Story | 01/10/2023 13:30:00 | 8 min Read time

What is left over after making pulp – and why should you be interested in it now?

Antti Isokangas

Teksti

The production of pulp creates a secondary product for which there was almost no use before. It is now being developed into adhesives, plastics and even high-grade aviation fuel. Lignin from wood can be used to replace petroleum-based raw materials – and at the same time sequester carbon for a long time in ordinary, everyday objects. How far will these innovations go in the fight against climate change?

Until the 1990's, lignin was mainly considered a waste product. When Suvi Pietarinen studied chemistry at university, even her professors downplayed lignin. This wood residue from pulp production was not considered worth investigating.

"Fifteen years ago, I was in South Africa at a fibre industry conference where a Chinese researcher, Professor Hou-Min Chang, gave a presentation on lignin. I knew that lignin had been studied since the early 1900's without any major breakthroughs and wondered why anyone would want to tackle such a worn subject. When Chang received an award at the same event for his life's work with lignin, I thought that it was a waste of a career", Suvi Pietarinen says.

It is possible that in the future the properties of lignin will be developed in a way that allows it to replace oil-based raw materials completely.

Most of the carbon in wood is bound in lignin, one of the main building blocks of wood. When lignin is recovered at the pulp mill and used, for example, in the production of glue, the carbon it contains is no longer released directly into the atmosphere but is stored for a long time in various end products.

Suvi Pietarinen, who was amazed by the lecturer's enthusiasm for lignin, is now the Development Manager of UPM Biochemicals' lignin business, where she is responsible for finding new commercial uses for lignin and products refined from it. She is also responsible for UPM's lignin-related patent portfolio, which includes inventions related to the production and use of lignin.

Did you know you can make glue from wood?

When wood pulp is boiled to make paper and cardboard, lignin is left over. More than 90% of it is still burned for energy. However, methods developed in recent years allow us to separate lignin from cellulose more accurately and more purely. It can therefore be used as a raw material for various products instead of energy production.

Almost everything around us contains fossil raw materials. Even if only a part of them were replaced by lignin-based materials, the use of oil could be reduced and carbon could be stored in buildings, furniture and everyday goods, for example.

Almost everything around us is made from fossil raw materials. Even if only a part of them were replaced by lignin-based materials, this would reduce the use of oil.

Lignin is used in the manufacturing of resins, adhesives, plastics and insulators, for example. For a long time, these products have been made of only oil-based, non-renewable raw materials.

"For example, resins are used in many durable materials, such as plywood. A piece of furniture made of plywood, such as the Artek stool, is passed down from generation to generation. Even laminate kitchen countertops can store carbon for decades", says Suvi Pietarinen, Development Manager of the Lignin Business at UPM Biochemicals.

 

Will lignin solve climate change?

Currently, lignin is usually used in combination with plastics or other petrochemical products. In the future, lignin will be able to replace an increasing proportion of plastic polymers, but due to its complex chemical structure, the manufacturing industry has not yet been able to create plastics made of 100% lignin. It is possible that in the future, the properties of lignin will be developed in a way that allows it to replace oil-based raw materials completely.

The first high-quality lignin-based resins and adhesives appeared on the market in the early 2000's, and their properties and applications have developed so rapidly that they could quickly replace oil-based ones. In the case of plastics, on the other hand, a breakthrough may take much longer. This requires not only technological advancements but also more cost-effective solutions. Technically, the use of powdered lignin requires different processes and equipment than liquid oil.

In recent years, the use of lignin has been investigated, for example, in the production of aviation fuels and in the battery industry. The substitution of fossil raw materials is often a cost issue, as new types of processes need to be developed and are not yet available.

But can we talk about lignin as the new oil? A scientific study published in Canada in 2020 estimates that lignin obtained as a by-product from the pulp industry could replace 2% of the world's petrochemicals. In other words, it would be a gross exaggeration to claim that the lignin currently available could solve the world's dependence on oil and its derivatives.

One hundred million tonnes of fossil substitutes

An estimated 100 million tonnes of lignin are produced annually as a by-product of the global paper and board industry. This means that there is enough lignin raw material to go around without cutting down any extra trees.

"To a chemist, lignin is a fascinating lump with many different properties. As our understanding of lignin grows, we may find surprising new uses for it. For example, there is still much to learn about the role of lignin in soil carbon reserves. It is known that lignin also acts as a carbon sink in the soil and forms compounds that are important for plants when it decomposes", says Suvi Pietarinen.

UPM looks for new ways to utilise lignin and helps its customers develop and apply the necessary technology. For example, the use of lignin in plywood production has been developed in cooperation with UPM's own plywood business and resin and glue companies. Similar cooperation projects are underway in different sectors.

Lignin is a type of natural glue, a biopolymer that binds wood cellulose together. It keeps the growing tree straight. When wood is used to make pulp, lignin is obtained as a by-product.

According to a study published a couple of years ago in Canada, for example, a single branch of the plastics industry, the phenolic resin industry, could use up to one million tonnes of lignin per year. This would represent about 1% of the total amount of lignin produced in the paper and board industry.

"Such a strong increase in the use of lignin would mean that it would no longer be a mere by-product for the forest industry, but an important source of income. It would change the whole forest industry", says Suvi Pietarinen.

What are the benefits of a pulp mill for food production?

It took an innovative pioneer and a clay-ridden field to find a climate-smart use for lignin in agriculture.

When fields are in good condition, they are more resistant to extreme weather events and produce more food. The microbes present in soil can be revitalised with wood-based materials, and at the same time more carbon is sequestered in the soil.

"Soil improved with wood fibres is more weather-resistant due to its better water and nutrient retention capacity," says Juuso Joona, farmer and one of the founders of the circular economy company Soilfood Oy.

When Joona was studying agriculture at the University of Helsinki and was about to take over his family farm in Joutseno, he started to research how to revitalise and improve the clay-heavy fields in South Karelia. Being from an area known for its forest industry, he became interested in the utilisation of forest industry by-products.

Founded in 2016 by Juuso Joona, Saara Kankaanrinta, Ilkka Herlin and Eljas Jokinen, Soilfood researches and develops environmentally friendly fertilisers and soil improvers from, among other things, forest industry by-products, such as fibre sludge and lignin, which have traditionally been burned for energy.

"Organic fertilisers and soil improvers help soils retain nutrients better than traditional mineral-based fertilisers. Yields have improved even though summers have been hot and dry", Joona says.

 
On this website, UPM publishes articles that reflect on the kind of tomorrow we want. We seek answers to the questions shaping the future and showcase the people who are changing the world through their actions. In the article you just read, you were introduced to one of them.

 
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