113
can increase the surface roughness depending on the longitudinal distribution of the
fillers (Rhim 2011; Gutiérrez and González 2017; Gutiérrez et al. 2018b). Such an
increase in surface roughness leads to a increase in the haze of the final material and
changes the surface wettability attributes (Peacock and Calhoun, 2012). In addition,
the chemical structure of the filler has a great effect on the surface roughness. For
example, porous fillers such as zeolites or fillers that have an affinity for water can
change the absorption behavior at the solid/liquid interface (Vartiainen et al. 2010).
The increase in the roughness, which is described by alterations in the friction coefficient, also depends on the concentration of filler and the type of biobased polymer.
The surface factors of biopolymers can also play an important role in different
situations, such as wettability, surface mobility, electrical charge, crystallinity and
the modulus associated with various reactions. For example, in response to a hydrophobic environment, molecules with low energy (more hydrophobic) can move to
the surface and reduce the interfacial energy. On the other hand, in response to an
aqueous environment, the surface can reverse its structure to interact with the polar
water molecules (Rastogi and Samyn 2015). The surface properties of biopolymers
can thus influence the barrier and mechanical properties. The surface hydrophobicity is sometimes a requirement to obtain a barrier against water vapor and water
resistance. The incorporation of low surface energy chemicals or the modification of
surface properties by incorporating nano-fillers are the easiest ways to improve the
hydrophobicity of an existing surface (Li et al. 2010).
6.5.6 Functional Properties
The term ‘functional nanocomposite’ is generally associated to a polymer or a polymer mixture containing an active nanostructured material, which confers an activity
such as antimicrobial activity or oxygen-scavenging capacity, to improve the quality
and safety of packaged food products (Rhim et al. 2013). These types of nanocomposites are of great interest due to their active properties, while remaining adequate
structural integrity. In addition to being a reinforcing agent, nano-fillers can be used
as carriers of functional additives, such as antimicrobials, antioxidants, minerals,
probiotics and vitamins, and can also be used in controlled release from packaging
materials through encapsulating them (Honarvar et al. 2016; Gutiérrez 2017b). The
functional properties of nanocomposites for food packaging applications are summarized in Fig. 6.3. Biobased polymers enriched with nano-fillers such as Ag, ZnO,
TiO 2 and magnesium oxide have the potential to inhibit various microorganisms and
can retard the oxidation (Huang et al. 2015). Nano-Ag has been accepted as one
of the most powerful agents showing intense toxicity for a wide variety of microorganisms (Kanmani and Rhim 2014). The proposed mechanism for Ag activity
includes the interaction of Ag NPs with phosphorus and sulfur- containing proteins
to prevent DNA replication, followed by cell death (Kanmani and Rhim 2014).
Nano-fillers readily adhere to a wide range of biological molecules with respect to
high surface-to-volume ratio, thus improving the effectiveness of these molecules
when exposed to the substance on which it is required to act (Honarvar et al. 2016).
6 Functional Biobased Composite Polymers for Food Packaging Applications
can increase the surface roughness depending on the longitudinal distribution of the
fillers (Rhim 2011; Gutiérrez and González 2017; Gutiérrez et al. 2018b). Such an
increase in surface roughness leads to a increase in the haze of the final material and
changes the surface wettability attributes (Peacock and Calhoun, 2012). In addition,
the chemical structure of the filler has a great effect on the surface roughness. For
example, porous fillers such as zeolites or fillers that have an affinity for water can
change the absorption behavior at the solid/liquid interface (Vartiainen et al. 2010).
The increase in the roughness, which is described by alterations in the friction coefficient, also depends on the concentration of filler and the type of biobased polymer.
The surface factors of biopolymers can also play an important role in different
situations, such as wettability, surface mobility, electrical charge, crystallinity and
the modulus associated with various reactions. For example, in response to a hydrophobic environment, molecules with low energy (more hydrophobic) can move to
the surface and reduce the interfacial energy. On the other hand, in response to an
aqueous environment, the surface can reverse its structure to interact with the polar
water molecules (Rastogi and Samyn 2015). The surface properties of biopolymers
can thus influence the barrier and mechanical properties. The surface hydrophobicity is sometimes a requirement to obtain a barrier against water vapor and water
resistance. The incorporation of low surface energy chemicals or the modification of
surface properties by incorporating nano-fillers are the easiest ways to improve the
hydrophobicity of an existing surface (Li et al. 2010).
6.5.6 Functional Properties
The term ‘functional nanocomposite’ is generally associated to a polymer or a polymer mixture containing an active nanostructured material, which confers an activity
such as antimicrobial activity or oxygen-scavenging capacity, to improve the quality
and safety of packaged food products (Rhim et al. 2013). These types of nanocomposites are of great interest due to their active properties, while remaining adequate
structural integrity. In addition to being a reinforcing agent, nano-fillers can be used
as carriers of functional additives, such as antimicrobials, antioxidants, minerals,
probiotics and vitamins, and can also be used in controlled release from packaging
materials through encapsulating them (Honarvar et al. 2016; Gutiérrez 2017b). The
functional properties of nanocomposites for food packaging applications are summarized in Fig. 6.3. Biobased polymers enriched with nano-fillers such as Ag, ZnO,
TiO 2 and magnesium oxide have the potential to inhibit various microorganisms and
can retard the oxidation (Huang et al. 2015). Nano-Ag has been accepted as one
of the most powerful agents showing intense toxicity for a wide variety of microorganisms (Kanmani and Rhim 2014). The proposed mechanism for Ag activity
includes the interaction of Ag NPs with phosphorus and sulfur- containing proteins
to prevent DNA replication, followed by cell death (Kanmani and Rhim 2014).
Nano-fillers readily adhere to a wide range of biological molecules with respect to
high surface-to-volume ratio, thus improving the effectiveness of these molecules
when exposed to the substance on which it is required to act (Honarvar et al. 2016).
6 Functional Biobased Composite Polymers for Food Packaging Applications