Bacterial Cellulose and Its Polymeric Nanocomposites - The Nanoscience and Technology of Renewable Biomaterials - page 263

(CMC and MC) nanocomposites which shifted from a fine fibrillar structure to a porous
structure with increasing MC or CMC content. As a result, the BC/CMC nanocom-
posites had superior absorption properties than neat BC and the PC/PVA nanocompos-
ites (29).

9.6 BC/Polymer Nanocomposites Based on Bacterial

Cellulose Nanocrystals

Other attempts at preparing nanocomposites based on bacterial cellulose have utilized
hydrolyzed cellulose nanocrystals (CNXL) (72-75). Since the discovery of their rein-
forcing potential in 1995, CNXLs have been shown to reinforce a wide variety of
thermoplastic polymers via a percolation effect (76-78). That is, above a percolation
threshold the stiff rodlike nanocrystals are able to interact via hydrogen bonding to form
a percolation network which induces a very significant stiffening of thermoplastics (78).
With the large Young modulus of cellulose I at around 140 Gpa (79), an outstand-
ing reinforcing potential of BC nanocrystals in polymer matrices might be expected.
Cellulose nanowhiskers are obtained by acid treatment of cellulose which hydrolyses the
amorphous region of cellulose and liberates nanocrystals, typically 10-20 nm in width
(Figure 9.29).
Grunert and Winter first reported on the use of bacterial CNXLs in polydimethyl-
siloxane (PDMS) polymers (72). In this work, CNXL from BC were derivatized by
trimethylsilylation with a view to improving the interfacial adhesion with PDMS. Con-
trol and surface modified CNXLs were thus blended with dimethylsiloxane and the
appropriate curing agents to develop films. Dynamic mechanical analysis (DMA) in
the - 60 ◦ C to 240 ◦ C range revealed a twofold increase in storage modulus of PDMS

300 nm

Figure9.29 Transmissionelectronmicrographofbacterialcellulosenanocrystals.(Withkind
permissionfromSpringerScience BusinessMedia:Journal of Polymers and the Environment,

Nanocomposites of cellulose acetate butyrate reinforced with cellulose nanocrystals, 10,
2002,27-30,M.GrunertandWinter,W.T.,Figure1.)

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