Focus on sustainability: Novel wood-based coatings and the fruits of close co-operation

The coatings and packaging industries would undoubtedly appreciate drop-in substitutes when shifting from fossil-based components to bio-based ones. Using bio-based raw materials, however, often calls for novel formulations and processes throughout the value chain. This is why 18 Finnish research institutes and companies got together to create new bio-based solutions for packaging, paints, adhesives and abrasives

Water-based dispersion coatings, also known as dispersion barriers, are applauded as a sustainable choice for protecting paper or paperboard from moisture and grease in food packaging, such as juice cartons or paper cups. They are, however, commonly created from fossil-based polymers.

“There are some bio-based dispersion barriers already available, but they have drawbacks such as being costly or based on raw materials that are potential food sources. By using wood-based raw materials we avoid these issues,” says Henrikki Liimatainen, Professor and Head of the Fibre and Particle Engineering Research Unit at University of Oulu.

Liimatainen and his research team are participating in the two-year project called SUSBINCO (SUStainable BINders and COatings), which aims to create bio-based aqueous formulations for packaging, paints, adhesives and abrasives. The project has brought together seven universities and research institutes and eleven industry partners, all based in Finland. They still have several months to go, but Liimatainen is ready to share research highlights on bio-based dispersion barriers.

“One of our starting points was to use wood-based extracts as a binder to form the dispersion matrix and other wood-based polymeric materials such as nanocelluloses as dispersants to stabilise the aqueous dispersion. Based on research and analyses made so far, we have created very promising materials.”

A promising match – suberin and nanocellulose

Suberin is a complex biopolymer, a blend of polyesters and other compounds, which functions as a natural barrier material in bark. Before the research project, Natural Resources Institute of Finland (Luke) had already worked for several years on suberin extracted from birch bark and was therefore well prepared, together with VTT Technical Research Centre of Finland, to provide raw material for research partners.

Liimatainen, together with research groups at Åbo Akademi and VTT, oversaw the next step, which involved making a stable dispersion from suberin and water by adding dispersants. They tested existing dispersants along with new ones based on nanocellulose and other biopolymers which they had developed for this purpose.

“We found out that our new dispersant made of nanocellulose not only stabilised the dispersion but also reinforced the barrier coating.”

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The whole value chain in the loop

Liimatainen is the first to admit that it will still take time and effort for suberin dispersions to be found on juice and milk cartons or paper cups or wraps. He is, however, confident that a lot of requirements typical in the coatings and packaging industries have already been met during the SUSBINCO research project – thanks to co-operation which he rates excellent.

“Binder developers, for example, got constant feedback from dispersion developers. We actually held our meetings together, which meant that some 25 to 35 people regularly got together.”

Dispersion developers, in turn, had their dispersions produced and tested by research partners at VTT and Lappeenranta University of Technology (LUT) focusing on manufacturing processes in the coatings and packaging industries. According to Liimatainen, the whole value chain was in the loop, including experts from University of Eastern Finland (UEF) and VTT specialised on food safety and the disposal and recycling of packaging materials.

“Besides research partners, our industry partners contributed to each stage of the research by sharing their ideas and requests on materials, which is quite exceptional in basic research,” Liimatainen says.

Lignin – the binder for coatings, adhesives and abrasives

One of the industry partners in the SUSBINCO project is Teknos, a global paints and coatings manufacturer headquartered in Finland.

“We are constantly looking for new sustainable raw materials with good availability. In the SUSBINCO project we were able to deepen our understanding of the present supply worldwide as well as the new opportunities emerging from the research on local wood-based materials,” says Pasi Virtanen, Group R&D Manager, Innovations, at Teknos Group.

Besides the research on dispersion barriers, Virtanen and his colleagues participated in the research on lignin. Lignin is a complex polymer which acts as a natural binder in trees and is a side-stream product from the wood pulping process.

“The research partners experimented with lignin and modified lignin from various sources. It’s not an easy material to utilise as a binder, but together we found promising solutions for all applications, which were wood and metal coatings, adhesives and abrasives.”

New formulas and processes needed in the industry

Virtanen points out that participating in the early phase of research was an eye-opening experience for him and his colleagues, as they are used to creating paints from ready-made components.

“It became quite clear to us that there will hardly be drop-in substitutes available, when shifting from fossil-based raw materials to bio-based ones. In the coatings industry, we need new formulas and new processes, and even new equipment. And to make all necessary changes in the whole value chain, tight co-operation is required.”

In the past, developers of paints and coatings have occasionally been able to use materials that have been developed to another application in the coatings industry or another industry altogether but, according to Virtanen, bio-based materials may narrow these chances.

“We need more research specifically directed to the coatings industry. However, this is a small industry when compared to the chemical industry as a whole. So, we need to be very active and co-innovative.”

SUSBINCO project is coordinated by CLIC Innovation and is part of the CLIC Innovation led 4Recycling ecosystem. The project is funded by Business Finland. for more information, visit: www.clicinnovation.fi/project/susbinco