A surprisingly robust, yet green, alternative to plastic packaging has been developed from the hemp plant–an age-old form of the cannabis plant that doesn’t get people high.
The non-toxic plastic alternative is a stretchy thermoplastic that can extend up to 1,600% of its size.
The material also has a high “glass transition temperature”—a quality that allows plastics to stay durable when it comes into contact with boiling hot water—according to a study published this week in the journal Chem Circularity.
“Very few, if any, plastics made from natural resources have this quality,” said study co-author University of Connecticut Professor Gregory Sotzing in a media release.
The research team hopes that cannabidiol (CBD) from the hemp flower can replace bisphenol-A, the synthetic industrial chemical found in today’s processed plastics, because bisphenol-A is “a known endocrine disruptor”—meaning it can disturb the delicate balance of our hormones.
Prof. 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, so the material can be formed and shaped—which the team has achieved in a hemp-based polycarbonate for the first time.
Co-author Dr. Mukerrem Cakmak, of Purdue University, said their work has established CBD-based polycarbonates 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.”
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Dr. Cakmak 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) into water, air, and food, which are linked to inflammation and cell damage.
While scientists have been searching for greener alternatives to PET, most polymers made from plants or plant waste lack hemp’s glass transition temperature and stretchability, and are more expensive to produce—especially with oil and gas prices skyrocketing.
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, Prof. Sotzing and his colleagues used hemp, which was finally legalized in the U.S. in 2019, to develop a plastic film and tested the processing parameters that give it the right structure and properties for widespread use.
“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 (thermal plastics).”
He added that materials with these properties can also be used as nanoparticles for drug delivery and for catheter coatings.
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The researchers 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, and it is a fast growing weed.
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Prof. 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, helping to revitalize their fields.
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