Study On The Dissolution Of Cellulose In Phosphoric Acid-Phosphate Solvent

In this thesis phosphoric acid was used to mix with one of several phosphoric compounds.The mixer were used as complex solvent to dissolve cellulose.The phosphoric compounds used are:urea phosphate,sodium hexametaphosphate,potassium dihydrogen phosphate,and dipotassium hydrogen phosphate.The pretreatment,the dissolving process,the rheological behavior of cellulose/phosphoric acid-phosphoric compound,and the regeneration of cellulose has been studied.The molecular dynamics simulation of cellulose/phosphate-urea phosphate were investigated.The results have shown that after pretreatment by ultrasonic,NaOH and CaCl2 respectively,cavities and cracks has occurred on the surface of the cellulose pulp.Among which the ultrasonic pretreatment was the most effective.The dissolving of cellulose treated by ultrasonic was fastest.After pretreating and dissolving,the regenerated cellulose were tested and measured with XRD and FTIR.The results showed that there was no new chemical bond formed,the ultrasonic pretreatment leading to the smallest crystallinity of the regenerated cellulose.The dissolving experiments have shown that with phosphoric acid-phosphoric compound the better temperature was 30-40?.The degree of polymerization of regenerated cellulose decreased smallest.For the same concentration of cellulose dissolved in one of the four phosphoric acid-phosphoric compounds,respectively,the time dissolving in phosphoric acid-urea phosphate was the shortest.The maximum mass fraction of cellulose dissolved in phosphate-urea phosphate would be high to 13.68%.The rheological research has shown that the cellulose/phosphoric acid-phosphate compound solution were all pseudo-plastic fluid.The non-Newtonian exponent increased with the increase of temperature and the decrease of cellulose content,which tended to closer to Newtonian fluid.In processing the solution temperature and cellulose concentration should be controlled in order to improve the stability.Through the molecular dynamic simulation of phosphate-urea phosphate,it is concluded that phosphoric acid plays a major role in the process of dissolving cellulose,and urea phosphate plays an auxiliary role.The mechanism of dissolving cellulose in phosphoric acid-urea phosphate has been explored.