|Xu, Jingyuan - James
|Ashby, Richard - Rick
Submitted to: Carbohydrate Polymers
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/14/2015
Publication Date: 3/20/2016
Publication URL: https://handle.nal.usda.gov/10113/5244604
Citation: Xu, J., Krietemeyer, E.F., Finkenstadt, V.L., Solaiman, D., Ashby, R.D., Garcia, R.A. 2016. Preparation of starch-poly-glutamic acid graft copolymers by microwave irradiation and the characterization of their properties. Carbohydrate Polymers. 140:233-237.
Interpretive Summary: With suitable modifications starch-based polymers can provide similar functional properties as petroleum based polymers. An inherent advantage of using renewably sourced starch as a main component in articles that are currently being produced from non-renewable materials is their biodegradability. Often the starch is chemical modified by placing other polymer directly bonded to the starch; the product of such a reaction is termed a starch graft co-polymer. These starch based copolymers have found utility in markets as varied as water purification/urinary incontinence to oil drilling muds. There is a continual need to produce new starch based copolymers to take the place of those products that use non-renewable starting materials. There are no reports regarding the preparative and properties of starch-poly-'-gutamic acid (PGA) graft copolymers. The scientists at NCAUR prepared corn starch-PGA graft copolymers using microwave irradiation method – a method that provides the most efficient means of heating in order to have the most ‘green’ process. Using this method, starch and PGA become graft copolymers, that is the two polymers become attached, during the microwave heating. Typically starch graft copolymers are synthesized by forming graft sites on the starch and then polymerizing a monomer (such as acrylamide, which are typically toxic) onto the starch. This study shows that two existing polymers – such as starch and PGA – can be covalently linked using microwave irradiation, which is quite unique. The final product of the starch-PGA graft copolymers powder can absorb water and swell into gels at room temperature. The rheological properties of starch-PGA graft copolymers were significant different from those of starches (controls). These findings are important for new graft copolymer materials development and will be of value to the starch utilizations.
Technical Abstract: Graft copolymers of waxy maize starch and poly-y-glutamic acid (PGA) were produced in an aqueous solution using microwave irradiation. The microwave reaction conditions were optimized with regard to temperature and pH. The temperature of 180 deg C and pH 7.0 were the best reaction conditions resulting in a PGA graft of 0.45% based on nitrogen analysis. The average graft content and graft efficiency for the starch-PGA graft copolymer prepared at 180 deg C and pH 7.0 were 4.20% and 2.73%, respectively. The starch-PGA graft copolymer produced at 180 deg C and pH 7.0 could absorb more than 20 times its own weight amount of water and form a gel. The preliminary rheology study revealed that the starch-PGA graft copolymer gel exhibited viscoelastic solid behavior while the control sample of waxy starch showed viscoelastic liquid behavior.