The impacts of filler loading and chemical modification (silane coupling) on the characteristics of the polypropylene composites filled with coir fiber were examined in this study. Tensile strength, tensile modulus, impact strength, and water absorption were among the physicomechanical characteristics of the polypropylene/coir fiber composites that improved with increasing coir fiber loading. The alkali pretreatment was followed by the addition of 3-aminopropyl trimethoxy silane and tetramethoxy orthosilicate, which improved the composites' overall mechanical characteristics and water desorption. As the coir fiber loading increased, this tendency became more apparent. The findings demonstrated that the best overall mechanical properties were found in polypropylene/alkali treated coir fiber/tetramethoxy orthosilicate composites. The horizontal flame rate was considerably decreased by the addition of magnesium hydroxide to polypropylene/alkali treated coir fiber/3-aminopropyl trimethoxy silane and polypropylene/alkali treated coir fiber/tetramethoxy orthosilicate composites. The addition of 3-aminopropyl trimethoxy silane and tetramethoxy orthosilicate for the coir fiber resulted in higher crystalline and melting peak temperatures as well as an improvement in the heat of fusion when compared to virgin polypropylene and polypropylene/coir fiber, according to the results of differential scanning calorimetry. The composites' thermal stability was enhanced by the addition of 3-aminopropyl trimethoxy silane and tetramethoxy orthosilicate. For the polypropylene/coir fiber composite systems, 3-aminopropyl trimethoxy silane and tetramethoxy orthosilicate are therefore regarded as effective coupling agents.
