Clay/Polymer Nanocomposites: Brief Outline
SUMMARY:nanocomposite and nanomaterial as nanotechnology example
In the field of
nanotechnology, the synthesis and applications of
polymer nanocomposites are an important and strategical field of nanomaterial science.
Polymer nanocomposites respresent a new class of material alternative to conventional filled polymers.
In this new class of material,
nanosized inorganic filler (at least one dimension)
are
dispersed in polymer matrix offering tremendous
improvement in performance properties
of the polymer.
Typically smectite-type clays are used as fillers. Montmorillonite and hectorite
layered structure are dispersed in polymer matrix.
According with the bonding
scenariuos between polymer chain and silicate layer, new material shows excellent mechanical properties compared to neat polymer:
superior mechanical characteristics higher tensile strength (40% increase), heat resistance and chemical resistance.
It´s worthwhile to note these results are achieved with only 0.1-10 %vol. addition clay nanosized.
It´s clear that polymer/clay nanocomposites are a typical example of nanotechnology: embedding nanoclay structure in polymer matrix we obtain a new class of materials.
Unlike to other nanotechnologies this material has an immediately applications and commercial
development.
Polymer nanocomposites history...
The true start of polymer nanocomposites history is in
1990 when Toyota first used clay/nylon-6 nanocomposites for Toyata
car in order to produce timing belt covers.
After that other automotive application was implemented:
-Mitsubishi´s GDI cover clay/nylon-6 nanocomposites engines;
-General Motors clay/polyolefin nanocomposites step assistant GMC Safari and
Chevrolet Astro vans.
The potential applications go beyond automotive industry. One of the most
promising is
drink packaging application considering
increased barrier properties
of polymer clay nanocomposites. It´s easy understand the commercial and technical importance
of this field.
FABRICATION TECHNIQUES: polymer clay nanocomposites
In order to disperse clay layers into polymer matrix it´s very important considering
polymer-clay
compatibility.
This means to provide organophilic character to the clay by a
pretreatment in order
to successful formation of polymer-clay nanocomposite.
In the case of hydrophilic polymers and silicate layers pretreatment is not necessary.
Most polymers are hydrophobic and are not compatible with hydrophilic clays.
Pretreatment involved only clays in order to obtain organic compatibility.
Organophilic clay can be formed from normally hydrophilic clay by means amino acids,
organic ammonium salts, or tetra organic phosphonium solution.
Well established methods are:
-Solution induced intercalation;
-In situ polimerization;
-Melt processing;
Solution induced intercalation method consists to solubilize polymer in an organic
solvent, then the clay is dispersed in the obtained solution and subsequently either the
solvent is evaporated or the polymer precipitated.
This approach leads to poor clay dispersion, besides other problem like: high costs of
solvents required, large amount of solvent needs to be used to achieve appreciable filler dispersion,
technical phase separation problem, health and safety problem.
Solvent route technique is used in the case of water-soluble polymers for clear reasons.
In situ polimerization consists to disperse clay layers into matrix by polimerization, mixing
the silicate layers with the monomer, in conjunction with the polymerization initiator and/or
the catalyst.
In the third technique the silicates layers are directly dispersed into the polymers during the melt.
In order to use this method, the silicates should need to be previously surface treated through
the organo-modification like previously mentioned.
DISCUSSION
When one talking about nanocomposites, underlining extraordinary improvements of material properties.
In reality, mechanical properties in the best clay/polymer nanocomposites are much lower than
conventional fiber reinforced composites.
Only in the low filler range 4% nanocomposites show better mechanical performance.
To obtain higher performance we have to add more filler, but, great physical-technological problem occurs.
Increasing reinforcing load increase the surface area of the silicate-filler, leading to insufficient
polymer molecules to wet enormous clay surface.
The main advantage of nanosized filler
become high hurdle to overcome.
Several difficulties facing clay-polymer nanotechnology especially fabrication problem:
-Difficulty in application to thermosetting polymers;
-Thermally instability of organoclay.
Clearly, the major difficulties of the development of clay/polymer nanocomposites are caused to
the poor understanding the primary mechanisms of nano-world.
Considering significant progress in the development of clay-polymer nanocomposites has been
made over the past last decade probably is not so long the way from the end of tunnel!!
