Abstract: The light-induced colour reversion (yellowing) of high yield pulps was mainly due to sensitivity of the specific structure in lignin to UV or near UV light combining with oxygen in the air producing chromophores through forming the intermediate free radicals. Application of UV absorbing compounds and radical trapper or antioxidants onto paper have been reported to stabilise the brightness against light exposure. This paper reports the investigations on application of UV absorbers (Tinuvin 1130 and its ester precusor), nitroxide free radical (a free radical trapper) and polyethlene glycol 300 (an antioxidant) onto poplar APMP handsheets. The effects on non treated and reduced pulps and with organic solvent solution or aqueous solution of additives were compared. The results show that application of Tinuvin 1130 mixed with dodecanol combining with reducing treatment of pulp could provide the handsheets with significant protection from yellowing.This technique was most close to commercial applications.

Key words: poplar, APMP pulp, yellowing, UV absorber, radical trapper