Production, characterization and end products of dissolving pulp Jimi Leivo, Antton Lahnalammi, Florian Burkhart Aalto University School of Chemical Engineering
Dissolving pulp High cellulose content (> 90 %) Different charasteristics not made into paper used to manufacture e.g. regenerated fibers or cellulose derivatives Chemical properties > fibre properties Reactivity to reagents and solvents describes the processability of the dissolving pulp Jimi Leivo 2
Production All types of wood and cotton linters are suitable for producing dissolving pulp Similar to the papermaking process; the main difference is to remove hemicelluloses Same process stages Longer cooking and bleaching time Bigger amount of reject Jimi Leivo 3
Production Prehydrolysis kraft cooking Currently most popular method Liquid or gaseous phase Continuous or batch process Environmentally friendly Sulfite pulping Cooking is longer and more acidic than conventional pulping One-step batch cooking + 0 Higher yield and reactivity + + + + Jimi Leivo 4
Dissolving pulp characterization Desired properties of dissolving pulp differ according to different end products Complete removal of noncellulosic impurities not feasible due to e.g. high yield losses laboratory scale simulations can be used to determine suitability in each case Most important property is pulp reactivity, which is affected by: the physcial structure of the cellulosic material (accesibility) the type of chemical interactions with the reagents (functional groups) Antton Lahnalammi 5
Residual fractions Hemicelluloses and residual ligning cause yellowing and worsen processability (e.g. filterability) Extractives can cause problems due to e.g. precipitaition, but may increase accessabilty due to lower surface tension Inorganics: e.g. Fe 2+ and Cu 2+ severly impair H 2 O 2 bleaching Antton Lahnalammi 6
Macromolecular properties Molar mass and molar mass distribution Mechanical properties: short chain molecule (DP<100) fraction corresponds strongly with weakened properties Functional groups Present in raw material and formed during pulping/bleaching Most important are the reducing end groups and oxidized OH groups in cellulose and carboxyl groups in hemicelluloses. Carbonyl and carboxyl groups cause e.g. strength loss and yellowing Antton Lahnalammi 7
Physical structure Supramolecular structure Ratio of amorphous and crystalline regions Cellulose polymorphism (e.g. Cellulose I -> Cellulose II) Cell wall structure Removal of primary cell wall during acid sulfite pulping Different arrangement of hemicelluloses across the cell wall in PHK and acid sulfite pulps Pore structure, accessibility Pore volume and distribution, WRV, hornification Fibre morphology Different cell types and dimensions (hardwoods) Antton Lahnalammi 8
Degradation of dissolving pulp Degradation expirements provide information about the supramolecular structure, funcionalities and changes in the molecular weight distribution Thermal, chemical, mechanical or radiaton degradation Example: resistivity or solublity in 10 m% and 18 m% NaOH (R10, S18 etc. ) R18 gives rough estimate of crystalline cellulose Hardwood alphacellulose content can be estimated as (R10+R18)/2 S10 estimates hemicellulose fraction S18 estimates the combined hemicellulose and low MW cellulose fraction Antton Lahnalammi 9
Products manufactured from dissolving pulp Cellulose regenerates & Cellulose derivates Cellulose in it s pure form Cellulose II Raw material dissolved Dope Spinnbath Post treatment Cellulose is modified Ethers and esters Different chemical engineering for different products Regioselectivity Florian Burkhart 10
Regenerated cellulose with modified intermediate step CV & CMD (viscose fibers, rayon, modal) NaOH treatment Xanthation with CS2 and dissolution Wet spinning Stretching of fibers Cutting of fibers Washing of fibers Florian Burkhart 11
Regenerated cellulose out of direct dissolved Cellulose Lyocell Tencel N-Methylmorpholine N-oxide (NMMO) as solvent NMMO is not toxic Dry-wet spinning with air gap Fibrillated For textiles and nonwovens Florian Burkhart 12
Fibers from cellulose derivates Cellulose triacetate Thermoplastic Esterification with acetic anhydride Primary and secondary CA Hydrophobic Production of flakes after flocculation in diluted acetic acid Melt spinning Florian Burkhart 13
Other Cellulose based fibers Cupro Cuoxam for cellulose dissolution Ioncell Ionic Liquids for cellulose dissolution BoCell superphosphoric acid; spun via air gap in aceton Michelin process cellulose formate (formic acid and phosphoric acid) DuPont process cellulose acetate dissolved to form liquid crystalline solution and spun into a coagulation bath of menthol Fortisan saponified cellulose acetate, dry spinning after dissolution in acetone All fibers show different properties for example in strength and water adsorption Florian Burkhart 14
Florian Burkhart 15
Conclusions Dissolving pulp: >90% cellulose Production and charaterization are similar to paper making pulp Wide variety of products can be derived from dissolving pulp Charasteristics vary according to the desired end products Jimi Leivo, Antton Lahnalammi, Florian Burkhart 16
Sources H. Mahlamäki, Upgrading Kraft Pulp to Dissolving Pulp Using Cold Caustic Extraction (Literature Review), 2013: Heini_Mahlamäki_ColdCausticExtraction.pdf T. Röder, J. Moosbauer, G. Kliba, S. schlader, G. Zuckerstätter, H. Sixta, Comparative Characterisation of Man-Made Regenerated Cellulose Fibres, Lenzinger Berichte 87, pp. 98-105, 2009 B. Saake, Cellulosederivate und Celluloseregenerate, Vorlesungsfolien Holzwirtschaft Universität Hamburg, 2013 H. Sixta, Lecture slides, 2012: Puu-04110_L21_Carbohydrate-based_Products_I.pdf H. Sixta, Pulp Properties and Applications, Dissolving Grade Pulp, in H. Sixta (ed.), Handbook of Pulp, WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim, 2006, pp. 1022-1067. Available online in Aalto University: http://onlinelibrary.wiley.com/book/10.1002/9783527619887 (accessed 29/10/2013) KnowPulp, Dissolving pulp: know.aalto.fi (accessed 3/11/2015) Jimi Leivo, Antton Lahnalammi, Florian Burkhart 17