Authors: T. Gopalakrishnan, Boopathi S, B. Niranjan, Mukesh P.M
Abstract: Global almond (Prunus dulcis) production leaves behind a shell fraction that exceeds the mass of the kernel it protects, and the great majority of this lignocellulosic by-product is presently burned, landfilled or sold at low value as biomass fuel. Because the shell is hard, largely cellulosic and available in very large and geographically concentrated volumes wherever almonds are processed, it is a natural candidate for the same role that walnut shell, groundnut shell, coconut shell and rice husk already occupy in the particulate-filled polymer composite literature: a low-cost, renewable, low-density filler for thermosetting resins. This review draws together what is presently known, and what is not yet known, about almond shell powder as a reinforcement for epoxy matrices. It begins with the scale and composition of the waste stream, since both bear directly on whether the material is a viable industrial filler rather than a laboratory curiosity. Processing considerations — drying, size reduction, sieving and surface treatment — are then examined, followed by the mechanical, physical, water-absorption, thermal and morphological behaviour reported for shell-powder-filled epoxy systems, read against the much larger body of work on chemically similar agro-waste fillers where almond-specific data are still sparse. The review closes by identifying the almond shell literature as considerably thinner than that for walnut or coconut shell despite comparable material properties, and names surface treatment optimisation, hybridisation with synthetic or other natural reinforcements, durability under moisture and weathering, and a proper life-cycle assessment against synthetic fillers as the most pressing gaps.
