The paper that is not afraid of water

Save favourite 13 Dec December 2017

You have probably heard a great many alarming reports about gigantic "garbage patches" in the seas and oceans, bags that end up in the natural environment and that will not degrade over five hundred years and animals that eat garbage that leads to a painful death. Many of the stories have a common denominator – plastic.

Something has to be done to reduce the use of plastic. Part of the solution may exist at Mid Sweden University.

One area where plastic has occupied a unique position for a long time is bags of various kinds. Strength and resistance to water have made it almost optimal for carrying home groceries and collecting rubbish that is later thrown away. Alternatives have appeared over the years such as carrier bags of cloth and paper without really ever coming close to driving out the plastic bag. You have probably had a thought or two at the supermarket and are probably well aware that it is not particularly environment-friendly. But at the same time nothing has existed that can do what the plastic bag can. But researchers at FSCN at Mid Sweden University may be on to something.

Improve the food waste bag

More and more people in Sweden are sorting their food waste. The “brown bin” has become an accepted concept and is today a common sight next to the green bin that the refuse trucks collect from households. But not everyone who collects their leftovers in a paper bag to place in a brown bin knows that the combination of paper and moisture does not function extremely well. In other words, the food waste bag is an excellent product to compare with when researching on paper that can withstand liquid. At the end of the year a preliminary study will be concluded the goal of which was to investigate if a food waste bag can withstand moisture, be environment-friendly and be made of paper all at the same time. The result? This research will probably not stop at the preliminary study stage.

“We think we have something worth going further with. At lab level we have come a long way both in research here at Mid Sweden University’s own labs and at MoRe Research in Örnsköldsvik. We have also been able to conduct tests on a larger scale abroad and the paper has attained the properties we were hoping for. But for it to be of interest to the industry from an economic point of view we need to conduct tests on an even larger scale to be able to simulate conditions in faster machines,” says Gunilla Pettersson, researcher at FSCN at Mid Sweden University.

Two processes in paper manufacture

To understand the complex nature of manufacturing paper of different kinds we have to start at the beginning. Paper pulp is manufactured using two different methods but common to the manufacture of both is that the wood fibres must be separated from each other to be able to be brought together later when the paper is made. This fibre separation is done in two ways and gives the paper different properties. When mechanical paper pulp is made, the fibres are separated by means of refiners (disc mills) that pulverise the wood chips, thereby separating the fibres. Paper made from this pulp is usually less strong and easily discolours in sunlight. Newsprint is made from mechanical pulp. The positive thing about the method is that more than 90% of the tree can be used. In the manufacture of chemical paper pulp, the chips are boiled together with chemicals, which gives a stronger product that is used in a wide range of products where high strength is important. Today’s paper bags are made of chemical pulp where only about 50% of the wood is turned into fibre. 

Mechanical pulp is used on the other hand as the raw fibre material in the research project at FSCN at Mid Sweden University. There is great interest in the project, not only here in Sweden but also in many other countries, where there are organisations eagerly awaiting the results. 

“There are EU directives that say that the use of plastic bags is to be reduced by 80% by 2025. But it might be easier said than done when there are no products that can adequately replace them. Our hope is that we’re on to something with this type of paper,” Gunilla goes on.

Save jobs

Together with her colleagues Hans Höglund, Sven Norgren and Per Engstrand, Gunilla is conducting a project that is special in many ways. Not least because it is rooted in the reality of companies that make paper from mechanical pulp, manufacturing that needs to develop its production with new products because of falling circulation in what has traditionally been the largest product group – the printed newspaper. 

“You can’t shut your eyes to the development and there are currently totally modern paper machines for making printing paper based on mechanical pulp that will need to be switched over to other areas of application to continue to be profitable. That’s what makes this project feel extra important. It’s not just a question of developing a new kind of paper but also keeping the paper machines running in order to continue provide jobs for people,” Gunilla goes on.

Close collaboration with the industry

Collaboration with the industry is an important part of the project; the companies involved include forest companies like Stora Enso and SCA and suppliers of process technology like Valmet and Sandvik Process Systems. The industry’s commitment has provided valuable support since it is a question of the possibility to redesign paper machines to implement the new technology. 

“The reason why the chemical pulp creates stronger paper is that the lignin in the wood is evaporated off. The mechanical pulp retains the lignin and the paper that is produced using the current paper-making technology is then weaker. By exposing the paper line to high temperatures and high pressure we can on the other hand turn the lignin’s negative properties’ effect on the paper into something positive where it behaves as a kind of binder for the cellulose and creates a paper where much of the strength is maintained in a wet condition,” Gunilla says.

With a stronger paper that resists moisture better, we can hopefully soon see food waste bags that keep wet food waste inside. A thinner variant where you no longer need to have double bags that leak anyway. But it doesn’t stop there.

“It’s really only our own imagination and creativity that set the limits. E-commerce is growing, as is food waste where traders and restaurants are forced to throw food away because of inadequate packaging. At the same time we have to protect our forest raw materials and use as much of the tree as possible when we make paper. We’re not there yet but we’ve come a good part of the way,” says Gunilla in conclusion. 


Related pages:

More information

Pettersson, G. , Norgren, S. & Höglund, H. (2017). Strong paper from spruce CTMP - Part I. Nordic Pulp & Paper Research Journal, vol. 32: 1, pp. 54-58.

Pettersson, G. , Norgren, S. & Höglund, H. (2017). Strong paper from spruce CTMP - Part 11ListenLyssna. Nordic Pulp & Paper Research Journal, vol. 33: 1, pp. 126-132.

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