'We are finding new ways to use the entire plant'
As the global pollution crisis caused by manufacturing and disposing of single-use plastics continues to grow, researchers have developed a non-toxic plastic alternative derived from the hemp plant-a non-psychoactive type of cannabis.
In a study recently published in Chem Circularity, a team of scientists and engineers demonstrates 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.
"Very few, if any, plastics made from natural resources have this quality," says author and UConn Department of Chemistry professor Gregory Sotzing. "Current day polycarbonate is made from bisphenol-A, a known endocrine disruptor. The hope here is that cannabidiol (CBD) can take the place of bisphenol-A found in today's processed plastics," says Sotzing, referring to the main chemical compound found in the hemp flower.
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. These 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.
"Our work has established CBD-based colycarbonates as sustainable replacements for widely used thermoplastics such as PET," says author Mukerrem Cakmak of Purdue University. "We have developed a rigorous processing science framework that links molecular architecture to melt processability, orientation development, and stretchability without compromising manufacturability."
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, into our 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. Furthermore, the catalysts used to produce bio-based plastics have typically required high temperatures and have posed challenges for catalyst removal and final product purification, making them impractical for large-scale production.
To overcome these challenges, Sotzing and colleagues developed a hemp-based plastic film and tested the processing parameters that give it the right structure and properties for widespread use, establishing guidelines for the material's industrial processing.
"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," says Sotzing, noting that materials with this property can be used as nanoparticles for drug delivery and for catheter coatings.
The researchers are in the process of studying the products formed when CBD reacts with commercial triphosgene, a crystalline solid used with hemp to produce the material. The team is 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.
Another important quality of the material is that it can be easily recycled, says Sotzing,
"We can chemically recycle it with a base where the polyesters can be depolymerized using a base to break it down to the starting materials. We don't need enzymes," says Sotzing. "What happens is it will hydrolyze or break apart the polymer chain, and the CBD can be recovered."
To date, not enough CBD is being produced worldwide to fully replace PET for plastics, according to the study. However, with hemp becoming a popular material in clothing, construction materials, and food products, hemp cultivation is on the rise. The plant can be grown across a wide 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.
Due to this versatility, Sotzing suspects hemp to become one of the top global crops eventually, and this research further highlights the crop's growing list of sustainable applications.
"We came together on this project to try to replace conventional petroleum-based plastics with something found in nature. We are finding new ways to use the entire plant. That's what was done with oil, in that they found a way to use every little drop, even down to the sludge that becomes asphalt," says Sotzing. "Now, we are doing that with hemp, too. There are plenty of things inside that plant that are useful."
