The Solution Properties And Rheological Properties Of Bacterial Cellulose Nitration

This work explored the solution properties and rheological properties of nitrated bacterial cellulose (NBC) in organic solvent. This result hopes to accelerate the applications of NBC in the future and provide a theoretical reference. The main research content of this paper are the following:(l)According to the national military standard GJB 770.109-93 (gunpowder analysis test methods nitrocellulose solubility determination), we studied the influence of temperature and solvent type on the NBC solubility. Where N,N-dimethylformamide (DMF) and acetone (AC) on the NBC dissolving ability is better, solubility increases with the increase of temperature.(2)We obtained the result that NBC did not produce the new peak of wave number before and after the dissolution by analyzing the FT-IR and DSC. The glass transition temperature of NBC is 79.5℃. It is a little relationship with the nitrogen content of NBC. In addition to, we obtained the specific viscosity of NBC with different nitrogen content in DMF by viscosity measurement. The specific viscosity of NBC in AC, DMSO and ethyl acetate (EA) was obtained by the same method. And the result is different from the value of traditional nitrocellulose.(3) We obtained the NBC of the absolute weight average molecular weight of the molecule, molecular chain size, molecular chain conformation and other information by GPC/MALLS. The NBC of molecular chain in an organic solvent rendered flat spherical. The NBC of root mean square radius of rotation is 68.7nm. NBC molecular coil expansion volume was 1.36×10-15cm3. NBC solvent exponent α is 0.83, which indicated that its molecular chain had a certain rigidity and good dissolution properties. The NBC of molecular chain conformation index was 0.33. AFM showed that NBC of molecular chain presented flat spherical.(4) To confirm the experimental results, we conducted molecular dynamics simulations. The results showed the oblatoid of molecular chain of NBC. The results were approximately corresponded to those obtained by AFM. The slow relaxation is dominated by NBC contributions, while the first scrunch is due to the contributions of the solvent. This result showed a process NBC chain from spherical to flat. The system had a relatively large cohesive energy density and electrostatic energy. In addition, the root mean square radius of rotation over time after the first increases stability, but the van der Waals force decreases with time in the dissolution process.(5) We studied the influence of concentration and nitrogen content on the viscosity of NBC by HAAKE rotational rheometer. Also the concentration and viscosity of the dependency relationship was studied. When NBC concentration was 0.5%-5.0%, the solution obey Newton’s law of viscosity. It is Newtonian fluid. Within this range of concentration, viscosity and density consistent with exponential growth relationship. When the concentration reached 5.5%, the relationship between shear stress and shear rate did not exhibit a linear relationship, but a non-Newtonian fluid and according to exponential growth. With different nitrogen content, the viscosity showed a trend of decrease then increase. When the nitro group content and molecular weight is increased, the stability of solution system is improved. And when the hydrophobic nitro groups and their molecular weight was increased, the solution system had a little response to external stimuli weakened.