Investigations on thermoforming of carbon fiber reinforced epoxy vitrimer composites
Stefan Weidmann, Petra Volk, Peter Mitschang, Nerea Markaide
Abstract
In contrast to thermosets, vitrimers have dynamic covalent bonds providing the potential to allow being thermoformed after stimulation by heat. However, it is unclear if the thermoforming of carbon fiber reinforced vitrimers (vitrimer-CFRPC) correlates to that of thermoplastic-CFRPC (TP-CFRPC). For this reason, their viscosity was investigated by means of a torsion clamp rheometer and tempered 3-point bending thermoforming. The results are compared with a well thermoformable TP-CFRPC. The investigated vitrimer-CFRPC base on epoxy formulations with disulfide crosslinks. The results show that the high viscosities of the vitrimers make defect-free thermoforming challenging. In the micrographs of the tempered 3-point forming of the vitrimer-CFRPCs wrinkling and no ply sliding occurred. A vitrimer-CFRPC was thermoformed to an omega profile, indicating that opposite forming radii lead to additional interlaminar shear forces promoting ply sliding. In order to approximate the thermoforming behavior of vitrimer-CFRPC, their viscosity at process temperature must be reduced.