Objective

The main objective of this paper is to analyze the composition of a biobased binary or ternary surfactant system with alkyl olefin sulfonate (AOS), alkyl polyglucoside (APG) and lauryl hydroxysultaine (Sultaine). The composition was optimized by observing critical parameters such as surface activity and rheological properties while varying the concentration of APG in a ternary system, varying the ratio of AOS and Sultaine in a binary system and studying the effect of sodium chloride addition. The experimental results can provide an alternative, more sustainable and natural surfactant system to replace the common system containing sodium laureth sulfate (SLES) and camidopropyl betaine (CapB), without compromising on the parameters previously mentioned.

Methods

A DuNouy Ring was utilized on a tensiometer to measure the surface tension of the samples. To observe foaming abilities of samples, a visual foaming study was conducted and recorded by taking pictures. A TA instrument mechanical rheometer was used to measure the viscosity.

Results

Studying the effect of APG concentration on surface tension illustrated as APG concentration decreases, surface tension decreases as well. The minimum surface tension was found to be 26.587 for 7.5 wt. % AOS and 7.5 wt. % Sultaine. When the ratio between AOS and Sultaine changed, the 1:1 system produced the lowest surface tension value again. As the concentration of AOS decreased in the ratio, the surface tension increase. When the ratio was held constant, and APG was introduced into the system, the systems containing APG had higher surface tension values compared to the systems with the same ratios but did not have APG added. As the concentration of salt increased, the surface tension decreased for AOS, increased for the binary mixture and had no effect on Sultaine. Foaming has a direct correlation with surface tension so a decrease in surface tension leads to better foaming abilities; therefore, the 1:1 ratio of AOS:Sultaine has the best foaming qualities. The AOS/Sultaine system exhibited Maxwellian behavior, suggesting the presence of worm-like micellar structures. As the concentration of APG increased, the viscosity decreased and at a concentration of 2.5 wt. % AOS, 5 wt. % APG and 7.5 wt. % Sultaine, the system changed from shear thinning non-Newtonian fluid to Newtonian. Experimenting with the ratio of AOS:Sultaine, showed as the ratio of AOS decreased, the viscosity decreased, and at a ratio of 1:3 AOS:Sultaine, the system was primarily Newtonian. As the ratio remained constant and APG was added, the viscosity continued to decrease and the 1:3 ratio was completely Newtonian. The addition of salt had no effect on the viscosity of Sultaine, but the viscosity of AOS increased at a salt concentration of 2 wt. %. The binary mixture saw as the concentration of salt increased, the viscosity profile decreased, even though the system remained non-Newtonian and shear thinning.

Conclusion

The surface activity and rheological study of the ternary biobased surfactant systems unveil a strong synergistic interaction between AOS and Sultaine specifically at a ratio of 1:1 resulting in high surface activity and corresponding good foaming and formation of entangled wormlike micelles resulting in excellent viscosity build in the system. This system on improves upon its naturality slightly. To enhance sustainability of the system without completely compromising the desired properties, the ternary surfactant system 4.5 wt. % AOS, 3 wt. % APG and 7.5 wt.% Sultaine should be considered optimal. Any further addition of APG or changing the ratio results in detrimental reductions of all performance controlling physio-chemical parameters.