Study On Reinforced Cellulose Acetate Hollow Fiber Membrane With Braided Tube

Cellulose acetate (CA), as an important derivative of natural cellulose, has played significant role in separation membranes because of its good film forming performance and relatively low cost. In order to improve the mechanical strength and extend the application of CA hollow fiber membrane, braid-reinforced (BR) CA hollow fiber membranes are fabricated in this study based on non-solvent induced phase separation (NIPS) mechanism and through concentric circles composite spinning technology, then their structure and performance are analyzed.Homogeneous-reinforced (HR) CA hollow fiber membranes are prepared with CA filament braid as the reinforcement and dope solution of CA in N,N-dimethylacetimide (DMAc) building the separation layer. Study shows that with the increase of CA concentration in the dope solutions, the separation layer of the membranes becomes denser and their outer surface gets smoother, the mean pore size reduces, the bovine serum albumin (BSA) rejection increases, the tensile strength (>11MPa) and bursting strength increase slightly; There is superior interfacial bonding state between the separation layer and the reinforcement when the CA concentration is higher than 10%. It is found from the comparative filtration test of activated sludge suspension that the HR CA membrane possesses lower flux decline than the reinforced polyvinylidene fluoride (PVDF) hollow fiber membrane, and higher flux recovery after simple physical cleaning, which indicates that the CA membrane has better anti-fouling performance than that of the PVDF membrane; The effluent total organic carbon (TOC) concentration of the membranes is lower than 20mg-L-1, and the TOC removal efficiencies are nearly 90%.BR CA hollow fiber membranes are prepared with CA/polyacrylonitrile (PAN) hybrid filament braids as the reinforcenment. The combination of homogeneous--reinforcement and hetegoneous-reinforcement is achieved with the hybrid filament braid; both homogeneous-reinforced interface and hetegoneous-reinforced interface coexist in the membranes. The hybrid braids can not only effectively regulate the interfacial bonding state of the membranes but also restrain the negative effect of CA fiber’s swelling on membrane permeability. Taking into account of both interfacial bonding state and membrane permeability, the best ratio of the fibers in the braid is 2/1(CA/PAN). The tensile strength of BR CA hollow fiber membranes which mainly depand on the reinforcement rises from 16.0 MPa to 62.9 MPa with the increase of PAN fiber proportion in the braid. It is found by changing the solvent in the dope solutions that the membrane has the bigger pure water flux with N,N-dimethyl--formamide (DMF) as the solvent, and the smaller pure water flux with dimethylsulfoxide (DMSO) as the solvent; The membranes with DMAc, DMF, N-methyl-2-pyrrolidone (NMP) as the solvent possess higher and close protein solution flux; All the membranes exhibit excellent anti-fouling performance when flux recovery rates reach round 90%. Acording to the pull-out test result, the solvent which results in the highest interfacial bonding strength of the membranes is DMAc, followed by DMF, DMSO and NMP. With the increase of CA concentration, the pure water flux of the membranes decreases, the decline speed of protein solution flux decrease, meanwhile the interfacial bonding strength between the separation layer and the reinforcement increases. As the coagulant temperature increasing, the pure water flux of the membranes inecreases, the decline speed of protein solution flux increase, the interfacial bonding state between the separation layer and the reinforcement becomes worse.BR CA/carbon nanomaterial hollow fiber membranes are prepared through doping carbon nanomaterials into the separation layer. The mechanical properties and permeation performance are less affected by the introduction of nano-silver. The nano-silver hybrid hollow fiber membrane is soaked in the activated sludge tank of the membrane bio-reactor (MBR), according to monitoring the variations of BSA rejection with soak time, nano-silver can improve the biodegradation resistance of the membranes. After doping carbon nanomaterials, namely carbon nanotube (CNT), grapheme oxide (GO) and their mixture, the separation layer of the membranes exhibits more and longer finger-like macro-void and thinner skin layer, the tensile properties are hardly affected, but the pull-out strength and bursting strength increase slightly. For the CA/carbon nanomaterials membranes, there is no obvious change in the pure water flux and protein solution flux compared with that of the CA membrane, but there is an increase in BSA rejection. The carbon nanomaterial hybrid hollow fiber membranes are applied in the continuous concentration of whey solution to separate the whey protein and lactose; The BR CA/carbon nanomaterials hybrid membranes, especially the CA/CNT/GO membrane, demonstrate the superior permeation and antifouling performance. Owing to the synergistic effect between CNT and GO, the CA/CNT/GO membrane shows the higher concentration efficiency, and the flux recovery ratio exceeds 90%.BR CA hollow fiber nanofiltration (NF) membranes are prepared by adjusting the dope solution composition and controlling the membrane-forming condition. Analysis reveals that the resultant BR CA NF membranes possess superior interfacial bonding state between the separation layer and reinforcement, the separation layer exhibits dense sponge-like structure; there exist two yield points in the stress-strain curves of the membranes, and the tensile strength of the membranes is close to the braid. With the increase of the C A concentration in the dope solutions, the water permeability of the membranes decreases, the molecular weight cut-off (MWCO) reduces, the salt rejection increases. When the CA concentration in the dope solutions are 17%,18%,19%, the MWCO of the resultant membrane are 1430, 1080,960, respectively; and the rejection toward Na2SO4 are 75.8%,94.0%,95.1%, respectively. During the dye removal experiments, the permeate flux and dye rejection maintain stable with time for the membrane; The permeate flux is about 7 L-m-2-h-’, the congo red rejection is higher than 99% and the Alphazurine A rejection exceeds 93%. During the whey separation experiments, the whey protein rejection approach 90% when the whey concentration of feed solution is 10 g·L-1; When the whey concentration is 50 g·L-1, the whey protein rejection exceeds 80%, but there is a slightly decline with time in the permeate flux for the membrane.