Anhydrous products play a primary role in make-up, especially for the decoration of lips and eyes, where they can deliver special effects and textures able to create peculiar sensory responses. Combining and balancing the ingredients to obtain all the various forms and consistencies of anhydrous formulations is a complex task, since just a slightly change in the proportion of the ingredients can affect the aesthetics of the final products. New ingredients surely allow to expand the textural palettes that can be built. However, the historical period dictates that materials are easily available and a plus is represented by natural derivation using agricultural by-products containing precious building blocks otherwise wasted. In this regard, the versatility of polyurethane chemistry was adopted to develop unique raw materials, tuned to the need of giving structure, shape, and improved cosmetic performance to new and more sophisticated anhydrous formulations.
In the present work, the focus was the obtainment of a family of materials with vegetable origin, exploiting polyurethane chemistry. Succinic and azelaic acids are precursors conveniently sourced from nature and used in the synthesis. In fact, succinic acid derives from the fermentation of biomass and it is generally used to produce biopolymers, coating resins and other applications, besides being used in pharmaceutical and food industry. The fermentation of succinic acid consumes more CO2 than is produced: indeed, the sequestration of carbon dioxide makes the process “carbon negative”. Azelaic acid, instead, derives from the transformation of vegetable oils from sustainable crops like cardoon, a typical cultivation of Sardinia (Italy). These organic diacids where esterified with naturally derived glycerin and bio-based short chain acids (C8-C10, e.g. from coconut oil) to obtain pre-polymer macro-diols that were further copolymerized with isophorone diisocyanate (IPDI) and lineseed oil-derived hydrogenated dilinoleyl alcohol. The synthesis was performed in vegetable-derived oils (Coco-Caprylate/Caprate). The polyurethanes were successfully synthesized. The introduction of derivates of succinic acid or azelaic acid as a macro-diol in the polymer structure was modulated together with an alkyl diol (hydrogenated dilinoleyl alcohol), and physico-chemical characterization (ATR-FTIR, DSC, SEC-GPC) was performed on the synthesized polymers to determine their structure, thermal behavior and molecular weight. The compatibility with common cosmetic ingredients was studied and the new materials were used as the staple component in a challenging make-up formulation: a comfortable super-glossy lip fluid.
The materials presented in this work are the first born of a new bio-based polyurethanes family. Conceived to improve skin adherence, shiny appearance, long-lasting and good sensory properties, they also boast high Natural Origin Index. The lip fluid containing bio-based polyurethanes displays a very glossy finish, and its principal characteristics is naturality, due also to the wise choice of co-ingredients in the formulation. The ongoing research on the design of polyurethanes for cosmetics is consolidating the knowledge on their structure-property relationships, making the way towards high performance biobased products increasingly viable. The present research fosters the continuous collaboration between raw material researchers and cosmetic formulators to satisfy market needs.