The influence of short-term water storage on the flexural properties of unidirectional glass fiber-reinforced composites

Objective: The aim of this study was to determine flexural properties of unidirectional E-glass fiber-reinforced composite (FRC) with polymer matrices of different water sorption properties. Methods: Rhombic polymer and FRC test specimens made of three commercially available diacrylate resin (Sinfony Activator, Triad Gel, 3M Scotchbond Adhesive) and different volume fractions of fibers were tested with three-point bending test according to ISO 10477 after storing in water for 30 days. Water sorption of specimens was also measured. Results: Flexural strength of specimens with 45 vol% fraction E-glass fibers varied from 759 to 916 MPa in dry conditions. Water-stored specimens showed flexural strengths of 420–607 MPa. ANOVA analysis revealed that the fiber-volume fraction and the water sorption of the polymer matrix had a significant effect (p<0.001) on the flexural properties. Dehydration of specimens recovered the mechanical properties. Decrease of flexural properties after water immersion was considered to be mainly caused by the plasticizing effect of water and the decrease depended on water sorption. Significance: Use of polymers with low-water sorption seems to be beneficial in order to optimize the flexural properties of FRC.