Influence of filler content and surface modification on physical and mechanical properties of epoxy/walnut shell particulate composites

The current study aims to examine the influence of treating micro-sized walnut shell particulates (WSP) with an aqueous solution of sodium hydroxide (NaOH) at the varied concentration on the physical and mechanical properties of a newly developed epoxy composite. Three sets of epoxy/WSP composites are prepared, i.e. Set A is for composites prepared with raw WSP, set B and set C is for composites prepared with treated WSP with 2 and 4 moles NaOH aqueous solution, respectively. For each set, four samples are fabricated for different WSP content (5, 10, 15, and 20 wt. %). It has been observed that the density of the composites reduces as the content WSP increases over the entire range of filler content. Against that, the volume of voids increases with WSP loading. Similarly, the water intake of composites also increases with filler loading. Mechanical properties like compressive strength, hardness, tensile and flexural modulus increase as a linear function of filler content whereas, tensile strength and flexural strength increase up to 10 wt. % of filler and decreases thereafter. Further, it is found that when WSP is modified with a 2-moles NaOH aqueous solution improves all the properties under investigation. Though, WSP treated with a 4-mole NaOH aqueous solution slightly deteriorates the properties of the material due to the excess concentration of NaOH.