Study On The Rule And Kinetic Of The Introduction Of Carboxyl Or Aldehyde Groups During The TEMPO-mediated Oxidation Of Cellullose

Oxidized cellulose as an important source of cellulose derivatives,not only itself has a wide range of applications,also can be used as an intermediate for further reaction to obtain more functional cellulose derivatives.TEMPO-mediated oxidation system is a common method to preparate oxidized cellulose,has become a hot spot in chemical modification of cellulose.At present,the study of the TEMPO-mediated oxidation system of cellulose mainly focus on the mechanism of oxidation,oxidation condition,characteristic and application of products,etc,however the oxidation kinetics of TEMPO oxidation system is relatively limited.Therefore,we study on the rule and kinetic of the introduction of carboxyl or aldehyde groups during catalytic oxidation of cellulose by TEMPO oxidation system,providing an important theoretical basis for the obtainment of oxidation products with specific performance.In this paper,the contents of carboxyl groups in pulp fibers were determind by UV spectrophotometer.The contents of carboxyl groups in pulp fibers can be accurately determined by measuring the copper ion exchang capacity.The rule and kinetic of the introduction of carboxyl groups during TEMPO/NaClO/NaBr-mediated oxidation of cellullose was investigated in this study.In certain concentration range,the oxidation rate are proportional to the concentration of TEMPO and NaBr.The effect of temperature on the rate constant can be well described by Arrhenius equation,and the apparent activation energy is about 55.340 kJ/mol.Furthermore,an empirical model of the introduction of carboxyl groups(The carboxyl content of the raw material before oxidation has been removed.)during TEMPO/NaClO/NaBr-mediated oxidation of cellullose was developed based on the concentration of NaClO,temperature,and reaction time.The good regression coeffcient(R2=0.9868)indicates that the model is justifiable for the introduction of carboxyl groups prediction.We also studied the effects of different pretreatments,different buffer system and TEMPO recycle on the TEMPO oxidation process and the introduction of carboxyl groups.the effects of different pretreatment were: beating pretreatment > endo-glucanase pretreatment > xylanase pretreatment.Na2CO3-NaHCO3 buffer solution and borax-Na2CO3 buffer solution can be used for the automatic control of TEMPO/NaClO/NaBr system.It was also found that the spent reaction liquor can be recycled and reused without additional TEMPO and NaBr and remains effective in generating carboxylic acid groups on the bleached Eucalyptus kraft pulp.Meanwhile,the effect of the bleached Eucalyptus kraft pulp by TEMPO/SDIC/Na Br system was studied.It was found that TEMPO/SDIC/NaBr system can be used for selective oxidation of C6 primary hydroxyl group.SDIC is more stable,higher content of active chlorine,and more resistant to storage.The oxidation condition can be controlled as follows,temperature 25 oC,TEMPO dosage 0.015g/g,NaBr dosage 0.1g/g.And an empirical model of the introduction of carboxyl groups during catalytic oxidation of pulp by TEMPO/SDIC/NaBr system was developed based on the NaClO dosage and reaction time.At last,we studied the effect of laccase-catalyzed TEMPO oxidation of Eucalyptus kraft pulp.The oxidation condition can be controlled as follows: temperature 35 oC,TEMPO dosage 10%,laccase dosage 20IU/g,pH 4.62.The treated pulp fibers exhibited obviously decreased curl values,kink index,and thermal stability.A large number of aldehyde groups and relatively small amounts of carboxyl groups were introduced into pulp fibers.