Tea Stem Waste Powders for Epoxy-Based Composites: Processing, Mechanical Properties, and Fracture Behavior

This study investigates the potential of mechanically processed tea stem waste powders as an environmentally friendly reinforcement for epoxy-based composites. Tea stem waste, a lignocellulosic byproduct of tea processing, was reduced in size by high-speed mixing and planetary ball milling without any chemical pretreatment, and incorporated into an epoxy system at varying weight fractions (1–10 wt.%). The composites were fabricated under controlled conditions and subjected to tensile, fracture toughness, hardness, thermal, and morphological evaluations. Mechanical testing revealed that tensile strength increased with filler loading up to an optimum of 7.5 wt.% (72.16 MPa), corresponding to a 14.8% improvement over neat epoxy, while higher content(10 wt.%) showed minor reduction due to potential filler agglomeration. The elastic modulus displayed a non-linear trend, decreasing slightly at low filler levels but reaching 1.30 GPa at 10 wt.%. Fracture toughness (Kıc) exhibited a continuous increase, with a maximum of 2,41 MPa√m at 10 wt.%—a 26.4% improvement compared to neat epoxy. Shore D hardness also improved progressively, with up to a 23% increase at the highest filler content. Thermal analysis confirmed that the addition of tea stem powder did not significantly affect the glass transition or initial degradation temperatures, while an increased char yield indicated enhanced thermal stability. FE-SEM fractography showed that fiber orientation strongly influenced crack propagation: longitudinal fibers remained intact, while transverse fibers fragmented and dissipated energy, thereby enhancing fracture resistance. These results confirm that tea stem waste powders, processed solely by mechanical means, can effectively reinforce epoxy matrices. Although samples made with 7.5% filler yield the best results in tensile testing, it has been observed that 10% content yields higher results in fracture toughness and hardness tests. The results of the study showed that the mechanical strength of the composite material made from this tea stem waste was higher than that of pure epoxy in all content variations tested here.