Cellulose and Chitin as Nanoscopic Biomaterials - The Nanoscience and Technology of Renewable Biomaterials - page 222

Cellulose Maleate, 9 hrs
Cellulose Maleate, 5 hrs
Cellulose Maleate, 3 hrs
Cellulose

0.30

d

0.25

a

0.20

0.15

c

b

0.10

0.05

0.00

− 0.05

− 0.10

4000 3000 2000

Wavenumber (cm − 1 )

1000

Figure8.13 ATR-FTIRspectraof surfacemodifiedcelluloseMFsatdifferent reactiontimes.
Important spectral features are labeled 'a' through 'd'. Band 'a' denotes the carbonyl
stretching frequency, band 'b' is the acid -OH stretching frequency, band 'c' marks the
cellulose hydroxyl functionality, and band 'd' marks both ester and acid C-O stretching
frequencies. All labels indicate the esterification of cellulose with the maleate functional
group.

band further supports the presence of carboxylic acid functionality from the maleated
product, with the absorption increasing with increasing reaction time and presumed
degree of substitution. A comparison of the spectra of the 3- and 5-hour products
with native cellulose suggests a progressive decrease of the cellulosic -OH contribution,
as marked by the decrease in the broad 3340 cm − 1 -OH band (band ' c '). However,
the 9-hour spectrum does not continue this pattern, possibly because of the overlapping
acidic -OH absorption band, or interactions between the acidic and cellulosic -OH units.
Finally, there were bands, consistent with both ester and acid carbonyl C-O stretches,
observed in the 1300-1100 cm − 1 regions (band ' d ') whose intensity increased with
increasing reaction time and presumed degree of substitution. No attempt was made to
further investigate these or other bands.
X-ray diffraction studies were carried out in order to determine whether there was any
change in crystallinity during the course of the reaction. Cellulose I has a characteristic
intense peak at a 2 θ value of 22.5 degrees (37, 38). This corresponds to the 002 plane
using the convention of the b axis as the chain direction. We find that with an increase
in esterification time there is a measurable broadening of the peaks associated with the
101 , 110 ,and 002 planes of reflection. (These indices use the convention of the fiber
axis parallel to the b axis.) This broadening implies shrinkage in crystallite size along
the normal to each indexed set of planes. Since there were no significant changes in the
position of maximum intensity during the course of the reaction, we conclude that the
crystalline core of these microfibers remained in the cellulose I allomorph. Since this