Paper processes - Preparing pasta

The principle of paper manufacture has changed very little since its invention. From an aqueous suspension of cellulose fibers, a sheet is formed on a wire by dewatering: this fibrous mat is then pressed and dried to remove excess water. Papermaking therefore involves bringing papermaking fibers into contact with water, to promote $\left(\text{—OH}\right)$ hydrogen bonds, and then extracting this water to stabilize the strength properties of the fibrous network. These bonds between fibers, created in the wet end of the machine, will provide the main qualities of the paper material, which will materialize during the various phases of sheet consolidation, i.e. pressing and drying.

While the principle has not changed, the technologies used in the various stages have evolved considerably. These successive transformations of the process have their origins in the industry's constant concern to produce paper of better quality, ever faster and at the lowest possible production cost.

The process can be divided into two main phases:

• the preparation of the pulp, the subject of this article [J 6 901], which enables the paper machine to be fed with a raw material that is adapted to the specifications of the desired paper, i.e. well dispersed, clean, decontaminated and supplemented, if necessary, with appropriate additives (fillers, colorants, etc.);

• paper or cardboard manufacture itself, on the paper machine, where the final shaping of the material takes place, which is the subject of this article. .

Paper pulp, whether produced by mechanical or chemical processes, or from recovered fibers, requires a preparation phase before being sent to the paper machine itself.

The main stages of preparation are as follows:

• disintegration and suspension ;

• refining ;

• introduction of various additives ;

• purification ;

• dilute to desired concentration.