Biodegradability and Water Absorption of Macadamia Nutshell Powder-Reinforced Poly(lactic Acid) Biocomposites

This study investigates the biodegradability and water absorption properties of Macadamia nutshell powder and poly(lactic acid) (PLA) biocomposites using a Design of Experiments (DOE) approach. The influences of processing methods, the Macadamia nutshell powder’s weight content, and the powder’s condition are studied. A biodegradability test is performed in accordance with the American Society for Testing and Materials (ASTM) D5338-11 by burying the test specimens in wet garden soil at a controlled temperature of 50 °C and 100% humidity. The specimens obtained by counter-rotating processing exhibit varying weight loss patterns with an increasing powder weight content, while the specimens obtained by co-rotating processing demonstrate consistent behaviour. This study highlights the complex nature of PLA biodegradation, which is affected by diverse factors such as test conditions and environments, thereby contributing to a deeper understanding of the sustainability implications. A water absorption test is carried out in accordance with ASTM D570-98. It is shown that the water absorption characteristics are predominantly determined by the hydrophilic nature of Macadamia nutshells, with an increased powder weight content leading to higher absorption. Pure PLA, due to its hydrophobic nature, exhibits minimal water absorption. By unravelling the complexities of PLA biodegradation and water absorption in Macadamia nutshell and PLA biocomposites, this study not only advances the understanding of materials’ behaviour but also underscores the potential sustainability implications of utilizing natural resources in composite materials. This research contributes valuable insights to the broader discourse on environmentally friendly materials and their role in promoting sustainable practices.