Discoloration of mechanical and chemimechanical pulps: Influence of wood raw material, process and ageing method

摘要

The change in colour of different types of unbleached and bleached high-yield pulps under both accelerated and long-term ambient light-induced ageing conditions was studied using the CIELAB colour system. It was found that accelerated ageing conditions that mimic indoor daylight exposure tend to increase mainly the b~*-value and decrease the L~*-value (i.e., yellow/darken the pulp). Long-term ambient ageing without indirect sunlight also increases the a~*-value, which makes the pulp more reddish. It was also found that accelerated light-induced ageing is characterised by rapid initial discoloration that is followed by a slower, secondary phase. The discoloration caused by long-term ambient light-induced ageing with no indirect sunlight present was more even over time.