Effect of Condebelt Drying on the Structure of Fiber Bonds, 1993 Papermakers Conference Proceedings

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Significantly higher strength properties related with bonding strength of the fibers are obtained with Condebelt drying when compared with conventional multicylinder drying. The better strength properties are usually explained by increased density and softening of lignin and hemicelluloses in the fibers.

In this study, the fiber bonds in a Condebelt dried sheet are examined by using confocal laser scanning microscopy. This technique makes possible the examination of fiber bonds per se, which has not earlier been possible. It is also possible to take 3D-photographs of the bonds. Various grades, with different fiber make-ups, have been studied.

The results clearly show that the fiber bonds are covered with a thin layer, which can resist water. This layer cannot be seen in conventionally dried sheets. The layer obviously increases the strength of the fiber bonds, and its ability to resist water results in better wet strength properties in Condebelt dried sheets. The change in bond structure takes place on both the hot platen side as well as on the cold platen side of the sheet. The results obtained seem to verify the earlier theories shown in the literature about the effect of press drying on the structure of fiber bonds.

The density distribution in the z-direction in a Condebelt dried web has been compared with that in a conventionally dried sheet.