Curing characteristics and mechanical properties of carbon fiber-interlayered fabric composites based on a polyurethane matrix

Polyurethane matrix composites based on fiber-interlayered carbon fabric laminates were prepared by compression molding to assess the feasibility of this approach, when using a highly reactive resin as matrix. The polyurethane matrix was prepared using the excess isocyanate to enhance the rigidity of the system through additional crosslinking. The fiber-interlayered laminates consisted of different amount of short fibers between two carbon fabrics. Three composites containing, respectively, 12%,18%, and 26% wt/wt total carbon fibers were produced for this study. Thermal and IR spectroscopic analysis were performed to select the most suitable thermal curing conditions for the matrix. The results showed that 70 degrees C represents the minimum curing temperature required to carry out the reactions between polyol and isocyanate groups at an economical rate. In this condition, a multistep reaction occurs to consume the excess isocyanate. Mechanical strength of the composites was measured by three-point bending tests, and the data were analyzed by the Weibull statistical method. Fiber content in the interlayer is a critical parameter in the manufacture of these types of composite materials. Composites with 13% and 21% wt/wt short fibers in the interlayers (giving a total carbon fiber content of 18% and 26% wt/wt) exhibit a wider cumulative distribution of strength data due to the restrictions that they impose on the flow of the resin, thereby resulting in an inhomogeneous distribution of resin throughout the samples. A composite with 12% total carbon content (7% wt/wt short fibers) exhibits a narrower cumulative distribution, denoting a greater reliability relative to the manufacturing method used in this study. (C) 2007 Wiley Periodicals, Inc.