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United States Department of Agriculture

Agricultural Research Service

Research Project: MODIFICATION OF NATURAL POLYMERS BY THERMO-MECHANICAL PROCESSING
2010 Annual Report


1a.Objectives (from AD-416)
The overall goal is to develop processes to enhance the conversion of cereal crops into value added polymers and chemicals, and thus generate expanded markets for cereals and reduce dependence on petroleum.


1b.Approach (from AD-416)
Investigate the effects of stirring during cooling on the rheological properties of hot dispersions prepared by jet cooking starch in both the presence and absence of non-starch additives. Further investigate the structure, properties and end-use applications of spherocrystals formed in slowly-cooled solutions of jet-cooked starch. Modify laboratory techniques to permit commerical scale-up of processes used for deposition of thin starch coatings onto plastic surfaces and modification of these coatings by graft polymerization. Prepare starch esters having low to high degree of substitution and controlled substitution patterns with high efficiency and minimal byproducts. Characterize structure-property relationships and identify applications. Prepare new, inexpensive hydrophobic starches by reaction of starch with unsaturated hydrocarbons and characterize utility as adhesives. Prepare starch graft copolymers by reactive extrusion.


3.Progress Report
This is the final report for the project 3620-41000-140. The overall goal of this project was to develop processes to enhance the conversion of cereal crops into value added polymers and thus generate expanded markets and reduce dependence on petroleum. Specifically, modified corn starches with novel properties were prepared by chemical, enzymatic and physical processing techniques. Substantial results were realized over the 5 years of the project. Procedures were developed to deposit thin coatings of starch onto the surfaces of water-repellent plastics (such as polyethylene) to impart water receptive properties to the surface. Some of the useful properties of water-receptive plastic surfaces are improved adsorption of water-based dyes and inks, reduced electrostatic charging, and improved compatability with biological fluids. Conditions were developed for maximizing the yields of spherulites formed in jet cooked starch/fatty acid mixtures. These uniform, micrometer sized spheres may have a number of applications in foods, controlled release and plastics. Critical-fluid extraction with 75/25 (v/v) ethanol/water was found to remove over 99% of the native lipid from corn starch, and thus proved to be a viable method for defatting starch samples. A process was developed for reducing the water sensitivity of starch films by applying coatings of polyethylene in organic solvents. Electrically conductive plastic films were prepared by mixing carbon black with jet cooked starch/fatty acid salts and SBR (rubber) latex. A variety of starch and sorbitol esters were prepared by new and more efficient processes and utility as water absorbents, antiscalants and flocculants was demonstrated. Starch acetates were prepared by microwave heating with reaction efficiencies of nearly 100%. Sorbitol citrates and aspartates were prepared by reactive extrusion and were effective in preventing mineral precipitation for water treatment. Starch phosphates were found to be effective at replacing polyacrylamide, a non-degradable, oil-based polymer, for removing suspended clay from water. A number of ionic liquids were found to be good solvents for starch. Starch stearates were easily prepared using ionic liquids as solvent and catalyst and were found to have liquid crystalline properties. Starch graft copolymers with acrylamide and acrylic acid were produced by reaction extrusion with ammonium persulfate catalyst with high conversion (>90%) and grafting (>75%) efficiencies. Much less water and organic solvent was required with the novel reactive extrusion process than conventional processes. These copolymers had good water absorption properties. Similar starch graft copolymers were also produced using an enzyme (horseradish peroxidase) as catalyst at room temperature thereby eliminating the need for conventional chemical catalysts and energy for heating the reaction. These basic and applied research results will assist 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.


4.Accomplishments
1. Electrically conductive starch-plastic films. Aqueous dispersions of carbon black are used commercially for a number of applications, but are difficult to prepare due to the hydrophobic nature of the carbon black particles. PPL Unit scientists at National Center for Agricultural Utilization Research in Peoria,IL, have discovered that non-coagulating, aqueous dispersions of carbon black can be easily prepared by using jet cooked starch/sodium palmitate as a polymeric emulsifier, and then using ultrasonic mixing to prepare the dispersions. Flexible films are obtained by drying mixtures of carbon black dispersion and SBR (rubber) latex. Since carbon black is electrically-conductive, this research provides a new method for preparing plastic films with electrically-conductive properties. Such films could be particularly useful for packaging electronic components where static charge can be damaging.

2. Novel modified starches. Corn starches with new kinds of chemical modifications are needed to develop biobased polymer products which can displace petroleum-based materials. This is because starch needs to be more water resistant for some materials applications and more water soluble for others. A PPL Unit scientist at National Center for Agricultural Utilization Research in Peoria, IL has developed a new strategy for the chemical modification of starch which could lead to a variety of properties. The sequence of reactions includes chloroacetylation, followed by reaction with sodium azide to give azido starch followed by reaction with alkynes in water to give a triazole. The structure of the alkyne can be chosen to optimize water solubility or water resistance. This new knowledge of basic chemistry of starch modification should allow researchers in academia, industry and government to develop modified starches with an expanded range of properties for a wide range of applications.


Review Publications
Biswas, A., Sutivisedsak, N., Cheng, H.N., Willett, J.L., Lesch, W.C., Tangsrud, R.R. 2012. Extraction and analysis of antioxidant capacity in eight edible beans. International Journal of Food, Agriculture, and the Environment. 10(1):89-96.

Shogren, R.L., Biswas, A. 2010. Acetylation of Starch with Vinyl Acetate in Imidazolium Ionic Liquids and Characterization of Acetate Distribution. Carbohydrate Polymers. 81(1): 149-151.

Last Modified: 11/23/2014
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