Various sodium bacterial cellulose sulfates (SBCS) were prepared via the homogeneous sulfation of bacterial cellulose (BC) with a SO 3 /pyridine (Py) complex in a dimethyl acetamide/lithium chloride solution. The SBCSs were characterized using Fourier transform infrared spectroscopy, X-ray diffraction (XRD), carbon nuclear magnetic resonance spectroscopy, gel permeation chromatography, elemental analyses, and thermal gravimetric analyses. A variety of conditions (including various amounts of SO 3 /Py, temperatures, and reaction times) were utilized to obtain SBCSs with DS values that ranged from 0.10 to 1.50. The XRD profiles indicated that the SBCSs had a cellulose II analog polymorphous structure. The differences between BC and microcrystalline cellulose (MC) were studied in their respective reactions. BC is more reactive than MC in both the sulfation and depolymerization processes. The order of reactivity for C OH is C6 > C2 > C3 for both BC and MC. Cellulose sulfates with DS values >0.31 were soluble in deionized water.
Yi-Ying Ma,Ze-Long Lu,Yun-Zhu Xing,Wei-Shi Zheng,Chun-Guang Liu
In this case, various characterization technologies have been employed to probe dissociation mechanism of cellulose in N , N -dimethylacetamide/lithium chloride (DMAc/LiCl) system. These results indicate that coordination of DMAc ligands to the Li + –Cl − ion pair results in the formation of a series of Li x (DMAc) y Cl z (x = 1, 2; y = 1, 2, 3, 4; z = 1, 2) complexes. Analysis of interaction between DMAc ligand and Li center indicate that Li bond plays a major role for the formation of these Li x (DMAc) y Cl z complexes. And the saturation and directionality of Li bond in these Li x (DMAc) y Cl z complexes are found to be a tetrahedral structure. The hydrogen bonds between two cellulose chains could be broken at the nonreduced end of cellulose molecule via combined effects of basicity of Cl − ion and steric hindrance of [Li (DMAc) 4 ] + unit. The unique feature of Li bond in Li x (DMAc) y Cl z complexes is a key factor in determination of the dissociation mechanism.
The cellulose catalytic oxidation system mainly comprises inorganic ion-based oxidants. Hence, the selective oxidation of C 6- primary hydroxy groups (C 6 -OH) of cellulose, catalyzed by piperidine free radicals, was limited to the homogeneous cellulosic system containing protic solvents or heterogeneous system. In this work, the use of the catalytic system containing 4-acetamido-2,2,6,6-tetramethylpiperidine 1-oxyl (4-AcNH-TEMPO) was extended to the cellulosic solution in N, N-dimethylacetamide (DMAc) and combined with chlorine dioxide. Results showed that the carboxyl content was 0.832 mmol/g. Meanwhile, the degree of polymerization decreased from 900 to 489. This study provides an effective route for the homogeneous selective oxidation of primary hydroxy groups in cellulose and explored its oxidation mechanism in DMAc solvent. Furthermore, studies showed that the reactive chlorine species- ClO·, Cl·, and ClO 2 played a crucial role in the oxidation process. The methodology developed here displayed great potential to be utilized to various biomolecules in aprotic solvents homogeneous system based on 4-AcNH-TEMPO as oxidation catalysts.
In this study, cellulosic fines were separated from corn stalk soda-anthraquinone (AQ) pulp, then dissolved in DMAc/LiCl solvent system and regenerated to form films. Pulp fines was separated from pulp fibers using different standard sieves. The results exhibited that the value of specific surface area for fines was increased with the reduction of particle size. The cellulose of fines was successfully dissolved in DMAc/LiCl solution and regenerated as biopolymeric films in the water bath. Mechanical properties of regenerated cellulose films were enhanced with the increase of raw-material fineness from 120 to 300 mesh. It was exhibited a remarkable decrease on the values of tensile strength and maximum decomposition temperature of the regenerated cellulose film from 500-mesh fines, indicating that too small dimensions of cellulosic particles took disadvantages on physical strength and thermostability.
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