漂白流程对桉木溶解浆白度稳定性的影响

Effect of the bleaching process to the brightness stability of eucalyptus dissolving pulp

研究了热暴露状态下溶解浆返黄(BR)的影响因素。通过次氯酸钠(NaCIO)氧化漂白浆人为地引入了羰基(CO)基团,研究表明羰基是造成白度稳定性(BS)下降的主要原因。碱抽提(E)段可去除部分羧基基团提高白度稳定性,而碱性过氧化氢(P)段羰基基团虽没有降低,但可较E段更有效地提高白度稳定性。在实验室对未漂浆进行无元素氯(ECF)与全无氯(TCF)漂白到相同白度,羰基基团含量都较低。ECF漂白纸浆白度稳定性较TCF漂白浆低得多,这一结果可认为未漂白浆中发色基团的化学特性也影响白度稳定性。通过电子顺磁共振(EPR)光谱与紫外共振拉曼光谱(UVRR)对漂白溶解浆中酚、苯醌发色基团进行原位检测,其含量取决于漂白流程,是造成白度稳定性差异的原因。

The factors governing the brightness reversion(BR)of dissolving pulps under heat exposure are investigated.Carbonyl(CO)groups were artificially introduced on fully bleached pulp by sodium hypochlorite(NaClO)oxidation.It was demonstrated that the CO groups are responsible for loss of brightness stability(BS).These groups were partly eliminated by an alkaline extraction stage(E),which improved BS.However,an alkaline peroxide stage(P)was more efficient than E to improve BS,but without any additional CO loss.Moreover,an unbleached dissolving pulp was bleached in the laboratory by elemental chlorine free(ECF)and totally chlorine free(TCF)(ozone-based)sequences to the same brightness.The very low CO content was about the same in both cases.the ECF bleached pulp showed substantially lower BS than the TCF pulp.These results are interpreted such that the chemistry of chromophores in the unbleached pulp also governs BS.In situ detection of phenolic and quinone chromophores in bleached dissolving pulp was performed by electron paramagnetic resonance(EPR)spectroscopy and ultraviolet resonance Raman(UVRR)spectroscopy.The content of these groups was leachingsequence-dependent,which may be related to the BS differences.