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Sahin
polymer structure into these gaps can enhance both adsorption capabilities and gives
additional physical, chemical, thermal, or mechanical new properties to the clay.
Synthetic [29] or natural polymers can be used, but using natural or more biodegradable polymers can be more environmentally-friendly, and it also promotes reuse of
the final product in the preceding production steps. These natural polymers can be
chitosan [30], carboxymethyl cellulose [31], and other polymers derivatives as well
as activated biochars [26].
5.1 Clay
According to AIPEA, clay is a natural material that is made up of fine-grained
minerals that pass to plastic state in the appropriate water content and became rigid
when it is heated or dried [32]. Clay mineral particles, especially the ones that are
smectite, are not exactly at a crystalline state. Smectite crystal is better than normal
smectite at bringing the silicate layers together. If the montmorillonite particles are
examined under an electron microscope, it will be seen that it does not have a regular
shape like real crystalline, but it does have an irregular shape like a ripped paper. The
core of the particles is covered with irregular silicate layers, bent, and have worn edges
[32]. Between layer stacks, the particles have a weak contact at lots of points. At these
‘breaking points,’ the particles can be easily crashed, or the rheological attitudes may
be affected by the mechanic forces [33]. Layered silicates which are generally used at
nanocomposites are members of 2:1 structural pyrosilicate family. Crystalline cape
structure of 2:1 phyllosilicates is made of a structure that is compressed between
tetrahedral layers that join the sides of octahedral layers of magnesium or aluminum
hydroxides. The layer thickness is 1 nm, and the lateral diameter varies between
300 (A) and several microns. These layers get into stack form with the interlayers
that are formed between the layers, or the Van der Waals spaces which are known
as gates. The isomorphic replacement of Si
+4 with Al
+3 at tetrahedral layers and
Al
+3 with Mg
+2 at the octahedral layer generates an excessive negative charge. This
negative charge is balanced with the Ca
+2 and Na
+ cations which are placed between
the layers. This type of layered silicates is characterized by a middle-level surface
charge which can be named as cation exchange capacity (CEC), and this charge
varies from one layer to another (see Fig. 4) [32].
Because of the water absorbency property of silicate layers, these layers and waterrepellent polymer matrices cannot make good interaction. To avoid this, the clay
surfaces should be modified. To modify the clay, there are many types of mechanisms
which are getting into reaction with acids, the attachment of organic and inorganic
ions, ion exchange using organic and inorganic cations, plasma, ultrasound, burning,
etc. Modified clays are also used as rheological control factor, at removing organic
pollutants from water, air, and oil with adsorption, and at cosmetics and dyeing fields
[34]. The process which makes clays organophilic is done with changing inorganic
alkali cations at the clay surface with the desired organic cation. To make the middle
E. Emekdar and U. K. ¸
Sahin
polymer structure into these gaps can enhance both adsorption capabilities and gives
additional physical, chemical, thermal, or mechanical new properties to the clay.
Synthetic [29] or natural polymers can be used, but using natural or more biodegradable polymers can be more environmentally-friendly, and it also promotes reuse of
the final product in the preceding production steps. These natural polymers can be
chitosan [30], carboxymethyl cellulose [31], and other polymers derivatives as well
as activated biochars [26].
5.1 Clay
According to AIPEA, clay is a natural material that is made up of fine-grained
minerals that pass to plastic state in the appropriate water content and became rigid
when it is heated or dried [32]. Clay mineral particles, especially the ones that are
smectite, are not exactly at a crystalline state. Smectite crystal is better than normal
smectite at bringing the silicate layers together. If the montmorillonite particles are
examined under an electron microscope, it will be seen that it does not have a regular
shape like real crystalline, but it does have an irregular shape like a ripped paper. The
core of the particles is covered with irregular silicate layers, bent, and have worn edges
[32]. Between layer stacks, the particles have a weak contact at lots of points. At these
‘breaking points,’ the particles can be easily crashed, or the rheological attitudes may
be affected by the mechanic forces [33]. Layered silicates which are generally used at
nanocomposites are members of 2:1 structural pyrosilicate family. Crystalline cape
structure of 2:1 phyllosilicates is made of a structure that is compressed between
tetrahedral layers that join the sides of octahedral layers of magnesium or aluminum
hydroxides. The layer thickness is 1 nm, and the lateral diameter varies between
300 (A) and several microns. These layers get into stack form with the interlayers
that are formed between the layers, or the Van der Waals spaces which are known
as gates. The isomorphic replacement of Si
+4 with Al
+3 at tetrahedral layers and
Al
+3 with Mg
+2 at the octahedral layer generates an excessive negative charge. This
negative charge is balanced with the Ca
+2 and Na
+ cations which are placed between
the layers. This type of layered silicates is characterized by a middle-level surface
charge which can be named as cation exchange capacity (CEC), and this charge
varies from one layer to another (see Fig. 4) [32].
Because of the water absorbency property of silicate layers, these layers and waterrepellent polymer matrices cannot make good interaction. To avoid this, the clay
surfaces should be modified. To modify the clay, there are many types of mechanisms
which are getting into reaction with acids, the attachment of organic and inorganic
ions, ion exchange using organic and inorganic cations, plasma, ultrasound, burning,
etc. Modified clays are also used as rheological control factor, at removing organic
pollutants from water, air, and oil with adsorption, and at cosmetics and dyeing fields
[34]. The process which makes clays organophilic is done with changing inorganic
alkali cations at the clay surface with the desired organic cation. To make the middle