Location: Sustainable Biofuels and Co-Products
Title: The effects of solvent polarity and pKa on the absorption of solvents into poly(glutaric acid-glycerol) films Author
Submitted to: Journal of Applied Polymer Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 23, 2013
Publication Date: N/A
Interpretive Summary: Developing new outlets for glycerol would have a significant impact on the economics of biodiesel production if value-added products made from glycerol can be identified. Glycerol is the major co-product produced from the process used to make biodiesel. Before the introduction of biodiesel-derived glycerol, the glycerol market was already saturated with uses in the food industry and in many pharmaceutical, chemical, and personal care applications. Therefore, increased production of biodiesel created a need to find new uses for glycerol. In this study, we have shown that polymer films (bioplastics) made from glycerol can absorb various solvents in response to the size, shape and polarity of the solvent, making them potentially “smart polymers”. These types of polymers are important to develop for use in areas such as soil conservation, water remediation, filters, and drug delivery. Production and marketing of such new high-value products would decrease cost of biodiesel production and provide new products to improve the environment and human health.
Technical Abstract: In this study, solvent absorption into the matrices of poly(glutaric acid-glycerol) films has been evaluated. It was determined that the combined effects of polarity and the size and shape of the solvent molecule, rather than pKa, have the most significant influence on absorption into the films. Polar aprotic solvents (with solvent polarity index values greater than 4.0) such as 1,4-dioxane (absorbed 163.8 +/-0.3 percent (w/w) of the original weight of the polymer), pyridine (200.4 +/-3.5 percent) and dimethyl sulfoxide (186.0 +/- 11.4 percent) were among the highest absorbed solvents into the polymer matrix. Solvents with polarity index values less than or equal to 4.0 were absorbed poorly (less than or equal to 5.3 +/-1.5 percent). The polymer films only absorbed less than or equal to 26.5 +/-2.1 percent of their weight of most protic solvents (water and mono-alcohols) but absorbed 72.6 +/- 6.5 percent of ethylene glycol, a diol. The only high absorbing polar protic solvent was acetic acid (131+/-13.1 percent). Except for chloroform, ethyl acetate and ethanol, all of the solvents examined displayed small increases in absorption (7.8 percent, on average) when the films were desorbed and used again to absorb solvent. Erosion of the films ranged from 0.0 +/-0.0 percent to 22.0 +/-3.2 percent after two-10h absorption cycles. Miscible (7.7 +/-2.3 percent to 15.1 +/-2.2 percent) and immiscible (12.3 +/-6.4 percent to 80.0 +/-1.9 percent) solvents were preferentially absorbed from aqueous solutions. However, up to approximately 5 percent of those absorption values could be from water absorption.