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releases water as a reaction by-product when curing. For both materials, volatiles (water and solvent) management is a critical issue to yield high quality, void-free laminates during composite fabrication. 4. Results and Discussion The processability of composites with reactive resin matrices involves a balance between the degree of volatile depletion and the residual fluidity remaining in the polymer [9-11]. When volatiles are not depleted adequately before the forced consolidation, voids develop yielding a laminate with inferior quality. On the other hand, excessive cure advancement in the resin results when excessive B- stage conditions (temperature and time) are employed, making the composite un-processable under moderate pressures, due to high resin viscosity. The kinetics of volatile diffusion through the liquid phase is strongly dependent upon resin chemistry, chemoviscosity, temperature and duration at the given temperature. While the reactive resin matrix continues to cure during the B-stage period, the resin fluidity continues to diminish and the composite processability suffers. In order to achieve a void-free laminate, the cure (molding) cycle must enable a sufficient extent of volatiles to be depleted through the thermal B-stage (in the absence of pressure) before consolidation. In the meantime, an appreciable degree of residual resin fluidity must remain after the B-stage allowing infiltration of resin through fiber bundles in the composite during the pressure consolidation stage initiated at the latter stage of the cycle. Such a balancing act between degree of residual volatiles and residual fluidity during composite fabrication is complex and makes the design of cure cycles very challenging. The DVB assembly and process described above have overcome the deficiencies of the SVB by affording superb and effective volatile management during the composite B-stage period. Examples of comparisons in quality between SVB and DVB molded composite laminates are described below. In these examples, the interior of a vacuum press serves as the Outer Bag in the DVB process as previously described in Section 2. 4.1 IM7/LARC‘ PETI-8 polyimide composite system LARCTM PETI-8 is a phenylethynyl terminated imide composite matrix material. The phenylethynyl groups on the ends of the linear polyimide react with each other upon heating to temperatures greater than ~300°C (~575°F). This resin exhibits a low viscosity, which is stable over a long period of time at temperatures between 200° to 275°C, rendering itself seemingly suitable for composite fabrication by an oven, vacuum bag processing technique. While this reaction produces no volatiles, the ring closure of the amide acid to imide, which occurs at temperatures greater that ~200°CPDF Image | Evaluation of Double-Vacuum-Bag Process For Composite Fabrication
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