Moulding prepreg platelets into high fibre loading fraction carbon fibre-reinforced syntactic epoxy foams

• Prepreg platelets can be moulded with hollow glass microsphere. • Hollow glass microspheres pack between the pores formed by the packing of prepreg platelets. • High carbon fibre loading can be achieved. • Mechanically anisotropic due to preferential alignment of platelets in the XY plane. This study presents a novel method for manufacturing high fibre content carbon fibre-reinforced syntactic epoxy foams by moulding prepreg platelets with hollow glass microspheres. The prepreg platelets were either (i) dry-mixed at room temperature or (ii) mixed at cryogenic temperature in liquid nitrogen with hollow glass microspheres prior to compression moulding. This approach achieves a carbon fibre volume fraction of up to 49 %, addressing the limitations of low fibre content in conventional syntactic foams. The resulting materials exhibit enhanced mechanical properties, including a compressive modulus of ∼6 GPa and ∼3.5 GPa in the in-plane and through-thickness directions, respectively. The anisotropy in mechanical properties is attributed to the anisotropic packing of the prepreg platelets. Packing simulations using PyBullet confirmed that microspheres did not disrupt platelet arrangement, maintaining a packing efficiency of ∼63 % while filling inter-platelet gaps. Although cryogenic processing improved the mixing process, its impact on mechanical performance was minimal. This study demonstrates a simple manufacturing approach to produce high performance carbon fibre reinforced porous polymer composites suitable for lightweighting applications.