Interfacial shear performance of hyperbranched polyamide surface-modified long polyvinyl alcohol fibers in cement by single fiber pull-out test

Herein, long polyvinyl alcohol fibers (PVAF) were immobilized on a custom-designed support and subjected to surface modification in a purpose-built flat-bottom reaction vessel. The influence of hyperbranched polyamide surface-modified PVAF on the interfacial shear performance in cement was systematically investigated. Hyperbranched polyamide was grafted onto the PVAF surface through a two-step chemical reaction involving succinic anhydride (SA) and 5-aminoisophthalic acid. Reaction conditions (temperature: 30 ∼ 50 °C; time: 0 ∼ 3 h) were optimized using a central composite design (CCD). Single-fiber pull-out tests revealed a significant improvement in interfacial shear strength between the modified PVAF and the cement matrix. Under optimal conditions (30 °C, 1.7 h), the load and interfacial shear strength reached 0.70 N and 2.79 MPa, respectively, representing a 2.5-fold increase compared to unmodified PVAF. Characterization techniques, including Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), X-ray diffraction (XRD), and thermogravimetric analysis (TGA), confirmed that the grafted hyperbranched polymers (HBPs) enhance fiber-matrix interfacial bonding. This method enables the production of uniformly modified fibers with consistent length, facilitating reliable single-fiber pull-out testing and enabling quantitative evaluation of fiber-matrix interfacial interactions. The proposed approach provides a robust platform for optimizing and screening surface modification strategies, thereby promoting the effective application of short PVAF in cementitious composites. • Hyperbranched polyamide surface-modified polyvinyl alcohol fibers were prepared. • A central composite rotatable design (CCD) was employed to optimize the reactions. • Single-fiber pull-out tests revealed the improvement in interfacial shear strength. • This approach provides a platform for optimizing and screening modification strategies.