Enhancement of mechanical properties in NaOH treated coffee husk HDPE composites for sustainable material applications

Abstract The commercial coffee processing industries in Ethiopia generate significant quantities of residual coffee material every year. To valorize this coffee waste, this study emphasizes coffee waste-based filler production reinforced with thermoplastic polymers as a viable pathway. Agricultural composite can replace synthetic-based fiber composites due to excellent mechanical properties, low cost, and low density. This study targets enhancing the mechanical properties of coffee husk fiber (CHF) high-density polyethylene polymer (HDPE) composite for industrial applications through chemical treatment. These fibers serve as reinforcement, complemented by HDPE as the matrix, acrylonitrile-butadiene-styrene (ABS) as a coupling agent, and kaolin clay as a filler material. The CHFs were treated with 10% sodium hydroxide (NaOH) treatment. The composite was prepared with 7wt% kaolin clay, 3wt% ABS, 15wt% CHF, and 65 wt% virgin (pure) HDPE. Composite samples were formulated with different treated CHF/HDPE ratios with 25/65 (T25), 20/70 (T20), and 15/75 (T15) and compared with the untreated CHF. The mechanical impacts of treated composites were evaluated using standard American Society for Testing Materials (ASTM) methods, and structural and morphological changes were determined using FTIR analysis and SEM. The maximum mechanical strength obtained by T25 for tensile strength, T25 for flexural, and T20 for impact test were 45.17 MPa, 2.91 MPa, and 3.45KJ/m2, respectively. The experimental analyses of treated CHF/HDPE composites presented superior mechanical properties compared to untreated CHF. The NaOH treatment of CHF has also presented a significant impact on fiber structure by reducing hydroxyl (-OH) groups and enhancing morphological changes of fiber surface by FTIR and SEM analyses, respectively. Generally, the results of the study find that the value applications of agricultural waste fiber-based composites would provide low-cost materials for industrial applications.