The tensile strength of natural fiber reinforced PLA composites did not show the improvement when
compared with neat PLA. Tensile strength of coconut fiber and vetiver grass fiber reinforced PLA
composite decreased with the increasing of natural fiber content as shown in Fig. 1(b). On the other hand,
tensile strength of bamboo fiber reinforced PLA composite almost remained constant and only slightly
decreased when bamboo fiber content reached 40 wt.%. This was due to that bamboo fiber has higher
fiber strength than other natural fibers. Moreover, the bonding between different natural fiber and PLA
matrix were different. As observed from SEM micrograph of fracture surfaces as shown in Fig. 2. The
fiber-matrix interface in bamboo fiber/PLA composite from the Fig. 2(a) which showed better adhesion
bonding than other reinforcement resulted in better tensile strength. The reduction of strength at high
bamboo fiber content may possible due to the increasing of the probability of fiber agglomeration.
Fig. 3 showed how the influence of the flexible epoxy surface treatment affected the stiffness of
biocomposites. It was found that the flexible epoxy surface treatment reduced the tensile modulus of
bamboo fiber/PLA and vetiver grass fiber/PLA composites. The reduction of tensile modulus may due to
the coating of natural fiber surfaces with the flexible material, which reduced the stiffness of the natural
fibers. However the tensile modulus of untreated and treated coconut fiber/PLA composite behaved
differently.