Chemical Modification of Natural Polysaccharides to Improve Their Functional Properties in Cosmetic Technology.

Sustainability has become a critical focus in personal care industry, aiming to reduce the environmental impact of formulations while fulfilling the consumer demand for eco-friendly products. This work focused on the development of thickening and emulsifying agents that influence the rheological behaviour, texture, and long-term stability of topical formulations. Initially, five commercial polymeric thickeners (PTs) were evaluated for their performance in both aqueous and oil-containing systems. Among these, synthetic PTs (Viscolam® AT 100 P and Sepigel® 305) were the best performing, as they formed weak gel systems with desirable textural properties and homogeneous, stable emulsions. Natural thickeners (PemuPur™ START and Insthatix®) could form sufficiently structured systems but failed to stabilize emulsions. In contrast, hydrophobically modified guar gum (GG) (Esaflor® HM 22) showed strong viscoelasticity but formed emulsions with large droplets. These results highlighted the need for new natural-based PTs with enhanced functionality. For this purpose, GG was chemically modified via esterification to improve its thickening and emulsifying properties while maintaining biodegradability. Esterification with glycolic and lactic acids, activated by carbonyl diimidazole, resulted in low reaction yields (1-12%) and derivatives with poor rheological properties; however, Glycolyl-GG with a molar substitution of 0.124 showed enhanced elastic properties in solution. Then, modification with acyl chlorides was used to introduce butyryl, isobutyryl, lauroyl, and stearoyl side chains, but the real degree of substitution (DS) was not determined for all derivatives since it was below the detection limits of the available analytical techniques. While rheological properties were generally unimproved, Stearoyl and Lauroyl-GG derivatives displayed better emulsifying properties, especially lauroyl derivatives obtained from depolymerized GG. Industrial scale-up of Lauroyl-guar derivatives both in slurry and in bulk conditions resulted in low reaction yields (7%) and products with poor rheological properties, with emulsifying effects largely attributed to formulations pH or residual sodium laurate. Similarly, the esterification with dodecenyl succinic anhydride achieved very low reaction yields (2.3%) and the derivatives showed only modest applicative improvements. A different strategy involved the modification of depolymerized GG via oxidation followed by reductive amination with ethylenediamine, ethanolamine, or hexylamine. While ethylenediamine derivatives were unsatisfactory, ethanolamine derivatives formed structured aqueous systems but lacked emulsifying abilities. In contrast, derivatives functionalized with hexylamine demonstrated both thickening and emulsifying properties: the derivative with DS 0.03 combined structuring properties and emulsified up to 10% oil, while the derivative with DS 0.05 was insoluble but could emulsify up to 25% of oil. The aminated derivatives were readily biodegradable and non-toxic toward keratinocytes at concentration up to 5 mg/mL. In conclusion, esterification did not substantially enhance the rheological and emulsifying properties of guar gum and was limited by low reaction yields. On the contrary, the modification through oxidation and reductive amination yielded biodegradable derivatives with promising functional features. Future research should prioritize the development of greener synthetic routes to advance sustainable personal care ingredients.