Nano fillers provide an excellent opportunity in plastics as usage of very small dosage of about 1-5% leads to improvement in properties, barrier properties as well as mechanical strength. However nano fillers adversely affect the flow behavior of polymers. Also, it is not easy to incorporate nano fillers even at such low levels because of poor dispersibility.
A research group at Virginia Tech in USA has developed a method for improving the dispersion, or exfoliation, of individual nano particles into polymers. Using supercritical carbon dioxide, the researchers are able to exfoliate nano particles at higher concentrations, leading to further enhancement of mechanical properties than presently possible using just mechanical mixing. Carbon dioxide is soluble in a lot of polymers and it is a benign, natural substance. It attaches to the particles so they don't attach to each other, and helps disperse the particles throughout the polymer.
The changed flow behavior is an indication that the material will exhibit improved mechanical properties. Nano clay particles well dispersed in polypropylene and polycarbonate plastics tend to promote polymer chain orientation, or alignment, and then retard relaxation or loss of orientation. The result is they make the polymer chains act like longer or higher molecular weight chains. The material is stronger than one would expect given the size of a polymer chain. |
