PMR‐15/carbon fiber composites produced from powder‐coated towpreg

Abstract An addition‐type thermosetting polyimide, PMR‐15, has a relatively high glasstransition temperature, T_g, of approximately 340°C and attractive high‐temperature composite mechanical properties after postcuring. PMR‐15 prepreg is typically produced by pulling carbon fibers through a methanol solution that contains the PMR‐15 monomers. One of the monomers, methylene dianiline, is highly toxic, thereby making the solution‐coating technique undesirable. To alleviate the toxicity problem in the prepregging step, “preimidized” PMR‐15 is now available in powder form, and this material can be used to produce towpreg using a powder‐coating method. The powder‐coating method that has been used in this work involves the use of an aqueous foam as a carrier medium to continuously deposit the PMR‐15 powder onto carbon fibers. The powder is slurried in a surfactant solution into which nitrogen is dispersed using a foam‐generating device. A predetermined amount of this foam is then applied to a moving carbon fiber tow. The foam is collapsed and the powder fused to the fiber in a set of tubular ovens. The powder appeared to be particularly sensitive to the heat treatment, but towpreg was produced and composites were consolidated successfully. The mechanical properties of the composites formed from powder‐coated towpreg compare favorably with the properties of composites fabricated from prepreg that was drum wound from a methanol solution.