Pine trees make plastic more sustainable

RESEARCHERS in the UK have found a way to produce a type of plasticiser from pinene, a chemical which gives pine trees their smell and is a waste product from the paper industry.

Sustainable, plant-derived plastics such as polylactic acid (PLA), used in plastic bags, disposable cups, medical implants and packaging, require the addition of a polymer called ε-caprolactone to make it more flexible. ε-caprolactone, however, is generally produced from crude oil, which makes the final plastic not wholly sustainable. The team at the University of Bath’s Centre for Sustainable Chemical Technologies (CSCT) has now turned sustainable pinene into a useable form of one such plasticiser, ε-caprolactone.

Around 350,000 t of turpentine, largely from paper mills, is produced each year, and around a third of this is pinene, making this suitable for a commodity chemical. The process to make ε-caprolactone requires four steps. The researchers, led by Helena Quilter, first convert β-pinene into the terpenoid nopinone with an 82% yield, using an ozonolysis process at -78?C. The next step, using a Lewis acid-promoted isomerisation at 0?C, produces cryptone. They convert the cryptone to 4-isopropylcyclohexone using a catalysed hydrogenation reaction. Finally, the 4-isopropyl-cyclohexone is converted into the desired 4-isopropyl-ε-caprolactone in a reaction which takes place between 0–25?C with meta-chloroperoxybenzoic acid.

The researchers say that all four steps are common transformations that would be easy to scale up. They also demonstrated the polymerisation of the 4-isopropyl-ε-caprolactone, using a process called ring-opening polymerisation, showing its suitability for use with polymers like PLA, which is also produced using ring-opening polymerisation.

“This research is part of a wider project that looks at using bio-based chemicals like pinene as a sustainable starting material for making a range of useful products, in the place of petrochemicals. This reduces our reliance on fossil fuels and provides a renewable feedstock that has the potential to revolutionise the chemical industry,” said CSCT director and professor of sustainable chemical technologies Matthew Davidson.

The next stage in the research will be to scale up the process to turn pinene into caprolactone, and to further investigate the potential for copolymerisation with PLA.

Polymer Chemistry DOI: 10/bwzp

TCE senior reporter Helen Tunnicliffe visited the CSCT and wrote an article about the centre and its terpene research in October 2016.