Improvement of thermal and mechanical properties of carbon fiber/phenolic composites by using H3PO4-coated carbon fibers

Carbon fiber/phenolic prepregs were prepared using PAN-based carbon fabrics with a pre-coating in a dilute solution of phosphoric acid and without a coating. Thermal stability and oxidation behavior according to temperature in air for the uncoated and coated 2-D carbon fiber/phenolic composites fabricated with these prepregs were studied by dynamic and isothermal thermogravimetric analyses. Behavior of thermal expansion and contraction for the two types of the composite was examined in N-2 atmosphere using a thermomechanical analyzer. As a result, use of the coated carbon fiber to process the carbon fiber reinforced composite material effectively improved thermal and oxidation resistances of the composite, especially at higher temperatures. With introduction of this coating technology, interlaminar shear strength and flexural strength of the composite were also improved about 23.4% and 14.5%, respectively. The explanation of the improvement on thermal and mechanical properties will be also provided with the result of microscopic observations in the present work.