AbstractThe effects of two pulp pretreatments, impregnation with ascorbic acid (AA) or purified kraft lignin (KL), on bleached pulp refining were investigated by examining and testing handsheets made from these pulps. The AA pretreatment of the pulp amplified the depolymerization of the cellulose and notably impaired the strength properties of the pulp handsheets. The effects were enhanced upon the combination of the AA pretreatment and intensive refining. Furthermore, heat treatments (at 225 °C, 30 min, in water vapor atmospheres of 1 and 75% (v/v)) promoted the depolymerization of cellulose and the total color difference in the AA impregnated handsheets more than for the KL impregnated and reference handsheets. In contrast to AA, the KL pretreatment of the pulp improved the burst index stability of the refined pulp handsheets after the humid thermal treatment (75% (v/v)). In addition, the total color difference of the KL impregnated handsheets was lower than the AA impregnated and reference handsheets.