The flexural properties of the polylactic acid/rubber wood
sawdust and the polylactic acid/CSR/rubber wood sawdust biocomposites
are shown in Fig. 3. As with tensile modulus,
the flexural modulus was largely dependent on the wood
sawdust content in the composites. In general, the flexural
modulus was raised with the increase in wood fiber concentration.
The flexural modulus of the polylactic acid/rubber wood
increased from 3.4 GPa to 7.9 GPa when the wood sawdust
was added at 30 wt%. The increment was presumably
due to the inclusion of the rigid wood particles. For
the polylactic acid/CSR containing 30 wt% rubber wood, the flexural
modulus increased from 2.4 GPa to 5.2GPa. The
flexural strength in Fig. 3b, exhibited a similar trend to
that found in the flexural modulus. Moreover, the flexural
strength was raised from 89 MPa to 190 MPa when the
rubber wood sawdust was added at 30 wt%. The rubber
wood particles acted as rigid filler responsible for the increase in the stiffness of the polylactic acid. This behavior was
expected, based on the rule of mixtures, as the modulus
of the wood particles was much greater than that of the
polylactic acid matrix. The addition of 5 wt% CSR to the
polylactic acid/rubber wood composites reduced the flexural
strength from 190 MPa to 130 MPa.