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6.4.3 Solution Based Approaches: Wet Chemistry
Solution-based techniques are often preferred instead of melt mixing methods to
develop biobased nanocomposites since the thermal degradation temperatures of
biobased polymers are lower than their T g (Xiong et al. 2018). These techniques are
influenced by the physicochemical properties of the biomaterial solutions, and the
following points must be taken into account: the selection of the solvent, the polymer concentration/solvent ratio, the external conditions such as pressure, temperature, and moisture during the solvent evaporation (Armentano et al. 2018). In this
method, the selected polymer is dissolved in an appropriate solvent and then the
dispersed nano-fillers (in the same or a different solvent) are mixed with the polymer solution to form a homogeneous dispersion. The choice of the suitable solvent
provides a rapid exfoliation of the filler and the consecutive addition of polymer
solution to the dispersed nano-fillers provides a strong interaction between them.
Once the polymer chains are intercalated, the solvent within the interlayer of the
filler is displaced and adsorbed onto the surface. The driving force to intercalate the
biobased polymer into nano-filler layers from a solution is the entropy gained by
desorption of the solvent molecules (Ojijo and Sinha Ray 2013). After evaporation
of the solvent, the final intercalated structure executes a desired nanocomposite
structure (Ojijo and Sinha Ray 2013). The frequently used solution based approaches
include layer-by-layer (LbL) assembly, fiber spinning techniques, one-pot
approaches and emulsion polymerization (Li et al. 2015; Wang et al. 2017; Xiong
et al. 2018; Valencia et al. 2019).
The LbL assembly is used to prepare thin multilayers and coatings that allow the
control of the distribution, thickness and components of biomolecules in a single
layer with the help of interactions taking place at the interface, such as hydrogen
bonding, hydrophobic-hydrophobic interactions and electrostatic interactions (Ding
et al. 2017; Xiong et al. 2018; Valencia et al. 2019). A wide variety of biobased
nanocomponents can be assembled into different biobased polymers through specific deposition techniques such as spray coating, spin coating and immersive/dipcoating (Richardson et al. 2015). These systems also allow the pH control to regulate
the behavior of NPs into the polymer matrix.
One-pot directed assembly includes cast drying and vacuum-assisted filtration
techniques, which require a homogeneous mixture of the biopolymer solution and
nano-filler dispersion (Wang et al. 2014). In the vacuum-assisted filtration technique, the colloidal mixture of polymer solution and nano-filler dispersion is passed
through a nano-sized pore filter while avoiding the aggregation of these nano-fillers
with bonded biopolymers in the upper layer. In the solution-casting technique, the
final film solution is poured into the dishes or poured on the different surfaces with
different methods, such as spraying or bar coating to fabricate layered films after
solvent removal (Xiong et al. 2018). Both techniques produce biobased nanocomposites with high compatibility, homogeneity and improved properties compared to
LbL (Hu and Tsukruk 2015).
H. Cakmak and E. Sogut
6.4.3 Solution Based Approaches: Wet Chemistry
Solution-based techniques are often preferred instead of melt mixing methods to
develop biobased nanocomposites since the thermal degradation temperatures of
biobased polymers are lower than their T g (Xiong et al. 2018). These techniques are
influenced by the physicochemical properties of the biomaterial solutions, and the
following points must be taken into account: the selection of the solvent, the polymer concentration/solvent ratio, the external conditions such as pressure, temperature, and moisture during the solvent evaporation (Armentano et al. 2018). In this
method, the selected polymer is dissolved in an appropriate solvent and then the
dispersed nano-fillers (in the same or a different solvent) are mixed with the polymer solution to form a homogeneous dispersion. The choice of the suitable solvent
provides a rapid exfoliation of the filler and the consecutive addition of polymer
solution to the dispersed nano-fillers provides a strong interaction between them.
Once the polymer chains are intercalated, the solvent within the interlayer of the
filler is displaced and adsorbed onto the surface. The driving force to intercalate the
biobased polymer into nano-filler layers from a solution is the entropy gained by
desorption of the solvent molecules (Ojijo and Sinha Ray 2013). After evaporation
of the solvent, the final intercalated structure executes a desired nanocomposite
structure (Ojijo and Sinha Ray 2013). The frequently used solution based approaches
include layer-by-layer (LbL) assembly, fiber spinning techniques, one-pot
approaches and emulsion polymerization (Li et al. 2015; Wang et al. 2017; Xiong
et al. 2018; Valencia et al. 2019).
The LbL assembly is used to prepare thin multilayers and coatings that allow the
control of the distribution, thickness and components of biomolecules in a single
layer with the help of interactions taking place at the interface, such as hydrogen
bonding, hydrophobic-hydrophobic interactions and electrostatic interactions (Ding
et al. 2017; Xiong et al. 2018; Valencia et al. 2019). A wide variety of biobased
nanocomponents can be assembled into different biobased polymers through specific deposition techniques such as spray coating, spin coating and immersive/dipcoating (Richardson et al. 2015). These systems also allow the pH control to regulate
the behavior of NPs into the polymer matrix.
One-pot directed assembly includes cast drying and vacuum-assisted filtration
techniques, which require a homogeneous mixture of the biopolymer solution and
nano-filler dispersion (Wang et al. 2014). In the vacuum-assisted filtration technique, the colloidal mixture of polymer solution and nano-filler dispersion is passed
through a nano-sized pore filter while avoiding the aggregation of these nano-fillers
with bonded biopolymers in the upper layer. In the solution-casting technique, the
final film solution is poured into the dishes or poured on the different surfaces with
different methods, such as spraying or bar coating to fabricate layered films after
solvent removal (Xiong et al. 2018). Both techniques produce biobased nanocomposites with high compatibility, homogeneity and improved properties compared to
LbL (Hu and Tsukruk 2015).
H. Cakmak and E. Sogut