1.4 Nanofillers for Bionanocomposites
11
Fig. 1.5 Schematic diagram of the modification of layered silicates by ion exchange reactions [81]
In order to make nanoclays miscible with hydrophobic polymers, their surface condition must be modified from hydrophilic to organophilic feature using ion-exchange
reactions according to a typical method where alkali-cation ions are substituted for
organic compounds like alkylammonium ions, sulfonium and phosphonium (Fig. 1.5)
[78, 79].
These organic surfactants can minimise surface energy of inorganic host and
enhance clay wettability by using hydrophobic polymers with increasing the interlayer spacing. In addition, functional groups of organic compounds have also been
utilised to improve the bonding between layered silicates and polymers [80, 81].
The chain length of surfactants and charge density of clays are known to play an
important role in controlling the interlayer spacing between clays. In general, the use
of a long molecular chain in combination with high charge density tends to increase
the interlayer spacing (Fig. 1.6) [79, 82].
Wang et al. [83] prepared organoclays with different chain lengths of alkylammonium. An increase in interlayer spacing values was achieved with increasing
the length of alkylammonium. It was reported that the interlayer spacing of MMT
modified with octadecylammonium was increased from 1.36 to 2.47 nm.
Fig. 1.6 Alkylammonium chain aggregation models [76]
11
Fig. 1.5 Schematic diagram of the modification of layered silicates by ion exchange reactions [81]
In order to make nanoclays miscible with hydrophobic polymers, their surface condition must be modified from hydrophilic to organophilic feature using ion-exchange
reactions according to a typical method where alkali-cation ions are substituted for
organic compounds like alkylammonium ions, sulfonium and phosphonium (Fig. 1.5)
[78, 79].
These organic surfactants can minimise surface energy of inorganic host and
enhance clay wettability by using hydrophobic polymers with increasing the interlayer spacing. In addition, functional groups of organic compounds have also been
utilised to improve the bonding between layered silicates and polymers [80, 81].
The chain length of surfactants and charge density of clays are known to play an
important role in controlling the interlayer spacing between clays. In general, the use
of a long molecular chain in combination with high charge density tends to increase
the interlayer spacing (Fig. 1.6) [79, 82].
Wang et al. [83] prepared organoclays with different chain lengths of alkylammonium. An increase in interlayer spacing values was achieved with increasing
the length of alkylammonium. It was reported that the interlayer spacing of MMT
modified with octadecylammonium was increased from 1.36 to 2.47 nm.
Fig. 1.6 Alkylammonium chain aggregation models [76]