Chemistry Reference
In-Depth Information
Accordingly its applications have been limited to only a few areas such as
paper and rayon.
Native cellulose is almost non-reactive with electrophiles or nucleophiles,
because almost all the hydroxyl groups are involved in extensive networks of
hydrogen bonds. Therefore, activation of hydroxyl groups in cellulose is
considered to be a way to realize its extensive application. We have explored
pulverization of fibers of cotton linter with high crystallinity as a native
cellulose by ball milling, and found that the resultant amorphous powders
exhibit unique characteristics with respect to specific interactions with water
molecules added to them. Activated cellulose powders are so reactive that
they can form ester bonds with maleic anhydride-grafted polyolefin (MPO)
2
in the solid state. This suggests strongly that novel cellulosic composites
with thermoplasticity are possible by formation of an interphase with MPO
chains bonded onto cellulose particles through ester bonds.
In this chapter, first, the molecular dynamics simulation of cello-
oligosaccharides is described to understand their conformations as well as
aggregation properties on the basis of intra- and intermolecular hydrogen
bonding. Then, micro-pulverization of cotton linter by ball milling is char-
acterized with respect to particle distribution, crystallinity, and degree of
polymerization, and unique properties of the resultant powders are dem-
onstrated on the basis of their specific interactions with water molecules.
Ball milling is also effective for grafting of maleic anhydrides onto polyolefin
like i-polypropylene. Finally, a description is given of the way in which ball
milling of cellulose and polyolefin gives rise to novel composites charac-
terized by an interphase between fine particles of cellulose and the
polyolefin phase.
9.2
Intra- and Intermolecular Interactions
of Cellulose
9.2.1 Conformation of Cello-oligosaccharides
Cellulose is a naturally occurring polymer consisting of
D-
glucopyranoses that
are bonded with each other by b(1
4) glycosidic linkages. We can under-
stand the major characteristics of cellulose by comparison with amylose,
which is another polymer composed of
D-
glucopyranoses, but through
a(1
-
4) glycosidic linkage (Figure 9.1). Amylose is soluble in water, in contrast
to cellulose. Umemura et al. carried out molecular dynamics simulation of
malto- and cello-oligosaccharides from monomer to hexamer in two thou-
sand TIP3P water molecules, and estimated the conformations of the isolated
chains in water (Figure 9.2).
3
The conformations are designated with a pair
of dihedral angles, F (H1-C1-O4
0
-C4
0
)andC (C1-O4
0
-C4
0
-H4
0
). Estimated
helical conformations with (F, C)
¼
(
301,
201) of malto-oligosaccharides
are entirely consistent with those with (F, C)
¼
(
301,
201) determined
from NMR spectroscopy;
4
for cello-oligosaccharides, their loose helical
conformations with (F, C)
¼
(
þ
401,
þ
51) do not agree with those with
-
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