Submitted to: Polymers for Advanced Technologies
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/2/2007
Publication Date: 3/3/2007
Citation: Orts, W.J., Nobes, G.A., Glenn, G.M., Gray, G.M., Imam, S.H., Chiou, B. 2007. Blends of starch with ethylene vinyl alcohol copolymers: effect of water, glycerol and amino acids as plasticizers. Polymers for Advanced Technologies. 18 (8): 629-635. (2007) Interpretive Summary: Production of biodiesel from vegetable oil for transportation fuel has increaseed significantly over the past 5 years. One by-product output of processing this ag-derived is glycerol, for every 10 kilograms of fuel, one kg of glycerol is produced. To offset this potential over-production of glycerol, and to prevent a negative cost-impact of lower prices, new uses are required for glycerol such as in plastics as a plasticizing/ softening agent. A series of blends of thermoplastic starch with poly(ethylene-co-vinyl alcohol) copolymer (EVOH) were melt extruded with water/glycerol as plasticizer. The end-use mechanical properties of these biodegradable plastics were then measured. Plasticized starch-EVOH blends stored at 0% and 50% relative humidity changed significantly over time. The addition of amino acids as additional plasticizers provided relatively minor, but significant changes in mechanical properties with time. The long-term effect of these plasticizers on end-use properties were evaluated. Glycerol has a significant impact on improving starch-blend properties.
Technical Abstract: A series of blends of thermoplastic starch with poly(ethylene-co-vinyl alcohol) copolymer (EVOH) were melt extruded with water/glycerol as plasticizer and than a series of amino acid additives. The biggest factor in end-use mechanical properties proved to be the relative humidity (RH) during storage. Plasticized starch-EVOH blends stored at 0% and 50% relative humidity changed significantly over time, with, for example, the tensile strength of the glycerol-plasticized blend increasing from 4.7 MPa to 26.3MPa over 8 weeks when maintained at 0% RH. In contrast, the tensile strength of this same sample stored at 75% RH remained unchanged for 8 weeks. Amino acids provided relatively minor, but significant changes in mechanical properties with time. Based on tensile strength, elongation-to-break, and modulus, b-alanine, sarcosine, and L-proline were more effective than glycerol at maintaining strong flexible blends. Increases in crystallinity and changes in morphology with time, as described by modulated DSC were correlated to these changes in mechanical properties.