Tensile properties such as tensile strength, elongation at break,
and Young modulus of the composites made from lignocelluloses
fillers (RH and BRH), PLLA/starch blends at different filler
loadings are shown in Figure 3 and Table II.
The RH–PLLA–starch composites have shown higher strength compared to the
BRH–PLLA–starch composites.
As the bleaching process removed the lignin content in the RH, therefore, one may conclude
that lack of lignin in the BRH is the main reason for the
observed behavior.
The tensile strength of RH–PLLA–starch composites is slightly increased by increasing the filler loading
(RH) and similar trend, that is, enhancement of tensile strength
on filler loading, can be seen in the case of adding BRH filler
The interesting point to be noticed here is that with increase in
the content of BRH the extent of enhancement of tensile
strength is slightly lower which proves that the removal of lignin
could reduce the tensile strength and this matter will be proved
by SEM results which will be described further.
Conversely, RH
leads to higher elongation at break as compared to the samples
filled by BRH.
Furthermore, elongation at break of samples,decreased by increasing of filler content.
It shows that introduction
of fillers has made the composites more brittle and this
could be due to the direct effect of silica which has been intensified
by lignin removal.
It has been reported that high content
of RH increases the probability of agglomeration, which
results in regions of stress concentration requiring less energy for
crack propagation.
The results show that the tensile strength of
BRH samples increases by increasing the filler.
However, at 15%
of filler content, a reduction in tensile strength was observed.
The elongation at break also demonstrates that removing the lignin
in higher content of the filler has a negative effect on the
properties.
As is shown in Table II, elastic modulus (E-Modulus)
of RH samples exhibit an increasing trend with increasing RH
and BRH.
During tensile loading, partially separated microspaces
are created, which obstruct the stress propagation between the
filler and the matrix.
As both modified and unmodified filler
loading increase, the degree of obstruction increases, which in
turn, increases the modulus and stiffness.
The results further
show the RH and BRH unplasticization property.