Nanocellulose Hybrid Reinforcement in Surface‐Modified Pistachio Shell/Epoxy Composites: A Multiscale Interface Engineering Strategy for Lignocellulosic Biomass‐Based Materials

ABSTRACT In this study, pistachio shell waste (PShW) was used as a lignocellulosic reinforcing phase in an epoxy matrix to develop sustainable composite materials, and its surface properties were tailored using various chemical modification methods. PShW surfaces were functionalized with maleic anhydride (MA), citric acid (CA), and linoleic acid (LA) following alkaline pretreatment (NaOH). In addition, cellulose nanofiber (NC) was incorporated to construct hybrid composite systems and generate a multiscale reinforcement effect. The morphological, chemical, thermal, and mechanical properties of the resulting composites were characterized using SEM/EDS, FTIR, TGA, DMA, and mechanical testing, while water uptake and chemical resistance were also evaluated. The results showed that surface modification significantly improved filler–matrix interfacial interactions and enhanced mechanical performance. In particular, composites containing MA‐modified PShW exhibited a tensile strength of 129.7 MPa, representing a 52% increase over neat epoxy. In hybrid systems, the composite containing 25 wt% MA‐PShW and 1.0 wt% NC exhibited the highest mechanical performance, with a tensile strength of 148.8 MPa. Furthermore, the hybrid structure reduced water uptake and improved chemical resistance, indicating enhanced durability. Dynamic mechanical analysis revealed an increase in glass transition temperature, while thermogravimetric analysis indicated improved thermal stability. These findings demonstrate that combining chemical surface functionalization with NC hybridization effectively enhances the mechanical and thermal performance of lignocellulosic filler–reinforced epoxy composites through multiscale interface engineering.