Strategies for the design of eco-sustainable functional formulations (G. D'Errico)

The circular-economy model of social growth drives chemical industry to re-design current products, including liquid formulations, in the perspective of environmental sustainability. Regulatory requirements are becoming increasingly stringent. They require concrete and effective responses. Here, we will present and analyze past, current and future approaches to designing environmentally sustainable functional formulations through a series of case studies.

A well-established strategy is to use biodegradable components, of which we now have a wide choice. The use of these components requires careful analysis of their properties and how they may affect the final characteristics of the product.

A second possible strategy is the design of water-free or water-poor formulations The low water content reduces the ecological footprint of the product, as less plastic packaging is used, and significantly decreases the transport costs and impact. However, the formulations based on concentrated surfactant mixtures have high viscosity, which hampers their processability during production and kinetically limits their water dissolution in use. A possible solution to this problem properties is the introduction of alkyl chain branching into the molecular architecture, which allows the rheological properties to be tuned without significantly affecting biodegradability [1].

More innovative approaches, which are expected to become important in the future, are based on bio-inspired or, even better, bio-derived molecules. Nature is a huge reservoir of functional components which, thanks to biotechnological advancements, are now available on a large scale. Furthermore, nature offers a guiding line for a new concept of formulation eco-design.

During evolution all living organisms have set up intra- and/or extra-cellular complex fluids, whose analysis in terms of the key concepts typical of colloid science reveals unexpected analogies between biological and industrial fluids, highlighting the solutions nature has optimized to solve each functional problem. As an example, exopolysaccharides (EPS) are biopolymers produced by

bacteria, suited as rheology modifiers, optimized to keep their functionality in harsh environment, as in the presence of high concentration of ethanol and methanol [2]. For this reason, it is a perfect component of virucidal and bactericidal ethanol-rich formulations. As a second example, bacterial biosurfactants, such as rhamnolipids (Rha) effectively replace synthetic surfactants and are less sensitive to changes of the solution conditions [3]. Indeed, Rha are able to micellize at extremely high content of ethanol and glycerol and show outstanding wetting and emulsifying activity.

Finally, the simultaneous use of different approaches is the key to addressing the issue of environmentally sustainable formulations in a more robust way.

References

[1]  J. Colloid Interface Sci. 2019, 552, 448. Colloids Surf. A. 2021, 613, 126091.

[2] Carbohydr. Polym. 2018, 201, 293. Carbohydr. Polym. 2022, 295, 119863.

[3]  J. Mol. Liq.,2022, 367, 120547. Curr. Opin. Colloid Interface Sci. 2024, 70, 101792.