Observation of the swelling behavior of kraft fibers and sheets in the environmental scanning electron microscope

The swollen state of kraft fibers and sheets was observed in an Environment al Scanning Electron Microscope (ESEM). Chemical fibers swelled to a great extent during wetting. ESEM observations clarified the morphological featur es of freeze-dried kraft fibers in a handsheet soaked, from a handsheet soa ked and defibrated, from a dry lap pulp beaten and of never-dried pulp. The fibers of a handsheet soaked in water for 3 days did not recover to comple te tube-like shape. Image analysis made on three fibers in a handsheet show ed that only fully collapsed fibers on the top surface, which faced a metal plate, recovered fairly to tube-like shape and the estimated vertical thic kness increase of the fiber was about 50%, corresponding to 11.5% width shr inkage. But, a less collapsed underlying fiber showed only a 20% thickness increase (4.0% width shrinkage). Mechanical action of defibering did not af fect shape recovery of fibers from a dried handsheet. Beating returned few dry lap pulp fibers back to tube-like shape though most of them remained co llapsed. Fibers from never-dried pulp appeared tube-shaped, yet, with some parts collapsed presumably due to compression of the fibers to 20% consiste ncy for storage.