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A Close-up of Paper Formation

Paper formation in a paper machine, when looked at closely, is found to be a complex process. When paper is made in a paper machine, one of the primary events that occur is when the fibers are made to stick together. This is done on the forming table in the wire section of the paper machine. Water is gradually drained away, leaving the fibers behind. While this occurs, water acts as an intermediate hydrogen bonding agent. When the water is finally drained away, the fibers become pressed together to become hydrogen bonded to one another in the press section of the paper machine.

Below is an illustration showing water(H-O-H) as an intermediary hydrogen bonding agent(hydrogen bonding is shown with dashed lines).

Hydrogen bonding is responsible for a multitude of things in other nature, such as the structure of ice in snowflakes and protein folding. Hydrogen bonding is partly what give paper its strength, but sometimes "wet strengtheners" are added as well. Too little of this bonding, and the paper can fall apart, too much, and the paper becomes inflexible, so papermakers have to make sure there is enough bonding to insure integrity, while simultaneously maintaining flexibility(unless containerboard is being made).

Below is a micrograph(a microscope photograph) of a Kleenex tissue paper(colorized for clarity).

At this magnification, one can easily see the pores and the fibrous and non-uniform nature of paper. This image is similar to what one would see if one looked at writing paper, though the fibers would be less slackened. There are two types of pores in paper:
  • Pores between individual fibers, which range from 10-100 Ám wide(1 Ám is 1/1000th of a meter). Fillers that are added to paper block some of these pores, so that liquid cannot(or is less able) to be absorbed by the paper.

  • Pores which are inside the fibers themselves, the width of which range anywhere from 0.001Ám to 0.05Ám.

The structure of paper is varied depending on the type and it helps one to understand why different types of paper have such varied properties, such as tear strength and flexibility.