(159d) Supercritical Carbon Dioxide Processed Rubber-Clay Nanocomposites: Structure, Rheology and Mechanical Behavior

Styrene-butadiene based rubber materials are used in a variety of very important applications and industries such as the automotive and aerospace industries for their tunable elastomeric nature and abrasion resistance.  Despite its inherent strengths, there is much interest in improving many of its material properties such as tensile strength, flammability, gas permeability etc.  In this study we present a set of SBS-layered silicate nanocomposites produced with a novel supercritical carbon dioxide method that display improvements in the tensile strength and rheology, even at relatively low weight fractions (5wt%) of nanofiller. 

Styrene-Butadiene-Styrene triblock copolymer was processed with commercial clay (Cloisite 10A) at 5wt% loading using two different methods: solution blending and a novel, solvent-assisted, supercritical carbon dioxide(scCO₂) processing method^[1].  Use of a co-solvent is a convenient way to reduce processing temperatures, allowing us to avoid thermal degradation of clay modifier, and enabling direct comparison of our nanocomposite properties with solution blended analogs^[2]. Characterization of the rheological behavior, morphology (SAXD and TEM), and mechanical properties of both sets of nanocomposites was accomplished to investigate any improvements in the material properties due to scCO₂ processing.  Results indicate that the fast depressurization protocol used in scCO₂ processing delaminates a large fraction of individual platelets and small platelet stacks, as well as reduces the average large tactoid size significantly.   These effects are not seen in samples produced with solution blending.  The effect of this change in morphology is over a 120% increase in tensile modulus over pure SBS which is an additional 50% increase over what the solution blended nanocomposite displays.  Additionally an order of magnitude increase in low frequency storage modulus was observed for the supercritical processed composite that was not observed for the solution blended composite.  The simplicity of the process, the low cost of montmorillonite clays and low weight fraction requirements make the scCO₂ process a reasonable option for producing significant property enhancements in rubber materials. 

1. Horsch, S.; Serhatkulu, G.; Gulari, E.; Kannan, R. M. Polymer 2006, 47, (21), 7485-7496.

2. Manitiu, M.; Bellair, R.; Horsch, S; Gulari, E.; Kannan, R. M. Macromolecules 2008, 41, (21), 8038-8046