Tomato stems to cardboard boxes: Slovenian researchers convert biomass waste into packaging for circular economy

27 Jul 2021 --- The Paper and Pulper Institute (ICP) of Slovenia has created corrugated cardboard packaging from tomato stems. Following three years of investigation, researchers at the institute say the findings could provide a major boost to the packaging circular economy.

The ICP, based in Ljubljana, is researching new uses for leftover biomass from wood, agriculture and industry crops, vegetable production, invasive plants, forestry, wood and paper production. More than 60 distinct streams have been examined for possible use in its research.

Speaking to PackagingInsights, Gregor Lavrič, a researcher at ICP, explains how his team discovered tomato stems could have ideal properties for replacing traditional pulp in cardboard production. 

“The chemical and morphologic characterization of tomato stems has shown that its cellulose fibers are suitable for paper manufacturing, both from a quantity and quality point of view.”

“The biomass fractionation process, fiber preparation and paper production were simulated and optimized at ICP’s laboratories. During the development of the tomato stem-based paper, the strength properties and water and vapor resistance have been improved, making the paper suitable for the production of tomato packaging bags.”ICP discovered tomato stems could have ideal properties for replacing pulp in cardboard production.

From bags to boxes
The scale-up and first production of the tomato stem-based material was created by ICP in 2019 for market tests on 25,000 carrier bags. 

Bio-based printing inks and starch-based adhesives were used to guarantee the paper and packaging products were biodegradable and met regulatory standards for food contact.

“Tomato stem paper has proven extremely popular on the market and as a result, the ICP is producing it on a regular basis on its pilot paper machine,” says Lavrič.

“To raise the efficiency and economic viability of the producer’s waste valorization, the next logical progression was the creation of a corrugated board. The base paper developed for the bags (patented process) was further optimized for liners and fluting in corrugated boards and again produced on ICP’s pilot paper machine.” 

Finding the corrugated board producer with the equipment adjustable for different input materials was the biggest challenge, he explains, but it was successfully solved with the help of a small Slovenian board producer.

Commercialization challenges 
Lavrič asserts that with the production of the pilot equipment (a digester and paper machine with the capacity of around 100 kg of paper per hour), the team has proven there is commercialization potential. 

“We have already produced approximately eight tons of tomato stem paper and approximately three tons of corrugated board this year.”A cardboard box prototype created using tomato stems at the ICP.

However, to raise the papermaking sector’s interest and reach full-scale production in pulping and paper production, the most important challenge remaining is ensuring a regular supply of suitable quality and quantity of biomass, Lavrič explains. 

“The majority of the alternative raw materials, in this case, tomato plant stems, are diverse, variable and seasonable. Therefore, the incoming feedstock is not available in quantities for big-scale production in one place, which is reflected in much higher logistic costs for the producers.”

Potential commercialization impacts
The impact of the project, if commercialization challenges are overcome, could be huge, says Lavrič. 

“It would promote the utilization of local waste and side streams, circular bioeconomy and the potential for development of new value chains, services and jobs especially in rural areas.” 

“Due to the seasonality of the crop residues and optimal collection rates, the industry would need to change from large volume material supply chains to more diverse and local ones.”

However, these changes can be enabled through machine learning and harvesting optimization models, which could mitigate the current crisis with raw material deployment, he asserts. 

“Moreover, industry should see that local agro-residue like tomato stems instead of wood biomass would also enable forest-based biomass to fulfill its function as a long-term carbon sink, which would improve the C02 emissions rates of the EU.”

By Louis Gore-Langton