The potential of oxalic – and glycolic acid based polyesters (review). Towards CO2 as a feedstock (Carbon Capture and Utilization – CCU)

Plastic materials are indispensable in everyday life because of their versatility, high durability, lightness and cost-effectiveness. As a consequence, worldwide plastic consumption will continue to grow from around 350 million metric tons per annum today to an estimated 1 billion metric tons per annum in 2050. For applications where polymers are applied in the environment or for applications where polymers have a bigger chance of ending up in the environment, (bio)degradable polymers need to be developed to stop endless accumulation of non-degradable polymers irreversibly littering our planet. As monomers and polymers represent more than 80% of the chemical industry’s total production volume, a transition from fossil feedstock today (99% of the current feedstock for polymers is fossil-based) to a significantly larger percentage of renewable feedstock in the future (carbon that is already “above the ground”) will be required to meet the greenhouse gas reduction targets of the Paris Agreement (>80% CO2 reduction target for the European Chemical Industry sector in 2050). The combination of the predicted polymer market growth and the emergence of new feedstocks creates a fantastic opportunity for novel sustainable polymers. To replace fossil based feedstock, there are only three sustainable alternative sources: biomass, CO2 and existing plastics (via recycling). The ultimate circular feedstock would be CO2: it can be electrochemically reduced to formic acid derivatives that can subsequently be converted into useful monomers such as glycolic acid and oxalic acid. In order to assess the future potential for these polyester building blocks, we will review the current field of polyesters based on these two monomers. Representative synthesis methods, general properties, general degradation mechanisms, and recent applications will be discussed in this review. The application potential of these polyesters for a wide range of purposes, as a function of production cost, will also be assessed. It is important to note that polymers derived from CO2 do not necessarily always lead to lower net overall CO2 emissions (during production of after use, e.g. degradation in landfills). This needs to be evaluated using robust LCA’s and this information is currently not available for the materials discussed in this review.