Study On Photocatalytic Bleaching Of Kraft Eucalyptus Pulp

Photocatalytic bleaching of pulp based on singlet oxygen mechanism is a novel environmentally friendly bleaching method. In the article, photocatalytic bleaching of kraft eucalyptus pulp based on singlet oxygen mechanism was investigated by using self-assembly device for photocatalytic bleaching.In the experiments, Rose bengal(RB) was used as photosensitizer to activate oxygen into singlet oxygen. Photocatalytic bleaching technology of kraft Eucalyptus pulp was optimized through single factor experiments .Then the effect of sulphate pretreatment and EDTA pretreatment on bleached eucalyptus pulp wrer discussed .Thirdly, the influence of supplying transition metal ion to photocatalytic bleaching Eucalyptus pulp was researched .At the same time, The changes of functional groups in pulp before and after photocatalytic bleaching of supplying transition metal ion were also probed by FTIR in order to infer the changes of internal structure of pulp. The conclusions drawn according to experimental data were followed as:Firstly, the effect of different photosensitizers on bleached Eucalyptus pulp : RB > EO> LF> MO >MB. The impact of photocatalytic bleaching was resemble as adopting 300W or 500W mercury lamp. Then the beforehand provide oxygen time was not too long. According to single factor experiments, the optimum bleaching conditions of photocatalytic bleaching were followed as: pulp concentration 1% , time 5hour, NaOH dosage 3%( based on oven dry pulp), Rose bengal(RB)0.1%( based on oven dry pulp), mercury lamp 500W, beforehand provide oxygen time 10 minutes.Secondly, brightness of bleached pulp after sulphate pretreatment was lower than that of bleached pulp that was not pretreated. Besides, bleached pulp after EDTA pretreatment, thatof brightness was improved, fall rate of K value was six unit, fall rate of viscosity was the same as that of bleached pulp after no pretreatment.Thirdly, supplying copper ion,bivalence iron ion ,manganese ion, trivalence iron ion and zinc ion during photocatalytic bleaching were disbennifit to the effect of photocatalytic bleaching, brightness and degree of wiping off lignin on bleached pulp were reduced. Supplying magnesium made for improving brightness and viscosity of bleached pulp.Finally, the IR spectrum analysis showed that photocatalytic bleaching of kraft eucalyptus pulp could only change the intensity of absorption peak partially and the main chemical structure of lignin has not changed yet. After supplying metal ion photocatalytic bleaching ,the brightness of pulp was changed, the reasons were absorption peak of 1034cm-1 ,1651 cm-1 and 1424 cm-1 that the intensity of absorption peak was changed .The changes of functional groups in pulp before and after supplying metal ion photocatalytic bleaching were also probed by FTIR in order to infer the changes of internal structure of pulp.