The Tetra Recart is a retortable food packaging, suitable for high viscous products, making it able to replace most food cans used for storage of food today. The packaging is built up by a paperboard, consisting of an unbleached bottom layer and a bleached top layer. Polymers and aluminium further cover the paperboard in order to protect the food against moisture and light, causing degradation. During the retorting process, the packaging develops a certain wet strength making it hard to disintegrate the pulp fibres in the board. The phenomenon of the developed wet strength is of high interest when inventing and developing new packaging materials.

To investigate why and how the phenomenon occurs, a series of trials were made through production of laboratory sheets with subsequent disintegration. The addition and amount of cationic starch was varied as well as the addition of alkyl ketene dimers, AKD, to investigate their influence on the developed wet strength. A hemicellulose or a cellulose derivative was adsorbed on the pulp fibres in order to see if the phenomenon could be prevented and thereby explained. Two types of lignin was also adsorbed on the pulp fibres to evaluate the influence of lignin on the phenomenon. Finally, the Klason lignin content in the non-retorted and retorted paperboard was measured to investigate a possible change in the chemical composition of lignin.