Paper or packaging usually consists of pulp obtained from wood. However, paper production is very energy-intensive. Moreover, wood grows only slowly and demand has increased in recent years, as the raw material has long since become an important source for sustainable products such as bio-based plastics. But there are alternatives: Cellulose can also be obtained from other plants such as grass.

Annual plants as an alternative to wood as a raw material

Researchers at Munich University of Applied Sciences now want to use so-called annual plants as raw material for paper production. A team of students led by Helga Zollner-Croll from the Faculty of Technical Systems, Processes and Communication has set its sights on hops, hemp and the miscanthus grass known as Chinese reed, with the aim of using them to produce pulp for paper manufacturing.

One of the most difficult steps in conventional paper production is the separation of the wood fibers from the lignin in order to achieve an optimum result in pulp extraction. This requires not only a lot of energy and water, but also chemicals. To determine the lignin content of hops, hemp and miscanthus, the researchers first dried and crushed the plant material. The analysis showed that compared to wood, which has a lignin content of 30%, the lignin content of hemp is significantly lower at 12 to 14% and of miscanthus and hops at 22% each.

Pulp extraction by cooking

To obtain the pulp, the team used different cooking processes. "We subjected small amounts of each of hops, hemp and miscanthus to three pulp cooking processes: the natural pulping process with methanoic acid, the acetosolv process with acetic acid and soda cooking with caustic soda," Zollner-Croll explains.

Miscanthus convinces with a high yield

Fiber properties and yields were then compared with data from pine and spruce pulp production. The main focus was on the fiber content of the pulp. With a yield of 86%, Miscanthus was particularly convincing here. According to the researchers, pulping wood by sulfate cooking only achieves a yield of about 55%, the rest being lye. "This confirms the great potential of annual plants and grasses," Zollner-Croll sums up. Next, the Munich researchers plan to conduct trials with larger quantities of plant material.

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