107
6.4.1 In-Situ Polymerization
In-situ polymerization method includes the polymerization of monomers in the
presence of the layered materials to begin the polymer formation (Unalan et al.
2014). First, the nano-fillers are swollen in a monomer solution, and then the polymerization is initiated by different polymerization techniques such as a suitable catalyst or organic initiator, diffusion, heat or radiation applications before the swelling
of the monomer (Koo 2006). The main disadvantage of this method is the phase
separation or sedimentation that may occur depending on the incompatible structure
of the organic polymer (proteins and polysaccharides) and the fillers (Chivrac et al.
2009). To overcome the problems of phase separation, the interaction between the
polymer solution and the filler is improved to stabilize the nanoparticle dispersions
by linking specific groups onto their surface (Althues et al. 2007).
6.4.2 Melt Processing
Melt processing is commonly used for thermoplastic polymers and is considered
economically viable and ‘green’ (solvent-free) techniques (Armentano et al. 2018).
In the melt processing method, the nano-fillers are incorporated into the molten
polymer, while being heated statically or under shear (Vaia et al. 1996; Vaia and
Giannelis 1997). The solvent-free structure (especially organic solvents) and compatibility with existing industrial processes (e.g. extrusion and injection molding,
etc.) make melt mixing process more advantageous compared to in-situ polymerization or solution-based techniques (Gutiérrez and Alvarez 2017b,c,d). In addition,
the melt intercalation can be used for the biopolymers that are not suitable for insitu polymerization.
Two main factors that control the level of dispersion of the nano-fillers within the
polymer matrix throughout the melt processing are: (1) enthalpy-driven interaction
between the polymer and the nano-filler, and (2) processing conditions (Ojijo and
Sinha Ray 2013). The polymer must be adequately compatible with nano-filler surface and there must be adequate enthalpic interaction between them to ensure a
favorable dispersion. The interaction between the NPs and the polymer depends on
the diffusion of polymer chains from the molten bulk through the filler layers, which
in turn effects the formation of biobased nanocomposites (Vaia and Giannelis 1997).
For the formation of biobased nanocomposites, the melt processing method has
a disadvantage, which is the polymer degradation due to the high temperature and
mechanical shear force. The processing instability results in the segmentation of
polymer chains with a reduction of molecular weight due to the thermal, oxidative
and hydrolytic degradations that occurs during processing. Therefore, the processing parameters should be optimized for the heat sensitive biobased polymers.
6 Functional Biobased Composite Polymers for Food Packaging Applications
6.4.1 In-Situ Polymerization
In-situ polymerization method includes the polymerization of monomers in the
presence of the layered materials to begin the polymer formation (Unalan et al.
2014). First, the nano-fillers are swollen in a monomer solution, and then the polymerization is initiated by different polymerization techniques such as a suitable catalyst or organic initiator, diffusion, heat or radiation applications before the swelling
of the monomer (Koo 2006). The main disadvantage of this method is the phase
separation or sedimentation that may occur depending on the incompatible structure
of the organic polymer (proteins and polysaccharides) and the fillers (Chivrac et al.
2009). To overcome the problems of phase separation, the interaction between the
polymer solution and the filler is improved to stabilize the nanoparticle dispersions
by linking specific groups onto their surface (Althues et al. 2007).
6.4.2 Melt Processing
Melt processing is commonly used for thermoplastic polymers and is considered
economically viable and ‘green’ (solvent-free) techniques (Armentano et al. 2018).
In the melt processing method, the nano-fillers are incorporated into the molten
polymer, while being heated statically or under shear (Vaia et al. 1996; Vaia and
Giannelis 1997). The solvent-free structure (especially organic solvents) and compatibility with existing industrial processes (e.g. extrusion and injection molding,
etc.) make melt mixing process more advantageous compared to in-situ polymerization or solution-based techniques (Gutiérrez and Alvarez 2017b,c,d). In addition,
the melt intercalation can be used for the biopolymers that are not suitable for insitu polymerization.
Two main factors that control the level of dispersion of the nano-fillers within the
polymer matrix throughout the melt processing are: (1) enthalpy-driven interaction
between the polymer and the nano-filler, and (2) processing conditions (Ojijo and
Sinha Ray 2013). The polymer must be adequately compatible with nano-filler surface and there must be adequate enthalpic interaction between them to ensure a
favorable dispersion. The interaction between the NPs and the polymer depends on
the diffusion of polymer chains from the molten bulk through the filler layers, which
in turn effects the formation of biobased nanocomposites (Vaia and Giannelis 1997).
For the formation of biobased nanocomposites, the melt processing method has
a disadvantage, which is the polymer degradation due to the high temperature and
mechanical shear force. The processing instability results in the segmentation of
polymer chains with a reduction of molecular weight due to the thermal, oxidative
and hydrolytic degradations that occurs during processing. Therefore, the processing parameters should be optimized for the heat sensitive biobased polymers.
6 Functional Biobased Composite Polymers for Food Packaging Applications