After MCC was added in the PLA matrix, the tensile fracture
surface of composites showed irregular protrusion and holes
(Fig. 4(b)–(d)). This is a typical fractographic feature of a brittle fracture
and the agglomerated MCC can be easily seen protruding out
of fractured surface. This is a clear indication of poor dispersion
of the MCC in PLA matrix. This demonstrated that the dispersion
of MCC was not uniform and showed a poor interfacial adhesion
between filler and matrix. This may likely be the explanation for the
decrease recorded for the tensile strength and elongation at break
for PLA/MCC composites as compared to pure PLA. The improvement
in Young’s modulus is due to the stiffening action of fillers,
which is a typical behavior of filled polymer systems. Similar result
has been reported by Cheng, Wang, and Rials (2009).