Polyols from cashew nut shell liquid (CNSL): corner-stone building blocks for cutting-edge bio-based additives and polymers

Polyols are versatile molecules present in many polymer materials that are used and often essential in daily life. However, most bio-based polyols are derived from sugar or vegetable oil, and thus, their production directly competes with the food industry. In this case, CNSL is a promising non-edible renewable resource, which is directly extracted from the shell of cashew nuts. The interesting chemical structure of CNSL and its derivatives (cardanol and cardol) has led to the synthesis of original polyols with hydrophobic and internal plasticizing properties. Useful for the development of additives such as surfactants and soft polymers, CNSL polyols are progressively occupying a unique position in the polymer industry. This review focuses on the use of CNSL as a building block for various polyols. Many different chemical pathways leading to CNSL-based polyols are reviewed and evaluated. Furthermore, we focus on the use of these CNSL-based polyols as surfactants and polymer precursors and the contribution of their specific chemical structure (aromatic ring and long unsaturated alkyl chain) to the properties of the resulting polyesters or polyurethanes.