MICHAEL FEVOLA
Vice President of R&D and Product Stewardship, Inolex, Philadelphia, Pennsylvania, United States

Abstract

Surfactant formulations must demonstrate safe and reliable preservation against microbial contamination over the entire product lifespan. To address evolving market demands, formulators increasingly turn to multifunctional ingredients as elements of a preservation strategy based on the hurdle technology approach. Multifunctionals such as medium-chain terminal diols (MCTDs) and chelating agents help overcome challenges associated with organic acid and aromatic alcohol preservatives. The physicochemical interactions between surfactants and multifunctionals must be carefully considered from the onset of formulation design to ensure that product performance and preservation requirements are achieved. So-called “drop-in” additions of multifunctionals to existing surfactant formulations should be avoided; instead, a holistic approach that considers the multifunctional ingredients as components of the surfactant system should be employed.

Formulators of surfactant-based products are increasingly challenged to design new and robust formulations in response to changing market demands. The expectations of sulfate-free surfactants, elimination of traditional preservatives, and increased interest in naturally-derived ingredients require formulators to embrace new approaches. Safe preservation remains a critical requirement for all formulations and the incorporation of multifunctional ingredients presents an opportunity for development of safe and consumer-accepted surfactant-based products.

Most rinse-off products, from shampoos and conditioners to face and body washes, are comprised primarily of aqueous mixtures of surfactants (1). As amphiphilic molecules, surfactants can adsorb at air-water interfaces to generate and stabilize foams and at oil-water interfaces to provide detergency and emulsification. Their amphiphilic character also enables surfactants to self-assemble into aggregate structures. The morphology of these structures, i.e. spherical micelles, rod-like or worm-like micelles, hexagonal or lamellar liquid crystals, etc., is governed by numerous intrinsic factors (surfactant chemica ...