groundwood

Groundwood is a pulp produced by mechanically grinding wood into fibers with little or no chemical pretreatment. It yields a high pulp yield and lower production cost because most of the wood’s lignin remains in the fibers, unlike chemical pulps where lignin is largely removed.

Historically, stone groundwood (SGW) was made by grinding logs or chips against a rotating stone. Modern production uses refiners and disc grinders to produce mechanical pulps, including thermomechanical pulping (TMP) and refiner mechanical pulp (RMP). These processes alter fiber structure to improve bonding and runnability, but they still leave substantial lignin compared with chemical pulps.

Groundwood pulp has a high yield, typically well above 85–90 percent, but its fibers are relatively short and retain lignin. This results in lower tensile strength and poorer brightness, with a tendency to yellow over time. It is commonly used in low-cost papers such as newsprint and other printing papers where opacity and economical production are prioritized.

Environmental and practical considerations include the energy required for grinding and the reduced brightness that often necessitates bleaching. Groundwood papers are generally cheaper to produce and print well at high speeds, but they tend to have shorter lifespans in terms of brightness and aging, making them less suitable for high-end or longevity-focused printing applications.