Study On The Preparation Of Nanocellulose And Transparent Paper By Carboxymethylation Pretreament

With the continuous excavating and protruding of various excellent properties of nanocellulose,the application and potential of nanocellulose are also expanding.In the past 10 years,the research on the preparation and application of nanocellulose has been carried out in full swing.In this paper,cellulose pulp was pretreated under alkaline?Na OH?conditions with monochloroacetic acid?MCA?as an etherification agent and anhydrous ethanol as a solvent.Nanocellulose and high transparent papers were prepared by high pressure homogenization and solution casting method,respectively.Translucent papers were prepared by carboxymethylated fibers?CMFs?through vacuum filtration method.Bytakingcarboxylgroupcontentasevaluationcriteriafor carboxymethylation efficiency,the properties of CMFs were evaluated by water retention value?WRV?and degree of polymerization?DP?,we obtained the better pretreatment conditions:sodium hydroxide:chloroacetic acid=1:1.092,the reaction temperature is in the range of 69-79?,the reaction time is in the range of 60-90min.After carboxymethylation pretreatment,the WRV of CMFs increased significantly,while the DP decreased slightly,and the fibers bubbled or even bloated in the water,and the diameter of fibers increased.Scanning electron microscopy was used to observe the surface of CMFs,many folds were formed on the surface of CMFs,this is the result of the loss of the fiber volume caused by loss of water and the sudden collapse of the fiber.The structure of the CMFs was characterized by Fourier transform infrared spectroscopy?FT-IR?and X-ray diffraction?XRD?.The thermostability of the CMFs was characterized by thermogravimetric analysis?TGA?.The results showed that the absorption peak of C=O in the CH₂COONa group was 1635cm^-1 in the infrared spectrum of the fibers,which proved the completion of the carboxymethylation reaction.There is no new characteristic peak in the X-ray diffraction spectrum of the CMFs,the crystal structure of fiber hasn't changed.The relative crystallinity of the CMFs has decreased,which indicated that carboxymethylation was not only carried out on the surface and amorphous zone of fibers,but also in the crystalline area of fibers.The initial thermal degradation temperature of the CMFs decreased,but still remained above 250?.The homogeneous energy consumption in the preparation process of nanocellulose was quantitatively analyzed by means of calculation of the energy conservation of the slurry,a formula for the calculation of homogeneous energy consumption was obtained,and the energy consumption was compared with the TEMPO oxidation method.The results showed that we can obtain nanocellulose with a size of around 15nm from CMFs under the energy consumption of 479k Wh/tons.The fiber content that can be passed through 800 mesh filter cloth can be raised effectively by increasing the carboxyl group content of the CMFs and homogeneous energy consumption.The high transparent papers with excellent properties were prepared by solution casting and air drying,and the structure of the fibers was analyzed by infrared spectroscopy?FT-IR?and X-ray diffraction?XRD?.Fibers in the high transparent papers is compact stacked,and the root-mean-square surface roughness?R_q?of the high transparent papers is only 2.47nm.The transmittance of the high transparent papers in visible wavelength reached 90%,and the tensile strength of hardwood and softwood high transparent papers is 88.2MPa and 173.1MPa,respectively.Compared with TEMPO oxidation method,more carboxyl groups can introduced on cellulose molecular chain by carboxymethylation pretreatment,while it has little effect on the DP and thermal stability of cellulose.When the carboxyl group content is as high as 2.08mmol/g,the DP of carboxymethylated nanocellulose only decreased by 4.8%,and the initial thermal degradation temperature is 270?,which hardly causes the yellowing of the high transparent paper induced by thermal aging.Cellulose pulp was carboxymethylation pretreated when the concentration of the pulp was 5%,the effects of dosage of chemical drugs on carboxyl group content andmorphologyoffiberswereinvestigated.Then,theobtained carboxymethylation pulp was vacuum filtered to prepare translucent paper.The results showed that the accumulation of fibers is becoming denser and denser,thus less and less porosity,with the increasing of the dosage of monochloroacetic acid.When the carboxyl group content of the CMFs is 1.6mmol/g,the desity of translucent paper reached 1.02g/cm³,and the transparency,breaking length,tearing index,burst index and air permeability is 82.8%,15.8km,1.79m N·m²/g,7.74k Pa·m²/g and 0.265ml/min,respectively,which shows good transparency and barrier property,excellent tensile strength and bursting strength.The initial thermal degradation temperature of the translucent papers can be kept above 280?,which shows good thermal stability.