From betulin potentially bioproduced from plastics wastes to sustainable and high-performance cycloaliphatic polyurethanes: Towards a Biotech-Chem approach

Abstract

By combining biotechnology and chemistry, sustainable and high-performance thermoplastic polyurethanes (TPU) have been (bio)produced from different renewable carbon sources like biomass and plastic waste, in the frame of a circular (bio)-economy. The bioproduction of betulin (cycloaliphatic diol) using engineered baker's yeast (Saccharomyces cerevisiae) has been demonstrated from a model carbon source for plastic waste. Sustainable TPUs were synthesized in a two-step route with betulin as a chain extender (in different amounts), and with methylene diphenyl diisocyanate as an aromatic diisocyanate and different poly(tetrahydrofuran) (PTHF), as a sustainable long polyol, with varying molar masses. A specific study of betulin hydroxyl (OH) groups have been developed. To the best of our knowledge, such reactivities study had never been studied. It clearly shows the lower reactivity of the secondary OH group and the importance of temperature and catalyst content control on the urethane bond formation. The different obtained sustainable TPUs exhibited high thermal stability due to the specific betulin cycloaliphatic structure. TPUs with only high molar masses PTHF have achieved good phase segregation and elastomeric behavior. The sufficient distance among hard segments allowed interactions between them, reducing the affinity between hard and soft segments, with a specific organization based on phase separation. These TPUs offered adequate thermo-mechanical properties and processability, with stiffness and high Young’s modulus, for a large range of potential applications. Taking into account their architectures, the end of life of these sustainable thermoplastics is largely open to physical or chemical recycling approaches.