Cellulose and Chitin as Nanoscopic Biomaterials - The Nanoscience and Technology of Renewable Biomaterials - page 221

OH

O(CO)CHCHCO 2 H

O

NaHPO 4
xylene
D

O

O

O

O

+ 3 O

HO(CO)CHCH(CO)O

O

HO

OH

O(CO)CHCHCO 2 H

n n

Cellulose MF Surface Maleic Anhydride Surface Modified Microfibers

OH

OH

OH

OCOCHCHCOOH

OH

HO

OH

HO

OH

HO

OH

OH

HO OCOCHCHCOOH

HO

OH

HOOCHCHCOCO

OH

OH

OH

OCOCHCHCOOH

OH

Scheme 8.1 Molecular modification shown at the top. A representation of nanocrystal
surfacemodificationisshownat thebottom.

the fiber matrix interface. Hydrophilicity of the cellulose particle surface can result
in poor interfacial adhesion of thermoplastics. This can be controlled by hydrophobic
modification of the particle surface. It is crucial to note that any chemical modification
of the hydroxyl groups in cellulose must be restricted to the surface, if the particles are
to be used as a reinforcing element in composites, since interior changes would decrease
crystallinity, particle size and thickness.
The surface of cellulose nanocrystals isolated from bagasse were decorated with
maleate ester groups, which can serve as branch points for subsequent grafting of
aliphatic chains onto the crystal surface, resulting in the formation of brushlike struc-
tures. The presence of an unsaturated alkene group on the surface of these microfibers
provides opportunity for further topochemical modification. A scheme for the maleate
derivatization of cellulose is provided in Scheme 8.1.
Attenuated total reflectance (ATR), FTIR was used to confirm chemical modification.
From the absorbance peaks at 1095 cm − 1

(C-O-C stretching), 3400 cm − 1

(-OH stretch-

ing), and 1725 cm − 1 (C

O stretching), it can be concluded that the spectra are consistent
with both cellulose (in the case of the starting material) and partially substituted cellulose
(Figure 8.13).
Several bands consistent with the maleated ester of cellulose are present in the spectra.
The most notable feature is a rather broad carbonyl band ' a ' that increases with reaction
time. The carboxyl band initially has a maximum near 1725 cm − 1 in the spectra of the 3
and 5 hour reaction time products, and then shifts to 1712 cm − 1 for the 9-hour reaction
time product. This suggests that it is a composite carbonyl with contributions from both
the conjugated ester and the carboxylic acid functionality. Both of these functionalities
would be expected to exist in the maleated product spectrum, and the increasing intensity
of the carbonyl is consistent with an enhanced degree of substitution in the product.
Another notable feature in the spectra of maleated cellulose is a very broad -OH band,
from 2100 cm − 1 to 3200 cm − 1 , consistent with acidic -OH functionality (band ' b '). This

=