Civil Engineering Reference
In-Depth Information
Figure 15.3
High-resolution TEM images of (a) CNCs and (b) CNFs [45]
but due to its highly crystalline nature should be called "nanocrystalline cellulose."
CNCs are rod-shaped or whisker-shaped structures remaining at er acid hydrolysis of
WF, PF, MCC, MFC, or NFC [42-44].
In the case of potential applications, these particular dimensions af ect the i nal
structure and properties of the fabricated products. According to dif erent terms of
nanocelluloses, these can be divided into two basic categories: (a) cellulose nanoi bers
(CNFs) and (b) cellulose nanocrystals (CNCs). Morphology (TEM images) of CNFs
and CNCs is shown in Figure 15.3.
Both types of nanocelluloses may show dif erent properties as a nanoreinforcement.
In this case, Xu
et al.
performed a comparative study between CNCs and CNFs regard-
ing their morphology, crystalline structure, dispersion properties, and reinforcing
ef ect in polyethylene oxide (PEO) polymer matrix. h ese are nanoscale cellulose i bers
having dif erent shape, size, and compositions.
Hence, they behave dif erently in the matrix as nanoi llers. For this study, transpar-
ent PEO/CNCs and PEO/CNFs nanocomposites having dif erent amounts (1-10 wt%)
of nanocellulose were fabricated via solution casting. Having the same concentration of
nanocellulose, CNFs exhibited higher strength and modulus than that of CNCs due to
larger aspect ratio and i ber entanglement of CNFs, but showed lower strain-at-failure
because of their relatively large agglomeration of i bers [45] .
Relatively speaking, NFCs are considered more ductile as compared to CNCs and
can be applied as a more useful template for further functionalization [46]. For the
systematic comparative study, the Halpin-Kardos and Ouali models were applied to
simulate the modulus of the nanocomposites and, as predicted, the experimental val-
ues showed good agreements. h erefore, on the basis of type of nanocellulose, sys-
tematic comparative study can help to develop the criteria for selecting the proper
nanocellulose as a biobased nanoreinforcement material in polymer nanocomposites
[45] . h erefore, these nanocellulose types such as CNCs and NFCs have attracted a
great interest in the i eld of industrial and biomedical applications. h erefore, CNCs
are ot en referred to as microcrystals, whiskers, nanocrystals, nanoparticles, and
microcrystallites. Hereat er, for convenience, they will be called "cellulose nanocrys-
tals" (CNCs).
