Effect of moisture absorption on the flexural strength of phenolic matrix composites reinforced with glass fibers and aluminum oxide nanoparticles

Abstract In this research, the effect of adding aluminum oxide nanoparticles on the flexural strength of glass/phenolic composites that were exposed to water environment was experimentally investigated. To make glass/phenolic composites, IL‐800 phenolic resin, H002 hardener, T400 bidirectional glass fibers and Al ₂ O ₃ nanoparticles were used. Four‐layer composite plates were made by hand layup method. Beam‐shaped samples were extracted from the plates with the help of laser cutting method. Rectangular composite beams made of glass/phenolic and Al ₂ O ₃ /glass/phenolic were subjected to three‐point flexural test. The moisture absorption test was continued until the amount of water absorption reached a constant level. Bending test was performed on the samples before and after immersion in water. Based on the results, the average flexural strength of the samples after water absorption shows a decrease of about 15%. This parameter is equal to 118.96 MPa for glass/phenolic composite samples immersed in water, and by adding 0.25 wt% of Al ₂ O ₃ nanoparticles into the matrix material of glass/phenolic composite samples, the flexural strength reaches 142.54 MPa, which shows an increase of 19.82% compared to samples without nanoparticles. Furthermore, the amount of flexural modulus decreases after water absorption, and the addition of nanoparticles in the base material can compensate this reduction. Scanning electron microscopy images illustrate that the addition of Al ₂ O ₃ nanoparticles into the phenolic resin can enhance the strength of matrix material and improve the adhesion of glass fibers to the resin. Highlights Addition of nano Al ₂ O ₃ reduces water absorption of glass/phenolic composites. Nano Al ₂ O ₃ improves composite flexural strength after water absorption. Addition of nano Al ₂ O ₃ increases the adhesion between the layers of the specimens.