December 20, 2017

From Pine to Renewable Plastic

Purple tree.jpg

Of the estimated 95 million Americans celebrating with Christmas trees this December, 81% are expected to choose plastic trees.  Why is plastic preferred? The cost of buying a live tree is 5%-10% higher this year, due to fewer trees planted during the Great Recession. Although the initial purchase of a plastic tree can cost as much as a live tree, plastic can be re-used, year after year.

In addition to thrift, allergies, ubiquitous needle spikes and fire phobia also play a role in tree material selection. However, an artificial tree is not fireproof. While not as prone to combustion as a dried-out pine, plastic trees can still burn when subjected to holiday hazards such as frayed light cords, candles, or discarded cigarettes.

Despite the benefits of plastic trees, 19% of American tree buyers opt for natural. For some, this decision is an environmental choice, since the purchase of a fresh-cut tree supports tree farms, conserving green space and farm land. Others simply love the smell of a live tree, a fragrance brought to you by the chemical pinene, from the terpene family. Recently, scientists at the University of Bath developed a renewable material from the fragrant beta-pinene that can be used in place of the petrochemical-derived caprolactone.

The Power of Pinene

Bio-based polyesters like (polylactide) PLA are susceptible to brittleness and are often mixed with caprolactone to improve mechanical properties. Although the addition of caprolactone is essential to expanding the plastic's suitability for medical and engineering applications, the resulting plastic is not renewable, since the caprolactone is made from crude oil. The University of Bath researchers' pinene material allows for the creation of sustainable PLA. The chemical similarity between caprolactone and pinene (both are hydrocarbons) makes the possibility of pinene substitution more economically feasible for manufacturers.

Be not afraid, fans of the Tannenbaum au naturel; the researchers have no Grinchly designs on your trees. The concentration of b-pinene in individual trees is fairly low. However, the paper industry produces pinene in large quantities as a waste byproduct of crude sulfate turpentine, making it cheap and readily available.

Possible applications of the new plastic include food packaging, bags, and medical devices. Thus far, only a few grams of the material have been created, and researchers seek to make their production of the pinene-sourced material both scalable and green.

Sustainable Raw Materials

Even the abundant supply of b-pinene generated by the paper industry is still not enough to replace all caprolactone in products currently in use. University of Bath is also investigating how to manipulate bacteria into transforming their natural terpene stores into more useful chemical precursors. If successful, terpene could be produced in mass quantities by fermentation of plant sugars and cellulose waste.

Pinene is just one of many bio-based chemicals currently under consideration as a crude oil alternative. Limonene, from citrus fruit, is another terpene of interest that could be used to create terephthalic acid, a monomer essential to the production of PET - poly(ethylene terephthalate), from renewable sources. The market for PET is huge, so a breakthrough on this front would have a significant environmental impact.

The ability to use bio-based, renewable sources as starting materials could revolutionize the plastics industry and help to mitigate climate change.