Enzymatic approaches to renewable monomers and polymers from nature

Tackling the plastics problem is of huge importance to the UK. New routes to new naturally sourced and degradable polymers will be one of the key approaches that will benefit our society. At Nottingham we have recently begun to explore the development of new monomers and polymers directly from Nature. In this project we bring together two sets of Nottingham expertise in biocatalysis and supercritical fluids to make a step change in the clean synthesis of valuable new materials.

Vernolic acid is a natural material from the seeds of Vernonia galamensis (ironweed), a plant widely available and native to eastern Africa that is also now being grown for potential commercial opportunities in both Canada and the USA. Vernolic acid makes up 80% of the fatty acids in the seed oil and is remarkable in that it contains very useful epoxide and olefinic functionalities. Our project is targeted at developing a range of novel polymers, surfactants and detergents from vernolic acid; with applications across packaging, personal care, cosmetics and even light-weight composites. These will be of particular interest to companies like Croda because of the ability to use a naturally available, renewable material and to lower the carbon footprint of their products. The unique functionalities retained in the fatty acid chain provide tremendous flexibility for developing new materials and applications. Moreover, this approach could also be the basis for a new business / supply chain that could benefit countries in sub-Saharan Africa and could tap into the current Global Challenges.

Initial work at Nottingham has proved promising and new monomers (the unsaturated diacid above is one of several that we have now trialled) and polymers from these monomers have been developed.

Monomers: Supercritical fluid extraction has proven to be a remarkably efficient and gentle methodology for extraction of the triglyceride oil from the seeds at low temperature whilst retaining the important reactive functionalities. We have then used conventional chemistries to hydrolyse and release the vernolic acid and then further conventional chemistries to convert into a wide range of new monomers (diols, diacids, diamines etc.). However, both of these processes have required routes that are not environmentally acceptable and are inefficient and wasteful. Now, we will exploit new Nottingham expertise in biocatalysis to overcome these hurdles. A screening program will be set up to carefully assess a wide range of esterases in order to find the most efficient route to releasing vernolic acid by hydrolysis from the triglyceride in an efficient and clean way. Additionally, conversion of the vernolic acid to useful functionalised monomers requires either functionalization of the olefin or opening of the epoxide and this could be much better achieved selectively via an enzymatic approach using hydratases and/or epoxide hydrolases.

Polymers: Polycondensation polymerisation is typically carried out in the melt and requires high temperatures to overcome viscosity issues and to drive off water. Enzymes cannot operate under such conditions and only metal catalysts have been used, also under these conditions the useful olefin or epoxy functionalities are lost. We have shown that scCO2 can dramatically lower reaction viscosity by plasticising the monomer and growing polymer and hence allows reactions at near ambient temperature. The scCO2 also assists in removing the water by-product. This lower temperature processing provides a unique opportunity to introduce enzymes to allow controlled polymerisation and to develop desirable functionalised linear materials.

Working together, we will now screen a wide range of lipases, hydratases and epoxide hydrolases to catalyse polymerisation and to create a library of new polymeric systems.