How Paper is Made
A Fourdrinier unit is pictured here. A slurry of fiber is being metered
onto the moving wire at the far right in this picture, with movement of
the wire toward the left. The drier units can be seen at the far end of
the production line.
(Photo courtesy: American Forest and Paper Association)
|This is a photo of softwood that has been chemically pulped. Note that the fibers are straight, smooth, and largely undamaged.|
|For the most part, however, smooth surfaces and rounded, undamaged fiber are not what is needed in making a quality sheet of paper. Fibers must be flattened to increase the contact area (and thus the bond potential) between them.|
Flattened fibers can be readily seen in this highly magnified photo of
the surface of paper.
(Photo by John Crist and Ron Teclaw)
Moreover, by unraveling microfibrils from the cell walls, surface area
(and thus hydrogen bonding potential) can be greatly increased as
illustrated by this photo of mechanically produced fiber.
(Photo: John Crist and Ron Teclaw)
The way that fibers are flattened, and subjected to a mechanical rubbing
action that unravels microfibrils, is through the use of a beater. A
simple beater (a Hollander beater) is shown here. A slurry of fiber
goes around and around in the tub, each time passing between a fixed
bedplate and the ribs of a rotating beater wheel. The opening between
the bedplate and wheel is set to about the width of a single wood fiber,
meaning that fibers are pounded and deformed with each pass.
(Image adapted from TAPPI)