How are cotton and linen rags cleaned before they are made into paper pulp?

To prepare cotton and linen rags for papermaking, they undergo a multi-step cleaning process to ensure the resulting rag paper meets high standards of purity and durability:

• Mechanical Preparation: Upon arrival at the mill, rags are mechanically threshed and sorted by hand to remove foreign materials like rubber, metal, and paper, as well as synthetic fibers or coatings.
• Cutting and Dusting: The sorted rags are cut into smaller pieces and dusted to eliminate fine particles of debris.
• Magnetic Separation: The material is passed over magnetic rolls to extract any remaining iron.
• Cooking: The rags are cooked in large boilers for three to ten hours using steam under pressure. The cooking liquor consists of a dilute alkaline solution—typically lime and soda ash or caustic soda—mixed with detergents or wetting agents to remove natural waxes, oils, grease, and fillers.
• Washing: Following the cooking process, the rags are thoroughly washed before proceeding to mechanical beating, which softens and fibrillates the fibers for better sheet formation.1