Mechanical pulp
Also: mechanical pulp, groundwood, TMP, CMP, CTMP
High-yield pulp made by mechanically separating wood fibers, retaining lignin. Used in newsprint and magazine papers.
Mechanical pulping tears fibers apart by friction rather than dissolving lignin. The main variants are stone groundwood (SGW, older), thermomechanical pulp (TMP, 95% of new installations), chemithermomechanical pulp (CTMP, with a mild chemical pretreatment), and pressurized groundwood (PGW).
Mechanical pulp has high yield (90 to 95%) but retains lignin, which makes papers that yellow over time. Used in newsprint, SC, LWC, and some book grades. Stronger and brighter than mechanical pulp but cheaper than kraft.
Related
- Kraft pulp. Chemical pulp produced by cooking wood chips with sodium hydroxide and sodium sulfide. The dominant pulp process globally.
- Lignin. The natural polymer that bonds wood cells together. Removed in chemical pulping, retained in mechanical pulping.