Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 8/29/2010
Publication Date: 10/13/2010
Citation: Mukhopadhyay, S., Onwulata, C.I. 2010. Thermoformed protein based composites in presence of organic acids [abstract]. Protein and Starch based Biopolymer Session 4:31. Interpretive Summary:
Technical Abstract: World industrialization has generated substantial quantities of petroleum-based plastics over many years, which are non biodegradable. There is a growing demand for the use of renewable agricultural sources to develop eco-friendly biobased composites. Agriculture-sourced proteins and starches are both renewable, biodegradable and can be thermoformed into bioplastics. However, starch and protein are often difficult to process in high throughput plastic polymer molders due to their high moisture content, low melt properties, and limited cross linking ability. These materials degrade above 140C, and exhibit discoloration and low mechanical strength. In this study, we investigated the effects of the presence of acetic acid (AA), citric Acid (CA) and alkyl citrate analogs such as trimethyl citrate (TMC) and triethyl citrate (TEC) for improved cross linking and mechanical properties as evidence of improved composite properties. Initial experiments was conducted in a torque rheometer with 40% whey protein isolate (WPI) and 30% corn starch (CS) and an aqueous solution of the organic acids in concentrations ranging from 0 to 30% (w/w). Torque rheometry results indicated optimum storage modulus, and flexibility of composite material at 15% organic acid concentration. Subsequently, we evaluated the properties of the CS and WPI composites with organic acids concentration of 15% using a twin-screw extrusion process. The CS and WPI (1:1 w/w) with organic acids (15% w/w) were processed using a ZSK30 twin screw extruder (Krupp, Werner & Pfleiderer Company, Ramsey, NJ) with nine zones and length to diameter ratio of 30:1. The temperature profile for extrusion was: 32, 47, 40, 82, 100, 120, 130, 90, and 80C. The extruded composite pastes were molded into ASTM D4065 strips in a Carver press for 30 min at 121C. The extruded composites color was dependent on the type of test organic acid. Though the dynamic mechanical properties were affected by high compounding moisture contents of 29% (AA), 24 % (CA), 24% (TEC), 12% (TEC) and 33% (control), product flexibility increased as moisture decreased after molding in order: TEC > CA > TMC > AA. The DSC melt property of composites increased sharply in the presence organic acids (CA 112C; AA 119C; TEC 130C; TMC 157C), compared to the control (110C) indicating cross linking and formation of new composite material. Mechanically, the storage modulus increased appreciably due to cross linking in the presence of alkyl citrate analogs. The storage modulus of composite made with TEC increased (327 MPa) compared to the control (159 MPa), reflecting more than 200% improvement in mechanical strength in the presence of TEC; a strong evidence of cross linking.