analysis-mass spectrometry (TG-MS) were performed to further elucidate the mechanisms underlying bubble formation within the adhesive-glass samples. The results of nanoindentation and SEM-EDS line scan revealed the deeper penetration depth of PU adhesive in glass than epoxy, which mainly explained the excellent bonding performance of PU-bonded composites. Moreover, tensile shear tests and X-ray photoelectron spectroscopy confirmed that in contrast to defects, the adhesion force and uniformly distributed interfacial interactions played a more pivotal roles in attaining satisfactory bonding properties.