Ball-milling Promoted Chemical Bonding between Cellulose and Plastics - Ball Milling Towards Green Synthesis: Applications, Projects, Challenges - page 230

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PEG content (%)

Figure 9.21 Dependences of the onset melting temperature ( & ) and enthalpy (DH)
( ' ) of the composite of cellulose and PEG on the PEG content.
Reprinted from ref. 35 with permission of the Chemical Society of
Japan.

with an increase in PEG content of 0-22 wt%. Strikingly, the CI value of the
washed cellulose increases to 30-50% according to an increase in the PEG
content, suggesting intensive recrystallization of cellulose into a phase of
cellulose I by extracting PEG molecules from the composite. Notably,
amorphous cellulose prepared by ball milling only native cellulose remains
amorphous even if it is washed with water. These results indicate that,
when a mixture of native cellulose and PEG is ball-milled, the mechanical
stress primarily makes cellulose amorphous and allows extensive inser-
tion of parts of PEG molecules between microfibrils or even between
cellulose chains in microfibrils, with other parts of the PEG molecules
involved in the PEG phase. Accordingly formation of hydrogen bonds
between cellulose and PEG molecules causes compatibilization between
cellulose and PEG phases, and the resultant composite can be classified
as a polymer alloy.
The composite is completely different from a corresponding blend pre-
pared from a solution of cellulose and PEG, because in the blend cellulose
and PEG molecules are considered to be miscible with each other. 36 The
cellulose phase in the composite exhibits recrystallization to cellulose I on
extraction of PEG, while removal of PEG from the blend makes cellulose
chains assemble to form a phase of cellulose II, because of its higher stability
than cellulose I. Therefore, the composite of cellulose and PEG is charac-
terized not only by high dispersion of fine particles of cellulose in the PEG
matrix, due to strong interactions between cellulose and PEG molecules, but
also by a parallel orientation of cellulose chains in each primary phase of