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On the Internal Sizing Mechanisms of Paper with AKD and ASA Related to Surface Chemistry, Wettability and Friction
KTH, School of Chemical Science and Engineering (CHE), Chemistry.
2007 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Paper and board are hydrophobized (sized) to control the spreading and absorption of waterbased inks and retard the absorption and edge penetration of liquid packaging by aqueous liquids. Alkenyl ketene dimers (AKD) and alkenyl succinic anhydride (ASA) are synthetic sizing agents that are generally used under neutral or slightly alkaline papermaking conditions.

The overall objective of this thesis is to improve understanding of the internal sizing of paper and board by AKD and ASA by establishing a link between the sizing mechanism on one hand, and properties of sized papers, such as surface chemistry, wettability and friction, on the other. Fundamental research has been conducted in parallel with more applied research on laboratory and pilot papers. Significant effort has been expended to study the spreading behavior of AKD. The main instrument to characterize the surface chemical composition of AKD and ASA sized papers was X-ray photoelectron spectroscopy (XPS). By combination with time-of-flight secondary ion mass spectrometry (ToF-SIMS) we have been able to determine the lateral distribution and the chemical state of the sizing agent at the paper surface. Combined with contact angle measurements using liquids with different surface tensions, and other methods to analyze the amounts of size in paper, this has enabled us to obtain a deeper knowledge of the sizing mechanisms of AKD and ASA.

The results indicate a definitive relationship between the redistribution of AKD at the surface of pilot papers and the drying profile used during papermaking. However, the spreading was not complete, as also seen on a model surface. Further spreading of AKD was shown to occur via surface diffusion in the form of an autophobic monolayer precursor. The spreading rate increased linearly with temperature and showed an inverse proportionality with respect to the melting point of the AKD. This monolayer spreading is relatively slow the diffusion coefficient being of the order 10-11 m2/s. AKD spreading was not hindered by hydrolyzed AKD (ketone) that spread as well. Moreover, AKD spread on the surface of crystalline calcium carbonate. In laboratory papers, the extractives present on CTMP fiber surfaces appeared to have enhanced the spreading of AKD when the fibers were in water.

In spite of a slightly lower retention, ASA covered the surface of unfilled and PCC-filled pilot papers to a significantly higher extent than AKD. The ASA sized papers, however demonstrated slightly lower resistance to water. This was attributed to formation of hydrolyzed ASA products. The results obtained confirm the proposed sizing mechanism for ASA, where the hydrolyzed ASA plays a key role. The sizing level of these papers stored wrapped in aluminium foil at 23 °C and 5O %RH was nearly unchanged over prolonged storage time. In contrast, the papers exposed to ambient conditions suffered from sizing loss, most likely due to hydrolysis and migration. The reduction of the sizing degree was higher for the AKD than ASA sized unfilled papers and the catalytic effect of PCC contributed to the hydrolysis of AKD in PCC-filled papers.

As expected, the use of sizing agent reduced the surface energy of paper. The higher the sizing degree of paper the lower the surface energy, and thus the higher the resistance to wetting. This was particularly seen in the contact angles with ethylene glycol having a lower surface tension than water.

AKD significantly decreased the friction between unfilled papers, whereas ASA had no impact. This difference was attributed to surface chemical composition. Friction reduction for the AKD sized papers started at the AKD coverage normally found in paper produced for low water absorption. As expected, PCC filler increased paper-to-paper friction.

Abstract [sv]

Papper och kartong hydrofoberas (limmas) för att kontrollera spridning och absorption avvattenbaserade tryckfärger och hindra kantinträngning av vattenbaserade vätskor ivätskekartong. Alkylketendimer (AKD) och alkylbärnstensyra anhydrid (ASA) är syntetiskahydrofoberingsmedel som allmänt används under neutrala eller något alkaliska förhållandenvid papperstillverkning.Arbetets övergripande målsättning var att förbättra förståelse för mäldhydrofobering avpapper och kartong med AKD och ASA genom att upprätta ett samband mellanhydrofoberingsmekanism på ena sida och ytkemi hos hydrofoberat papper och dessvätningsförmåga och friktion på den andra sidan. Grundläggande studier parallellt med mertillämpade undersökningar på laboratorie- och pilotpapper har utförts. En betydande strävanhar använts för att studera spridning av AKD. Huvudinstrumentet för att karakterisera kemisksammansättning av ytan av pilotpapper hydrofoberade med AKD och ASA var röntgenfotoelektron spektroskopi (XPS). Genom att kombinera det med sekundär jonmasspektrometri (ToF-SIMS) har lateral fördelning och kemiskt tillstånd av AKD och ASAvid en yta av papper kunnat bestämmas. Kombinerat med mätningar av kontaktvinkel medvätskor med olika ytspänning och andra metoder för att analysera halten avhydrofoberinsgmedel i papper har gjort det möjligt att erhålla djupare kunskap omhydrofoberingsmekanismer av AKD och ASA.Resultaten indikerar en klar koppling mellan omfördelning av AKD på ytan av pilotpapperoch torkningsprofil vid papperstillverkning. Emellertid, spridningen var inte fullständig, vilketvar fallet även på modellytor. Fortsatt spridning av AKD visades ske som ytdiffusion i formav ett autofobiskt monoskikt (precursor film). Spridningshastigheten ökade linjärt medtemperatur och visade omvänd proportionalitet med avseende på AKD:s smältpunkt. Dennamonoskiktspridning är relativt långsam, diffusionshastighet är i storleksordningen 10-11 m2/s.Hydrolyserat AKD (keton) hindrade inte AKD:s spridning utan spred även den. Dessutomspred AKD på ytan av kristallina kalciumkarbonat. I laboratoriepapper är extraktivämnennärvarande på ytor av CTMP fiber och tycktes ha förbättrat AKD:s spridning när fibrerna varunder vatten.ivTrots något lägre retention täckte ASA ytan av icke-fyllda och PCC-fyllda papper tillsignifikant högre grad än AKD. ASA-papperen visade dock något lägre motstånd mot vatten.Detta var hänvisat till bildning av hydrolyserade ASA-produkter. De uppnådda resultatenbekräftar den föreslagna hydrofoberingsmekanismen för ASA, där hydrolyserat ASA spelaren avgörande roll. Hydrofoberingsgraden av papper lagrade inlindade i aluminiumfolie vid23 °C och 50 RH var nästan oändrad över den förlängda lagringstiden. Som motsatsgenomgick papperen som exponerats mot omgivande atmosfärsförhållanden genomgick enminskning av hydrofoberingsgraden, troligen på grund av hydrolys och migrering. Minskningav hydrofoberingsgraden var större för icke-fyllda papper av AKD än av ASA. PCC:skatalytiska effekt bidrog till hydrolys av AKD i PCC-fyllda papper.Som förväntat reducerade användning av hydrofoberingsmedel reducerade ytenergin avpapper. Ju högre hydrofoberingsgrad desto lägre var ytenergin och därmed desto högremotstånd mot vätning. Detta sågs särskilt i kontaktvinklar med etylenglykol som har lägreytspänning än vatten.AKD minskade signifikant friktionen mellan icke-fyllda papper, medan ASA inte hadeinverkan. Denna skillnad hänfördes till skillnad i ytsammansättning. Minskning av friktion förAKD-hydrofoberade papperen påbörjades vid en sådan yttäckning av AKD som är normaltför papper tillverkat för låg vattenabsorption. Som förväntat ökade PCC-fyllmedel friktionenmellan papperen.

Place, publisher, year, edition, pages
Stockholm: KTH , 2007. , vii, 62 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2007:77
National Category
Physical Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-4537ISBN: 978-91-7178-801-6 (print)OAI: oai:DiVA.org:kth-4537DiVA: diva2:12738
Public defence
2007-11-30, F3, KTH, Lindstedtsvägen 26, Stockholm, 14:00
Opponent
Supervisors
Note
QC 20100817Available from: 2007-11-16 Created: 2007-11-16 Last updated: 2010-08-17Bibliographically approved
List of papers
1. Mechanism of internal sizing by alkyl ketene dimers (AKD): the role of the spreading monolayer precursor and autophobicity
Open this publication in new window or tab >>Mechanism of internal sizing by alkyl ketene dimers (AKD): the role of the spreading monolayer precursor and autophobicity
2000 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 15, no 5, 452-458 p.Article in journal (Refereed) Published
Abstract [en]

Alkyl ketene dimers (AKD) only partially wet cellulose and silica surfaces. Further spreading of AKD molecules is shown to occur by surface diffusion in the form of an autophobic monolayer precursor, which grows from the foot of the AKD drop/particle. The surface area covered by the monolayer grows linearly with time. The rate of the precursor growth is proportional to the ambient temperature and decreases with increasing AKD melting point. Overall, the monolayer diffusion process is shown to be quite slow. The apparent surface diffusion coefficient is of the order 10-(11) m(2)/s.

The effect of the monolayer spreading can he seen in the time evolution of the hydrophobicity during storage of AKD sized hand-sheets. There are clear indications that the relatively slow monolayer spreading process plays a key role for the build-up of paper hydrophobicity. The rate of this process is, for instance, observed to be compatible with the AKD monolayer spreading rates. The temperature dependence of the monolayer spreading and the build-up of sheet hydrophobicity are also similar. After long storage times, the build-up of hydrophobicity of the hand-sheets is expected to level off due to the fact that the AKD reservoirs in the form of surface retended AKD particles are limited. This predicted behaviour was observed in the present study. The sizing efficiency was indeed found to revert after prolonged storage. This de-sizing effect is attributed to desorption and vapour phase transfer of surface spread sizing agents.

Keyword
AKD; Alkyl ketene dimer; Autophobic; Contact angle; Hydrophobicity; Monolayer; Paper; Sizing; Spreading; Wetting; Cellulose; Contact angle; Desorption; Diffusion; Hydrophobicity; Molecules; Monolayers; Temperature; Wetting; Autophobicity; Phase transfer; Surface spread sizing agents; Sizing (finishing operation); Area; Dimers; Hand sheets; Internal sizing; Ketenes; Size; Spreading
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-24132 (URN)10.3183/NPPRJ-2000-15-05-p452-458 (DOI)000167751400018 ()
Note
QC 20100817Available from: 2010-08-17 Created: 2010-08-17 Last updated: 2017-12-12Bibliographically approved
2. On the monolayer spreading of AKD: influence of relative humidity,hydrolysed AKD, spreading promotor and the type of spreading surface
Open this publication in new window or tab >>On the monolayer spreading of AKD: influence of relative humidity,hydrolysed AKD, spreading promotor and the type of spreading surface
(English)Manuscript (preprint) (Other academic)
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-24133 (URN)
Note
QC 20100817Available from: 2010-08-17 Created: 2010-08-17 Last updated: 2010-08-17Bibliographically approved
3. The role of pulp type and drying profile in AKD sizing: sizing degree of papers determined by XPS and gas chromatography
Open this publication in new window or tab >>The role of pulp type and drying profile in AKD sizing: sizing degree of papers determined by XPS and gas chromatography
(English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669Article in journal (Refereed) Submitted
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-24134 (URN)
Note
QC 20100817Available from: 2010-08-17 Created: 2010-08-17 Last updated: 2017-12-12Bibliographically approved
4. Surface energy characterization of AKD-sized papers
Open this publication in new window or tab >>Surface energy characterization of AKD-sized papers
2004 (English)In: Journal of Pulp and Paper Science (JPPS), ISSN 0826-6220, Vol. 30, no 3, 70-73 p.Article in journal (Refereed) Published
Abstract [en]

Experimental papers with varying alkylketene dimer load were prepared and characterized with respect to size retention, reaction and hydrolysis. The characterization was done by using extraction studies, in combination with X-ray photoelectron spectroscopy and gas chromatography. The surface energy of the produced papers was evaluated using the Good-Oss method. It was shown that by stepping up size additions, both the polar and van der Waals components of the surface energy are reduced.

Keyword
Dimers; Electron microscopy; Gas chromatography; Ketenes; Size; Surface energy; X ray spectroscopy; Dimers; Extraction; Gas chromatography; Hydrolysis; Interfacial energy; Reaction kinetics; Van der Waals forces; X ray photoelectron spectroscopy; Long-term stability; Polymeric size; Size retention; Sizing efficiency; Dimers; Esca; Extraction; Gas Chromatography; Hydrolysis; Paper; Reaction Kinetics; Surface Energy; paper
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-24135 (URN)000221133800003 ()
Note

QC 20100817

Available from: 2010-08-17 Created: 2010-08-17 Last updated: 2017-12-12Bibliographically approved
5. AKD and ASA sizing of pilot papers: a comparative study. Surfacechemical composition in relation to wetting and friction properties
Open this publication in new window or tab >>AKD and ASA sizing of pilot papers: a comparative study. Surfacechemical composition in relation to wetting and friction properties
(English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669Article in journal (Refereed) Submitted
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-24136 (URN)
Note
QC 20100817Available from: 2010-08-17 Created: 2010-08-17 Last updated: 2017-12-12Bibliographically approved
6. Durability of the Sizing Degree of AKD and ASA Sized Papers Investigated by Contact Angle Measurements and ToF-SIMS
Open this publication in new window or tab >>Durability of the Sizing Degree of AKD and ASA Sized Papers Investigated by Contact Angle Measurements and ToF-SIMS
2009 (English)In: Journal of Dispersion Science and Technology, ISSN 0193-2691, E-ISSN 1532-2351, Vol. 30, no 6, 937-948 p.Article in journal (Refereed) Published
Abstract [en]

The influence of storage conditions on the sizing degree of AKD and ASA sized pilot papers was evaluated. A number of pilot papers sized with AKD or ASA were prepared from ECF bleached pulp fibers, unfilled and filled with 20% PCC, respectively and investigated in terms of sizing degree over a period of several months. The papers were stored at 23C and 50% RH either wrapped in aluminium foil or as separate sheets exposed to open atmosphere. The unfilled papers stored protected from ambient atmosphere after papermaking showed only a marginal reduction in sizing during prolonged storage. Only the paper having the lowest AKD-dosage suffered from reduced water-resistance, the Cobb60-value changed from 34 to 79g/m2. The PCC filled papers stored in the same conditions lost some of their sizing, to a higher extent in the case of AKD than for ASA sized papers. This was attributed to the further hydrolysis of the size catalyzed by PCC. In comparison, the sizing of the papers stored as separate sheets dropped significantly even after a few weeks in storage. In the end of the storage the AKD papers, particularly the unfilled ones had lost their sizing efficiency to a clearly higher extent than the ASA papers. The reduction in the sizing level occurred mainly during the first five weeks for the unfilled ASA and AKD papers, after which the process continued at a slower rate. The ToF-SIMS analysis revealed that both AKD and hydrolyzed AKD, the latter being the major portion, were present at the outermost surface of the unfilled AKD sized papers, but in significantly lower levels than in the case of the corresponding protected papers. In other words, a significant loss of AKD mass had occurred for the papers exposed to an open atmosphere. This was attributed to migration of AKD. The results demonstrated that ASA sized papers also suffered from size loss. The ToF-SIMS results showed no signal for active, nonbonded ASA and instead clear signals were observed for hydrolyzed ASA and for calcium and aluminium. As in the papers wrapped in aluminium foil, ASA was mainly in its hydrolyzed form. Although to a markedly lower extent, the reason for sizing loss in the case of ASA was the same as for AKD.

Keyword
AKD; Alkenyl succinic anhydride; Alkyl ketene dimers; ASA; Contact angle; ECF pulp; PCC; Sizing; Sizing degree; Sizing loss; Storage; ToF-SIMS; Wettability; XPS; Alkylation; Aluminum; Aluminum foil; Angle measurement; Bleached pulp; Calcium; Contact angle; Dimers; Paper sheeting; Secondary ion mass spectrometry; X ray photoelectron spectroscopy; Sizing (finishing operation); Aluminum Foil; Dimers; Durability; Hydrolysis; Ketenes; Mass Spectrometers; Paper; Sizing; Storage; Succinic Anhydride; Water Resistance
National Category
Paper, Pulp and Fiber Technology
Identifiers
urn:nbn:se:kth:diva-24137 (URN)10.1080/01932690802646330 (DOI)000266436200024 ()
Note
QC 20100817Available from: 2010-08-17 Created: 2010-08-17 Last updated: 2017-12-12Bibliographically approved

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