Decreased Wet Strength in Retorted Liquid Packaging Board Master of Science thesis in the Master Degree Programme Materials and Nanotechnology MARIA GUNNARSSON Department of Chemical and Biological Engineering Division of Organic chemistry CHALMERS UNIVERSITY OF TECHNOLOGY Göteborg, Sweden 2012 Report No. 2012:001 Decreased wet strength in retorted liquid packaging board Master of Science Thesis MARIA GUNNARSSON SUPERVISOR: Gunnar Westman EXAMINER: Gunnar Westman Department of Chemical and Biological engineering CHALMERS UNIVERSITY OF TECHNOLOGY Göteborg, Sweden, 2012 Decreased wet strength in retorted liquid packaging board MARIA GUNNARSSON ©MARIA GUNNARSSON, 2012 Report no 2012:001 Department of Chemical and Biological Engineering Chalmers University of Technology SE-412 96 Göteborg Sweden Telephone +46 (0)31-7721000 Cover: The Tetra Recart packaging. Department of Chemical and Biological Engineering Göteborg, Sweden 2012 Decreased wet strength in retorted liquid packaging board Maria Gunnarsson Department of Chemical and Biological Engineering Division of Organic Chemistry CHALMERS UNIVERSITY OF TECHNOLOGY ABSTRACT 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. Results showed that the addition and amount of cationic starch as well as the addition of AKD has an effect on the developed wet strength. Adsorption of a hemicellulose or a cellulose derivative on the pulp fibres can be used to prevent the phenomenon to occur. Adsorption of a lignin on the pulp fibres cannot be used to evaluate its influence on the phenomenon. Instead, adsorption of a lignin prevents the phenomenon to occur in the same way as a hemicellulose or a cellulose derivative. Measurements of the Klason lignin content showed a decrease in Klason lignin when retorting the paperboard for 1 hour but an increase in Klason lignin again when rertorting the paperboard for 1.5 hour and 2 hours. Keywords: Liquid packaging board, wet strength, retorting, cationic starch, AKD, lignin. CONTENTS 1. INTRODUCTION ............................................................................................................. 5 1.1 Background .................................................................................................................. 5 1.2 Purpose ........................................................................................................................ 6 1.3 Limitations ................................................................................................................... 6 1.4 Specification of question formulation ......................................................................... 6 2. THEORY ........................................................................................................................... 7 2.1 Wood and wood fibres ................................................................................................. 7 2.2 Cellulose ...................................................................................................................... 7 2.3 Hemicellulose – Xylan ................................................................................................ 9 2.4 Lignin ......................................................................................................................... 10 Lignin measurements ............................................................................................. 12 Kappa number ....................................................................................................... 12 The phenomenon auto-adhesion ............................................................................ 12 2.5 Starch ......................................................................................................................... 12 2.6 Cellulose derivatives .................................................................................................. 13 2.7 Sizing and sizing agents ............................................................................................ 14 AKD ....................................................................................................................... 14 ASA ........................................................................................................................ 15 2.8 IR spectroscopy ......................................................................................................... 15 2.9 Food and liquid food packaging ................................................................................ 16 2.10 Liquid packaging board ............................................................................................. 16 Retortable board .................................................................................................... 17 Board process ........................................................................................................ 17 2.11 Sterilization ................................................................................................................ 17 Retorting ................................................................................................................ 18 3. MATERIALS AND METHODS ................................................................................... 19 3.1 Pulps and chemicals ................................................................................................... 19 3.2 Modification of lignin ................................................................................................ 19 3.3 Production of laboratory sheets ................................................................................. 20 Reference sheets .................................................................................................... 20 Variation of starch addition .................................................................................. 20 Addition of xylan ................................................................................................... 20 Addition of HPC .................................................................................................... 21 Addition of HPMC ................................................................................................. 21 Addition of HPMC-P ............................................................................................. 21 Addition of lignin and modified lignin .................................................................. 21 Addition of antioxidant .......................................................................................... 21 3.4 Industrial retorting ..................................................................................................... 21 3.5 Laboratory retorting ................................................................................................... 22 Laboratory retorting in N 2-atmosphere ................................................................ 22 3.6 IR-spectroscopy ......................................................................................................... 22 3.7 SEM - Scanning electron microscopy ....................................................................... 23 3.8 Disintegration ............................................................................................................ 23 3.9 Klason lignin .............................................................................................................. 23 3.10 Acid soluble lignin ..................................................................................................... 24 3.11 Carbohydrate analysis ................................................................................................ 24 4. RESULTS AND DISCUSSION ..................................................................................... 25 4.1 IR-spectroscopy analysis ........................................................................................... 25 4.2 SEM-pictures of non-retorted and retorted material .................................................. 26 4.3 Temperature as an effect of disintegration ................................................................ 27 4.4 Addition of starch with and without AKD as an effect of disintegration