Effects of sodium sulfonate with different alkyl chain lengths on starch in starch-rich system: Structure, surface properties, and interaction mechanism

The inherent limited compatibility of starch with other synthetic polymers or natural polymers significantly impedes its utilization efficiency, compromising the mechanical strength and stability of starch-based materials. Introducing emulsifiers to starch molecule to alter its surface properties is an efficient way to promote its compatibility with various matrices. This study examined the effects of sodium sulfonates with varying alkyl chain lengths, specifically sodium dodecyl sulfate (SDS), sodium hexane sulfonate (SHS), and sodium octadecyl sulfate (SOS) , on the structural and surface properties of starch. The underlying interaction mechanisms were investigated through both experimental and simulation methods. Results showed that the short-chain SHS were predisposed and imbedded within starch molecules, effectively performing dual roles as emulsifiers and cross-linking agents while the moderate-chain SDS were likely to act as emulsifiers. However, the long-chain emulsifiers were found to envelop the surfaces of starch aggregates, fostering a degree of cross-linking through hydrophobic interactions, ultimately contributing to an expansion in size. The molecular simulations supported lower energy requirement and higher Van der Waals interaction were adequate to form the SDS/Starch complex system. Once the inclusion complexes were formed, this would change starch's molecular flexibility and complex stability, leading to improved surface properties.