|
In alkaline conditions when the primary and secondary alcohols exist, the 2,2,6,6 - tetramethylpiperidine oxide radical (TEMPO) in a common-oxidant system (NaClO, NaBr) in the presence, can select only oxide primary alcohol, and no effect on the secondary alcohol. Under the optimized experimental conditions, we study different oxidation temperature (15 ℃, 20 ℃, 30 ℃, 35 ℃, 40 ℃, 50 ℃) under the TEMPO-NaClO-NaBr on microcrystalline cellulose (MCC) C6-bit primary hydroxyl choice oxide. There are a lot of microcrystalline cellulose molecule hydrogen bonds, hydrogen bonds form a huge network of hydrogen bonds, led directly to the formation of a dense crystalline structure. Dense crystal structure severely hampered chemical reagents or solvents with hydroxyl groups in cellulose molecules effective contact and role. In order to improve the yield of oxidation, this paper uses an oxidation pretreatment, ultrasonic pretreatment, mercerizing dissolved ionic liquid pretreatment and four methods for microcrystalline cellulose pretreatment pretreatment, pretreatment methods were investigated four kinds of microcrystalline cellulose surface morphology, chemical structure, crystalline phase transformation and the role of consumer influence and use SEM, XRD, FTIR and other means of pre-test characterization of the structure and properties of the product were measured. Test results show that these four pretreatment method does not change the chemical structure of the microcrystalline cellulose, but will cause aggregation structure and surface morphology changes. XRD displayed once oxidation pretreatment, ultrasonic pretreatment pretreatment method and an ionic liquid solution of the microcrystalline cellulose does not change the crystal type, but have, to varying degrees elimination-crystallization, wherein the ionic liquid dissolved eliminate pre-crystallization methods the most significant. Mercerized alkali pretreatment method makes microcrystalline cellulose crystal by the type Ⅰ type Ⅱ completely transformed into crystalline form, eliminate dissolved ionic liquid crystal effect after pretreatment method. Better with a pre-oxidation pretreatment MCC, MCC and alkali pretreatment mercerized dissolving ionic liquid pretreatment of MCC as a starting material for TEMPO-NaClO-NaBr oxidative modification, the use of 13C-NMR characterization testing methods for product Determination of the structure and properties of TEMPO-NaClO-NaBr found on pretreated MCC still selective. And once oxidation pretreatment MCC oxidation at high temperatures presents a more interesting phenomenon - the phenomenon of self-emulsifying, and three kinds of pre-oxidation of the MCC have greatly improved the yield of the ionic liquid dissolved oxidation pretreatment MCC yield at low temperature 15 ℃ The following can reach 84.7%.
|