Green Chemistry Blog

A biorenewable polymer could replace synthetic plastic used in water bottles, claim US scientists. 

Polyethylene terephthalate (PET) is the third most common synthetic polymer behind polyethylene and polypropylene, with over 50 million metric tonnes of PET produced each year. Its unique thermal and physical properties make it ideal for use in industry, food packaging and soft drinks bottles. However, growing environmental concerns are causing a drive for more eco-friendly polymeric materials derived from biorenewable feedstocks to replace these petroleum-based plastics, but their properties have proved hard to mimic. 

PET is made up of alternating units of the fossil fuel feedstocks terephthalic acid and ethylene glycol, and it is this aromatic-aliphatic structure that is the key to its thermal stability. Now Stephen Miller at the University of Florida Gainesville in the US and colleagues have used lignin – one of the most abundant naturally occurring organic polymers – to produce a polymer that possesses alternating aromatic and aliphatic segments. Thus it not only bears a structural resemblance to PET but, importantly, it also has very similar thermal properties. 

Miller and co-workers combined acetic anhydride with vanillin – a by-product in the manufacture of paper from lignin – to form the monomer acetyldihydroferulic acid. Polymerisation of this monomer forms poly(dihydroferulic acid), PHFA, which mimics the structure and thermal properties of PET. Miller explains that ‘not only is the polymer designed to have a sustainable ‘green birth’, it is designed to have a ‘green death’ as it degrades into molecular units that resemble the building blocks of lignin itself.’ 

Geoffrey Coates, an expert on the design, synthesis and application of polymers, at Cornell University in Ithaca, US, comments ‘unlike some biorenewable polyesters that have poor thermal properties that limit their applications, this work focuses on materials that are comparable to PET. If other chemical and mechanical properties are suitable, and the economics of production are favourable, these polymers could have a promising future.’ 

In future, Miller’s team plan to investigate the long-term degradation characteristics of PHFA as well as performing scale-up fabrication studies to compare the biorenewable polymer with PET in different forms, such as a cup, plate or water bottle. 

Mary Badcock 

See full paper published in Green Chemistry

Biorenewable polyethylene terephthalate mimics derived from lignin and acetic acid
Laurent Mialon, Alexander G. Pemba and Stephen A. Miller, Green Chem., 2010, advanced article.