Characterization of Quasi-static Mechanical Properties of Polymer Nanocomposites Using a New Combinatorial Approach

Recently, it has become very important to rapidly characterize the processing-structure-property relationships in polymer nanocomposites using minimal quantities of expensive nanoscale fillers. To address this issue, we present a new combinatorial approach developed for characterizing the variation in mechanical properties as a function of filler composition in polymer nanocomposites. The fundamental basis for the combinatorial approach is the generation of compositional gradients through transient operation of a twin-screw extruder (TSE). The compositional variation in the specimens could be rapidly predicted a priori using a convolution process model and was verified a posteriori using pycnometry measurements and thermogravimetric analysis. To characterize the quasi-static mechanical properties along the compositional gradient, sub-scale specimens that are proportional in size to ASTM type I specimens but with a gage section that is a factor of 10 smaller, were tested using a microtensile tester. The properties of the sub-scale specimens processed in the combinatorial approach correlated well with those of sub-scale specimens of similar composition processed in steady-state, thereby indicating that the properties were unaffected by the transient operation of the TSE. Furthermore, the quasi-static mechanical properties of the steady-state ASTM type I standard specimens were compared with those of the sub-scale specimens to determine the effect of specimen size. The results were nearly identical, except the increased size of the ASTM type I standard specimens resulted in substantial reductions in ductility that are most likely due to an increase in the number of processing-related defects.