The effect of sizing and paper structure on paperboard for retortable packaging
2007 (English)In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, Vol. 22, no 2, 200-209 p.Article in journal (Refereed) Published
Food packaged in a retortable paperboard-based carton is sterilised by exposing the container to high-temperature steam. The board used must have greater water repellence than common liquid packaging board, since heated steam will condense on the uncovered edges. The research reported in this paper studied critical factors affecting edge wicking in sized paperboards immersed in water at 95 degrees C or placed on a cooling plate and exposed to saturated steam at 130 degrees C. The paperboards were made from refined and unrefined bleached pulp as well as from refined unbleached pulp, in one or two plies, with different sizing levels and densities. The swelling of the boards was also examined before and after treatment at 150 degrees C for 6 hours.
For samples immersed in water, the sizing level, paper structure and fibre swelling of the board affected the edge wicking. The unsized edges had a marked effect on the results, for this was where edge wicking was initiated. Boards with lower sizing levels, lower density, made from unrefined pulp and made from unbleached pulp showed more edge wicking than other boards.
All the samples exposed to saturated steam on a cooling plate showed similar patterns of edge wicking, except that boards with a low level of AKD showed far more edge wicking than others. However, the moisture content profiles in the samples measured with NIR spectroscopy were more uniform in the sample made from unrefined pulp and the low-density samples than in samples with higher density, which had much higher moisture content at the cut edge. These results can be explained by the fact that the saturated steam condenses at the edge of the high density boards resulting in liquid edge wicking by diffusion into the fibre network while the steam is also able to be transported into the pore structure of the low density board followed by condensation or diffusion into the fibre network.
Heat-treated boards immersed in water showed a lower moisture content and a lower expansion in the z-direction than untreated references. The reduction was larger in boards made from unbleached pulp, which may explain the different findings relating to edge wicking when boards made from bleached and unbleached pulp were immersed in water or exposed to steam.
Place, publisher, year, edition, pages
2007. Vol. 22, no 2, 200-209 p.
edge penetration, moisture content, fibre swelling, AKD sizing, paper structure, liquid packaging board, autoclaving, density
Paper, Pulp and Fiber Technology
IdentifiersURN: urn:nbn:se:kth:diva-6274DOI: 10.3183/NPPRJ-2007-22-02-p200-209ISI: 000248057800009OAI: oai:DiVA.org:kth-6274DiVA: diva2:10946
QC 20101125. Uppdaterad från Manuskript till Artikel (20101125). Tidigare Titel: "The effect of sizing and paper structure on board for canned food".2006-10-232006-10-232010-11-25Bibliographically approved