Preparation Of Cellulose Nanocrystals Iridescent Films

Cellulose nanocrystals, CNC, are processed by mechanical and chemical method with cellulose as raw material. CNC is biopolymer which has the basic structure and properties of cellulose and nanoparticle characteristics. In CNC suspension, the rod like nano particles were randomly oriented, because of their nanosize and the sulfate groups were introducred on the surface of CNC when prepared by sulfuric acid, CNC particles could suspended in the water steadily. When the concentration of the suspension was increased, the liquid crystal texture was formed, and the spiral orientation of the nano crystal was formed.Rodlike CNC particles with 100?400nm in length,5?22nm in diameter,high degree of crystallinity, higher specific surface area and intensity were prepared by 64%(wt) sulfuric acid hydrolysis cellulose at 45 ?. However,There were lots of sulfuric acid,some not fully hydrolyzed cellulose fragments, monomer sugars and oligo in the waste liquid in preparing cellulose nanocrystals (CNC) by sulfuric acid. When CNC was separated, these substances still existed in the hydrolysis residue, and caused the instability of the hydrolysis residue system. The concentration of sulfuric acid in the waste liquid was adjusted by adding 80%(wt) sulfuric acid, then the not fully hydrolyzed materials were converted to glucose with heating. The sulfuric acid and glucose were separated by anion exchange membrane,and the concentration of them was increased with rotary evaporation and concentration system. Results showed that glucose concentration in the waste liquid reached maximum when sulfuric acid concentration was 56%(wt), with 45? water bath heating for 3h. The recovery percent of sulfuric acid was 90.31% after the liquid was treated twice by anion exchange membrane, and 10.06mol/L sulfuric acid and 36 g/L glucose solution were obtained after being concentrated. They could be used in the experiment again, thus making it practicable to reuse and make full use of biomass resource.Carboxymethyl cellulose was prepared according to the method as 1g cotton(dry):15mgTEMPO:150mgNaBr:10mL 10% (wt) NaCIO, and reacted at pH=10.3?10.5.Then cellulose nanofibril (NFC) was prepared with homogenizing at 100MPa by high pressure homogenizer for 20 cycles.According to the liquid crystal properties of CNC, iridescent film materials with polarizing effect could be made by casting the suspension into film method. The films made with pure CNC were brittle and fragile, which was not conducive to the popularization and application. By adding different proportions of cellulose nanofibril (NFC), polyvinyl alcohol (PVA), water-soluble vinylon respectively to the CNC suspension, the prepared iridescent films' color could be changed, and the tensile strength of the films could be improved. The results showed that NFC-CNC blendinging iridescent films with blue, pink etc. color could be made by the addition of NFC. PVA-CNC blendinging iridescent films with grass green, sky blue, dark gray etc. color could be made by the addition of PVA.VL-CNC blendinging iridescent films with blue, reddish brown, gray etc. color could be made by the addition of water-soluble vinylon. The iridescent films' section structure was observed by SEM. It was found that the pure CNC iridescent film section, perpendicular to the plane direction was layered structure, parallel to the plane direction was spiral aligned.The iridescent films section structure of adding these three substance was similar to that of simple CNC films', and was same to their liquid crystal arrangement. But when refer to the appearance in the form, it is apparent that the perpendicular to the plane direction was layered structure. The referring to the spiral arrengment, PVA-CNC blendinging iridescent films was the most clear, VL-CNC blendinging iridescent films was slight, and NFC-CNC blendinging iridescent films was most fuzzy observed by SEM. Adding NFC could make the iridescent films tensile strength increased to a maximum value of 29.8N, adding PVA could make it reach 174N, and adding water-soluble vigylon could make it reach 52.87N.The tensile strength of iridescent films increased rapidly with the addition of the three substance,but after the maximum value,the tensile strength of iridescent films gradually reduced to remain unchanged, but adding PVA remained basically unchanged along.