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Delamination due to an inferior adhesion between reinforcement material and matrix in carbon fiber-reinforced thermoplastic (CFRTP) composites is a crucial problem to be solved. To this end, this study aims to overcome poor wettability between reinforcing phase, i.e., carbon fiber (CF), and thermoplastic matrix, i.e., polyetherether ketone (PEEK). Herein, CF's surface was tailored by application of different polymeric sizing agents which have different chemical structures. Morphology and topology analyses were performed by Scanning Electron Microscope and 3D laser scanning, respectively. Later, a variety of wettability results were obtained by the sessile drop method used in Contact Angle (CA) measurements for CFs throughout application of each sizing agent applied by dip coating. Sizing materials were designed such that the chemical structure of CF's surface could exhibit compatibility with the matrix itself. Consequently, complete wettability (CA: 0°) was achieved for CFs sized by HPEEK (CF/hydroxylated PEEK (HPEEK)) and the surface free energy (SFE) of CF was enhanced from 5.43 to 72.8 mJ/m2 while the SFE of the PEEK matrix is 40.1 mJ/m2. Moreover, sizing by HPEEK improved the average surface roughness of CF by 32% which enables optimized adhesion. Afterward, repetitive tensile tests were carried out to observe effects of improved interfacial interlocking on the mechanical properties of the final CFRTP composite. Stress–strain curves revealed that the tensile strength of CFRTP improved from 473 to 508 MPa through the sizing of CF by HPEEK whereas pristine PEEK has a much smaller tensile strength (98 MPa) than the aforementioned CF-reinforced composites. The sizing of carbon fiber's surface by HPEEK resulted in an enhanced adhesion with the PEEK matrix. Since the chemical structure and physical properties of sizing agent and matrix are compatible, potential debonding between them was eliminated. Thus, the improved wettability led to a substantial increase in the mechanical strength of the final TP composite. [ABSTRACT FROM AUTHOR]

To meet the lightweight production requirements of automobiles and achieve high strength, reinforced thermoplastic composite materials are gradually replacing metal materials. Injection molding is the preferred manufacturing method to enable the production of complex‐shaped parts, facilitate production, and reduce costs. In this study, carbon fiber (CF) was added to the commonly used resin‐reinforcing material, polyamide (nylon) PA6, to create a CF‐reinforced thermoplastic composite (polyamide 6 [PA6]/CF) that was welded using injection molding. This study not only investigates the impact of different welding conditions on shear strength but also discusses the sequence of welding. Achieving 85% of the shear strength of the PA6 base material under ideal circumstances. The CF distribution and reinforcement mechanism were analyzed by observing the connection interface and cross section using a polarizing microscope and a scanning electron microscope. When PA6/CF was used as the secondary molded body, the welding results were better. The addition of CF had a significant strengthening effect on the strength of the PA6 injection welding. Highlights: Carbon fiber‐reinforced thermoplastic composite materials were prepared, and welding with PA6 was achieved using the injection molding method.The optimal welding parameters were determined by varying the mold, injection speed, injection temperature, and order of injection. The maximum welding shear strength reached 85% of the base material shear strength.The positive effect of specific fiber distribution on welding strength was analyzed by observing the interface using a scanning electron microscope and a polarizing microscope.This study provides valuable insights into the optimization of welding processes for carbon fiber thermoplastic composite materials, offering possibilities for connecting dissimilar materials with poor compatibility. [ABSTRACT FROM AUTHOR]

To overcome the dependence of continuous carbon fiber reinforced thermoset composites (CCFRTCs) on molds during the curing, a thermoset continuous fiber prepreg filament and thermoplastic filament alternate printing method was proposed. CCFRTCs with thin thermoplastic shells were prepared based on the method, and the confinement of thermoplastic shells enabled the mold‐less curing of CCFRTCs. The influence of key curing process parameters on the flexural properties of the specimens was systematically investigated. The experimental results showed that the flexural properties of the prepared composites were correlated positively with the vacuum degree and showed a tendency of first increasing and then decreasing with the increasement of impregnation time and curing temperature. Through x‐ray computed tomography (CT) and scanning electron microscope (SEM) analysis, the effect of key curing process parameters on the flexural properties of the CCFRTCs was clarified. Under the guidance of suitable curing process parameters, the flexural strength and modulus of the composite reached 482.89 MPa and 35.11 GPa, which were significantly better than most existing 3D printed continuous carbon fiber reinforced polymer composites. Finally, complex components were prepared to verify the feasibility and versatility of the technique. Highlights: A CCFRTCs mold‐less curing method was proposed.The effect of key parameters on the properties of CCFRTCs was clarified.Both the advantages of thermoset and thermoplastic materials were obtained.Complex components with low porosity were prepared. [ABSTRACT FROM AUTHOR]