Crystallization behavior of thermoplastic resins near fibers and the influence of molding conditions during carbon fiber composite 3D printing

Crystals known as transcrystals (TC) are formed near the carbon fibers of carbon-fiber-reinforced thermoplastics (CFRTPs). This study examined the crystallization behavior of 3D-printed resins associated with fibers under varying molding conditions using carbon fiber/polyphenylene-sulfide (CF/PPS) filaments. As the nozzle temperature increased, TC thickness increased linearly. In addition, the shear force during 3D printing likely facilitated the formation of TC at a temperature close to the melting point, which was not observed in previous studies. A high TC thickness value resulted in high interlaminar strength, which caused fiber fracture. The crystal structure of TC was confirmed at the fiber fracture site, presumably because of an increase in the interfacial strength of TC. In addition, the micro-Vickers test demonstrated that the hardness of the resin near the fibers with the TC was approximately twice that without the TC. This study applied TC to CFRTP 3D printing and proposed a new approach for improving interfacial strength.