Comparative Analysis of Impregnation Methods for Polyimide-Based Prepregs: Insights from Industrial Perspective

This study presents a comparative analysis of two industrially relevant technologies for manufacturing of prepreg composite materials based on polyimide (PI) resin: hot-melt and solvent-based technology. More specifically, the study focuses on evaluating the relationship between key processing parameters and the final properties of the composite material manufactured with unidirectional (UD) C-fibers and woven fabrics used as reinforcement for both technologies. The impregnation process was carried out using a custom-designed coating equipment developed by Mikrosam D.O.O. Manufactured prepregs were characterized in terms of their resin content, volatile content, weight, width, and quality of the applied resin film. The hot-melt method that involves applying the resin in a semi-molten state with minimal solvent content provided a stable resin content (34–35%) and low volatiles (~1.2–1.5%) in the final product. The solvent-based method, using a resin/solvent ratio of 50:50, enabled deeper resin penetration into the fibers, particularly in woven fabrics (resin content: 34–37%) and lower residual volatiles (~0.3–0.5%). These results showed that the hot-melt technology consistently produced prepregs with very stable resin content, which is critical for structural applications requiring increased mechanical performance. In contrast, the solvent-based method demonstrated better adaptability to different reinforcement forms, improved impregnation depth, and excellent film uniformity, particularly suitable for woven fabrics. Representative SEM micrographs confirmed uniform resin distribution, full fiber wetting, and absence of voids, validating the impregnation quality obtained by both techniques. These findings highlight the technological relevance of selecting the appropriate impregnation route for each reinforcement architecture, offering direct guidance for industrial-scale composite manufacturing, where the hot-melt method is preferred for UD prepregs requiring precise resin control, while solvent-based impregnation ensures deeper and uniform resin distribution in woven fabric structures.