Impregnation Dynamics of Carbon Fiber Tows

Axial and normal (transverse) impregnation of fiber bundles are in vestigated. A slow curing epoxy system is used with the impregnation being driven solely by capillary forces. Axial impregnation rates are found to be faster than expected based on Lucas-Washburn type capillary wicking. For normal mode impregnation, geometric limi tations and the dependency of contact angles upon wetting speed give rise to rates which are an order of magnitude slower than axial wetting. Transverse impregnation is also strongly influenced by pores much smaller than the overall average porosity of fiber bun dles. These results indicate that incomplete wetting and void formation may result from: (1) (dynamic) contact angles larger than 45°, and (2) large differences in the rates of axial and normal impregnation.