Preparation And Characterization Of Solid-liquid Phase Cellulose Carbamate And Its Regenerated Cellulose Membrane

Cellulose is considered as the most promising substitute for petroleum based materials today.It has been applied in lots of fields,ranging from foods,energy to materials.Because of the existence of a large number of hydroxyl groups,the extensive hydrogen bonding networks are formed in cellulose,these make cellulose difficult to be melted at high temperature and dissolved by common solvents.This restricts the processing and applications of cellulose.In order to dissolve the biopolymer in some common solvents and develop a low-cost,green and environmentally friendly route,using cullulose and urea as raw materials,cellulose carbamates were synthesized by esterification reaction in N,N-dimethylacetamide?DMAC?,an inexpensive,high boiling,aprotic and polar solvent.The structures and properties of products were characterized by Fourier transform infrared spectroscopy?FTIR?,¹³C solid state nuclear magnetic resonance spectrometry(¹³C-NMR),Thermal gravimetric analysis?TG?,Scanning electron microscopy?SEM?,X-ray diffractometry?XRD?and Polarizing microscope and so on.The preparation and solubility of CC,the properties of CC solutions,as well as the properties of CC regenerated membranes were study in this paper,.The FTIR and ¹³C-NMR results showed that cellulose cabamates have been successfully synthesized in DMAC system.And the optimum reaction temperature,reaction time and the mass ratio of alkali-treated cellulose,urea and DMAC for preparation CC in DMAC system are 160?,6h and 1/4/16,respectively.The XRD results showed that the cellulose crystalline form won't be changed in the modification and regeneration process in H2SO4 aqueous.The degree of crystallinity of cellulose decreased slightly in the esterification process and relatively largely in regenerateing process.The TG results demonstrated that the thermal stability of cellulose decrease slightly after the modification and relatively largely for CC membranes prepared from H2SO4 aqueous due to the lower degree of crystallinity and the presence of sodium ions Na+ which have catalytic oxidation.Rheology testing showed that CC solutions are pseudoplastic fluid.With the increase of temperature,the viscosity of the CC solutions firstly decreased and then increased.At the same shear rate,the solutions with higher CC mass fraction had greater viscosity,lower the gel temperature and more unstable than others.SEM results indicated that the cellulose carbamates have a rough and coarse surface with a large number of deep grooves along the axis and some peeling pieces beacuse the structures of cellulose are damaged in the esterification process.For CC regenerated membrane,a film with a rougher and porous surface could be obtained when the mass fraction of H2SO4 is not high in coagulation bath.And vice versa,a denser structure of the membrane could be prepared when the mass fraction of H2SO4 is high.The pure water flux and rejection tests showed that the pure water flux of the membranes increase with an increase of pressure and decrease with an increase of the contents of H2SO4 in coagulation,and those membranes prepared from 5%H2SO4 coagulation have great prospects in waste water treatment,and their rejection for methylene blue as high as 97.5%.