Submitted to: American Institute of Chemical Engineers Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 5/17/2004
Publication Date: 11/12/2004
Citation: Chiou, B., Yee, E., Glenn, G.M., Wood, D.F., Orts, W.J., Imam, S.H. 2004. Bio-based nanocomposites produced from native wheat starch and montmorillonite nanoclays. American Institute of Chemical Engineers Annual Meeting, Austin, Texas, November 7-12, 2004. Paper No. 357D (Abstract).
Technical Abstract: We produced biopolymer nanocomposites with improved water resistance and mechanical properties by incorporating montmorillonite nanoclays into native wheat starch formulations using a twin-screw extruder. We first examined the rheological properties of different modified and unmodified nanoclays before and during gelatinization of the starch-nanoclay composites. Frequency sweep and creep measurements of the most hydrophilic nanoclay, Cloisite Na+, mixed with wheat starch and water showed the samples formed a more gel-like material than the samples containing the more hydrophobic, modified nanoclays. The Cloisite Na+ samples had elastic moduli that were nearly frequency independent at the lower frequencies and had much lower creep compliance than the other nanoclay samples. We also monitored the evolving elastic modulus during gelatinization of the nanoclay composites. The Cloisite Na+ samples had the highest elastic modulus peak and retained the highest modulus values during the gelatinization process. These data indicated that the Cloisite Na+ nanoclays became better dispersed and intercalated in the starch matrix than the other nanoclays. From these rheological studies, we chose the Cloisite Na+ nanoclay for producing the biopolymer nanocomposites using the twin-screw extruder. X-ray diffraction studies on the extruded samples showed that the solid to liquid ratio had the largest effect on the intercalation of the nanoclays. A smaller solid to liquid ratio resulted in lower nanoclay diffraction peaks. When we increased the specific mechanical energy by increasing the screw speed, the nanoclay became less intercalated and had higher diffraction peaks. This may be due to lower residence times at the faster screw speeds. We then extruded the nanoclay samples at low solid to liquid ratios (1.5:1 to 2:1) and low screw speed (30 rpm) to produce intercalated nanoclay composites with improved water resistance and mechanical properties. Adding 2.5 wt% Cloisite Na+ resulted in a 27% reduction in water absorbance, whereas adding 7.5 wt% nanoclay resulted in a 40% reduction in water absorbance. Moreover, the flexural modulus increased in value and the stress and strains at yield decreased in value for higher nanoclay concentrations.