Study On Effect Of Enzymes And Transition Metal Ions On Hydrogen Peroxide Bleaching Of Recycled Pulp

Some microorganism and complex components of recycled pulp can affect on thehydrogen peroxide bleaching. This paper studied the effect of biology enzyme and transitionmetal ions on hydrogen peroxide bleaching of waste-paper pulp, mainly including fouraspects:firstly, studied the effect of peroxidase and catalase on hydrogen peroxide bleaching ofrecycled pulp;secondly, studied the effect of Cu²⁺, Fe²⁺, Mn²⁺ on hydrogen peroxide bleachingof recycled pulp; thirdly, observed the morphology of sheet surface of bleached pulp withbiology enzyme through SEM. At last, studied on dynamics of decomposition of H₂O₂catalysed by Mn²⁺.Through discussing the effect of biology enzyme on decomposition of H₂O₂ in alkalinemedium and optimal bleaching condition of recycled pulp,it was found that suited conditionsof H₂O₂ bleaching with biology enzyme, pulp consistency 10ï¼…, H₂O₂ 5.0ï¼…,NaOH 3.0ï¼…,Na₂SiO₃ 3.0ï¼…,MGSO₄ 0.5ï¼…,EDTA 0.15ï¼…, 60℃and 2h. Bleaching results indicatedthat,with increasing of enzyme dosage, residual H₂O₂ and brightness of bleached pulpsdecreased.It explained that H₂O₂ was catalyzed decomposition by enzyme.Through measureof enzyme activity, it was found that activity of catalase higher than peroxidase.With the samedosage of enzyme,catalase leaded much more decreasing of residual H₂O₂ and brightness ofbleached pulps than peroxidase.When enzyme dosage reached 120mg/kg pulp,the brightnessof bleached pulps with catalase was 59.67ï¼…ISO, residual H202 consistency was 1.10 g/l;Andwith peroxidase, the brightness was 62.07ï¼…ISO, residual H₂O₂ consistency was 1.22g/l.Effect of transition metal ions on hydrogen peroxide bleaching of recycled pulp wasstudied. The results indicated that, decomposition of H₂O₂ could be catalyzed by Cu²⁺,Fe²⁺and Mn²⁺. A strong chelated condition was used to deal with pulp (pulp 10.0ï¼…,pH 3.0,EDTA 1.0ï¼…,70℃and 2h).Then Cu²⁺, Fe²⁺and Mn²⁺ solutions were added in the pulp again.Thebleaching results indicated that,with increasing of Cu²⁺, Fe²⁺and Mn²⁺charge, residual H₂O₂and brightness of peroxide bleached pulps decreased. Especially for Mn²⁺,at the end ofreaction, the consistency of residual H₂O₂ was almost zero.When the dosage of Mn²⁺improveded to 25mg/kg pulp,the brightness of bleached pulp almost same the unbleached.Theresult showed that H₂O₂ was catalyzed decomposition full this time.SEM observation revealed that less short fibers of hydrogen peroxide bleached pulp wereexposed on the sheet surface, some long fibers exposed.It meaned some thin fibers degradedduring bleaching.Through observation of fiber morphology, it could found more thin fibers ofH₂O₂ bleached pulp with enzyme were saved on fiber surface.It meaned decomposition ofH₂O₂ faster by enzymatic catalytic during bleaching.So less thin fibers were degraded duringhydrogen peroxide bleaching.Through studying on the dynamics of decomposition of H₂O₂ catalysed by Mn²⁺.It wasfound that the temperature was very important to the decomposition of H₂O₂.Throughcalculating of reaction speed constant and energy of activation,it was found that Mn²⁺ had acatalysis to decomposition of H₂O₂.