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, Vol. 15, no 5, 452-458 p.Article in journal (Refereed) Published
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.
Place, publisher, year, edition, pages
2000. Vol. 15, no 5, 452-458 p.
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
Paper, Pulp and Fiber Technology
IdentifiersURN: urn:nbn:se:kth:diva-24132DOI: 10.3183/NPPRJ-2000-15-05-p452-458ISI: 000167751400018OAI: oai:DiVA.org:kth-24132DiVA: diva2:344062
QC 201008172010-08-172010-08-172010-08-17Bibliographically approved