Comparative Study of MAPP Compatibilization and H2O2 Surface Treatment for Recycled GFRP-Reinforced Wood–Plastic Composites: Interfacial Properties and Performance

Recycled glass fiber-reinforced polymer (GFRP) powder from decommissioned wind turbine blades offers sustainable reinforcement for wood–plastic composites (WPCs), but its efficiency is limited by poor interfacial adhesion with the polypropylene (PP) matrix caused by surface epoxy residues. In this study, GFRP/WPCs with a fixed formulation of 15 wt% GFRP, 10 wt% wood flour, and 75 wt% PP were used to compare two modification strategies: MAPP compatibilization (1–7 wt%) and H2O2 treatment (5–30%). MAPP modification improved the mechanical properties of GFRP/WPCs, with the optimal concentration varying by property: flexural strength reached its maximum (75.45 MPa, +24.7%) at 1 wt% MAPP, while tensile strength (+9.2%), flexural modulus (+20.7%), and impact strength (+18.9%) were maximized at 3 wt% MAPP. H2O2 at 10% achieved higher strength gains (tensile: +23.65%, i.e., 26.7 MPa; flexural: +27.93%, i.e., 77.4 MPa; impact: +35.29%, i.e., 16.98 kJ/m2) but moderately reduced flexural modulus. FTIR confirmed up to 71.7% epoxy removal by H2O2, exposing cleaner fibers. Both modifications slightly lowered thermal decomposition temperatures but increased char residues and PP crystallinity via enhanced nucleation. SEM showed that MAPP created a compatible interphase, while H2O2 enabled direct mechanical interlocking. Surface free energy analysis revealed that MAPP increased polar components, whereas H2O2 increased dispersive components. Overall, MAPP offers simpler processing and balanced properties, while H2O2 provides superior strength at the cost of some stiffness—providing practical guidance for tailoring recycled GFRP/WPCs for construction and sustainable applications.