Comparative Study on the Effect of Coconut and Baobab Fruit Shell on the Mechanical Properties of Natural Rubber Composites

The main objective of this study is to produce Natural rubber (NR) based reinforced composites with higher mechanical properties for various industrial applications, using eco-friendly, agricultural waste fillers materials to substitute expensive fillers. The fillers were sieved through a 125 µm sieve and were dried under the shade for 120 hrs. This research aims to examine the effect of coconut and baobab fruit shell filler loading on the physio-mechanical properties of the composites. Various amounts of filler loading (5, 10, 20, 30 and 40 phr) were used in the NR matrix compounding and were cast using the hand layup mould technique. The rubber compound with coconut shell (CS) or Baobab shell (BS) was fabricated using a two roll mill machines at 70–75 °C, pre-masticated for 2–3 minutes, and additives added. The rubber was then cured using a hydraulic press machine, cooled, and pressed for 10 minutes at 130 °C. The moisture absorption of all the composites increases up to a maximum of 3% with an increase in the filler loading. The specimens are vulcanized at 150 °C, 150 kg/cm² pressure for 20 minutes. The samples were cut, and the moisture absorption and mechanical properties were evaluated according to the ASTM standards. The results indicate that a more uniform dispersion of coconut, baobab fruit shell filler and NR improves the interfacial adhesion between all the composite's phases. Enhanced filler loading increased the tensile strength and hardness but decreased the elongation at break. The study compares natural rubber composites' mechanical and moisture absorption properties reinforced with coconut shell (CS) and baobab shell (BS) fillers. Both fillers reduced elongation at break, indicating increased stiffness. CS-filled composites showed slightly lower elongation, suggesting greater rigidity. Both fillers significantly enhanced tear strength, hardness, and tensile strength. CS fillers were more effective in reducing moisture uptake, while BS-filled composites absorbed more moisture. CS fillers generally provide better mechanical reinforcement, but BS fillers may limit their use in moisture-resistant applications.