2009 Annual Report
1a.Objectives (from AD-416)
The goal of this research is to develop new biobased materials from starch and new fundamental knowledge of their properties. Objectives of this work fall into three topic areas: materials development, molecular modeling and simulations, and analysis techniques.
1b.Approach (from AD-416)
Develop new biobased materials from starches with novel properties, utilizing the inherent properties of starch so that it is an active component rather than a low cost, biodegradable filler. Develop molecular modeling tools for use in rational design approaches. Develop novel sophisticated instrumental analytical techniques to characterize the structures and properties of multicomponent biobased materials.
Corrosion of metals is a serious and challenging problem faced by industries worldwide. Two important electrochemical parameters used to characterize corrosion protection are the corrosion rate (cr) and the polarization resistance (Rp). Water-dispersible bacterial exopolymer samples (EPS) were evaluated for Rp using SAE 1010 steel as the working electrode. Rp was determined by two independent methods - the Nyquist diagram from impedance and the Tafel plot from polarization studies. Spray coated samples had an average thickness of 50 nm and adhered to the substrate as determined by atomic force microscopy (AFM) and quartz crystal microbalance spectroscopy (QCM). The use of a polyelectrolyte solution to disperse the EPS in water resulted in thicker films with better surface coverage. A patent on strain-specific bacterial EPS for corrosion protection will be filed in July 2009. A breakthrough computational method using density functional (DFT) calculations enabled modeling studies on systems approximately three times larger than previous methods. As an example, the size of amylose fragments that can be routinely studied increased fewer than 10 residues to more than 20 residues. This has been applied to the study of starch double helix fragments (15-16 residues), and solvated maltose and cellobiose structures. Physical and thermodynamic properties of glucose epimers calculated with this approach as in good agreement with experimental data, confirming the validity of the improved method. DFT calculations provide highly accurate structural and energetic parameters for carbohydrates. The inclusion of explicit and implicit solvent models has provided optical, vibrational, energetic, chemical shift, and other structural properties of carbohydrates. Our constant energy density functional molecular dynamics study of different conformations of maltose and cellobiose has led to a better understanding of the structural fluctuations expected when studying dynamic structures in solution. Questions of the effect of solvent on conformation of larger amylose fragments are being addressed. Hydroxyl orientation and respective conformation is strongly solvent dependent, and becomes more important as the number of glucose residues increases. These studies are important to the understanding of material properties of starch like materials. Preliminary results show that the transition temperatures of responsive starch-based hydrogels can be modified by incorporating comonomers in the gel. Selection of appropriate comonomers and addition levels allow the transition temperature to be increased by approximately 10 degrees Celsius. The hydrogels show rapid response to temperature changes, and undergo large volume changes over narrow ranges of temperature. Control of the transition temperature (and range) is important for designing materials with specific and controlled responses for sensor technology and controlled release. These results enable industrial and academic scientists to design products and applications that utilize starch and other biobased polymers to replace petroleum-based products in a cost-competitive manner.
Flexible PLA/starch fibers. There has been considerable interest recently in developing corn starch-based fibers and films for use as biodegradable packaging and hygiene products. However, pure starch fibers tend to dissolve in water and are rather brittle. It was found that flexible, water resistant fibers could be formed by extruding and drawing blends of polylactic acid (PLA) with starch. Such blends have the potential to break down at controlled rates and may also have properties such as fiber softness and absorbency not found in pure PLA. These results should help companies and university scientists develop new starch-based materials for disposable consumer products to replace those derived from imported petroleum.
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Schnupf, U., Willett, J.L., Bosma, W.B., Momany, F.A. 2009. DFT Conformation and Energies of Amylose Fragments at Atomic Resolution Part I: Syn Forms of Alpha-Maltotetraose. Carbohydrate Research. 344(1):362-373.
Shogren, R.L. 2008. Starch-Poly(Hydroxylalkanoate) Composites and Blends. In Yu, L. Biodegradable Polymer Blends and Composites from Renewable Resources. Hoboken, NJ: J. Wiley & Sons. p. 211-226.
Finkenstadt, V.L., Liu, C., Cooke, P.H., Liu, L.S., Willett, J.L. 2008. Mechanical Property Characterization of Plasticized Sugar Beet Pulp and Poly(lactic acid) Green Composites using Acoustic Emission and Confocal Microscopy. Polymers and the Environment. 16(1):19-26.
Schnupf, U., Willett, J.L., Momany, F.A. 2009. DFT Conformation and Energies of Amylose Fragments at Atomic Resolution Part 2: “Band-flip” and “Kink” Forms of Alpha-Maltotetraose. Carbohydrate Research. 344(1):374-383.
Han, J., Heaven, M.C., Schnupf, U. 2008. Spectroscopy, Dissociation Dynamics and Potential Energy Surfaces for CN(A)-Ar. Chemical Physics. 128(22):224309.