Preparation And Application Of C-6Oxidized Cellulose

Cellulose has a wide range of source and a large output, while its added value is low. The chemical structure of cellulose needs to be changed to obtain new functions. C-6oxidized cellulose as important cellulose derivate can be used as medicinal anticoagulants, absorbable hemostatic gauze, tobacco substitutes and ion-exchange materials of photographic paper, etc. In this paper, the microcrystalline cellulose was used as raw material. It was oxidized by HNO3/H3PO4-NaNO2system, and the products were characterized and analyzed. The prepared C-6oxidized cellulose (C-6OC) was used as adsorbent and the adsorption properties for bisphenol A (BPA) were investigated. Meanwhile C-6oxidized cellulose calcium salt was prepared by C-6oxidized cellulose and calcium ion, and its thermal stability and carbonization performance were researched. The main contents and results are listed as follow:(1) The microcrystalline cellulose after alkali swelling was used as raw material, it was oxidized by HNO3/H3PO4-NaNO2systems. The structure of the product was characterized by Fourier Transform Infrared Spectrometer (FTIR) and solid-state13C NMR. The results indicated that the oxidation reaction happened at C-6primary hydroxyl, the hydroxyl groups was oxidized to carboxyl groups. The carboxyl content and polymerization degree of the oxidation product were respectively determined by acid-base titration method and viscosity method. The results showed that the carboxyl content of the product was about20%, the polymerization degree decreased obviously after96h oxidation by HNO3/H3PO4-NaNO2system. It indicated that the oxidizing agent enter into crystalline region from amorphous region of cellulose in the oxidation process, which caused the rupture of glycosidic-bond. The X-ray diffraction results showed that the crystal type of the microcrystalline cellulose after alkali swelling and the oxidation product were both Ⅱ, and the crystallinity of the oxidation product declined again after oxidation. It indicated that the oxidation reaction destroyed the intramolecular hydrogen bonding interaction, which caused the crystal elimination.(2) C-6oxidized cellulose with20%carboxyl content was used as adsorbent and the adsorption properties for bisphenol A were investigated. The results revealed that the adsorption equilibrium time was about30min at298K, the maximum adsorption capacity of C-6OC for BPA was12.67mg/g, the adsorption capacity increased with the rise of initial BPA concentration. Neutral condition and low temperature were beneficial to adsorption, but the presence of electrolytes in the solution caused the decreasing of adsorption quantity. It was found that the adsorption of BPA followed the second-order equation and Langmuir model, which indicated that the adsorption was monolayer adsorption and a chemisorption process.(3) C-6oxidized cellulose calcium salt was prepared by C-6oxidized cellulose and calcium ion. The content of calcium ion measured by atomic absorption spectrophotometer was8%. Thermal gravimetric analysis showed that the initial thermal decomposition temperature of C-6oxidized cellulose and its calcium salt were129℃and142℃respectively, the amount of carbon residue were22%and32%respectively at800℃. It indicated the calcium complexing C-6oxidized cellulose improved the thermal stability and carbonization performance. The morphology of the carbon residue tested by scanning electron microscope showed the carbon layer was a dense structure without holes. FTIR of the carbon residue showed that CaCO3was covered on the surface of the carbon layer. A combination of thermal gravimetric analyzer and evolved gas analysis by Fourier transform infrared analysis was applied to study the pyrolysis of C-6oxidized cellulose calcium salt. The results showed that the pyrolysis temperature of the product is low, and calcium ion catalyzed C-6oxidized cellulose to form intermediate products which would generate more coke in the pyrolysis. CaCO3covered on the surface of the product cut off the air and heat to the material, inhibited further pyrolysis and led to more char and less volatile gas. Therefore C-6oxidized cellulose calcium salt had high thermal stability.