Characterize the interactions between Chitosan and Sophorolipid by studying rheology (i.e.- viscosity and bulk elasticity). Utilize this knowledge to engineer required microstructure. Optimize the rheological properties of the chitosan – sophorolipid system through variation of composition and advanced characterization techniques. Investigate the effect of salt and pH on the rheological properties of the chitosan – sophorolipid system to further optimize the formulation
Polymers and surfactants are a main area of focus within the cosmetic and personal care industry. The interactions between an oppositely charged surfactant and a polyelectrolyte results in the formation of an association structure. This complex can modify the bulk and interfacial properties of the system which directly corelates to critical performance parameters like cleansing, foaming and lubrication. Evolving consumer inclinations and expectations are now driving a wider range of non-toxic, sustainable and biodegradable innovations in the cosmetic and personal care industry. In this regard, biopolymers and biosurfactants constitute an important area of research. This study explores and engineers the interactions between a cationic biopolymer – chitosan and a mildly anionic biosurfactant - sophorolipid. Sophorolipid is commonly found in two forms- the lactone form and acidic form. Lactone sophorolipids are known to contribute to the lowering of surface tension whereas acidic sophorolipids have better foaming properties. The free COOH- groups of the ASL molecules in the ASL-LSL mixture also contribute to SL’s mildly anionic nature. Chitosan is derived from the deacetylation of chitin ((1,4)-N-acetyl-D-glucos-2-amine) which is naturally found in crustacean exoskeletons and fungi cell walls. Chitosan by itself is insoluble in water. On preparation of chitosan solution with glacial acetic acid, the H+ ions of acetic acid and the NH2 groups of chitosan form NH3+ groups. This prepares a self- balanced, positively charged backbone which attributes to its cationic nature. This gives to an electrostatic repulsion force between the NH3+ groups resulting in molecular swelling and enhanced viscoelastic properties.
Chitosan- Poly(D-glucosamine) cationic biopolymer. Sophorolipid- 47.5% REWOFORM ® SL ONE mild anionic biosurfactant. Sodium Chloride – Fisher Scientific. The Discovery Hybrid Rheometer (DHR-3) from TA Instruments was employed to determine the rheological response of the chitosan-SL systems.
Effect of biopolymer concentration: SL on its own has low viscosity and exhibits Newtonian behavior while chitosan at 0.5 wt % shows significant viscosity build. On the addition of chitosan to SL, the system shows an increase in bulk viscosity. This can be explained by the electrostatic binding of the mildly anionic sophorolipid molecules to the cationic chitosan molecules which results in the formation of a gel-like network due to polyelectrolyte complexation and thus builds the viscosity of the system. Effect of salt on the bulk rheological properties of Chitosan – SL system: Addition of salt to 0.5 wt% chitosan and 12 wt% SL system resulted in a decrease in the viscosity of the system. This can be explained by the fact that salt screens the charges and reduces the positive interactions between chitosan and SL. Effect of pH on Chitosan – SL system: It was observed that the viscosity increases as pH of the system is increased due to increased ionization of the acidic sophorolipid.
Sophorolipid exhibits low viscosity on its own. Addition of Chitosan significantly improves the rheological properties of Chitosan- Sophorolipid combination systems due to strong interactions between Chitosan and Sophorolipid leading to potentially forming an integrated network. Salt has a negative impact on the rheology of the system due to the charge screening effect of salt. An increase in pH enhances the bulk rheological properties the system due to increased ionization of the acidic sophorolipid. A variation of these parameters generates novel textures and has potential for improved foaming and cleansing through bulk rheological modifications.
Further explore the effect of Chitosan on Surface Tension and Surface Elasticity at the air-water interface. Carry out microrheological studies to understand further impacts on microstructure and dynamics. Explore the wet lubrication effect of the chitosan – sophorolipid system in order to investigate its potential for use in hair care products.
We acknowledge the contribution of the following companies and institution for making this project possible: Evonik, TA Instruments
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