Enhanced mechanical properties and reduced anisotropy of material extrusion-manufactured short carbon fibre-reinforced plastic via cold isostatic pressing

The increasing adoption of short carbon fibre-reinforced plastics (sCFRP) manufactured through material extrusion (MEX) in high-value-added industries has driven the development of various post-processing methods to enhance MEX-manufactured sCFRP mechanical properties. However, conventional post-processing methods require high temperatures and extended processing times, leading to potential polymer degradation. This study presents a novel room-temperature approach using cold isostatic pressing (CIP) to enhance mechanical properties with reduced anisotropy in MEX-manufactured sCFRP components. The effects of various CIP pressures (250-1000 bar) on the mechanical properties were evaluated through tensile, flexural and interlaminar shear strength (ILSS) tests. Additionally, mechanical anisotropy was assessed using tensile tests at different raster angles (0°, 90°) before and after CIP treatment. The mechanical properties significantly improved after CIP treatment, with the optimal pressure of 500 bar, resulting in a 103% increase in tensile strength for 0° raster angle specimens and a 143.3% increase for 90° specimens, effectively reducing the anisotropy from 77.3% to 42.1%. Microstructural analysis revealed reduced voids and enhanced layer adhesion with increased crystallinity. CIP-treated sCFRP maintained excellent dimensional stability within a 3% variation. This study demonstrates the potential of room-temperature CIP as a post-processing method for improving the mechanical properties of MEX-manufactured composites.