Interface structure and characterization analysis of carbon fiber/polypropylene with β-crystals

• The CF/PP composites with transcrystalline layers of varying β-crystal contents was obtained. • An increase in interfacial β-crystal content can enhance the IFSS of the single CF/PP composites. • Characterization of interface thickness was conducted by PF-QNM. • MD simulations revealed the mechanism behind the enhanced IFSS of the single CF/PP composites. Interface structure between thermoplastic polypropylene and carbon fiber is crucial for determining the reinforcement effect in the carbon fiber reinforced polypropylene composites (CF/PP). Currently, the controlled regulation and quantitative characterization of different crystal forms within the interfacial crystallization remain unresolved challenges. In this study, carbon fibers were functionalized with polyethyleneimine (PEI) and immobilized with varying concentrations of the β-nucleating agents (β-NAs), enabling controlled formation of β-crystals in the transcrystalline (TC) layers. Advanced characterization confirmed tunable β-crystal concentration and morphology. Results demonstrate that increased β-crystal content enhances interfacial shear strength (IFSS). Peak Force Quantitative Nanomechanical Mapping (PF-QNM) revealed that enhanced IFSS is primarily attributed to increased interface thickness induced by β-crystal formation. Molecular dynamics (MD) simulations further elucidated that interfacial crystallization and increased thickness strengthen interfacial interactions at the molecular scale, validating experimental trends. This work provides multiscale evidences for tunable interfacial β-crystals, offering new strategies for designing high-performance CF/PP composites.