Chemical pretreatment of wood prior to making refiner groundwood

Abstract From the Canadian patent

The specification discloses a process for making an improved refiner mechanical pulp from pieces of wood such as, wood chips. The process may preferably comprise: a) Comminuting the wood chips largely by splitting along the wood grain to make smaller particles; b) Wetting said particles with a solution of a sulphite salt of an alkali metal to add an amount of said salt within the range of 1% to 10% of the oven dry weight of said particles, said solution having a pH within the range of 7 to 12.5;, c) Steam heating the sulphite solution bearing particles to a temperature within the range between 80°C and 165°C and holding them within that temperature range for a period of 0.5 to 80 minutes;, …