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United States Department of Agriculture

Agricultural Research Service

Research Project: MODIFICATION OF NATURAL POLYMERS BY NOVEL PROCESSES

Location: Plant Polymer Research

Title: Rheological properties of reactive extrusion modified waxy starch and waxy starch-polyacrylamide copolymer gels

Authors
item XU, JINGYUAN
item FINKENSTADT, VICTORIA

Submitted to: Starch
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 1, 2013
Publication Date: December 10, 2013
Citation: Xu, J., Finkenstadt, V.L. 2013. Rheological properties of reactive extrusion modified waxy starch and waxy starch-polyacrylamide copolymer gels. Starch. 65(1):984-990.

Interpretive Summary: Starch-based polymers can have similar functional behaviors as synthetic polymers, but have much better environmental properties because of their biodegradability. In order to be suitable for those uses that were historically filled by synthetic polymer, the starch needs to be modified. One of the processing methods to prepare modified starch-based polymers is reactive extrusion. Extrusion technique, the main method for processing thermoplastics such as polyethylene, is the preferred method for producing an economical product. Reactive extrusion is a variant on this technology where chemical transformations take place in the extruder, thereby dramatically reducing chemical waste. One chemical reagent that can be attached to starch using this technique is acrylamide (after polymerization, the reagent would be called polyacrylamide). Previously, scientists at NCAUR found out that starch and starch-graft-polyacrylamide copolymers processed through reactive extrusion absorb a great deal of water and swell into gels at room temperature. How these gels flow is an important parameter in many markets. The science of rheology studies how materials flow. We explored many starch/starch-graft-polyacrylamide gels and how their rheological properties changed with the amount of material placed in water. The results of our study suggest that these gels may have applications in some cosmetic and agricultural products.

Technical Abstract: The rheological properties of modified waxy starch and waxy starch-polyacrylamide graft copolymers prepared by reactive extrusion were investigated. Both materials can absorb huge amount of water and form gels. The modified waxy starch and waxy starch-polyacrylamide graft copolymer gels all exhibited viscoelastic solid properties. The waxy starch-polyacrylamide graft copolymer gels with the concentration =10% showed weaker viscoelastic behaviors than those of the same concentrations of modified waxy starch gels. However, at concentration =11.25%, the waxy starch-polyacrylamide graft copolymer gels displayed much stronger viscoelastic properties than those of the same concentrations of modified waxy starch gels. The analysis of modulus and concentration dependence and stress relaxation measurements indicated that both modified waxy starch and waxy starch-polyacrylamide graft copolymer gels were physical gels meaning the cross-linkers between the molecules were physical junctions. The non-linear steady shearing rheological properties studies indicated that both modified waxy starch and waxy starch-polyacrylamide graft copolymer gels exhibited shear thinning behavior, which can be well fitted with the power law constitutive equation. The function and behavior of the modified waxy starch and waxy starch-polyacrylamide graft copolymer gels suggest that these starch-based biomaterials should be potential candidates for applications in cosmetic gels, wound skin care materials, and agricultural products.

Last Modified: 8/19/2014
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