UG looking for alternatives to agricultural plastics

Researchers testing bio-based options

By Lilian Schaer for Livestock Research Innovation Corporation

As Canada continues down its path of phasing out single use plastic, agriculture will also need to find replacements for everything from bale wrap and silage bags to plant pots, semen straws, and more.

A research team at the University of Guelph, led by Dr. Erica Pensini, is working on finding those alternatives – and the project is receiving funding from both Beef Farmers of Ontario and Dairy Farmers of Ontario. 

Agricultural plastics in general contain contaminants that make them harder to recycle, but even if they didn’t plastics recycling overall isn’t as effective as it could be, noted Pensini during a Horizon Series webinar presentation hosted by Livestock Research Innovation Corporation (LRIC). 

Only nine percent of Canada’s annual plastic waste production is recycled, with the rest going into landfill, waste-to-energy facilities or into the environment. Stateside, the situation is similar with less than nine percent of the United States’ 36 million tons of annual plastic waste being recycled. As well, China, a traditional market for plastic wastes, is no longer accepting shipments. 

“It’s not just about improper disposal, but also the process of making the plastic, which starts with petroleum extraction, then fractionation into components to make polymers. Extraction takes about 6.5 barrels of water per barrel of oil,” said Pensini, who is an associate professor in the Department of Engineering. “There is a big environmental cost associated with the use of plastics. I’m not saying we have to phase out oil in a day, but it is another reason we need to think about other options.” 

So, what alternatives exist and when do they become viable? According to Pensini, any plastic replacements will start to make economic sense when oil prices rise, or water becomes scarce – as seen in California and the southwestern United States, for example. 

Pensini and her team have been exploring different options, starting with a corn protein called Zein that is very versatile and simple to work with. A spray-on film dried rapidly and although it prevented erosion and run-off in the lab, it was less successful in the field. That’s because its tortilla chip-like flavour is also extremely appealing to rodents. 

Adding linseed or tung oil not only kept the rodents away but also created a rigid bioplastic that can be mixed with natural fibres to make plant pots. 

“This would be a good alternative to pots used in greenhouses, for example,” she said. “Ideally you would put them directly into the soil without removing the seedlings, so you’re not only reducing environmental impact, but also avoiding trauma to the plant.”

Another challenge with Zein was that it wasn’t flexible enough, so they mixed it with cutin, a component found in tomato and grape peels. Although this created a water repellent coating – and had the added benefit of repurposing a food processing waste product – the product was hard to make and although flexible, didn’t meet the level of stretchiness plastics needed for applications like bale wrap. 

This led Pensini’s team to consider using vegetable oils like linseed or soybean oil as the base for a spray-on film. On-farm tests with hay revealed the liquid penetrated between the layers, and farmer feedback showed interest in a pre-fabricated film instead of a spray-on product. The resulting modification, although bendy enough for mulch or silage wrap, still wasn’t stretchy enough to be a suitable substitute for conventional bale wrap. 

“So we mixed epoxidized soybean oil, used citric acid as a hardener, added oleic acid to make it stretchier, and cured it in an oven,” she said. “It’s the best one we have so far in performance, it is flexible and stretchy, but it would need to be fabricated in a dedicated facility.” 

As a next step, the team will be introducing fibres in an effort to upcycle agricultural waste products and make them into useful solutions for agricultural applications. They’ll also be experimenting with other fatty acids to see if they can be used in place of citric or oleic acids to further enhance the new materials’ properties. 

According to Pensini, the need to find commercial partners is also important, but conventional plastics will either need to start being phased out or become more expensive before bio-based alternatives will come into largescale production and use. 
“Many people have expressed interest in the pots, for example, and the idea of leaving the pot in the soil,” she said.  

Pensini’s Horizon Series webinar is available on this website along with the other 13 webinars, which cover everything from regenerative agriculture and animal-free products to One Health and greenhouse gas emissions. 

This article is provided by Livestock Research Innovation Corporation as part of LRIC’s ongoing efforts to report on research developments and outcomes, and issues affecting the Canadian livestock industry.  It was originally published in the January 31, 2023 edition of Ontario Farmer.