The pulp and paper industry supplies consumers with 360 million tons of print-outs, newspapers, and cardboard boxes annually. When the Internet age dawned, many predicted blank paper to become history but instead our consumption has grown about 60% in the last 20 years.
The entire process – from the log falling in the forest to the fine white sheet of paper in our hands – involves many different refinement steps. Starting from scratch the wood logs need to be debarked and chipped. The wood chips then go through a chemical, a semichemical, or a mechanical process.
Enzymes can, with their degrading abilities, help several steps of these different processes. By using enzymes, paper mills can save resources and costs while improving the overall quality of the final paper.
In the chemical process the wood chips are pressure cooked in a strong alkali or acid which disintegrates the chips into individual fibers. The resulting slurry, called brownstock, has a color far from the pristine white you associate with paper because of a dark-colored substance called lignin, which is released when cooking the chips. After cooking, the lignin is washed from the fibers, which can be optionally bleached to produce a pulp ready for papermaking. The magazine in your hands and the bag that holds your groceries both come from chemical pulp, which makes strong paper.
The bleaching process of paper demands many chemicals. The bleaching plant normally uses chemical pulp with chlorine dioxide and hydrogen peroxide to achieve a brighter color. “The xylanase Pulpzyme® HC can, already in the preceding brownstock washing stage, open up the fiber structure and release the lignin so that it can be washed away more easily. This means mills can save on bleaching chemicals,” says Bo Damgaard, Global Marketing Manager for Novozymes.
Transforming wood into pristine paper
In the mechanical process, mills use horsepower rather than chemicals to grind the wood chips into individual fibers. In the old days, they used a grindstone for the job, which explains the term “pulp mill,” but today the stones have been replaced by ridged metal discs. Because the mechanical pulp is not cooked, none of the dark-colored lignin is released at this stage. Instead, the pulp can be bleached but will not reach the same levels of whiteness or colorfastness as chemical pulp. Although the paper from mechanical pulp may be weaker, this inexpensive paper holds enough strength to entertain some 1.7 billion newspaper readers world-wide every day*.
Reusing our resources
A mere 50% of the tree is used when producing paper chemically and about 90% using the mechanical process. The remaining volume ends up in the waste streams and is incinerated, discharged, spread on land, or land filled. With an increasing demand for paper products and a need to care for our resources, recycled paper has received a more prominent place in paper production. As much as 43% of the world’s paper comes from recollected paper**.
From old newspaper to recycled paper
Producing recycled paper is a different story than virgin paper. After we have thrown our old newspapers and cardboard boxes in the recycle bin, they are bundled together in big bales and sent off to the paper mill. At the mill, the paper is dissolved by mixing it with water and chemicals and then chopped into small pieces. To remove bits of plastic and globs of glue, the pulp is heated and sieved in a mechanical screening process.
Although the paper has now turned into a gray porridge-like mass, it still contains ink from printed material and glue residues from envelopes and so on. In the deinking process the pulp is washed with large amounts of surfactants. “Enzymes like the cellulase Novozym® 342 and the amylase Novozym 51055 help loosen the ink from the paper fibers, and as a result mills can reduce the amount of harsh chemicals they use,” says Bo Damgaard.
The optional final step, just as for virgin pulp, is bleaching where bleaching agents like hydrogen peroxide or chlorine dioxide makes the paper white.
Enzymes – Pulp mills’ little helpers
Regardless of process type, the production of paper requires large amounts of energy and harsh chemicals. Enzymes can do much of the work at the mill with less effort and with a lower impact on the environment. For pulp mills, this means savings on electricity, water, and chemicals, which not only translates into environmental savings but also significant cost savings for papermakers.
"When refining, both chemical and recycled-pulp papermakers can add FiberCare® R, a cellulase, to reduce the energy consumption of the refiner and to increase paper strength,” says Bo Damgaard. “Or they can add FiberCare D, another cellulase, after the refiner to reduce drying energy and increase mill productivity.
”The sticky tree sap, also called pitch, causes a lot of headaches in pulp mills. “The gluey liquid sticks to machine parts and sometimes even to the paper roll itself, creating real messes in the form of torn paper or ruined machines, so it’s important for mills to remove it. Pitch is normally controlled with talc but by adding the lipase Resinase®, the tree sap is degraded through hydrolysis and the problem is solved,” says Bo Damgaard.
Enzymes give a helping hand in the paper production process but also result in cost savings due to the reduced downtime of the paper machine. “Use of Resinase HT furthermore helps the environment because both chemicals and energy are saved,” says Per H. Nielsen, Manager for sustainability development at Novozymes.
Another good example of a common problem is the glue from for instance old envelopes, also called stickies in pulp mill language. If left untreated, it can create lumps and tear the paper on the rolls or jam the paper machines. Mills normally use polymers and talc to control stickies, in combination with a mechanical cleaning process where solvents and surfactants are added. “The esterase StickAway® reduces the amount of solvent and talc needed in this process. By degrading the stickies more effectively with enzymes mills can avoid many machine stops for cleaning which translates into energy savings,” says Per H. Nielsen.
Giving the planet a helping hand
A lifecycle assessment (LCA) conducted by two Danish universities in collaboration with Novozymes shows that considerable environmental savings are realized when using enzymes compared to traditional methods. “To give an example, about 20% of the CO2 emission can be avoided in refining thermomechanical pulp with FiberCare R and about 7% in the bleaching process when using Pulpzyme HC. Bear in mind though that the LCA only shows some of the environmental savings that can be made when using enzymes.
There is a considerable potential for further implementation of enzymes in the pulp and paper industry, which could result in more savings on production equipment, raw materials, chemicals, and fossil energy,” says Per H. Nielsen.
Despite these promising figures, the penetration of enzymatic processes into the pulp and paper industry is rather limited. “We are now trying to create better awareness of the environmental advantages and cost savings enzyme usage can deliver,” says Bo Damgaard.
Notwithstanding fears that the computer age would make printed paper obsolete we have continued to consume an increasing amount of paper products. Nobody today believes paper will become outdated any time soon, and with fossil fuels soon running out it is time to rethink how we use our resources. Enzymes can turn the page for pulp and paper production and deliver savings both for the planet and the industry. They can help us preserve our environment and use our resources in a better way.
* Estimate from the World Association of Newspapers (WAN).
** Sam Martin, Paper Chase, The ecology global network, 2008 http://ecology.com/features/paperchase/index.html.