To further verify the effect of surface topochemistry on the
interaction between CNCs and PLA, the peak of the Tan Delta (i.e.
damping factor) from DMA analysis was examined and the results
are shown in Fig. 8. Tan Delta is related to polymer chain relaxation
and, therefore, provides insight into the effect of CNC topochemistry
on modified CNC-PLA interactions [47]. In the case of
increased modified CNC-PLA interactions, the following changes in
the Tan Delta vs. Temperature plot should be observed: i) a shift in
the peak maximum to higher temperature, ii) a decrease in the
intensity at the peak maximum and iii) broadening of the transition
[28]. In fact, all of these changes were observed when comparing
Tan Delta vs. Temperature transitions for the modified CNCs to
those of HCl-CNC. At 5% HCl-CNCs, there is a small decrease (10%) in
the Tan Delta peak height and the peak temperature (59 Ce58 C)
indicating poor adhesion between HCl-CNCs and PLA [48]. In
contrast, AA- and LA-CNCs show 38 and 64% decreases in Tan Delta
peak heights at 5% loading. Furthermore, maxima for the Tan Delta
peaks for AA- and LA-CNC are at 61 C and 65 C. Hence, these
results indicate that interactions between PLA and the CNCs vary as
a function of the modification chemistry in the following order: LACNC
> AA-CNC > HCL-CNC.