Biomedical Engineering Reference
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4500
4000
Pure Cellulose
3500
5 h reaction
3000
2500
9 h reaction
2000
1500
1000
500
0
0
10
20
30
40
50
2
q
Figure8.14
X-raydiffractionstudiesshowingtherelativedecreaseincrystallinityatdifferent
reactiontimes.
crystal structure cannot accommodate the bulky maleate groups, we conclude that the
esterification reaction was restricted to the surface at low reaction times.
We did find a decrease in the intensity of the
002
peak with an increase in reaction
time. The cellulose MFs that were esterified up to nine hours showed a significant
decrease in peak intensity at 22.7
◦
indicating the possibility that the reaction had pro-
gressed from the amorphous regions to the crystalline domains at long esterification
times (Figure 8.14).
Chitin nanoparticles were derivatized with medium-chain aliphatic esters to improve
their surface hydrophobicity. These materials were characterized by FTIR. The IR spec-
tra for the chitin nanocrystals, chitin hexanoate, chitin nonanoate, and chitin stearate
are shown in Figure 8.15. Arrows on the top spectrum representing the chitin stearate
denote the most significant new features associated with esterification. After reaction,
with any of the organic acids, a signal arises at 1750 cm
−
1
that can be assigned as
the ester carbonyl stretching frequency by analogy with cellulose esters, where the ester
carbonyl signal appears at a very similar frequency (39). FTIR spectra of the corre-
sponding pure organic acids shows a higher frequency for the acid carbonyl stretching
signals, at 1760 to 1780 cm
−
1
(40). The presence of a carbonyl signal in the chitin
esters, its moderate shift to lower energy relative to the typical free acid carbonyl signal,
and its stability to repeated washing with various solvents lead us to conclude that the
long aliphatic side-chains are attached to chitin through an ester linkage, as opposed
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