Effect of surface treatments on the physical mechanical properties and interfacial microstructure of wood fiber-reinforced geopolymer composites

Natural fibers are regarded as sustainable alternatives to synthetic fibers in fiber-reinforced geopolymer composites, offering significant environmental and economic advantages. However, their long-term performance and widespread application are hindered by the inadequate fiber-matrix adhesion and the strongly alkaline geopolymer environment. This study explores the reinforcing effects of graphene (G) and graphene oxide (GO) surface pre-treatments on wood fiber (WF) in metakaolin-based geopolymer composites. Surface modification was confirmed using contact angle, scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD) analyses. A systematic comparison was conducted among pure geopolymer (GP) and composites reinforced with 2 wt% untreated and treated WF (WFGP, G-WFGP, and GO-WFGP). Among these, G-WFGP exhibited the most promising outcomes: water absorption and porosity decreased by 51.59 % and 48.61 %, respectively, simultaneously compressive and flexural strengths increased by 13.68 % and 36.27 % compared to WFGP. G-WFGP exhibited lower thermal degradation, and retained higher strength than both untreated and GO-treated counterparts after 100 wet/dry cycles. Microstructural observations further revealed that G treatment filled surface micro-pores of WF, increased the fiber contact angle from 45° to 91°, and promoted the formation of a compact interfacial transition zone, thereby strengthening interfacial bonding and enhancing mechanical performance and durability. These findings demonstrate that graphene-based surface modification provides an efficient and sustainable approach for fabricating high-performance plant fiber-reinforced geopolymers for eco-friendly construction applications. • Wood fibers were modified with G and GO for geopolymer reinforcement. • G and GO treatments improved fiber-matrix interfacial bonding and microstructure. • Durability after 100 wet/dry cycles indicating enhanced long-term stability.