How does pulping turn wastepaper into material for new paper?

Pulping is the essential first step in recycling wastepaper, designed to transform used paper products back into a usable fibrous state. The process occurs in a pulper, which is a large cylindrical tank equipped with rotating agitator blades.12

When wastepaper is fed into the pulper, it is mixed with water to create a pulp-water slurry. The agitator blades circulate this mixture, mechanically separating and dispersing the cellulose fibres. In cases where the paper must be de-inked—such as for printing-grade or white papers—hot water and various chemicals, most commonly caustic soda, are added to assist in breaking down the material and dispersing inks.12

Once the fibres are separated, the resulting stock undergoes further processing:
* Screening: Special devices and screens remove larger pieces of trash, dirt, and other foreign materials.1
* Washing: The stock is washed to remove dispersed ink, chemicals, and finer particles.1
* Bleaching: In some instances, hypochlorite is used to improve the whiteness of the recovered fibre.1

After these steps, the cleaned fibres are ready to be used as material for new paper products.1