桉木硫酸盐浆ECF漂白引入臭氧漂白的效果

The effect of introducing ozone in elemental chlorine free bleaching of eucalyptus kraft pulp

巴西桉木浆（巨桉和柳桉）氧脱木素采用了ZDED和DEDD漂白工序。对比ZDED和DEDD漂白工序,计算出的置换率（1k g臭氧可代替的纯二氧化氯量）为2.5-3.5k g,而理论值为1.7kg,表明ZDED漂白工序中无效反应较少。随着臭氧用量的增加,纤维黏度大幅降低（臭氧用量0.8%时,纤维黏度降低50%）。与采用DEDD漂白的桉木浆相比,采用ZDED漂白的桉木浆其他典型特性有：易打浆、保水值低、纤维连接比例高和湿零距裂断长低（仅发生在臭氧用量为0.8%时）。

ZDED and DEDD sequences were applied on an oxygen- delignified eucalyptus （mixture of E. grandisand E. saligna） kraft pulp from Brazil. When ZDED and DEDD were compared, the displacement ratio calculated as the quantity of pure chlorine dioxide replaced by l kg ozone was found between 2.5 and 3.5 kg, as compared to 1.7 kg in theory--indicating that less wasting reactions occur in the ZDED sequence. The cellulose viscosity decreased substantially with the increase in the ozone charge （down to 50% at 0.8% ozone）. Other typical characteristics of the ZDED pulps were easier beating, lower water retention value, higher proportion of kinked fibers, and lower wet zerospan breaking length （seen only at 0.8% ozone charge）, as compared to DEDD. The viscosity loss due to the introduction of ozone in an elemental chlorine free sequence did not translate into a similar loss in strength. A comparison with the depolymerizing effect of cellulase suggests that the determining factoris not the extent of the drop in viscosity but rather the heterogeneity of the attack along the fibers. It is concluded that ozone oxidation of cellulose in the fibers would be rather homogeneous. Moreover, the appearance of morecurls and kinks would not benecessarily related to the viscosity loss. For example, a （2,2,6,6- tetramethylpiperidin-l-yl） oxidanyl （TEMPO） treated DEDD pulp, enriched in carboxyl groups, had more straight fibers than the original DEDD pulp, despite its lower viscosity. The presence of ionic groups would be a more important factor; the lower content in carboxyl groups in the ZDED pulps, compared to the DEDD pulps, could promote the easier formation of curl and kinks during the ZDED sequence.