Faculty of Technology and Science Chemical Engineering Carolina Larsson Sizing of different pulp qualities Master thesis in Chemical Engineering specialised in Pulp Technology, 30 credit points Date: 2008-04-03 Supervisors: Ing-Marie Bernskiöld Stora Enso Skoghall Annki Karlsson Stora Enso Research Centre Lars Ödberg Fiber- and Polymer Technology, KTH Examiner: Ulf Germgård Karlstad University Karlstads universitet 651 88 Karlstad Tfn 054-700 10 00 Fax 054-700 14 60 [email protected] www.kau.se Preface The work presented in this degree project was carried out between September 2007 and April 2008 at Stora Enso Research Centre in Karlstad, Sweden. This thesis concludes the M.Sc study in Chemical Engineering at Karlstad University. First of all I would like to thank everyone at Stora Enso Research Centre and Skoghall Mill who has helped me during this project. Thank you for lending me your equipment and answering all my questions and also for making me feel welcome. I am especially grateful to my supervisors Annki Karlsson and Ing-Marie Bernskiöld for your engagement and enthusiasm in this project. I would also like to thank Professor Ulf Germgård at Karlstad University for being my examiner. Finally I would like to thank Professor Lars Ödberg for your valuable knowledge and for contributing in designing this project as well as analysing the results. Summary Edge wicking, i.e. in-plane wetting, is an The kraft pulps gave sheets with satisfactory edge important parameter for liquid packaging board wicking even at the lowest size dosage (1 kg/t) products. Before filling of the products at the while CTMP required a dosage of 4 kg/t to reach dairy the web is being sterilised with hydrogen the same wick index. peroxide (H O ). A tube is shaped and cut into 2 2 To achieve acceptable pressurised edge wicking packages which mean that new surfaces are values the most important parameter was found to created. If a short stop occurs in the sterilising be the density of the sheets. The kraft pulp sheets bath the raw edges exposed to H O could absorb 2 2 gave the lowest edge penetration while the high the liquid and when the package later is being freeness CTMP sheets did not give satisfactory filled this absorption could lead to tube burst. For penetration resistant even at the highest size the end products it is also important to prevent the dosage ( figure i ). liquid from penetrating the raw edges of the board in order to maintain the functionality and fresh The edge wicking of lactic acid could be look of the package. prevented by sizing with AKD only. Sheets made from mono sized sheets containing rosin size did To control edge wicking different kinds of not manage to avoid a large in-plane wetting of internal hydrophobic sizing agents are used. Alkyl the board structure. Hence, dual sizing to improve ketene dimer (AKD) is the most common size in the edge wicking of lactic acid is not necessary. neutral sizing and rosin in conjunction with alum The density was found not to be an important is the traditional acidic sizing agent. AKD and parameter in lactic acid edge wicking, all the rosin size are often used in combination (dual pulps got equal edge wicking regardless of sizing) to make the board hydrophobic. density. Retention above 1 kg/t AKD in sheets The objective of this work was to examine the was enough to prevent penetration. Retention effects of the sizing agents on different pulps in above 1.5 kg/t AKD in sheet did not improve the different dosages. The pulps used in the sheet edge wicking any further. preparation were unbleached kraft pulp as well as No significant difference in sizeability between bleached and unbleached CTMP refined to unbleached and bleached CTMP was observed. different levels. Apart from varying the size dosages, the wet sheets were also pressed at 10 Unbl. CTMP, different levels to vary the density. The major CTMP 1 kg/ton low CSF ] 2 9 part of the study included dual sizing but a Bl. CTMP, 2 kg/ton minor part also concerned mono sized sheets. 8 low CSF Unbl. CTMP, 4 kg/ton The parameters investigated on the laboratory 7 medium1 CSF sheets were STFI-Density, hydrogen peroxide 6 Unbl. CTMP, edge wicking, pressurised edge wicking, lactic medium2 CSF acid edge wicking (LA) and AKD and rosin 5 Bl. CTMP, Kraft pulp medium2' CSF size content. 4 Unbl. CTMP, In hydrogen peroxide edge wicking the 3 high CSF Bl. CTMP, amount of size was the central source of 2 high CSF improved wick index. The retention was 1 Unbl. kraft pulp, therefore of great significance for the results. 0.15 bar pressurised edge wicking [kg/m low SR 0 Unbl. kraft pulp, The dual sized sheets were found to give least 150 250 350 450 550 650 750 850 3 high SR edge wicking, due to the synergy effect STFI-density [kg/m ] between AKD and alum rosin size. Figure i. Pressurised edge wicking (0.15 bar) as a function of STFI-Density for dual sized sheets made with CTMP and kraft pulp respectively. Red symbols (high freeness), black and green symbols (medium freeness) and blue symbols (low freeness) represent CTMP. Pink and grey symbols represent the kraft pulps. AKD and rosin size at three different dosages (1, 2 and 4 kg/t of each size) are shown with different signs. The sheets were pressed at three different levels. Contents 1. Introduction ................................................................................................1 1.1. Theory............................................................................................1 1.2. Scope..............................................................................................3 2. Materials.....................................................................................................4 2.1. Pulps...............................................................................................4 2.2. Chemicals.......................................................................................4 2.2.1. Chemicals used for sheet forming .....................................4 2.2.2. Chemicals used for edge wicking tests..............................4 3. Methods......................................................................................................4 3.1. Sheet preparation ...........................................................................4 3.2. Fibermaster ....................................................................................6 3.3. Charge analyses .............................................................................6 3.4. STFI-Density..................................................................................7 3.5. Amount of size in paper.................................................................7 3.6. Edge wicking tests .........................................................................8 3.6.1. Hydrogen Peroxide edge wicking......................................8 3.6.2. Pressurised edge wicking ..................................................8 3.6.3. Lactic Acid edge wicking..................................................8 3.7. Standard deviation .........................................................................9 4. Results and discussion.............................................................................10 4.1. Fibermaster ..................................................................................11 4.2. Retention......................................................................................12 4.3. Dual sizing ...................................................................................14 4.3.1. Hydrogen peroxide edge wicking....................................14 4.3.2. Pressurised edge wicking ................................................16 4.3.3. Lactic acid edge wicking .................................................19 4.4. Mono sizing .................................................................................21 5. Conclusions ..............................................................................................24 6. Further Work ............................................................................................25 7. References ................................................................................................26 [Sizing of different pulp qualities ] Appendices ....................................................................................................A Appendix 1: Experimental plan and results .........................................A Appendix 2: FiberMaster ..................................................................... E Appendix 3: Charge analysis ................................................................F Appendix 4: Retention .........................................................................G Appendix 5: Hydrogen peroxide edge wicking ...................................H Appendix 6: Pressurised edge wicking................................................. J Appendix 7: 24 h Lactic acid edge wicking......................................... L Appendix 8. Standard deviation.......................................................... M Appendix 9: Unbleached vs bleached CTMP......................................N [Sizing of different pulp qualities ] 1. Introduction In-plane wetting, or edge wicking, is a very critical parameter for liquid packaging boards. It is necessary to control the penetration of aqueous liquids into the packaging board during filling in the filling machine to avoid tube breaks and at the raw edges in the end use products. Before filling of the products the reel of packaging material