Flow and void characterization of stitched structural composites using resin film infusion process (RFIP)

The resin film infusion process (RFIP), which is similar to resin transfer molding (RTM), was applied to investigate the possibility of manufacturing high performance stitched composites. With the objective of understanding the resin flow mechanisms and void formation in stitched fibrous perform, two recent technological developments in homogeneous tough resin and bendable stitching fibers were incorporated in producing stituched composites with RFIP. These included new lightly crosslinked thermosets (LXT) that were phenolic or amine based. Second, bendable carbon stitching reinforcement (T-900) was utilized as a stitching fiber. Flow characteristics were inferred by ultrasonic C-scan analysis of cured panels. Microscopic studies indicated that voids were distrubuted along the stitching fiber because of low consolidation pressure in the resin-rich area (stitching fiber region) where the fiber volume content was lower. In contrast to stitched composites, non-sitiched composites contained lower void content and irregular void distribution because of uniform fiber compaction. Microscopic studies of partially resin infused quasi-istropic stitched composites demonstrated that the resin flows along the stitching fiber region and then infuses into the fibrous preform. These infusion phebnomena were the result of anistropic permeability in the preform. Consequently, anisotropic resin flow in the stitched fibrous preform was found to be related to the heterogenous textile structure caused by the stitching process.     

Macro-/mesoporous Metal–Organic Frameworks Templated by Amphiphilic Block Copolymers Enable Enhanced Uptake of Large Molecules

The first synthesis of hierarchical porous metal–organic frameworks (HP-MOFs) is reported through a solvent evaporation-induced co-assembly of polystyrene-block-poly(ethylene oxide) (PS-b-PEO) and MOF building blocks. The growth of MOFs is restricted to confined spaces formed by self-assembled PS-b-PEO, and mesopores and/or macropores are created after removing PS-b-PEO by solvent rinsing. This approach avoids phase separation and competitive interactions between templates and MOF building blocks. Both amorphous and crystalline HP-MOFs can be synthesized by finely controlling MOF growth conditions. Additionally, HP-MOFs (ZIF-L sheets) with honeycomb-like channels show significantly enhanced incorporation of large guest molecules compared to microporous MOFs. This study establishes an efficient synthetic strategy for preparing HP-MOFs with highly accessible mesopores and macropores for applications involving large molecules.