Macadamia nutshell particulates as sustainable fillers in epoxy- and cement-based polymer composites

Abstract

The growing global emphasis on sustainable materials has intensified interest in cellulosic resources for structural applications. Traditional high-performance materials, such as steel and glass fibers, have significant environmental drawbacks due to energy-intensive production and high carbon footprints. In this study, macadamia nutshell particulates (MNPs) were explored as a sustainable filler in synthetic polymer–natural fiber composites, aiming to address the limited compatibility between hydrophilic cellulose fibers and hydrophobic polymer matrices. The physical characteristics of the polymer–filler composites are influenced by intrinsic polymer structure (e.g., molecular weight, crystallinity, crosslinking) and external conditions (e.g., temperature, loading rate, and aging). Structural, physical and chemical characterization were performed. Various mixture ratios and processing conditions were investigated for both epoxy resin- and cement-based matrices. Results indicate that MNPs provided superior interfacial bonding and structural performance compared with other fillers, such as coconut shell and sawdust, particularly in epoxy resin systems, where improved adhesion and workability were observed. However, incorporating cellulosic fillers reduced stress and stiffness in epoxy-based composites. Interfacial strength was found significantly weaker among MNP and cement-based matrix. These findings demonstrate the potential of MNPs as an environmentally friendly filler, offering a viable pathway toward sustainable polymer composite development.