Ball-milling Promoted Chemical Bonding between Cellulose and Plastics - Ball Milling Towards Green Synthesis: Applications, Projects, Challenges - page 219

characteristic of cellulose II, 19 while MC 0 2h and MC 10 2h remain amorphous.
The signals due to cellulose II are stronger for MC 30 2h than for MC 50 2h .
Further, for the samples MC 30 t , the signals show increasing intensities with
the milling time (t). These results indicate clearly that addition of greater
than 30 wt% water to the amorphous cellulose induces a crystalline trans-
formation into cellulose II, accelerated by ball milling. Of most interest, a
diffraction pattern of cellulose II even appears in MC 30 0 , which is prepared
only by addition of 30 wt% water to the amorphous cellulose powders. This
is a spontaneous transformation into cellulose II. It is the first demon-
stration that the transformation from a phase of cellulose I into a cellulose II
phase even occurs in the solid state.
Table 9.2 lists spin-lattice relaxation times (T 1 1H ) of some samples, based
on a proton inversion-recovery sequence with CP/MAS 13 C-NMR spec-
troscopy, in order to understand the mobility of cellulose chains and their
interactions with water molecules. The amorphous cellulose MC 0 has a
smaller T 1 1H than original cellulose (cellulose I). Addition of 30 or 50 wt%
water decreases significantly T 1 1H ; ball milling causes further a decrease in
T 1 1H for MC 30 2h but, conversely, a slight increase for MC 50 2h . The smaller
T 1 1H values correspond well to the greater degrees of crystalline transfor-
mation into cellulose II described above. This kind of relaxation is princi-
pally due to interactions of water molecules with cellulose chains in
amorphous or disordered regions. 24 Accordingly, on addition of 30 wt%
rather than 50 wt% water, a specific kind of interaction between cellulose
chains and water molecules probably greatly increases the mobility of cel-
lulose chains, particularly in disordered or amorphous parts, so that these
interacting chains can self-assemble to transform into a phase of cellulose II.
As described above, cellulose chains are parallel in a phase of cellulose I
but anti-parallel in a phase of cellulose II. It is reasonable that amorphous
cellulose, prepared by ball milling of native cellulose, is assumed to consist of
microfibrils with parallel-arrayed cellulose chains. This leads to the logical
deduction that the transformation into cellulose II is based on interactions
between oppositely oriented cellulose chains belonging to different microfibrils.

1 H spin-lattice relaxation times (T 1 1H )of
cellulose-water systems determined by
CP/MAS 13 C-NMR. Reprinted from ref. 22
with permission of Springer Science and
Business Media.

Table 9.2

T 1 1H (s) Sample

Original cellulose CF11 (cellulose I) 5.77

MC 0 4.53

MC 30 0h 1.22

MC 30 2h 1.11

MC 50 0h 1.33

MC 50 2h 1.43

MC 30 0h (D 2 O) 3.20

MC 30 2h (D 2 O) 3.04