Effect of alkali treatment and particle size on the dynamic mechanical performance of almond shell-reinforced epoxy composites

The growing interest in sustainable engineering materials has encouraged the utilisation of agricultural waste as reinforcement for polymer composites. Though alkali treated natural fillers have been studied, few studies have examined the relationship between the alkali treatment, particle size and filler loading with the dynamic mechanical properties of almond powder (ASP)-reinforced epoxy composites. In this study, these parameters have been analysed together by Dynamic Mechanical Thermal Analysis and Field Emission Scanning Electron Microscopy. NaOH treated almond shell powder was added to the epoxy as fillers of 10–50 wt.% and particle sizes of 75, 150 and 300 µm. Alkali treatment of the composite with 150 µm particle size resulted in the highest storage modulus (6277.65 MPa) and damping factor (0.516) at around 60.67 °C, compared to the untreated composite, suggesting an improvement in stiffness and stress transfer ability of the treated composite. The improvement in particle–matrix adhesion, the decrease in interfacial defects and the effectiveness of crack deflection were confirmed by FE-SEM observations after treatment. The results indicate that the thermo-mechanical properties of epoxy composites can be improved using an optimum alkali treatment, particle size and filler loading which can give valuable information and guidance for formulation of lightweight and sustainable engineering materials.