Environmental Engineering Reference
In-Depth Information
6.3.1.4
Nanocellulose
The hierarchical structure of cellulose allows the extraction of nanoparticles by
mechanical and chemical and/or enzymatic dissolution of its amorphous part
[11]. These nanoparticles are called cellulose nanocrystals or microfibrillated
cellulose (MFC) and can be obtained from various natural resources [12].
Defibrillation of individual microfibrils is obtained through mechanical shearing
actions followed by a strong acid hydrolysis treatment to longitudinally cut the
fibrils and change the size and aspect ratio of the cellulose-based nanoparticles
(Table 6.3).
These nanoparticles have many advantages, including good mechanical proper-
ties (Young's modulus around 100 GPa), abundance, low density, high surface
area (several hundred squared metres per gram) and biodegradability, and are
today used to produce bionanocomposites [13]. Their main drawback however,
which is related to their natural origin, is their hydrophilic nature, limiting the use
of these natural nanofillers in classical thermoplastic and/or thermosets resins. As
a result, many research programmes are now focusing on the surface modification
of these nanoparticles [14].
6.3.1.5
Bacterial Cellulose
Bacterial cellulose (BC) is an ex-cellular product of various bacteria, but only the
Gluconacetobacter produce enough cellulose to justify a commercial interest.
While it has a gel-like appearance with a solid content of <1%, it is almost pure
cellulose and contains no lignin and other extra compounds such as hemicellu-
loses and pectins. Apart from its purity, the second main advantage of BC is the
possibility to grow it to any desired shape and structure, offering remarkable
physical properties similar to those of nanocellulose particles from plant cellu-
lose. Production yields are still relatively low (around 10-40 g L -1 ) depending on
the bacteria and substrate used, keeping its price high [15]. However, BC is
already being used commercially in diet foods, filtration membranes, paper
additives and biomedical products and devices [16].
Table 6.3
Nanocellulose dimensions [13].
Cellulosic structure
Diameter (nm)
Length (nm)
Aspect ratio (L/D)
Microfibril
2-10
>10 000
>1000
Microfibrillated cellulose
10-40
>1000
100-150
Cellulose whisker
2-20
100-600
10-100
MCC
>1000
>1000
~1
 
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