Friction Properties of Chemically Modified Starch

Authors: Biresaw, Girma; Shogren, Randal

Submitted to: Journal of Synthetic Lubrication
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/7/2007
Publication Date: 1/3/2008
Citation: Biresaw, G., Shogren, R.L. 2008. Friction Properties of Chemically Modified Starch. Journal of Synthetic Lubrication. 25(1):17-30.

Interpretive Summary: Surplus corn, soybean, wheat, barley, and other cereals have suppressed prices that farmers get for their crops. One way of overcoming this problem is to develop new uses for starches, proteins, and oils, which are the many ingredients of most cereals. An important application area for agricultural products is in lubrication, which is currently almost exclusively dominated by petroleum based products. In the work described here, starch was chemically modified to improve its solubility in water. Solutions of starch in water were formulated into dry film lubricants by the incorporation of canola oil. The resulting formulation was investigated for its friction properties as a function of the starch chemical structure, degree of chemical modification and the concentration of canola in the formulation. The result indicated that dry film lubricants with acceptable friction properties can be developed using all farm-based ingredients.

Technical Abstract: Starch is a high molecular weight polyglucose biopolymer that, in its native state, is insoluble in water at room temperature. One way of improving its water solubility is by esterification of its free hydroxyl groups. Waxy maize, normal corn, and high amylose corn starches were esterified with acetic anhydride (AA). Waxy maize starch was also esterified by a mixture of AA and either octylsuccinic anhydride or dodecylsuccinic anhydride. The resulting chemically modified starches, with varying degrees of substitution (DS) of the hydroxyl groups, were dissolved in water, formulated into dry film lubricants with the addition of canola oil, spray applied onto clean sheet metals, and its friction properties investigated. The results showed that, in the absence of canola, chemically modified starch displayed very high coefficient of friction (COF). Addition of canola resulted in a sharp decrease in COF, which decreased with increasing canola until it attained a minimum and constant value that was independent of further increase in canola. This observation was attributed to adsorption of the canola onto starch due to H-bonding between the ester groups of the canola triglycerides and free hydroxyl groups of starch. Analysis of the canola vs. COF data using the Langmuir adsorption model showed stronger adsorption of canola to modified starch with lower DS, which was attributed to the availability of more free hydroxyl group adsorption sites on starches with lower DS than those with higher DS.