36D-4 |
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Y. RONG and J. L. Kokini. Dept. of Food Science, Rutgers, The State Univ. of New Jersey, 65 Dudley Rd., New Brunswick, NJ 08901-8520 Polymers with rigid or semi-rigid main chains can form liquid crystalline states in suitable conditions. The special molecular orientation of the liquid crystalline gives the polymers a wide range of stiffness, strength, and gas and water vapor resistance. Low molecular weight Dextran is a semi-rigid polymer which favors the formation of lyotropic liquid crystals in appropriate solvents. The molecular interactions of polymer chains in the solutions, especially the hydrogen bonding, affect the formation of the liquid crystalline phase. The objective of this study is to explore a food biopolymer that has liquid crystalline properties and use it as a model system to combine with other plastics to provide cost-effective films and other forms of packaging for products requiring high performance. Dextran with molecular weight 10,000 was used in the study. Critical concentration to form liquid crystalline state was determined by polarized light microscope. The rheological properties of dextran solutions were analyzed using Advanced Expansion Rheometric System (ARES). Differential Scanning Calorimetry (DSC) and X-ray scattering helped in identifying the liquid crystalline structure change in the solution. Our results showed that, in water and acetic acid, concentrated dextran solutions (>70% and >50%, respectively) demonstrated the liquid crystalline properties. The ARES measurements of the concentrated solutions showed very clearly three regions of flow behavior for liquid crystalline materials. The WAXS showed no real crystal formed in the samples and the refraction patterns suggested a special structure of the polymer solutions. The DSC investigations indicated that water was associated with dextran and different dextran-water environments may influence the motion of dextran and contribute to the melting behavior. The low molecular weight dextran demonstrated partial liquid crystalline properties in water and acetic acid. The liquid crystalline phase can be formed more easily in the system with more hydrogen bonding between polymer chains and the solvent.
Session 36D, Food Engineering: Rheology
2005 IFT Annual Meeting, July 15-20 - New Orleans, Louisiana |