The effect of reinforced structure on thermo-oxidative stability of polymer-matrix composites

A new concept in improving the thermo-oxidative stability of carbon fiber polymer-matrix composites (CFPMCs) by adopting integral reinforced structure was investigated. Specimens of three-dimensional and four-directional braided carbon fiber/epoxy composites (BC) and laminated plain woven carbon fiber/epoxy composites (LC) were subjected to isothermal aging at 90℃, 120℃, and 150℃ in air circulating ovens for various durations up to 13 days. The process resulted in progressive deterioration of the matrix reins and fiber/matrix interfaces, in the form of chain scissions, weight loss, and fiber/matrix debonding, which significantly led to the decrease of the flexural strength. Besides, the flexural properties’ retention rates of BC were higher than those of LC at the same aging conditions due to the difference of the reinforced structures. On the one hand, LC lost more weight than that of BC because the percentage of fiber ends area exposure to air in LC specimen was three times more than that in BC specimen. On the other hand, the BC specimens can resist the flexural load as an integral structure although the resin was damaged and the adhesive force between fiber bundles and resin decreased after thermo-oxidative aging, and no delamination happened like the LC specimens. Therefore, adopting three-dimensional and four-directional braided preform as the reinforcement of CFPMCs is an effective way to improve their thermo-oxidative stability.