Ball-milling Promoted Chemical Bonding between Cellulose and Plastics - Ball Milling Towards Green Synthesis: Applications, Projects, Challenges - page 229

(Figures 9.19 and 9.20). The data depicted in Figures 9.19 and 9.20 are also
valuable from an engineering viewpoint, because they make it possible to
choose the grafting conditions when synthesizing an MA-graft product with
desired graft degree and MFI.

9.5 Novel Composites of Cellulose and Plastics by
Ball Milling

9.5.1 Compatibilization of Cellulose with
Poly(ethylene glycol)
Cellulose exhibits essentially no thermoplasticity and moreover insolubility
in usual solvents. Accordingly, mechanochemical compounding of cellulose
with thermoplastic polymers is considered to be a useful method to yield
novel thermoplastic composites with cellulose. First, we describe a com-
posite of native cellulose with poly(ethylene glycol) (PEG; M W ¼ 2.0 10 6 )asa
polymer with high anity to cellulose, using highly crystalline cotton linter
as a pure cellulose for basic studies. As described briefly in preparing fine
particles of cellulose in Section 9.3.1, ball milling of a mixture of native
cellulose and PEG yields a new composite through hydrogen bonds between
cellulose particles and PEG molecules surrounding them. 35 Interactions
between cellulose and PEG have been confirmed by differential scanning
calorimetry (DSC), which is useful in determining the temperature and
enthalpy of a phase transition of PEG. The transition temperature (onset)
and enthalpy of PEG in the composite, which is smaller than those of
genuine PEG, decrease with decreasing PEG content (Figure 9.21), sug-
gesting stronger restrictions of PEG molecules by cellulose with a decreasing
content of PEG in the composite. Such phenomena do not occur in a simple
mixture of native cellulose and PEG without ball milling. This is also con-
firmed by DSC analysis of the constituents of cellulose and PEG separated by
washing with water a composite with a PEG content of up to 20 wt%, where
the separated cellulose and PEG are hereafter named washed cellulose and
extracted PEG. Thus, the washed cellulose shows no phase transition in the
region of temperature concerned, while the extracted PEG exhibits almost
the same melting temperature and enthalpy as genuine PEG shown in
Figure 9.21. Further, IR spectra of the composites reveal almost simple
superposition of spectra due to amorphous cellulose and the extracted
PEGs without any new signals, except for a broad OH signal that shifts to
smaller wavenumbers with an increase in PEG content. These results prove
that the PEG and cellulose constituents in the composite undergo no
chemical change, except for interactions of cellulose and PEG as well as a
decreasing molecular weight of PEG (e.g., M W ¼ 1.5 10 5 for the extracted

PEG from the composite).
The cellulose phase in a composite has a slightly increasing crystallinity
index 19

(CI) due to cellulose I, ranging from 0 to 11%, nearly amorphous,