Mechanical, Viscoelastic, and Fracture Characteristics of Tea Waste and Boron Nitride Nanoplatelet-Reinforced Epoxy...

This study presents the fabrication and characterization of sustainable hybrid epoxy nanocomposites reinforced with tea stem waste powder and 0.5 wt % boron nitride nanoplatelets (BNNPs). The tea stems were ball-milled to an average of 70 μm and added to the epoxy matrix in proportions ranging from 1 to 10 wt % relative to the epoxy resin. The mechanical performance was evaluated using Shore D hardness, tensile testing, and single-edge notch bending, while the thermal and viscoelastic behaviors were examined through dynamic mechanical analysis (DMA), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC) analyses. The hybrid composites exhibited significant enhancements compared with neat epoxy: Shore D hardness increased from 79.40 to above 97.00, tensile strength reached 63.09 MPa at 7.5 wt % tea stem, and fracture toughness improved from ∼1.70 to ∼2.10 MPa·m^1/2. DMA revealed a clear glass transition at 94-97 °C, along with nearly double the storage modulus in the glassy region of the E-10 sample. The TGA results demonstrated increased thermal stability, with the residual char increasing to 9.58% for E-5. Although both 7.5 and 10 wt % tea stem contents yielded strong improvements, 7.5 wt % provided the best balance of strength, toughness, and filler efficiency. Overall, the findings show that untreated tea stem waste can be effectively combined with BNNPs to develop cost-efficient and environmentally friendly hybrid epoxy nanocomposites.