The topic
Packaging paper, as produced by the Mondi Group, has to satisfy high demands on consistency, stiffness and usability. The high quality demands have to be met alongside the demands on the use of materials and resources. To be precise: how many layers (i.e. material) are required for the desired quality and can the use of material be optimized (reduced) during the production procedure? The basic principle of paper production has been known for a long time: cellulose fibres are suspended in water and the fibres form a network on a sieve and bond to each other when they dry. However, the key question to control this basically simple process and to ensure a constant and high quality has still not been solved: what holds the paper fibres in the network together?
The research question: what causes the cohesion?
Paper has a very long history. After 2,500 years of production and about 1,000 years of more or less systematic research and development the general consensus was that the fibres are held together by both entanglement (friction) and hydrogen bonds. But the Mondi Group wanted to know more. Could forces other than friction and hydrogen bonds play a part? If so, can they be described and quantified and how can they be controlled?
Collaboration in the CD Laboratory
Its attempts at investigating these fundamental questions with the largest paper-related research institutes in Scandinavia seemed to be reaching a dead end, so the Mondi Group decided on a completely different approach. The company reasoned that a breakthrough would be much more likely if it looked at the problem in an interdisciplinary way, not only with the tools of chemistry but also from a physicist’s perspective. An intense search ultimately led to the Graz University of Technology and to Prof. Robert Schennach, an outstanding surface physicist and chemist. He had previously had nothing to do with paper but was ready to tackle the company’s basic questions. What mechanisms hold the fibres together and can they be quantified and controlled?
Results
The work in the CD Laboratory led to the identification and quantification of seven mechanisms with a role in the binding of fibres, such as the Van der Waals force, dipole linkage and mechanical interlocking. Another force was described for the first time and its mode of action revealed: a single-molecule film of water in combination with friction. The new knowledge is permitting the company to control paper quality more precisely. The research and the publications from the CD Laboratory have contributed to an advance in the field of paper. In the meantime, several research groups (mainly in Europe) are working in the area and establishing new expertise. The Mondi Group has been involved since the start of the development so enjoyed a head start; at the same time, the company is benefiting from the worldwide scientific advances initiated by Prof. Schennach. The company is ahead of its competitors in many performance indicators. The basic research benefited particularly from the programme’s continuity: the scientists could work on the issue for seven years instead of having to spend time writing applications for funding.
