Application of sunflower husk, hazelnut shell and walnut shell as waste agricultural fillers for epoxy-based composites: A study into mechanical behavior related to structural and rheological properties

In the present study three types of agricultural waste materials were applied as fillers for manufacturing epoxy-based composites: walnut shell (WS), hazelnut shell (HS) and sunflower husk (SH). The influence of different filler grades and content (15-35 wt%) on the mechanical properties of composites was related to physicochemical properties of the agricultural materials, rheological properties of the compositions, and the morphology of the cured samples. The mechanical properties were affected by the addition of natural fillers. The addition of particle-shaped fillers with low aspect ratio (WS and HS) allowed to produce composites with improved stiffness and hardness. Incorporating fiber-shaped SH as a filler led to a significant increase in the viscosity of the composites which created a porous structure, resulting in a decrease in the mechanical performance of the EP-SH composites. Nevertheless, the decrease in strength properties is not a contraindication for manufacturing ecological and inexpensive products.