Manufacture Process And Characterization Of Poplar Cellulose Micro/Nano Fibrils

In this paper, we selected the poplar fibers as raw materials to study the chemical treatmentthat could separate hemicelluloses and lignin in order to get highly purified cellulose. And thenenzyme treatment and mechanical treatment were used to obtain cellulose micro/nano fibrils.This thesis characterized the cellulose micro/nano fibrils by different methods, includingparticle size analysis, FTIR analysis, degree of ctystallinity, SEM analysis, free radicals analysis.What’s more, the properties of PVA films that modified by cellulose micro/nano fibrils werediscussed. The conclusions are as follows:（1） Poplar materials would move most of lignin and hemicellulose after three steps: part ofhemicellulose would release after ultrasonic alkali and alcohol extraction as well as hot-waterpre-extraction. In the digesting treatment, the temperature, concentration of Na₂SO₃and thetime of treatment were considered as variation for univariate analysis. Lignin content wouldreduce to1.99%in the condition of200℃,3%Na₂SO₃,2.5h. In the alkali treatment,temperature, concentration of NaOH and the time of treatment were considered as variation forunivariate analysis. Hemicellulose content would reduce to0.84%in the condition of80℃,8%Na₂OH,3h. After digesting treatment and alkali treatment, the cellulose content of fibers was94.60%, which was a good substrate of enzyme treatment.（2） The solid enzyme activity of cellulase was99.65FPU/g. The best conditions of enzymetreatment process were: temperature50℃, pH4.8, solid to liquid ratio1:50, time of enzymetreatment32h, added enzyme dosage30FPU/g. Grind treatment and ultrasonication treatmentwere used after enzyme treatment. The best conditions of grind treatment were:15times,1500rpm. Conditions of ultrasonication treatment were: power1500W, ultrasonic interval2s, ultrasonic work time4s, total work time30min. After centrigugation treatment, we get theupper suspension of cellulose micro/nano fibrils.（3） Particle size analysis showed that: the diameter of cellulose micro/nano fibrils werebetween100-300nm, fibrils were disperse in the distilled water. FTIR analysis showed that:enzyme treatment and mechanical treatment only changed the shape and size of cellulose, theyhad no influence on the chemical construction of cellulose micro/nano fibrils. Degree ofctystallinity showed that: enzyme treatment and mechanical treatment did not transform thecrystal form, cellulase could hydrolyze the amorphous area of poplar fibers to improve thedegree of ctystallinity. However, mechanical treatment would decrease the degree ofctystallinity. Free radicals analysis showed that: the free radical intensity reduced after enzymetreatment. SEM analysis showed that: the width of fibrils met the requirement of micro/nanofibrils with high specific surface area.（4） Mechanics properties analysis of cellulose micro/nano fibrils/PVA composite filmshowed that: cellulose micro/nano fibrils made the tensile strength of PVA films higher than those with no cellulose micro/nano fibrils inside. Rigidity of films increased, while theplasticity reduced. On the other hand, Thermal properties analysis of cellulose micro/nanofibrils/PVA composite film showed that: cellulose micro/nano fibrils improved the glasstransition temperature and thermostability. Moreover, the reaction kinetics of the pyrolysis isstudied by the integration method of Coats-Redfern. The cellulose micro/nano-fibrils/PVAcomposite film pyrolysis reaction can be divided into low temperature stage（reaction order is2）and high temperature stage（reaction order is1.5）. Its apparent activation energy increasedobviously in the second stage.