Study On Preparation And Mechanism Of Modified Cellulose Membrane Used For Reuse Of Papermaking Wastewater

Cellulose is cheap, renewable, biodegradable, and is the most abundant organicraw material in the world. To improve the properties of cellulose and enlarge itsutilization range, modification methods of physical and chemical properties of thecellulose have been continuously studied to investigate the required properties inorder to prepare modified cellulose membrane used for reuse of papermakingwastewater in this thesis.The homogeneous grafting of methylmethacrylate (MMA) onto cellulose wascarried out by using ammonium persulfate as an initiator. LiCl/DMAc was used as thesolvent for the dissolution of cellulose and the media for the homogeneous graftcopolymerization. The preferable reaction conditions of the grafting reaction wereconfirmed by weighing methods. The results showed that the efficient reactionconditions were as follows: reaction time,2h; mass ratio of MMA/cellulose,1/1(g/g);mass ratio of initiator/cellulose,6/50(g/g); and reaction temperature,80°C. Underthese conditions, the GP of cellulose under homogeneous conditions reached76%,higher than that under heterogeneous conditions. The grafted polymer wascharacterized by FTIR, SEM, TG-DTA and XRD. The results showed that the originalcrystalline structure was destroyed during the dissolution process of cellulose, whichhelped to improve the effectiveness of grafting copolymerization reaction. This typeof materials has good thermal stability.After grafting in the preferable grafting conditions and blending withpolyethersulfone to cast coated membrane by using L-S phase inversion method, theblend membranes were characterized by the break strength, elongation, pure waterflux, scanning electron microscope and differential scanning calorimetry. The resultsshowed that the blend membrane was a partially compatible system and the blend ratio should be controlled in about1:16. The introduction of the grafted cellulose mayresult in the increase of pores size and pure water flux. The blend membrane shouldbe classified as a microfiltration membrane from the pore size angle.Cellulose linter was dissolved in lithium chloride/N,N-dimethylacetamide(LiCl/DMAc) used as the solvent for the dissolution of cellulose and the cellulosemembranes were prepared by the phase inversion technique. The cellulose membraneswere subjected to surface crosslinking modification in presence of glutaraldehyde.The effects of surface crosslinking modification conditions on the mechanicalproperties of cellulose membranes were studied．The results showed that the breakingstrength of cellulose membranes were only modestly improved after crosslinkingmodified with glutaraldehyde. The break strength of modified cellulose membranewas only1.532MPa when the preferable crosslinking conditions were as followed:reaction time,40min; glutaraldehyde mass fraction,5%; reaction temperature,70℃.FT-TR analysis has proved the presence of crosslinking reaction.Using non-woven fabric as base material of the membranes, CA/PES blendmembranes were prepared by L-S phase inversion method. DMAc was used as thecasting solvent and polyvinylpyrrolidone (PVP K30) was used as polymer additives.The influence mechanism of the various factors in the membrane preparation processwas explored and the mechanical properties, the filtering capabilities (including purewater flux and BSA rejection), the thermal stability, the morphology, the anti-foulingproperty and the compatibility of blend membranes were analyzed and characterized.The best preparation conditions of CA/PES blend membranes were as follows: PESconcentration,18%; CA concentration,3%; PVP concentration,4%; evaporation time,20s. The results showed that the pure water flux and the anti-fouling property ofCA/PES blend membranes were higher than those of pure PES membranes and thecompatibility results indicated the partially compatibility of the CA/PES blendmembranes. As a microfiltration membrane, CA/PES blend membranes had goodthermal-stability below300℃.The UF composite membranes were prepared by interfacial polymerization ofmetaphenylenediamine (MPD) with trimesoylchloride (TMC) using CA/PES blendmembranes as support membranes. The influence mechanism of the various factors inthe interfacial polymerization process was explored. The preferable preparationconditions of the functional layer on the surface of CA/PES blend membrane were asfollows: MPD concentration,2%; SDS concentration,0.1%; TEA concentration,2%;dip-coating time,30min; TMC concentration,0.1%; reaction time,60s; temperature and time of heat treatment,70℃and20min. Under those conditions, the pure waterflux and BSA rejection can reach8.54L.m-2.h-1and65.37%. The success of theconducted interfacial polymerization procedure and morphology of compositemembranes was corroborated by SEM, ATR-FTIR and XPS. The application resultsshowed that the UF composite membranes with certain anti-fouling property couldefficiently reduce the COD, turbidity and TOC of papermaking wastewater.By adding different macromolecule polymer additives into the casting solutionand using non-woven fabric as base material of the cellulose membranes, the cellulosecomposite membranes were prepared. The effects of different macromolecule polymeradditives on pure water flux of composite membranes were preliminary studied byanalyzing viscosities of the casting solution and PWF of composite membranes. Thepreliminary results showed that PEG-800was the right macromolecule polymeradditive for the cellulose composite membranes. The effects of PEG-800massfraction on PWF, break strength and elongation of the cellulose composite membranesbased on non-woven fabric were preliminary studied and the preliminary resultsshowed the optimum quality ratio of cellulose/solvent/PEG-800in the casting solutionwas4/90/6.