High temperature peroxide bleaching of mechanical pulps

A method of brightening mechanical pulps, comprising the steps of:

• providing cellulosic materials derived from softwood or hardwood trees, said materials having an initial brightness level,
• introducing the cellulosic materials to a refining system for conversion to a pulp,
• providing a bleaching liquor to the refining system, wherein the liquor comprises a first amount of hydrogen peroxide and an alkali, wherein the alkali comprises at least one of Mg(OH)2 and Na2CO3, or a combination thereof;
• providing the pulp with the bleaching liquor at a temperature in the range of about 85° C. to about 160° C. for a time of about 2 to about 180 minutes;
• and
• increasing the brightness of the pulp about equal to or less than a brightness level which can be obtained if the bleaching liquor comprises a second amount of hydrogen peroxide, which is greater than the first amount, wherein 100% of the alkali is NaOH, and the pulp and bleaching liquor are held under about the same temperature and time conditions.

A method of brightening mechanical pulp, comprising the steps of:

• providing cellulosic materials derived from softwood or hardwood trees, said materials having an initial brightness level,
• introducing the cellulosic materials to a refining system for conversion to a pulp,
• providing a bleaching liquor to the refining system, wherein the liquor comprises hydrogen peroxide, silicate and alkali, wherein the alkali comprises at least one of Mg(OH)2 and Na2CO3, or a combination thereof;
• holding the pulp and the bleaching liquor at a temperature in the range of about 85° C. to about 160° C. for a time of about 2 to about 180 minutes;
• and
• increasing the brightness of the pulp at least to a brightness level which can be obtained if 100% of the alkali is NaOH and the pulp and bleaching liquor are held at about the same time and temperature conditions.