Professor Lars Wågberg
Recent investigations have unambiguously shown that the external layers of the fibre wall (i.e. the last 20 nm) are very important for the properties of the wood fibres in conventional products such as printing and writing paper as well as in hygiene products. A very good interaction between the external parts of the fibres is a prerequisite in order to form strong joints between the fibres (and hence strong paper) and the light scattering properties of the fibres are determined by the structure of the fibres and fines (wood fines or added fillers).
In hygiene papers it has also been found that the surfaces of the fibres will totally dominate the interaction with liquids and a change of the surface energy and/or geometry of the fibre surface can dramatically change the properties of the fibres. A fundamental knowledge of the external parts of the fibre wall and their interaction with light, liquids and other solids is therefore essential in order to utilise the, to a large extent, unused potential of wood fibres.
There is also a vast scientific knowledge available in the area of general surface modification and once the physical chemical nature of wood fibres is known this knowledge can be used to also modify wood fibres. A striking example of this possibility is the application of polymeric multilayers to enhance paper strength (Wågberg et al 2001).
The technique of using polymeric multilayers for surface engineering in general has had a large development during the last 5-10 years (Decher 1997). In this technique different types of surfaces are consecutively treated with for example cationic and anionic polyelectrolytes and different evaluation techniques show that this treatment produces multilayers of the polymers on the surfaces (Decher 1997). By application of the polyelectrolyte multilayer (PEM) technique to wood fibres it was found that 5 layers of polyallylamine and polyacrylic acid increased the strength of bleached softwood fibres to the same extent as a mechanical beating (Wågberg et al 2001). This shows the large potential of fibre surface modification in order to expand the application areas of wood fibres. By tailoring the surface energy, surface modulus and geometry of the fibres or other products from wood fibres, such as for example microfibrillated cellulose, these materials can most probably be used in totally new application areas.
The knowledge needed for this tailoring of surface properties is however very limited and there are very few techniques available to evaluate these properties of films and fibres. It is therefore essential to
• develop relevant methods for determination of properties of thin interfaces of cellulose and/or multilayers of different types of additives and the interaction between these thin layers
• clarify how the chemistry of the components in the different layers will determine the properties of the layers and how they will interact with other materials
Decher, G., "Fuzzy Nanoassemblies: Toward Layered Polymeric Multicomposites", Science , 277:1232(1997)
Wågberg, L. Forsberg, S. and Juntti, P., "Engineering of fibre surface properties by application of polyelectrolyte multilayers. I-Modification of paper strength", Submitted to J. Pulp Paper Sci 200