deinked

Deinked refers to pulp produced by removing printing ink from recovered paper during the recycling process. The resulting deinked pulp (DIP) is used as a raw material for making white or light-colored papers and is a key component in chemical-physical recycling of printed materials. Deinking aims to separate ink from fibers while preserving fiber strength to produce a usable pulp.

The deinking process typically involves repulping the recovered paper in water, screening to remove large contaminants, and flotation deinking where inks are released from fibers and attached to air bubbles. In flotation, conditioned pulp is aerated so ink particles collect at bubble surfaces and are skimmed off as froth. The slurry is then washed to remove residual ink, chemicals, and fines. The pulp may be thickened, refined, and sometimes bleached to reach target brightness before forming DIP for a specific grade. Feedstocks commonly include old newspapers (ONP), old magazines, and office waste paper (OWP), with old corrugated containers (OCC) often diverted to non-deinking recycling streams.

Chemicals and additives used include alkaline pulping agents (such as sodium hydroxide and sodium silicate), surfactants, dispersants, flotation agents, and polymers for fines retention and brightness improvement. Process conditions are adjusted to optimize ink removal for different ink types and fiber furnishes.

Applications and quality: DIP is used to manufacture various grades of paper, including printing and writing papers, packaging boards, and blends for higher-quality papers. Brightness, cleanliness, and fiber integrity are key quality metrics, influenced by ink type and processing conditions.

Environmental considerations: Deinking generates wastewater containing ink particles, resins, and additives, requiring treatment. The process reduces reliance on virgin fibers and can lower bulk landfill waste when integrated with comprehensive recycling systems.