Nanocomposites – From Research to Reality
Although plastic nanocomposites have been available since 1995 in Japan, the year 1999 will mark their emergence to widespread commercial availability worldwide. The most advantageous nano-particles have been identified and compatibilized for use into a wide array of plastic matrices. A number of techniques for nano- particle dispersion have been developed & proven.
In the 50's, researchers at Toyota Central R&D Laboratories embarked upon a project to apply the concept of developing nanocomposites. Their goal was limited to creating under-the-hood automotive parts that were heat resistant, but lighter than metal. Their work yielded something rare in the research arena, short-term success in the immediate goal & long term potential far exceeding their expectations.
During the decade of the 90's, after millions of research hours & millions of dollars, plastic nanocomposites were ready for prime time.
What is a Polymer Nanocomposite (PNC)?
In the context of plastics, a nanocomposite is a near-molecular blend of resin molecules & nano-scale particles.
A nano-scale particle is a material with at least one dimension in the nanometer range. Conventional plastic composites can now contain functional fillers of around 0.5 micron in size. A nanoparticle is 50,000 times smaller in at least one dimension.
In this case size does not matter. Many physical & gas barrier properties are greatly enhanced when these infinitesimal particles interact at the molecular level.
Nanoparticles of Interest
For plastics applications, nano-scale particles are most appropriate if they are sheet-like or platy in structure. Once the particle has been identified, it must be compatibilized to disperse in the given polymer matrix. Researchers have keyed in
on four silicates as potential nanoscale particles.
• Hydrotalcite • Octasilicate • Mica fluoride • Montmorillonite
The first two, hydrotalcite & octasilicate have limitations, both from a physical & cost standpoint. The next two are promising candidates for developing PNCs. A number of factors combine to generate interest in nanocomposites technology using montmorillonite.
• Low loading level • Transparency • Ease of incorporation • Safety • Synergy with other additives • Low cost
Nanocomposites typically contain 2-10% loadings on a weight basis, yet property improvements can equal & sometimes exceed traditional composites containing 25 to 35% mineral fillers / glass. Machine wear is reduced & processability is claimed to better. Because minerals & glass fibers have densities twice that of polymers weight sensitive applications, such as automotive parts, offer attractive opportunities.
Montmorillonites have a dimension below the visible light wavelength. Properly oriented, the particles are transparent, a critical requirement for barrier packaging films. The particles are tough. They can withstand solvents; polymerization temperatures and shear during melt compounding. Consequently, they can be processed without concerns of degradation.
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