Ball-milling Promoted Chemical Bonding between Cellulose and Plastics - Ball Milling Towards Green Synthesis: Applications, Projects, Challenges - page 213

Table 9.1 Crystallographic data of major cellulose polymorphs. Reproduced from
refs 10 and 15 with permission of American Chemical Society.
Cellulose I b 10

Cellulose II 15

Chemical formula C 12 H 20 O 10 C 12 H 20 O 10

Space group Monoclinic, P2 1 Monoclinic, P2 1

a (nm) 0.7784(8) 0.801

b (nm) 0.8201(8) 0.904

c (nm) 1.0380 (10) 1.036

g (1) 96.5 117.1

V (nm 3 ) 0.6583(11) 0.6678

Z 2 2

Density (g cm 3 ) 1.64 1.61

Chain alignment Parallel Anti-parallel

Conformation:
F a (1) -98.5 (o), -88.7 (c) -95.4 (o), -91.3(c)
C b (1) -142.3 (o), -147.1 (c) 92.3 (o), 89.4 (c)
w c (1) 170 (o), 158 (c) — (o), — (c)
w 0 c (1) -70 (o), -83 (c) -172.4 (o), 148.4 (c)
tg (o and c) gt (o and c)
a The dihedral angle to describe the relative orientation of adjacent glycosyl residues in the
same chain, defined by O5-C1-O1-C4. Note that the definition is different from that in
Section 9.2.1.
b Another dihedral angle, defined by C1-O1-C4-C5 and C1-O1-C4-C3 for cellulose I b and II,
respectively. Note that the definition is different from that in Section 9.2.1.
c Dihedral angles with regard to the conformation of hydroxyl methyl group, which are defined by
w(O5-C5-C6-O6) and w 0 (C4-C5-C6-O6).

Notably, for I p , H2 is located principally in the direction to O6, with co-
operative orientation of H6 toward O3 0 in a neighboring chain in the same
sheet, whereas for I d another orientation of H6 to O2 causes H2 to occupy a
position off the line of O2-O6. Accordingly, for I p , origin chains are hydro-
gen-bonded with each other in a sheet, through intermolecular hydrogen
bonds O6-H6 O3 0 with the aid of intramolecular hydrogen bonds O2-
H2 O6/O1 and O3 0 -H3 O5 0 , while center chains are bonded through
intermolecular hydrogen bonds O6-H6 O3 0 /O2 0 supported by intra-
molecular hydrogen bonds O2-H2 O6 and O3 0 -H3 0 O5 0 (Figure 9.7).
These results prove that chains are aligned in both sheets through inter-
molecular hydrogen bonds of principally O6-H6 O3 0 and partly O2-
H2 O6 0 , holding a flat ribbon structure through intramolecular hydrogen
bonds of dominantly O3-H3 O5. Notably, there are almost no hydrogen
bonds between sheets, which are held together only by hydrophobic
interactions. 10
On comparing cellulose II with cellulose I b , the significant difference is
the orientation of center chains opposite to that of origin chains. In add-
ition, the hydroxymethyl groups in both chains are in a gt conformation.
Thus, both origin and center chains are aligned in each sheet in a zigzag
fashion when projected on the ab plane, with a relative displacement along
the c axis of ca. 1/4c, allowing a network of hydrogen bonding not only be-
tween origin chains or center chains but also between origin and center