to show the overview of
the fracture surfaces. From Fig. 6 it can be seen that the dispersion of cellulose nanofibers has not been uniform
and aggregates of CNF can be found in all composite materials.
Due to the increasing amount of cellulose nanofibers
in the composites with 15 and 20 wt.% of CNF the amount
of aggregates also increases, which is most likely the reason
why the tensile strength did not increase in the case
of these materials.
The cellulose nanofibers were used in 12 wt.% water
suspension in the composite preparation in order to avoid
the formation of nanofiber aggregates. However, as the
SEM images show, it seems that this water content was
inadequate, as aggregates were formed. It is also possible
that the water evaporated too fast from the material in
extrusion, causing the aggregation of CNF. In addition,
modification of the screw configuration to more shearing
could favor uniform dispersion of cellulose nanofibers.