VA Polytechnic Institute & State University
NER: Process for Increasing the Exfoliation and Dispersion of Nano-particles into Polymeric Matrices Using Supercritical Carbon Dioxide
Background: All the promises and claims that the addition of nano-particles to polymer matrices will miraculously lead to exceptional mechanical, barrier, electrical, and thermal stability properties have not been completely fulfilled because the improvements in properties seem to plateau when reaching levels of about 4 wt%. Only for nylon 6 have levels of 7-wt% been reached before the properties plateau because of hydrogen bonding between the amide groups and the nano-clay particles. The plateau of properties is attributed to the inability to keep the nano-particles exfoliated as the concentration is increased. The three most common methods used to synthesize nano-clay composites, i.e. intercalation of a suitable monomer and subsequent in situ polymerization, intercalation of polymer from solution, and polymer melt intercalation, have not been successful in leading to loading levels greater than about 4 wt%. However, reaching nano-clay particle levels of the order of 10 wt% could lead to a modulus increase of the order of a factor of 5 or more rather than a factor of 1.5 to 2.0(at 4 wt %).
Goal: The Goal of this research is to explore the possibility of using supercritical carbon dioxide (sc CO2 ) to increase the level of nano-clay particles which remain exfoliated at levels greater than 5 wt% and preferably as high as 10 wt%. Several previous studies provide evidence that sc CO2 can swell the layered silicates, which thereby may enhance the ease of polymer intercalation into the galleries of the clay. A continuous method is proposed for swelling nano-clays and exfoliating them with sc CO2 and then subsequently injecting the mixture into a molten polymer stream. Furthermore, it is expected that because sc CO2 is highly soluble in a number of polymers it will aid dispersion of the exfoliated clay particles and at same time lower the viscosity of the melt. Once mixing is complete sc CO2 can be extracted from the system leaving the particles dispersed within the thermoplastic. In addition to using microscopy and rheological techniques to identify the degree of exfoliation, mechanical properties of thermoplastic composites will be determined.
Intellectual Merit: The concept of a novel, high risk, environmentally benign process for exfoliating and dispersing nano-particles into polymer melts will evolve from this work which should be applicable to a range of nano-particle systems beyond nano-clays and toother polymer matrices.
Broader Impact: The approach proposed here is novel and should lead to the filing of a patent application. It has the potential to lead to a signficant increase in the level of nano-partilces and, hence, a significant increase in properties. The increase in properties will extend the range of use of nano-composites especially in the automotive industry and rapid prototyping. The project will initially be one-year duration and, hence, the education of students will have to be planned carefully. However, at least one undergraduate (from an underrepresented group) and a graduate student, who are part of our polymer program, will be exposed to the field of nano-composites and the use of environmentally benign methods for generating improved materials. Furthermore, as part of an interdisciplinary research team, they will learn the importance of a cooperative team effort in solving technical problems.
Research Theme (Manufacturing Process): A novel environmentally clean manufacturing process is proposed for generating thermoplastic nano-composite materials with signficantly improved properties.
