mechanicalpulp

Mechanical pulp is pulp produced primarily by mechanical processes that separate wood fibers with little chemical modification. It encompasses groundwood, refiner mechanical pulp (RMP), thermo-mechanical pulp (TMP), and chemi-thermo-mechanical pulp (CTMP). In groundwood, wood is ground directly in water to create a fiber slurry. RMP uses refining equipment to separate fibers with mechanical action, preserving most of the original wood structure. TMP combines steam heating with refining to soften lignin and facilitate fiber separation, while CTMP adds a small amount of chemicals before or during thermal treatment to improve yield, brightness, and strength relative to plain TMP.

Key characteristics of mechanical pulp include a high wood-to-pulp yield, typically well above 85% and often in the 90% range, owing to limited chemical removal of lignin. The fibers are more damaged than those from chemical pulping, producing papers with greater bulk and opacity but lower tensile strength and faster yellowing due to residual lignin. Because lignin is retained, mechanical pulps tend to darken and lose brightness over time, especially under light exposure.

Common uses for mechanical pulps are low-cost printing papers such as newsprint, catalog and phone-book stock, and certain light packaging papers, often in blends with chemical pulps to balance strength and appearance. Environmental considerations include high energy consumption for grinding and refining, but lower chemical usage. Recyclability remains feasible, though repeated recycling can further shorten fibers and degrade performance.