Biomedical Engineering Reference
In-Depth Information
An example of this type of system is carboxymethyl cellulose (CMC) (Choi and
Simonsen 2006), in which glycerine is added as a plasticizer at a concentration of 10%.
The addition of 5% CNXLs results in an improvement in mechanical properties, including
elongation at break (Figure 10.5). The resulting nanocomposite is not only stronger and
stiffer, but tougher. It is known that the addition of fillers at low filler volumes can
increase the toughness, as has been reported, for example, for silica-filled polypropylene
(Wu et al . 2002).
To overcome the issue of water susceptibility, crosslinking methods have been
employed. For CMC, in the salt form (which is the form produced industrially) the
preparation of the composite starts by converting the matrix to the acid form, by passing
a solution of sodium CMC, NaCMC, through a cation exchange column. The resulting
acid form can be confirmed by potentiometric titration (Figure 10.6).
Conversion of the NaCMC to the acid form and subsequently heat treating the resulting
composite increases the tensile strength of the 5% filled material by a factor of 2.6
compared to the NaCMC sample. The elongation to break was reduced from 5.5% to
3.8% (Figure 10.7). This result is explained by the increased cross-linking in, which
produced an increased brittleness. The nanocomposite thus shows significantly improved
mechanical properties compared to the unfilled composite at the 5% filler level. However,
loadings greater than 5% showed no improvement or even a decrease in properties. This
is postulated to be the result of agglomeration.
4
6
4
2
2
0
5
10
15
20
25
30
0
5
10
15
20
25
30
CNXL Content (wt%)
CNXL Content (wt%)
38
36
34
32
30
28
26
0
5
10
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25
30
CNXL Content (wt%)
Figure10.5 MechanicalpropertiesofCNXL-filledNaCMCwithnoheattreatment.Theerror
barsrepresent
±
onestandarddeviationof thedata(ChoiandSimonsen2006).
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