Biaxial Straining of Handsheets During Drying- Effect on In-Plane Mechanical Properties, 1998 Engineering Conference Proceedings

If paper could be prevented from shrinkage or even stretched in the cross machine direction of a paper machine the stiffness of the paper in the cross machine direction could be substantially increased and it would be possible to remove the undesired cross machine variation in paper properties.

The purpose of this investigation was to study isotropic handsheets in an apparatus where the strains in both in-plane directions could be varied independently of each other and to obtain fundamental knowledge of how different combinations of strains in two in-plane perpendicular directions of a wet isotropic paper influence the final paper properties.

The two perpendicular in-plane directions of the wet paper were defined as the l-, and 2-direction. The strain in the l- direction was varied in the same way (from shrinkage to stretch) in four different trials. In the first trial, strain (2) was equal to strain (1). In the second, strain (2) was zero (restrained dried). In the third, strain (2) was 2% (2% stretch). In the fourth trial, strain (2) was -3 % ( 3% shrinkage).

Tensile stiffness index, tensile index and compression index increased and strain at break decreased with increasing strain during drying. The studied paper properties in either of the two directions were independent of the strain in the perpendicular direction in the studied isotropic handsheets. If the results could be transferred to the paper-making process, it would be possible to improve the cross machine paper properties by preventing shrinkage or even stretching the paper in this direction without any negative influences on the properties in the machine direction. Note, however, that this requires that the strain can be controlled in both directions independently of each other.