| Membrane separation technologies have attracted worldwide research attentiondue to their great potential for wastewater reclamation, separation of substances,drinking water purification, sea water desalination, and so on. However, mostmembranes are prepared with non-biodegradable petrochemical materials. Thesenon-degradable plastic materials used as disposable items are more evidentiallydisturbing and damaging the ecosystem. Cellulose is commonly used to preparemembranes, and is attractive alternative to traditional petrochemical materials becauseit is biodegradable, biocompatible, reproducible, and inexpensive. However,application of cellulose-based membranes has been limited by an important drawback,which biological matters can build up on the membrane surface and lead to biofouling.Hence, there is a strong need to develop bio-membranes with antimicrobial activities.Cellulose membranes were successfully prepared with ZnCl2aqueous solution assolvent and bamboo cellulose as raw materials, and then antimicrobial cellulosemembranes were prepared with grafting and blending modification. We successfullyprepared cellulose membranes grafted in situ with guanidine hydrochloride, chitosan/cellulose membranes and chitosan/cellulose-（nano silver particles） membranes.Research on the three membranes’ preparation, surface morphology, mechanicalproperties, pure water flux, crystal structure, thermal stability, chemical compositionand antibacterial properties were carried out. Membrane separation technology wasused for the depth treatment of wastewater from the pulp and paper mill with chitosan/cellulose-（nano silver particles） membranes. The relative effect of various foulingcontributions of flux decline were quantified. The index of wastewater with the depthtreatment and the cleaning of the membranes were investigated. The researchbasically solved the antimicrobial problem of cellulose membrane. It provided animportant theoretical and scientific basis for depth treatment of wastewater from thepulp and paper mill with cellulose membranes.We successfully prepared novel microporous membranes from cellulose in zincchloride aqueous solutions by coagulating with water. The cellulose membranes were prepared under the following appropriate conditions such as ZnCl2weight percentof72%in the solvent, weight percent of the bamboo cellulose4%, the solutiontemperature of80°C and the dissolution time for25min. The wet membranes possesshomogeneous porous structure on the surface and relatively dense microporousstructure in the inner. The pore width and water permeability of the membranesdecreased with the increasing drying time, while the mechanical properties increased.The tensile strength of the membranes incread from5.0MPa to23.2MPa and thepure water flux decreased from55.0(mL·cm-2·h-1) to6.2(mL· cm-2·h-1) with thedrying time increased from4.5h to11.5h in constant temperature and humidity. Thecrystal form of the membrane was transformed from cellulose I to cellulose Ш.Compared with the original cellulose, the membrane had lower degree of crystallinityand thermal stability. There was no chemical reaction occurred during the dissolutionand phase transformation process, the chemical composition of the membrane wassimilar to the original cellulose.Firstly, cellulose was oxidized by periodate and then it was further grafted in situby guanidine hydrochloride while dissolved in zinc chloride aqueous solutions.Graft-modificated cellulose membranes were prepared. The grafting modificationreacted at50℃for35minute, under which the grafting percentage of guanidinehydrochloride reached over10.1%, and the tensile strength of the membranes was10.8MPa after drying for15.5h in constant temperature and humidity. The wetmembrane possess homogeneous porous structure on the surface and relatively densemicroporous structure in the inner. The tensile strength of the membranes increadfrom4.0MPa to10.8MPa and the pure water flux decreased from19.0(mL·cm-2·h-1)to4.2(mL· cm-2·h-1) with the drying time increased from11.5h to15.5h in constanttemperature and humidity. The crystal form of the membrane was attributed tocellulose Ш. Compared with the oxidized cellulose, the membrane had lower degreeof crystallinity and thermal stability. An obvious antimicrobial capability ofgraft-modificated cellulose membranes against E. coli and S. aureus had beenobserved.Chitosan/cellulose blend membranes were successfully prepared using zinc chloride aqueous solutions as a solvent. The influence of chitosan content on themembranes’ properties was investigated. The pure water flux decreased from4.0(mL·cm-2·h-1) to2.3(mL· cm-2·h-1) while the chitosan content increased fromchitosan/cellulose=1:10to chitosan/cellulose=1:4, however the tensile strength ofthe membranes decread from18.2MPa to13.8MPa with dried for11.5h in constanttemperature and humidity. Obvious antimicrobial capability of chitosan/cellulosemembranes against E. coli was observed, and the antimicrobial capability increasedwith the increasing chitosan content. The proper chitosan content was chitosan/cellulose=1:6, and the pure water flux of the membrane was3.3(mL·cm-2·h-1) withthe tensile strength16.5MPa after dried for11.5h in constant temperature andhumidity. The Homogeneous structures without obvious phase separation betweenchitosan and cellulose for all blend membranes were observed by scanning electronmicroscope analysis. The pore width, water permeability and the tensile strengths ofthe blend membranes decreased with the increase of chitosan content. The results ofX-ray diffraction analysis indicated that the crystal structures of chitosan andcellulose were disrupted during the processes of dissolving and regeneration. Also, thereformation of hydrogen bonds between chitosan and cellulose during dissolution andregeneration processes resulted in the shift of diffraction peaks. Fourier transformsinfrared spectroscopy and thermogravimetric analysis results confirmed thisobservation. Therefore, zinc chloride aqueous can be regarded as a promising solventto prepare degradable membranes with antibacterial properties.Nonetheless, chitosan will lose antimicrobial activity under alkaline conditionsdue to its loss of the cationic. We propose that proper chemical modifications onchitosan can help to overcome this major limitation and enhance its antimicrobialproperty. The presence of free-NH2groups in chitosan should allow chemicalincorporations of AgNPs. Together, chitosan and AgNPs could be more effectivelyagainst a broad range of microbes in a sustained manner. Silver nanoparticles （AgNPs）encapped with polyacrylic acid （PAA） were bioconjugated with the chitosan/cellulose blend membranes using the1-ethyl-3-（3-dimethylaminopropyl）carbodii-mide hydrochloride （EDC） and N-hydroxysuccinimide （NHS） as biocoupling agent. The average size of the AgNPs is9nm. The scanning electron microscopeimages show that the AgNPs distribute evenly in the film without agglomeration. Thestrong reflections around34°and41°in X-ray diffraction provide a clear evidence forthe presence of AgNPs in the chitosan/cellulose-AgNPs membranes.Thermogravimetric analysis analysis indicates the presence of6.90%silvernanoparticles （weight percent） in the chitosan/cellulose-AgNPs membranes. Fouriertransforms infrared spectroscopy analysis confirmed the amide bonds between theprimary amino groups of chitosan and the carboxylic residues of coordination to silvernanoparticles. The disk diffusion tests with E. coli were conducted to determine theantimicrobial properties of the chitosan/cellulose and chitosan/cellulose-AgNPsmembranes. The results revealed that, as compared to the chitosan/cellulosemembranes, the chitosan/cellulose-AgNPs membranes showed significantlyimproved antimicrobrial activity. Therefore, the chitosan/cellulose-AgNPsmembranes could provide a promising novel degradable membranes with enhancedantimicribrial property.Finally, membrane separation technology was used for the depth treatment ofwastewater from the pulp and paper mill. Series resistance model and flux loss ratioswere used to quantify the relative effect of various fouling contributions of fluxdecline. The theoretical analysis and experimental results show that the flux lossratios is more accurate description of the fouling contributions leading to the fluxdecline. Chitosan/cellulose-AgNPs composite membranes compared with otherpolymer membranes such as polyvinylidene fluoride （PVDF） membranes andpolyether sulfone （PES） membranes exhibited very low adsorption fouling. After thedepth treatment of pulp and paper mill wastewater with chitosan/cellulose-AgNPsmembranes(MWCO=10w，pure water flux=45mL· cm-2·h-1), the effluent meetedrequirements of the National Institute of Standards（GB3544）2008). The fluxrecovery rate of membranes after treatment washed after the tap water reached73%and further after alkaline cleaning and acid cleaning, the flux recovery rate ofmembranes could reach90%. |
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