Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 4/1/2004
Publication Date: 6/6/2004
Citation: Sessa, D.J., Selling, G.W. Mechanical properties of sodium dodecyll sulfate-modified zein. Meeting Abstract.
Technical Abstract: Zein, the predominant protein in corn, may be used as an alternative source for various commercial plastics. To alleviate brittleness in plasticized zein, plasticizers such as triethylene glycol (TEG) and water have been used. When zein is blended with water and subjected to heat and shear in a torque rheometer, zein aggregates giving rise to a rapid increase in torque which can be detrimental in industrial processes such as extrusion. Sodium dodecyl sulfate (SDS), a known protein denaturant, will be investigated for use to control viscosity increases of zein when subjected to torque rheometry. Because extrusion is the standard method for processing plastics our second objective is to assess the mechanical properties of extruded, SDS-modified zein. Freeman grade F4000, with a dry-basis protein content of 93.14%, was subjected to torque rheometry on a Haake Fison, Rheocord 90, torque rheometer equipped with high shear roller rotors was used where initial temperature was varied between 90 and 105 degrees C with rotor speed set at 50 rpm. Our findings with torque rheometry show that water alone allows zein to aggregate in approximately 1 min. as evidenced by a rapid torque rise while varied combinations of TEG and water delayed the increase to 2 to 4 min. into the run. When SDS is added to zein in combination with water and TEG, the time at which the viscosity rise takes place is significantly delayed. A linear relationship was obtained when the onset time of the torque is plotted against the amount of SDS added. For our second objective, we blended zein with 10% TEG, 7% added water and varying amounts of SDS in a Hobart mixture prior to extruding on a Brabender Model PL2000 single screw, 30:1 L/D, laboratory extruder, fitted with a feed-type screw configuration and a 2 mm die. The resulting rope was pelletized where half the weight of pellets was subjected to freeze-grinding in a Wiley mill and the resulting powder subjected to compression molding on a Carver Press while the other half was re-extruded through a 2 cm. ribbon die. Mechanical properties of SDS-modified zein tensile bars from the Carver press and those cut in a parallel direction from the ribbon die, evaluated after storage for 1-week at either 50 or 70% RH on an Instron with a cross head speed of 1 cm/min., diminished in strength with increased amounts of SDS. Our results with torque rheometry and mechanical properties of extruded SDS-modified zein indicate that SDS is acting as a plasticizer. Models were developed to explain the SDS-modified zein pheonomena.