Submitted to: Journal of Polymers and the Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/14/2015
Publication Date: 3/2/2015
Citation: Selling, G.W., Utt, K.D., Finkenstadt, V., Kim, S., Biswas, A. 2015. Impact of solvent selection on graft co-polymerization of acrylamide onto starch. Journal of Polymers and the Environment. 23(3):294-301. doi: 10.1007/s10924-015-0714-y.
Interpretive Summary: In order to broaden the use of starch in consumer products, the starch is often modified. One method to modify starch is by attaching other polymers to the it. For example, when polyacrylamide is attached to the starch, creating a starch graftpolyacrylamide (SPAM), the amount of water than can be absorbed increases dramatically. The produced SPAMs will have utility in paper production, drilling muds, water treatment or cosmetics. It is known that by changing the reaction conditions, the product of a chemical reaction can be altered. In this research, we examined how the selection of solvent changes the properties of the SPAMs produced. The properties of the SPAM were evaluated after production in water, the standard solvent, and dimethylsulfoixde (DMSO). It was found that in all cases, when the SPAM was produced in DMSO, that the length of the polyacrylamide chains attached to the starch were shorter. Surprisingly, the number of polyacrylamide chains per starch was increased after reaction in DMSO. The polymer produced from DMSO solution was more ‘comb-like’. Testing is underway to determine how this change in architecture impacts final properties of the SPAM. This information will be beneficial to manufacturers involved in the production of corn starch as well as those companies interested in producing biobased (corn) articles that can compete with articles made using petroleum based ingredients.
Technical Abstract: The impact on polymer properties [molecular weight, monomer conversion, graft content, graft efficiency and anhydroglucose units between grafts (AGU/graft)] that result from changing the solvent for the graft co-polymerization of acrylamide onto starch from water to dimethylsulfoxide (DMSO) was evaluated. Other reaction conditions were varied to determine their impact on properties, including solution solids (2.8-10.5%), acrylamide (0.18-0.89 M), initiator (0.91-3.78 mM), and temperature (40-90 °C). Changing the solvent from water to DMSO had a large impact on the properties of the starch graft co-polymer at all reaction conditions. The most important difference was observed in the architecture of the resulting starch graft co-polymer. The number average molecular weight (Mn) of the polyacrylamide grafts as well as the number of AGU/graft was much lower when the reaction was performed in DMSO; the polymer was more comb-like. When conducted in water the Mn of the polyacrylamide grafts could be as high as 450,000 with over 6,500 AGU/graft. When DMSO was the solvent the Mn could be as low as 7,500 with 200 AGU/graft. The ability to control and generate starch graft co-polymers with dramatically different architecture may allow starch to be tuned to deliver improved properties for current or new applications.