semichemical pulp

Semichemical pulp is a type of wood pulp produced through a process that combines chemical and mechanical methods. Wood chips are treated with chemicals, such as sodium sulfite, under conditions that soften the lignin but do not dissolve it completely. The softened chips are then processed in disk refiners to separate the fibers.1

This method results in a higher yield of pulp compared to fully chemical processes, typically ranging from 66 to 90 percent of the original wood weight. Semichemical pulps possess intermediate chemical and strength properties between mechanical pulps and fully chemical pulps.1

These pulps are used in various paper products, with a significant portion going into corrugating medium for cardboard boxes due to their stiffness and strength. They are also used in some lower-cost printing papers. The term "semichemical" itself indicates that the wood is cooked very lightly by chemical means to increase yield while producing less pure fiber.12