Plant-Sourced Polysaccharides for Turbulent Drag Reduction

The cost of polymer additives has been a key impediment in the adoption of polymer drag reduction techniques in large-scale marine applications. In this study, we investigate the mucilage extracted from the bran of plant seeds such as flax, chia and psyllium, as potential sources of inexpensive, water-soluble, high molecular weight polyelectrolytes for drag reduction in turbulent boundary layer flows. To this end, skin friction measurements in dilute solutions of both synthetic as well as plant-based high polymers are performed using a custom-built Taylor-Couette apparatus, operating in the fully turbulent flow regime, at Reynolds numbers between 10⁴ and 10⁵. As a specific example, we characterize the drag reducing properties of the aqueous mucilage extracted from flax seeds (Linum usitatissimum), and compare its performance to that of a commonly-used synthetic flexible homopolymer, namely, polyethylene oxide (PEO). The molecular and viscoelastic properties of the principal polysaccharide constituent in flax mucilage is also studied using size exclusion chromatography and extensional rheology techniques (CaBER). Finally, we compare the shear-induced degradation of both polymers under prolonged turbulent flow conditions, and explore the possibility of mitigating chain-scission processes by the use of appropriate ionic and non-ionic surfactant additives to modify the chain flexibility and develop polymer-surfactant complexes . The dilute mucilage solutions are seen to exhibit comparable drag reduction and degradation behavior as aqueous PEO, but on a much cheaper cost-basis, and can potentially serve as an effective, eco-friendly, and economical alternative to synthetic polymers in real-life drag reduction applications