Hygrothermal Aging Studies on Adhesion Behavior of Titanium Dioxide Nanoparticle‐Reinforced Mild Steel Adhesive Joints

ABSTRACT In this research study, mild steel adherends were bonded using unreinforced and titanium dioxide (TiO ₂ ) nanoparticle‐reinforced adhesives (1.0 wt%, 2.0 wt%, 3.0 wt%, and 4.0 wt%) to form single‐lap joints. The adhesive joints were exposed to hygrothermal aging for 1, 2, 3, and 4 weeks. Lap shear tests revealed that the mean shear strength of unreinforced adhesive joints was 10.627 MPa, and with reinforcement, the shear strength increased by up to 54% in unaged conditions. After 4 weeks of aging, shear strength reductions were observed, with unreinforced joints experiencing a 66% loss, while 3.0 wt% reinforced joints exhibited the lowest reduction at only 13%, demonstrating their effectiveness in maintaining adhesive strength. Water absorption was significantly reduced by up to 56% with reinforcement, minimizing moisture‐induced degradation. Contact angle measurements showed an increase in surface hydrophobicity, with the 3.0 wt% reinforced adhesive reaching the highest contact angle of 89° ± 2°. Differential Scanning Calorimetry (DSC) analysis confirmed changes in glass transition temperature ( T _g ) due to aging. High‐resolution (HRSEM) analysis revealed morphological changes and crack formations, highlighting the impact of hygrothermal aging on adhesive joint durability.