Scientists develop ‘green’ plastic alternative from form of cannabis

By Stephen Beech

A "green" alternative to plastic packaging has been developed from a form of cannabis.

Scientists developed the non-toxic plastic alternative derived from the hemp plant - a non-psychoactive type of weed.

Researchers are looking for alternative forms of packaging as the global pollution crisis caused by manufacturing and disposing of single-use plastics grows.

Now a team of American scientists and engineers have developed a stretchy, hemp-derived thermoplastic that can extend up to 1,600% of its size.

The material has a high "glass transition temperature" — a quality that allows plastics to stay dry and durable when they come into contact with boiling hot water, according to a study published in the journal Chem Circularity.

The research team hope that cannabidiol, or CBD, the main chemical compound found in the hemp flower, can replace bisphenol-A, the synthetic industrial chemical found in today's processed plastics.

Study co-author Professor Gregory Sotzing, of the University of Connecticut, said: "Very few, if any, plastics made from natural resources have this quality.

"Current day polycarbonate is made from bisphenol-A, a known endocrine disruptor.

"The hope here is that cannabidiol can take the place of bisphenol-A found in today's processed plastics."

Sotzing says the hemp material is suitable for producing transparent plastic films, coatings, and other common materials currently made from petroleum-based materials such as polyethylene terephthalate (PET), which is widely used in single-use water bottles, food packaging, and substrates for flexible electronics.

Those applications require medium- to high-temperature stability and melt processability, or the ability to easily melt, deform, and shape a material — which the team has achieved in a hemp-based polycarbonate for the first time.

Co-author Mukerrem Cakmak, of Purdue University, said: "Our work has established CBD-based colycarbonates [sic] as sustainable replacements for widely used thermoplastics such as PET.

"We have developed a rigorous processing science framework that links molecular architecture to melt processability, orientation development, and stretchability without compromising manufacturability."

He explained that PET requires large quantities of fossil fuels — specifically, crude oil and natural gas — and, once discarded, breaks down into tiny particles called "microplastics" that leach chemicals including PET, which are linked to inflammation and cell damage, in water, air, and food.

While scientists have been searching for greener alternatives to PET, most polymers made from plants lack its glass transition temperature and stretchability and are more expensive to produce.

The catalysts used to produce bio-based plastics have also usually required high temperatures and have posed challenges for catalyst removal and final product purification, making them impractical for large-scale production.

To overcome the challenges, Sotzing and his colleagues developed a hemp-based plastic film and tested the processing parameters that give it the right structure and properties for widespread use.

He said: "This polycarbonate has, as a smooth film, a very high contact angle with water.

"We were not expecting our polyCBD-carbonate to have a higher contact angle than most polyolefins."

He added that materials with the property can also be used as nanoparticles for drug delivery and for catheter coatings.

The research team is in the process of studying the products formed when CBD reacts with commercial triphosgene, a crystalline solid used with hemp to produce the material.

They are also working to develop a version of the hemp-derived plastic with greater mechanical strength and to pilot a scaled-up version of their manufacturing process.

Not enough CBD is currently being produced worldwide to fully replace PET for plastics, according to the study.

But with hemp becoming a popular material in clothing, building, and food products, its cultivation is on the rise.

Sotzing says the plant can be grown across a range of climates, with relatively little water and little to no pesticides, and can be rotated with corn, soybeans, and other food crops, making it a versatile choice for farmers.

He added: "Costs of CBD would drop upon the planting of more hemp."