It starts with hemp, and ends with a plastic alternative that can stretch to 1,600 percent of its size.
Researchers have developed a non-toxic thermoplastic from cannabidiol, or CBD, from the hemp flower, according to a study published this week in Chem Circularity. The material also has a high glass transition temperature, which allows plastics to stay durable when they come into contact with boiling hot water.
“Very few, if any, plastics made from natural resources have this quality,” study co-author Gregory Sotzing, a professor at the University of Connecticut, said in a media release.
The team says CBD from hemp could replace bisphenol-A, or BPA, the synthetic industrial chemical used in today’s processed plastics. The study says BPA is “a known endocrine disruptor” that can disturb hormone balance.
Sotzing said the hemp material is suitable for transparent plastic films, coatings and other materials now made from petroleum-based products such as polyethylene terephthalate, or PET. PET is widely used in single-use water bottles, food packaging and substrates for flexible electronics.
Those applications need medium to high temperature stability and melt processability so the material can be formed and shaped. The team said it has achieved that in a hemp-based polycarbonate for the first time.
Co-author Mukerrem Cakmak of Purdue University said the 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.”
Cakmak said PET requires large quantities of fossil fuels, specifically crude oil and natural gas. He also said that once discarded, it breaks down into microplastics that leach chemicals, including PET, into water, air and food, which are linked to inflammation and cell damage.
The study says most polymers made from plants or plant waste have not matched hemp’s glass transition temperature and stretchability, and are more expensive to produce, especially with oil and gas prices rising. It also says catalysts used to make bio-based plastics have usually required high temperatures and created problems for catalyst removal and final product purification, limiting large-scale production.
To address those problems, Sotzing and his colleagues used hemp, which was legalized in the US in 2019, to develop a plastic film and test the processing parameters that give it the structure and properties needed for broader 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).”
Sotzing said materials with those properties could also be used as nanoparticles for drug delivery and catheter coatings.
The researchers are also working on a version of the hemp-derived plastic with greater mechanical strength and on a pilot scaled-up manufacturing process.
The study says not enough CBD is currently being produced worldwide to fully replace PET for plastics. It also says hemp cultivation is increasing as the plant becomes more widely used in clothing, building and food products, and that it is a fast-growing weed.
Sotzing said hemp 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.
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