Is there no limit to what ionic liquids can do? They can help us make almost anything out of cellulose – in an efficient and environmentally friendly way.

Ilkka Kilpeläinen, professor of organic chemistry at the University of Helsinki, holds up two square pieces of wood.

“Try it, they don’t smell like anything other than wood.”

He’s right. This is a surprise, since the two pieces were stuck tightly together until recently. Had they been glued together, we would have been able to smell it. But these pieces had been attached without glue, with the help of ionic liquids developed by Kilpeläinen’s research group on the Kumpula Campus.

This is how the process works: the ionic liquid is spread on the wood surface, the pieces are clamped together and put into an oven. Under the right pressure and temperature, the ionic liquid disintegrates back into its components, which can be harvested through extraction. The ionic liquid is, in a way, distilled out from between the pieces of wood.

Once the pieces of wood are taken out of the oven, they are stuck together tightly. The ionic liquid has dissolved some of the cellulose and lignin on the surface of the pieces. Once the solvent is extracted, the pieces are fused together.

“There’s no join between the pieces, they have become part of each other. Under a microscope, the cross section of the point where the two pieces meet just looks like an annual growth ring,” says Kilpeläinen.

SUSTAINABLE CLOTHING

During the past few years, Kilpeläinen’s research group has enjoyed an exceptional amount of publicity, as the ionic liquid developed by the chemists has been used to manufacture a new cellulose-based textile fibre called Ioncell-F. The sustainable Ioncell-F fibre is expected to revolutionise the textile industry. It could make it possible to manufacture clothes from waste paper, for example, and using a process that is vastly more environmentally friendly than the production of cotton, which requires tremendous amounts of water to farm, or viscose, which requires toxic carbon disulfide.

A project with Aalto University and the forest industry has progressed to the point where pilot factories are being set up. Marimekko has participated in the development process, and has tested the fibre in its products. Ioncell won the Global Change Award in 2016.

“However, gluing wood without glue may prove to be an even more significant achievement than the fibre,” says Kilpeläinen.

The invention enables the manufacture of plywood from sawdust, without the traditionally required phenol formaldehyde resin.

CELLULOSE BEADS

But wait, there’s more! Researchers on the Kumpula Campus are examining possibilities to replace the microplastics in shower gels, toothpastes and face washes with biodegradable cellulose beads that would be equally effective.

Microplastics are a scourge upon our waterways, and demand for a biodegradable alternative is high.

Matti Leskinen is working on his master’s thesis, but the research results are so impressive that he’s actually already well into his doctoral dissertation,” Kilpeläinen introduces a young colleague at the organic chemistry laboratory.

For his master’s thesis, Leskinen started to use ionic liquids to manufacture cellulose particles of varying sizes as candidates for replacing plastic microbeads.

“The project got off to a good start, and we started seeing one interesting new product after another, almost like on a conveyor belt,” explains Leskinen.

The different types of cellulose beads already fill several hundred sample jars. Some have been coloured with food dyes, while others contain magnetite dusts which makes the beads magnetic. By using different manufacturing and drying methods, the researchers can use cellulose to produce beads with densities ranging from 0.04 to 1.3 grams per square centimetre.

“We do feel like crazy inventors here.”

WHAT IS AN IONIC LIQUID?

One of the experiments at the organic chemistry laboratory has to do with using ionic liquids and cellulose in 3D printing. In principle, it should be possible to replace plastic with cellulose in almost all cases.

“We’re already having trouble focusing on just one thing. Ionic liquids have opened new possibilities in so many different directions,” Kilpeläinen enthuses.

Ionic liquids, or ionic solvents, are salts that dissolve at temperatures under 100 centigrade, and have been known in chemistry for more than a century. Initially, ionic liquids were considered unimportant as chemists were unable to make them crystallise. Early chemists equated a crystallised substance with purity, while a liquid compound could contain anything.

Uncrystallised salts must have seemed quite useless.

It wasn’t until the beginning of the 2000s that chemists began to try ionic liquids on cellulose and other types of biomass.

THE MYSTERY OF THE DISSOLVING LIGNIN

During the early 2000s, Kilpeläinen was studying lignin derived from paper. It is found, for example, in trees as a bonding agent. It is usually impossible to completely remove the lignin in the cellulose manufacturing process, which is the reason why paper tends to become yellow after it is exposed to light.

Kilpeläinen’s group set out to study the chemical structure of the colouring agents in lignin, but none of the solvents they used could dissolve the lignin to a sufficient degree. The group was about to abandon cellulose altogether after a string of failures.

“We tried almost everything, and almost threw in the towel. We decided to return to the topic when we found out that some researchers had experimented with using ioninc liquids to dissolve cellulose. Using the same liquids, we managed to dissolve our lignin samples.”

It didn’t take the researchers long to realise that if it was possible to dissolve cellulose and lignin with an ionic liquid, it could also be used to dissolve wood.

“That was the spark that set off our work.”

RECYCLEABLE LIQUIDS

Ionic liquids have many positive sides for a chemist: they have excellent dissolving properties and a low vapour pressure, which means that they are not particularly combustible or volatile. Compared to many other compounds, this makes them easy to use.

Ionic liquids are currently being studied in many different parts of the world, they are not the sole dominion of Kilpeläinen’s group. What makes the ionic liquids used by the chemists in Kumpula special is that they can be recycled.

The ionic liquids used by Kilpeläinen’s group leave almost no trace in the dissolved material - in this case, cellulose – and there is practically no loss of the liquid in the dissolution process.

“We intentionally set out to develop compounds that we knew could be recycled. Many of the recycleable ionic liquids that can dissolve cellulose are made at our laboratory,” says Kilpeläinen.

INDUSTRIAL INTEREST

Efficiency, environmental sustainability, lack of toxins and the potential for recycling have also made the ionic liquids developed by Kilpeläinen and his colleagues a tempting target for the commercial sector. While the liquids are more expensive than traditional solvents, experts believe that the Ioncell-F textile fibre, for example, is not only innovative, but also competitive.

“The cost-efficiency of the overall process depends on how efficiently the solvent is recycled. If it can be almost fully recycled, it becomes an investment, not a cost.”

In practice, nothing in chemistry is 100% effective, but the ionic liquid for Ioncell is very close.

“Our successes have garnered the interest of the industrial sector,” says Kilpeläinen.

GUITAR HEROES

However, Kilpeläinen emphasises that industrial cooperation does not mean commissioned research. The researchers are not accepting commissions, but they’re willing to see what practical applications could arise from their basic research. They can also be active themselves.

“We have to be able to look at our own research in terms of whether it’s useful to someone. If the answer is yes, the next step could just be a phone call away to find out if there’s interest.”

A recent partnership with the Finnish guitar company Versoul began from just such an idea. Gluelessly glued Versoul guitars may soon show up in the hands of the world’s top guitarists. Previous Versoul customers include Ronnie Wood of the Rolling Stones and Pete Townshend of The Who.

Using the new adhesive method in an internationally acclaimed product is also a good way to get more attention for the research itself.

“Very few patent applications ever end up in industrial production, but just one such case could have a great financial impact on the University.”

IN WITH THE NEW

Glueless glue, cellulose beads and Ioncell may be set for major international breakthroughs. All of them have potential in such times when we are now forced to think about the future of our planet and find ways to reduce our environmental impact.

According to Kilpeläinen, researchers should not get stuck on a single product, however promising it may be.

“Many research groups make the mistake of focusing on one isolated topic and forgetting the world beyond it. A university must always be making new innovations and setting new things in motion.”

Ilkka Kilpeläinen is also a sheet iron worker by training. After studying to become a laboratory assistant, he became so interested in chemistry that he applied to study it at the University of Helsinki. He is still on that same path, looking for new discoveries.

Sometimes the breakthrough comes as a side effect of a completely different strand of research, or even after years of hard work seem to have led to failure, as was the case with the ionic liquids. //

The article has been published in Finnish in Yliopisto magazine 03/18.

Bacteria detect poison

Ionic liquids are usually less toxic than other solvents used in industrial chemistry. In addition, they don’t evaporate easily or generate dust as solids do.

Some of the ionic liquids are downright potable, while others cause chemical burns with the briefest skin contact. A tiny change in a molecule can significantly change its toxicity. In determining toxicity, Ilkka Kilpeläinen’s group cooperates with the research group led by University Lecturer Susanne Wiedmer.

“While Ilkka and his colleagues synthesise different structures, we tell them whether a particular compound is viable or whether it is toxic. We’ve been quite successful in determining how the ionic liquids should be changed to make them as harmless as possible,” Wiedmer explains.

One of the most important methods employs the marine bacterium Vibrio fischeri, which generates bioluminescent light in the course of its normal metabolism.

“As soon as there are external stimuli, the bacteria stop generating light. This lets us know that something is going on.”

Just half a gram of an ionic liquid is enough to determine whether the substance is too toxic for industrial use.

“If the molecule is the same, its toxicity is the same, whether the amount is one gram or one tonne.”