Biaxial straining of handsheets during drying - Effect on delamination resistance

The purpose of this work was to investigate the influence of drying strateg ies on the delamination properties of handsheets. Laboratory experiments we re performed on a biaxial dryer. Different combinations of shrinkage and st retch were applied in two perpendicular directions of the handsheets. The d elamination properties, Z-toughness, Scott Bond and Z-direction tensile str ength, were evaluated. Regardless of how the shrinkage or stretching was performed during drying, the total change in area was found to be the controlling factor for the del amination properties. An area decrease resulted in an increase in the delam ination resistance whereas an area increase resulted in a loss of delaminat ion resistance. The decrease in delamination resistance was attributed to a reduction in bonded area between fibres in the sheet, characterised by an increase in the light scattering coefficient.