Civil Engineering Reference
In-Depth Information
Freeze drying (FD)
•
Frozen suspension in very low temperature (around-65°C)
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Transfer suspension to freeze dryer for lyophilisation
(Beck et al., 2012)
Supercritical drying (SCD)
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Dehydration of suspension with non-aqueousmedia like ethanol
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Repacement of non-aqueousm with liquid CO2
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Pressurizing and heating of liquid C02 and cellulose mixture to the suspercritical conditions
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Elimination of liquid CO2 by decompression it to the atmosphere
(peng et al., 2012)
Atomization drying (AD)
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Spraying suspension
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passing material through a nozzle
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drying by hot air low.
(Quievy et al, 2010)
Spray drying (SD)
•
Pre-concentration of initial liquid to appropriate viscosity
•
Pumping liquid through atomizer
•
Dehydration process in stream of hot gas
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Powder separation
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Cooking
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Packaging
(Peng et al., 2012)
Figure 11.19
Various nanocellulose drying processes steps.
h e particular feature of crystallization at temperatures lower than the freezing tem-
perature of water increases the rate of freezing, thus preventing aggregation [148]. Flow
rate of suspension and temperature of hot air are some of the key factors in this context
[149]. In addition, parameters such as concentration and feed rate of liquid as well as
gas l ow rate have ef ects on this process [143]. Oven drying, freeze drying and atomi-
zation process [149], spray drying and supercritical drying [150] have been utilized by
researchers to evaluate their ef ects on properties of resultant NFC.
11.6
Modii cations of Nanocellulose
Modii cation of NFC has received signii cant interest from the scientii c community.
It is envisaged to improve the hydrophilic nature of cellulose in polar and nonpolar
environments, thus, increasing compatibility with a wider variety of matrices. Numbers
of reactions have been performed to modify the surface properties of the cellulose
[151, 152] including corona or plasma discharges [153], surface derivatization [154],
grat copolymerization [155] or application of surfactant [156, 157]. Some approaches
aiming to hydrophobize nanocellulosic materials are briel y discussed in the following
sections.
