Short water-hyacinth fiber was used as a filler in natural rubber. In terms of mechanical properties, it was found that the hardness and the modulus of the rubber products mixed with water-hyacinth fiber were superior to those without the fiber. On the other hand, the tensile strength and the abrasion resistance were decreased, especially in the case of untreated fiber. The amount and the particle size of the fiber also affected the mechanical properties of the rubber products. When the amount and particle size of the fiber were increased, the hardness and modulus of the products would increase, whereas the tensile strength and abrasion resistance would decrease. The decline in these mechanical properties was probably due to the poor adhesion between the rubber and the fiber. This can be confirmed by the microscopy study since it was clearly noticed that the rubber and the fiber were adhered together mostly via physical bonding. In order to increase
bonding between the rubber and fiber, the fiber was treated with a coupling agent before mixing. The effect of the coupling agent was clearly exhibited since several mechanical properties were remarkably improved when the treated fiber was employed. Moreover, in this experiment, some common reinforcing agents, such as carbon black, have not been used. Mechanical properties might be improved in their presence.