| Cellulose is the most abundant natural macromolecule on earth and will be the main industrial materials in future. NaOH/urea aqueous solution is a novel and green solvent of cellulose. Synthesizing derivatives of cellulose as well as preparing functional materials can be realized directly from this cellulose solution. In our work, the interaction between urea and cellulose was investigated. Moreover, the quantitative structural information of cellulose and its diravatives were obtained by Quantitative Cross Polarization (QCP) NMR method. Furthermore, fluorescent cellulose hydrogel "soft material" was fabricated from the cellulose solution, and polysiloxane "hard material" was also prepared. A brief summary of results is as follow:1. The dissolution mechanism of cellulose in NaOH/urea aqueous solution is still in dispute. It’s very important to understand the interaction mechanism in this solvent system. A combination of solid state NMR and extended Huckel charges was used for studying the interaction between cellulose and the solvent components. The results indicated that complicated complex is formed by urea, NaOH and cellulose in the cellulose solution. The dissolution of cellulose can be improved by adding a certain amount of urea. However, extra urea is in a free state, explaining why7wt%NaOH/12wt%urea/81wt%H2O is optimal ratio selection in some way. A possible interaction model was proposed in our work:the cellulose chain is surrounded by NaOH and urea molecules which may be in the same surface layer of cellulose chains.2. Solid-state high-resolution NMR technologies were applied to study the structures of cellulose and its dirivatives quantitatively. The aggregation structures of the native cellulose, regenerated cellulose as well as chemically cross-linked cellulose were studied by QCP NMR method. The results showed that the native cellulose possesses high degree of crystallinity while its crystallintye is lowered by regenerative process. The structure of chemically cross-linked cellulose is completely amorphous by forming network. It was found that the CP enhancement factors of crystalline and amorphous region are almost the same for cellulose system. Hence13C CP/MAS NMR spectra can be used to calculate the crystallinity of cellulose directly within short CP contact time. The cross-linking reagent (ECH) mainly reacted with C6-OH of cellulose in the NaOH/urea aqueous solution and signals of the cross-linking section can be found out in the13C CP/MAS NMR spectra after peak deconvolution. The results showed that Quantitative Cross Polarization (QCP) NMR technology can be used to detect the cross-linking density of chemically cross-linked cellulose. Moreover, solid-state high-resolution NMR was also applied to study the structure of PCL/NCG and the grafting degree was obtained through QCP NMR. It’s the first time to quantitatively characterize the structure of cellulose derivatives by QCP NMR method, proving that this method has good applicability for cellulose system.3. Fluorescent cellulose hydrogels were successfully prepared by embedding typical organic fluorescence substances such as3,4,9,10-perylene tetracarboxylic dianhydride and1,8-naphthalide derivatives in the cellulose hydrogel matrix. The photophysical properties of the prepared samples were studied. And the factors which influenced the fluorescent properties, such as the concentration, the electronic effect and the aggregation configuration of fluorescent molecules in the samples, were also studied. With increase of the fluorescence molecules’ concentration, the fluorescence intensity of the materials increased firstly and then decreased, the maximum was related to the kinds of fluorescence molecules and their substituents. The results also showed that the concentration self-quenching effect was mainly caulsed by "reabsorption-reemission" and formation of dimer or aggregates.4. Several kind of1,8-naphthalimide derivatives doped fluorescent polysiloxane materials were prepared by sol-gel process. It was found that the fluorescence intensity of part of the prepared materials is far higher than the small molecules. The main factors that affect the fluorescence intensity of such materials are chemical crosslinking and the condensation polymerization degree of polysiloxane. On one hand, the probability of collision and aggregation of fluorescence molecules decreases after co-hydrolysis and condensation polymerization with siloxane. On the other hand, the free degree of molecular vibration, rotation and motion also decreases in polysiloxane network structure. All the factors mentioned above lead to increasement of fluorescence intensity. Moreover, the fluorescence intensity of the materials is decreased by "reabsorption-reemission" of the fluorescence molecules when their concentrations are high to a considerable extent. |
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