Generally, the un-notched impact strength of polymers
or its composites is higher than that of notched impact
strength because the un-notched specimen can absorb
higher energy or show greater resistance against the load
(See Fig. 5a and 5b). Fig. 5a represents Izod notch impact
strength of neat PLA and wood fiber reinforced PLA biocomposites.
It can be seen that with the addition of
20 wt.% wood fibers with PLA, the notched impact strength
of composites increased relatively as opposed to PLA. The
neat PLA has impact strength of 23 J/m compared to 24 J/m
of PLA/WP bio-composites. PLA/WP/bioadimide composites
has impact strength of 30 J/m. The impact strength
was improved significantly due to addition of bioadimide
with PLA/WP bio-composites. These effects could be
related to the fiber–matrix adhesion where bioadimide
generated a strong network or bonding between fibers and PLA. These results proved that bioadimide worked as
an adhesion promoter. Bledzki et al. (2009) described that
the improvement of reinforcement by fibrous material is
more significant with unnotched samples than that of
notched ones. This is why the improvement of unnotched
impact strength was observed for better comparison
between PLA and its bio-composites. Fig. 5b shows the
results from unnotched impact strength of PLA and fiber
reinforced bio-composites. The significant increase in
impact strength of neat PLA was observed in contrast to
PLA/WP bio-composites. PLA/WP bio-composites became
fragile because there was not any adhesion promoter to
make bridge in between them. As a result, they showed
poor unnotched impact strength. Oksman et al. (2003)
described that the charpy impact strength of PLA/flax
(60/40) bio-composites was found to be decreased. Our
results are in line with the studies conducted by Oksman
et al. (2003). The addition of bioadimide in PLA/WP biocomposites
leads to significant improvement in unnotched
impact strength. With the presence of bioadimide, reinforcing
PLA/WP bio-composites leads to better adhesion
at the interface which could be the main contributor in
improving the unnotched impact strength.