How is mechanical pulp made from wood?

Mechanical pulp, also known as groundwood pulp, is produced by subjecting wood to an abrading action that separates and fragments the wood fibers. This process is achieved by pressing debarked wood against a revolving grinding stone or by passing wood chips through a mill.123

To ensure quality, the wood must maintain a moisture content of at least 30 percent, ideally between 45 and 50 percent, often requiring presoaking or spraying. Modern industrial grinders utilize large, artificial pulpstones made from silicon carbide or aluminum oxide, powered by high-capacity electric motors. Hydraulic cylinders exert significant pressure against the stone face to grind the wood into fibers.2

Following the grinding process, the resulting pulp stock passes through rifflers and screens to remove impurities such as bark, knots, and unfibred wood. Because this method retains all the chemical constituents of the wood—including lignin—the resulting paper is prone to yellowing over time and possesses lower strength compared to chemical pulp, though it offers excellent opacity and printing qualities.2