Ball-milling Promoted Chemical Bonding between Cellulose and Plastics - Ball Milling Towards Green Synthesis: Applications, Projects, Challenges - page 231

cellulose. The composite exhibits a thermoplastic property owing to the high
fluidity of fine particles of cellulose in it, and accordingly yields various
molds by usual hot-pressing. A similar composite is obtained by ball milling
of cellulose and poly(e-caprolactone), another polymer with high anity for
cellulose, and is readily hot-pressed to yield various molds with water-
resistance, differing from the composite with PEG.
9.5.2 Composite of Cellulose and Maleated Polyolefin
Synthesis of composites consisting of hydrophilic cellulose and hydro-
phobic polyolefin usually requires a compatibilizer such as maleated
polyolefin, in marked contrast to the composite of cellulose with PEG
described above. Melt mixing of fibrous crystalline cellulose (FC) with
maleic anhydride-grafted polyethylene (MPE) at 200 1C for 10 min yields
strong adhesion of FC to MPE in an FC-MPE composite, while there is no
adhesion of FC to unmaleated PE (UPE) in an FC-UPE composite. 37 The
strong adhesion between FC and MPE phases is obtained even on using
MPE with a slight MA content of 0.25-0.5 wt%. Such interfacial structures
of the FC-MPE and the FC-UPE composites cause quite different behaviors
of crystallization as well as melting. 38 Accordingly, the FC-MPE composite
exhibits an increase in tensile strength and Young's modulus in the range
of FC content r 60 wt%, suggesting improved transfer of the high tensile
strength and elasticity of FC to the MPE phase, in marked contrast to the
FC-UPE composite, which exhibits decreases in both tensile properties.
Furthermore, the FC-MPE composite exhibits a greater storage modulus
than the FC-UPE composite, particularly in the FC content of 60 wt%,
strongly suggesting the more improved dispersion of FC fibers in the
MPE matrix. 37 Nevertheless, the FC-MPE composite still exhibits a sig-
nificant decline in toughness z with an increasing FC content, owing to a
remarkable decrease in elongation. 37 Similar results have been observed
also on FC-MPP and FC-UPP composites obtained by melt-mixing,
where MPP and UPP denote maleated and unmaleated polypropylene,
respectively. 39,40
The marked decrease in toughness and fluidity of cellulosic composites
with an increase in cellulose content makes it dicult to develop novel
composites with a greater content of cellulose. This suggests strongly the
necessity of the formation of an interphase between FC and PE or PP phases,
with PE or PP chains bonded onto cellulose particles. The formation of ester
bonds between OH groups of FC and MA grafts of MPE or MPP was not
confirmed for the FC-MPE or the FC-MPP composites obtained by melt-
mixing. 37,39
z Toughness is directly proportional to the multiplication of tensile strength and elongation.