| Cellulose is a natural biodegradable polymer material that is abundant and renewable.The natural fiber with a certain length-diameter ratio can be used to prepare cellulose-based film materials with special pore structure and mechanical properties through wet papermaking process.These film materials are widely used in lithium-ion batteries,sewage purification,food packaging,biological tissue repair and other fields.In this paper,the micro/nano cellulose films were prepared by the wet papermaking method using the bleached eucalyptus wood pulps,bleached radiant pine pulps and the cotton linter pulps as raw materials.The effects of cellulosic fiber raw material characteristics,beating degree,mixing micro nano cellulose(MNC)with eucalyptus pulp fibers to co-forming films,using of TEMPO-oxidized pulp fibers as film preparation raw materials,organic solvent treatment,and drying methods on the pore structure and mechanical properties of cellulose films were studied;the effects of cross-linking of glutaraldehyde(GA)on the pore structure,surface properties and mechanical properties of micro/nano cellulose films were investigated.The purpose of this thesis is to control the pore structure and mechanical properties of cellulose films at different structural scales.The main conclusions are as follows:1.Cellulose films were prepared using different fiber morphology materials,and the pore structure and mechanical properties of films were regulated at the micrometer scales by adjusting the beating degree of the slurries.Using bleached eucalyptus pulps,bleached radiant pine pulps and cotton linter pulps as the raw materials,when the beating degree was increased from 19°SR to 77°SR,the average pore size of cellulose films was between 3.26?m and 10.5?m,the porosity was at 55.89%~81.84%,the elastic modulus and tensile strength changed between 116MPa~1.74 GPa and 2.30MPa~37.5MPa,respectively.Among the three raw materials,the pore size and porosity of cellulose films prepared by cotton linter pulps were larger than those of cellulose films made from bleached eucalyptus pulps and radiata pine pulps.The cellulose films prepared by bleached eucalyptus pulps had the best mechanical properties,the obtained cellulose film had a maximum elastic modulus of 1.74 GPa and a tensile strength of 37.53 MPa when the beating degree of the cellulose was 72°SR.The average pore sizes of the cellulose films prepared by these three pulps were all at 1~10?m,which did not meet the requirements of lithium ion battery separators.2.Cellulose films were prepared by mixing MNC with bleached eucalyptus pulps,the pore structure and mechanical properties of the films were studied by changing the amount of MNC.When the amount of MNC increased from 10wt% to 60wt%,the average pore size of cellulose films decreased from 5.77?m to 4.17?m,and the porosity decreased from 78.96% to 51.58%.The elastic modulus and tensile strength of prepared films increased from 599 MP and 18.8MPa to 1.32 GPa and 35.9MPa,respectively.Compared with cellulose films without MNC added,the pore size and porosity of cellulose films added with MNC were reduced,and the mechanical properties were enhanced as well.Whereas,the pore size of acquired cellulose films still did not conform to lithium ion battery separators.3.Cellulose films were prepared by using TEMPO oxidized pulps as raw materials,the pore structure and mechanical properties of the films were regulated by changing the oxidation degree of the cellulose at micro and nano scales.When carboxyl content of oxidized pulps was 0.77~1.09 mmol/g,the micron-sized pore size of cellulose films decreased from 9.03?m to 7.11?m.When carboxyl content was 1.37~1.69mmol/g,the nano-sized pore size of cellulose films reduced from 9.55 nm to 6.08 nm.Furthermore,the porosity of the cellulose films decreased from 79.67% to 12.41% with the increase of carboxyl content,the elastic modulus increased from 337 MPa to 3.23 GPa,and the tensile strength increased from 6.17 MPa to 46.7MPa.4.Organic solvents(n-butanol,carbon tetrachloride and n-heptane)were used as the pore-forming agents to treat the cellulose films prepared by TEMPO oxidized pulps.When the cellulose films were treated with n-butanol solvent,the average pore size of cellulose films changed in the ranges of 5.14?m~ 8.40?m,and the variation was not significant.When using carbon tetrachloride and n-heptane solvent to treat the cellulose films,the average pore size of the films changed obviously,especially when the carboxyl content of TEMPO oxidized pulps was1.37,1.60 and 1.69 mmol/g,respectively,the average pore size of the cellulose films increased from 9.55 nm,7.46 nm and 6.80 nm to 44.5nm,39.2nm and 46.8nm.The pore-forming effects of n-heptane were more obvious,especially when the carboxyl content was 1.37 and 1.60mmol/g,the average pore size of cellulose films was 52.83 nm and 34.48 nm,respectively.When the carboxyl content of the TEMPO oxidized pulps was 1.37,1.60 mmol/g,the average pore size of the cellulose films treated with the carbon tetrachloride and n-heptane solvent can meet the requirements of the lithium ion battery separators.5.The effects of drying methods on the pore structure and mechanical properties of cellulose films prepared by TEMPO oxidized pulps were studied.Compared with air-dried films,the average pore size of the freeze-dried cellulose films became larger which increased relatively little when the carboxyl content of the cellulose was relatively low(0.77~1.09 mmol/g).However,as the carboxyl content increased from1.37 mmol/g to1.69 mmol/g,the average pore size of the films increased significantly from 9.55 nm,7.46 nm,and 6.80 nm to 5.22?m,5.27?m,and 5.98?m,respectively.Also compared with air-dried films,the average pore size of vacuum-dried cellulose films was smaller when the carboxyl content was at 0.77~1.09 mmol/g,but when the carboxyl content was higher(1.37~1.69 mmol/g),the average pore size of the vacuum-dried cellulose fims became rather large.With the increase of carboxyl content,the porosity(19.62%~74.87%)of the vacuum-dried cellulose films had the same decreased trends as that of the air-dried films,while the porosity of freeze-dried cellulose films increased from 75.30% to 83.11%.6.TEMPO oxidized cellulose was crosslinked with GA to improve the hydrophobicity of cellulose films.When the dosage of GA was 8wt%,the crosslinking time was 6h,the reaction temperature was 60?,the contact angle of the prepared crosslinked film was 107.1°,and its hydrophobicity was the best.7.Different processes and treatments can control the pore size,porosity,and mechanical properties of cellulose films at different structural scales.In particular,when the cellulose films were prepared by using TEMPO oxidized pulps as raw materials and after solvent treatment with carbon tetrachloride and n-heptan,the average pore size of the cellulose films was between 34.5nm and 52.8nm,which can meet the requirements of the lithium ion battery separators.The research results had important guiding significances for the preparation of lithium ion battery separators and other porous cellulose films. |
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