Frontal polymerization-assisted 3D printing of short carbon fibers/ dicyclopentadiene composites

Discontinuous carbon fibers (d-CFs) with different surface modifications (sizing, carboxyl-grafting, and norbornene-grafting) were separately dispersed in dicyclopentadiene (DCPD) resins, and the resultant d-CF/ DCPD mixtures demonstrated shear-thinning characteristics. Subsequently, d-CF/DCPD mixtures were printed and further transformed into crosslinked polymers through self-propagating frontal polymerization. The norbornene groups grafted on the d-CF surfaces also reacted with the DCPD monomers during the fontal polymerization-synchronized printing, resulting in covalent connections between d-CFs and DCPD resins. The tensile strength of as-printed norbornene-grafting d-CFs/DCPD composites was around 43.3 MPa, which was 170% higher than that of as-printed neat DCPD resin and 15% higher than that of the sized d-CFs/DCPD composites. The toughness of as-printed norbornene-grafting d-CFs/DCPD composites was -14 MPa, -33.3% higher than that of the sized d-CF/DCPD composites. More importantly, the presence of norbornene-grafted d-CFs significantly strengthened the bonding strength of printed layers since d-CFs bridged two neighbored layers. The bonding strength of printed layers was enhanced by -255% with addition of 3 wt% norbornene-grafting d-CFs compared to the neat resin. This method provides a new way to improve the interlayer bonding in energyefficient 3D printing thermosetting composites.

Automated summary

Discontinuous carbon fibers were modified and dispersed in dicyclopentadiene resins, then printed and transformed into crosslinked polymers through self-propagating frontal polymerization. The addition of norbornene groups on carbon fiber surfaces significantly enhanced the bonding strength of printed layers, leading to improved tensile strength and toughness of the composites.