Studies On Technology And Mechanism Of Bamboo Pulp Biomimetic Bleaching Catalyzed By Co-salen Complexes

There are abundant bamboo resources in China.Developing the bamboo pulp industrialization according with the local conditions,what is an available way to solve the shortage of fiber material for papermaking.Due to conventional bleaching technology with chlorine containing agents bring severe pollution on environment,especially bleaching effluent,it is necessary to look for a new environment friendly bleaching technology for bamboo pulp,and it is beneficial to promote bamboo pulp industrialization. Furthermore,it is significant to the sustainable development of Chinese papermaking industry.For the requirement of developing low impact bleaching technology,many researchers try to use microorganisms,their enzymes and biomimetic system in pulp bleaching process to reduce the pollution.Biomimetic catalyst has characteristics of both enzymatic catalyst and chemical catalyst.Therefore,it is an efficient approach of green chemistry.In this paper,Bamboo pulp TCF bleaching with Co-salen biomimetic systems,which was composed by Co-salen complexes,pyridine,NaOH,H₂O₂ and O₂ was studied.The technology research mainly included the condign way of Co-salen biomimetic catalytic bleaching,catalytic effects of various factors and reasonable conditions.The advantages and disadvantages of Co-salen biomimetic systems were evaluated by the comparison of blank sample,the brightness,viscosity,physical properties of resultant bleached pulp, wastewater pollution and bleach dosage were included.The results showed that it was advisable for independent biomimetic pretreatment,and the optimum conditions were as follows:Co-salen 0.03%,molar ratio of Co(salen):pyridine =1:1,NaOH 3%,H₂O₂ 1.5%, oxygen pressure 0.2MPa,pulp consistency 5%,temperature 90℃,time 5h.The brightness of resultant bleached pulp was 90.5%SBD,and its viscosity was 620 mL·g^-1through the bleaching sequence of OCoEpPaP.After biomimetic pretreatment,the physical properties of the resultant bleached pulp were impoved and the pollution load of the bleaching wastewater was reduced.The peracetic acid and hydrogen peroxide dosage were saved more than 40%through the pretreatment.On the basis of the studies about optimum technology conditions,the present studies focused on the mechanism of the delignification and bleaching in bamboo pulp biomimetic bleaching with Co-salen complexes.The mechanism research mainly included the changes of lignin structure,the formation of lignin degradation products,the pathway of lignin degradation,and so on.Mechanism of delignification during the process of biomimetic bleaching were studied by the methods of FTIR,NMR(¹H-NMR,¹³C-NMR, ³¹P-NMR,¹H-¹³C 2D-HMQC NMR),GPC,and so on.The results showed that the main ways of lignin degradation during the Co-salen biomimetic bleaching were involved with demethylation,quinone-type structure formation and opening,alkyl - aryl ether bond cleavage and carbon-carbon linkage breakage in side-chain.Accordingly,p-hydroxyphenyl was increased,and the guaiacyl and syringyl was reduced.The content of the methoxy was reduced.Some hydroxyl were oxidized to carbonyl.The content of aliphatic hydroxyl and phenolic hydroxyl group were both reduced,and carbonyl content was increased.β-O-4,β-5,β-β,5-5' and other linkages of lignin were ruptured.The degraded products contained more carbonyl compounds,especially benzaldehyde-type compounds as result of catalytic oxidation of Co-salen biomimetic system.The brightness of pulp was improved because of the removal of some quinone-type structures,conjugated carbonyl and phenolic compounds.Thus the technology of bamboo pulp bleaching catalyzed by Co-salen complexes,and the mechanism of the delignification in the bamboo pulp biomimetic bleaching process were founded.The function of Co-salen biomimetic pretreatment in the bamboo pulp bleaching with efficient pollution-free short sequence were explained reasonably.The studies could provide better theoretical guidance and foundation for further research, development and application of the clean bleaching technology with salen complexes,and found a new pathway and theory of clean bleaching production for the bamboo resources, which was advantaged in the forest-pulp-paper integration planning of our country, especially Yunnan province.