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Effective Parameters on Fabrication and Modification of Braid Hollow Fiber Membranes: A Review

November 2021
Membranes 11(11):884

November 2021
11(11):884

DOI:10.3390/membranes11110884

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CC BY 4.0

Authors:

Azadeh Nazif

Ferdowsi University Of Mashhad

Hamed Karkhanechi

Ferdowsi University Of Mashhad

Ehsan Saljoughi

Ferdowsi University Of Mashhad

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Hollow fiber membranes (HFMs) possess desired properties such as high surface area, desirable filtration efficiency, high packing density relative to other configurations. Nevertheless, they are often possible to break or damage during the high-pressure cleaning and aeration process. Recently, using the braid reinforcing as support is recommended to improve the mechanical strength of HFMs. The braid hollow fiber membrane (BHFM) is capable apply under higher pressure conditions. This review investigates the fabrication parameters and the methods for the improvement of BHFM performance.

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

Membranes2021,11,884.https://doi.org/10.3390/membranes11110884www.mdpi.com/journal/membranes

Review



EffectiveParametersonFabricationandModificationofBraid

HollowFiberMembranes:AReview

AzadehNazif

,HamedKarkhanechi

*,EhsanSaljoughi

,SeyedMahmoudMousavi

andHidetoMatsuyama



DepartmentofChemicalEngineering,FacultyofEngineering,FerdowsiUniversityofMashhad,

Mashhad9177948974,Iran;azadehnazif@gmail.com(A.N.);saljoughi@um.ac.ir(E.S.);

mmousavi@um.ac.ir(S.M.M.)

ResearchCenterforMembraneandFilmTechnology,DepartmentofChemicalScienceandEngineering,

KobeUniversity,1‐1Rokkodai,Nada‐ku,Kobe657‐8501,Japan

*Correspondence:karkhanechi@um.ac.ir(H.K.);matuyama@kobe‐u.ac.jp(H.M.)

Abstract:Hollowfibermembranes(HFMs)possessdesiredpropertiessuchashighsurfacearea,

desirablefiltrationefficiency,highpackingdensityrelativetootherconfigurations.Nevertheless,

theyareoftenpossibletobreakordamageduringthehigh‐pressurecleaningandaerationprocess.

Recently,usingthebraidreinforcingassupportisrecommendedtoimprovethemechanical

strengthofHFMs.Thebraidhollowfibermembrane(BHFM)iscapableapplyunderhigherpres‐

sureconditions.Thisreviewinvestigatesthefabricationparametersandthemethodsfortheim‐

provementofBHFMperformance.

Keywords:braidhollowfibermembrane;fabricationparameters;mechanicalstrength;braid

reinforcing



1.Introduction

Membranetechnology,includingpolymericmembranes,isoneofthebest‐advanced

separationandtreatmentsystemsthathavebeenwidelyusedindifferentapplications

suchasdesalination,wastewatertreatment,oil/waterseparation,andwaterreuseappli‐

cations[1,2].Hollowfibermembranes(HFMs)possessdesiredandcompetitivead‐

vantagesrelativetoflat‐sheetmembranesformanymembraneseparationapplications

duetohighmembranesurfaceareapervolumeofamodule(e.g.,theratioofareaper

volumeisreported40m

forflatsheetand170m

forHFMs[3]).Theyalsohave

highpermeabilityandporosity,desirablefiltrationefficiency,propermechanicalproper‐

ties,self‐supportedstructureandcharacteristics,smallfootprint,highpackingdensity

relativetootherconfigurations,easeofhandlingandmaintenance[4–12].Duealsotothe

spacer‐freemodule,theassemblycostwillbereduced.Hollowfibermembraneshadbeen

widelyusedformicrofiltrationandultrafiltrationaloneorasthepretreatmentofnanofil‐

trationandreverseosmosisinseawaterdesalination,forwardosmosis,andmembrane

bioreactortothetreatmentofindustrialwastewater(suchasmedicine,food,andtextiles)

andgenerationofdrinkingwater.Hollowfibermembranesareoftenpossibletobreakor

damageduringhigh‐pressurecleaning,modulepreparation,aerationprocess.Itisdueto

sponge‐likeandasymmetricfinger‐likemorphologythatledtomakingbrittleandporous

structures.Hence,theirlifetimemayreducedespitetheirmanyadvantages[4,11,13].

Inordertodesignmembranestructure,lifetimepredictionandreliability,under‐

standing,andanalysisisimportanttoevaluatethemechanicalbehaviorunderactualop‐

eratingconditions.Mechanicalabrasionofmembranesarisingfromphysicalandchemi‐

caldamagebyharshfeedwater,fouling,chemicalcleaning,andback‐washingbring

aboutthereductioninmembranestrength[4,14].Generally,themechanicalpropertiesof

Citation:Nazif,A.;Karkhanechi,H.;

Saljoughi,E.;Mousavi,S.M.;

Matsuyama,H.EffectiveParameters

onFabricationandModificationof

BraidHollowFiberMembranes:A

Review.Membranes2021,11,884.

https://doi.org/10.3390/

membranes11110884

AcademicEditor:MariaGraziaDe

Angelis

Received:12October2021

Accepted:12November2021

Published:17November2021

Publisher’sNote:MDPIstaysneu‐

tralwithregardtojurisdictional

claimsinpublishedmapsandinstitu‐

tionalaffiliations.



censeeMDPI,Basel,Switzerland.

Thisarticleisanopenaccessarticle

distributedunderthetermsandcon‐

ditionsoftheCreativeCommonsAt‐

tribution(CCBY)license(https://cre‐

ativecommons.org/licenses/by/4.0/).

Membranes2021,11,8842of31



polymericflatsheetmembranesareimprovedbyapolyestersupportlayer.Thenonwo‐

venpolyesterpossessesstrongmechanicalstrengthcantoleratevigoroushydraulicim‐

pact[15–19].Hosseinietal.[15]utilizedpolyestersupportinordertoimprovetheme‐

chanicalstrengthinhighpressure.Recently,usingtubularbraid(orthreads/fabric)asre‐

inforcedsupportisproposedtoimprovethemechanicalstrengthofhollowfibermem‐

branes.Braid‐reinforcedhollowfibermembraneshaveattractedattentionandinterest

duetotheirlowcost,efficientseparation,relativelysimplepreparation,andhighmechan‐

icalproperties[6,7,11,20,21].Thistypeofhollowfibermembranepossessesasupreme

tensilestrength(contributestothelonglifetimeofthemembranes),andthustheycould

applyunderhigherpressureconditionsrelativetocommonhollowfibermembranes.A

braidhollowfibermembrane(BHFM)isfabricatedbycoatingathinfilmonthesurface

oftubularbraid(i.e.,reinforcedfiber).Thepresenceofbraidsupportincreasesthefluxof

ultrafiltration/microfiltrationduetothethinnerthicknessoftheselectivelayer,thanksto

toleratingrelativelyhigherpressurecomparedwiththetypicalHFM[4,21–24].Thefirst

studiesinreinforcedHFMsarerelatedtothepatents.Cooperetal.[25]introducedthe

conceptofbraidedmembraneforthefirsttime.Theycastthemembraneonasupporting

surfacesuchasfabric‐likematerialconsistingofmonofilamentmaterial(e.g.,polyesters,

nylon,rayon,polyolefin,Teflon,acrylic)withasmalldiameter.ZenonEnvironmentalInc.

producedatypeofhollowfibermembraneconsistingoftubularmacro‐poroussupport

andatubularsemipermeablethinfilmofthepolymer.Thepreparedbraidhollowfiber

membranecouldendureto10.3MPainhydrauliccompactionforces[26].

Thepeelingofthesurfacelayerfromthetubularbraidisthedrawbackofthebraid

hollowfibermembranesduetothermodynamicincompatibilitybetweenthesetwolayers

[21].Thebraidhollowfibermembranecansignificantlyenhancetheeffectiveareadueto

fewerstickingfiberstogetherintheassembledmodule[27].Thebraidsupportabsorbs

themoleculesofwaterduetotheporousstructure.ThethinseparationlayeroftheBHFM

alsocontributedtothewaterfluxenhancementbecauseoflowerthicknesscomparedto

self‐supportHFMs[24].Chenetal.[28]reportedthatthefluxofbraidPMIA‐BHFMswas

higherthanthePMIA‐HFMs.ItisduetothePMIA‐BHFMscontaininganinnerlayerwith

arelativelyporousstructurethatleadstoareductioninmembraneresistanceforwater

transfer.TheBHFMswiththedenseoutersurfacecanpreventtheadsorptionoffoulants

andthepore‐blockageintheinnerporesofthemembrane.Therefore,theoccurredfouling

isformingthecakelayertype,caneasilyremovebywashing,whiletheopenporesofthe

HFMeasilyadsorbedthemoleculesofprotein.Inthiscase,theporesofthemembrane

willbeblocked.Thistypeoffoulingisirreversibleandhardlyeliminatedthroughwater

washing.Therefore,thecaseofirreversiblefoulingrequiredacombinationofchemical

cleaningandback‐washing[29].

BHFMsarefabricatedbytwospinningmethods:electrospinningmethodandnon–

solvent‐inducedphaseinversion(NIPS)basedonthedry‐wetspinning.Basedonthelit‐

erature,membranespreparedbytheNIPSmethodbasedonthedry‐wetspinningprocess

aremorecommonandhavehigherwaterfluxduetothinseparationlayers[24].Asshown

inFigure1,thetubebraid(liketheborefluidinjectioninthefabricationofcommon

HFMs)isinsertedthroughthemiddleofthespinneret.Thenthepolymersolutionisuni‐

formlycoatedonthebraidtube.Thepreparedbraidhollowfibermembraneisimmersed

intoacoagulationbath,anditisfinallywounduponthedrum[4,30].

Membranes2021,11,8843of31



Figure1.Schematicillustrationofthefabricationofbraid‐reinforcedhollowfibermembranes(BHFM).

Recently,theelectrospinningmethodhasbeenattractedmuchattentiontogenerat‐

ingpolymerfibersintherangeofseveralmicronstonanometerdiameter(50nmand10

μm).Desirableproperties(functionality,porosity,weight,andstrength)canbeachieved

bythetypeofpolymerandefficientcontrolofoperatingconditions.Alargespecificarea,

ahighratiooflengthtodiameter,anduniformporesizedistributioncanbeachievedby

theelectrospinningmethod.Thebaseofthismethodisahigh‐voltageelectricfieldforthe

productionofnanofibersfromapolymericstreamthatisreleasedbyanozzlesystem.This

techniquecontributestoproducingofultrathinlayersfromdifferentfibers,particles,and

polymers.Thegeneratedfibersfromthismethodareaffectedbypolymericsolutionprop‐

erties(concentrationandthemolecularweightofpolymer),environmentalconditions

(humidityandroomtemperature),andoperationparameters(solutionflowrate,applied

voltage,andtip‐collectordistance).Intheelectrospinningmethod,thesyringefillswitha

polymericsolution,thenpumpstothenozzleataspecifiedflowrate.Thebraidlayeris

locatedonathincylindricalthatisjoinedtotherotatingshaft.Thefiberswillbegenerated

bycoatingthepolymersolutiononthebraidlayerbyapplyingtheelectricpowertothe

nozzle(Figure2)[31,32].Aslanetal.[31]fabricatedtubularelectrospunnanofibermem‐

branesasmicrofiltrationmembranes.Polyacrylonitrile(PAN)nanofiberscoatedonthe

braidedrope.Themorphologyandfiltrationcharacterizationshowedexcellentproperties

intermsofcross‐sectionthickness,waterflux,turbidity,porosity,hydrophilicity,anduni‐

formdistributionofporesize.

Membranes2021,11,8844of31



Figure2.Schematicdiagramofanelectrospinningsetup[31].

Kimetal.[5]introducedpatternedmorphology(prismandpyramid)tothesurface

ofBHFM,asshowninFigure3,byaimingtodeclinethefoulinginMBRforwastewater

treatment.Theinjectionrateofthenon–solventmainlyaffectedthemorphologyofthe

membranes.Uniformdistributionofmacrovoidsobservedforthehighinjectionrateon

thetotalcross‐sectionsurface.Inalowinjectionrate,adenseandthickpolymerfilmwas

formedinwardandoutwardofthebraid,andlargemacro‐voidswerecreatedexternal

sideofthepolymerfilminthevicinityofthebraid.Thisobservationcanbeexplained

basedontheinfiltrationofthenon‐solvent.Inalowinjectionrate,thenon‐solventwould

inducephaseinversioninsideandnearthebraidrelativetoinfiltrationfurthertothe

braid.Hence,thebulkofthepresentpolymeroutsidethebraiddiffusestowardthebraid

thatleadingtocoagulation.Therefore,adenseandthickpolymerfilmwasformedinside

ornearthebraid,andlargemacrovoidswerecreatedoutsidethebraidbecauseofan

insufficientcontentofthepolymer.Inahighinjectionrate,thenon‐solventdiffuses

quicklyinthetotalareaofthepolymericsolution.Hence,phaseinversionwouldhappen

withmorespeedalloverthepolymersolutionrelativetothemigrationofthepolymerto

thebraid.Therefore,amoreuniformdistributionofmacrovoidsiscreated.



Figure3.TheschematicofpatternedBHFM(b)lowinjectionrateofnon‐solvent(c)highinjection

rateofnon‐solvent[5].

ThereisalimitedamountofpapersthatreviewedtheBHFMs[33,34].Wespecially

reviewedtheeffectivefabricationparameters,modification,andperformanceofbraid

hollowfibermembranesinthedifferentapplications.Hence,thetypeandcontentofpol‐

ymer,additive,themethodsforincreasinginterfacialbondingbetweenthebraidandsep‐

arationlayer,andotherefficientparametersarediscussed.

Membranes2021,11,8845of31



2.EffectiveFabricationParameters

Dopeandbraidcompositionsuchastypeandconcentrationofpolymerandadditive,

fabricationparameters,andoperationalconditionsplayvitalrolesinthesuccessofthe

BHFMfordifferentapplications.Accordingly,theresearchersinvestigatedthevarious

aspectstoenhancetheperformanceofBHFMsfordifferentapplications.

2.1.TypeofPolymerinaDopeSolution

Theselectionofmaterialisanessentialfactorintheachievementofdesiredperfor‐

manceinmembraneapplication.Polymericmembranesarethemostusedmembranesfor

differentapplicationswithhighdesignflexibility[35].Severalpolymershavebeenem‐

ployedforthepreparationofBHFM,suchaspolyacrylonitrile(PAN),poly(vinylchlo‐

ride)(PVC),celluloseacetate(CA),polysulfone(PSf),andpolyvinylidenedifluoride

(PVDF).Table1providesthepropertiesofpolymersusedforthepreparationofBHFM.

Table1presenttheusedpolymersforBHFMandtheirproperties.

PVCisoneoftheusualandpromisingpolymersformembraneapplication.How‐

ever,foulingproblemscanrestrictthePVCmembranesinwaterapplicationowingto

theirhydrophobicnature.TheblendingofanamphiphiliccopolymerandPVCinthedope

solutionisoneofthemethodsthatcanovercometheantifoulingproperties.Thehydro‐

philicpartoftheamphiphiliccopolymerisconnectedtothemembranesurface,which

leadstoamembranewithgoodantifoulingproperties.Thehydrophobicsectioncreates

goodcompatibilitywiththemembranematrixandincreasesthemaintenanceofcopoly‐

merinthemembranematrix.Zhouetal.[36]preparedtheBHFM‐purePVCandblended

BHFMwithdifferentblendratiosofPVC/copolymer.Theburstingstrengthandtensile

strengthofBHFMwerehigherthan2.1and170MPa,respectively,whichwerelargerthan

thoseoftheself‐supportingHFMs.

Copolymers,includingpoly(ethyleneoxide)(PEO)orpoly(ethyleneglycol)(PEG)

chains,cancreateahydrationlayer,preventingthebindingofthefoulantsmoleculesto

thesurfaceofthemembrane.However,PEG‐basedcopolymerissuggestedtoimprove

theantifoulingpropertiesandhydrophilicityofPVCmembranes.SincePEGiscatego‐

rizedinsoftpolymers,increasingthePEGcontentinthedopesolutioncanreducethe

mechanicalstrength.Henceitcanlimitthemembraneapplicationinpracticalwastewater

treatmentduetodamagingthemembranestructureduringthebackflushprocessoraer‐

ation[36].Therefore,theoptimizationofPEGcontentisessentialinordertoobtainanti‐

foulingpropertiesanddesirablemechanicalstrengthforpracticalapplication.Zhouetal.

[36]usedamphiphiliccopolymerpoly(vinylchloride‐co‐poly(ethyleneglycol)methyl

ethermethacrylate)(poly(VC‐co‐PEGMA))toendowhydrophilicitytoPVCbraidhollow

fibermembrane.Considerableimprovementwasobservedinantifoulingpropertiesand

hydrophilicitywhenthecopolymer/PVCblendingratiointhecoatingsolutionwasused

inoptimumcontent.

PANhollowfibermembraneshavebeenwidelyutilizedinpervaporation,thetreat‐

mentofindustrialwastewater,andenzymeimmobilizationapplications.Fabricationof

thesubstrateforcompositemembranesisanotherPANapplicationduetofavorableprop‐

erties.LowmechanicalstabilitylimitsPANapplicationinmicro/ultrafiltrationandMBR

systems[7].Quanetal.[7]preparedthePAN‐BHFMbycoatingPANsolutionsonthe

PET(Polyethyleneterephthalate)andPANtwo‐dimensionalbraidsurface.ThePAN‐

BHFMbasedonthePANbraidhadexcellentmechanicalpropertiesduetogoodinterfa‐

cialbondingbetweenthepolymerandthebraid.Itwaspossessedatensilestrengthhigher

than80MPa.

Theexcellentmechanicalstrengthandotheradvantages(asshowninTable1)ofPSf

membranesuggestthisisagoodcandidateforwastewatertreatmentsystems,textiledye‐

ing,anddesalination.PSfmembranesrequiresurfacemodificationinordertoenhance

hydrophilicityandwaterpermeation[24].Theincorporationofhydrophilicnanoparticles

Membranes2021,11,8846of31



inthePSfmembranecanimproveantifoulingpropertiesandincreasethefluxrate.Peech‐

manietal.[24]fabricatedhybridPSf/zincoxide(ZnO)BHFMstoincreasefluxandim‐

provehydrophilicity.TheBHFMswerepreparedwithdifferentconcentrationsofZnO

nanoparticles.TheZnOnanoparticlesleadtoanincreaseintheoverallfluxandabsorp‐

tionofwatermoleculesontothemembranesurfaceduetohydrophilicnatureandwater‐

lovingproperties(absorptionofhydroxylgroups).Increasingthehydrophilicityofthe

membranesurfaceleadstodecreasingtheinteractionsbetweenorganicmattersandthe

membranesurface.Hence,lessfoulingbyorganicfoulantshappensonthehydrophilic

membranes.

CAmembranesareanothertypeofpolymermembranethatplaysasignificantrole

inmembraneseparationduetofavorablepropertiesbasedonTable1.Despitethegood

propertiesofCAhollowfibermembranes,theweakmechanicalstrengthlimitedtheirus‐

ageinpracticalapplicationssuchasmembranebioreactors.TheHFMinthesubmerged

MBRcaneasilybebrokenordamagedduringtheback‐washingprocessoraeratedair‐

flow.Hence,itisrequiredthistypeofmembranepreparedwithhighmechanicalproper‐

ties.CAmembraneasahydrophilicmembraneshowedthehighperformanceforanti‐

foulingpropertieswhenfacedwithBSAsolution.ThedenseoutersurfaceofBHFMcould

avoidorlimittheblockingoftheinnerpore.Hence,thecreatedfoulingismainlydueto

adsorptionand/ordepositionofpollutantsonthemembranesurface,whichiseasilyelim‐

inatedbywaterwashing[21].

OneofthemainaromaticpolyamidesisPoly(m‐phenyleneisophthalamide)(PMIA)

withhydrophilicproperties,goodmechanicalproperties,excellentthermalstabilitydue

tothehydrogenbondnetwork,andaramidgroups.Thispolymeriswidelyusedfornan‐

ofibersproductionandinwatertreatmentapplications.Chenetal.,preparedPMIAhol‐

lowfibermembranescontainingseparationlayersandreinforcedbraids.ThePMIA‐

BHFMexhibitedgreatantifoulingpropertyrelativetoPVDFmembranes.ThePMIA

membranesexhibitedahighernegativitychargerelativetothePVDFmembranesdueto

thestrongpolaramidegroups(–NH–CO–)inthemacromolecularchainofPMIA.These

groupsleadtocreatingstrongelectronegativityandsuperiorhydrophilicityPMIAmem‐

branes.Thesepropertiesarethemaingoaltoimprovetheantifoulingproperty[28].

Membranes2021,11,8847of31



Table1.Used‐polymersforBHFMandtheirproperties.

PolymerChemicalStructure.Advantages Disadvantages/ImprovementApproachApplication Ref.

PAN



- Lowprice

- Excellent ag‐

ing‐resistance

- Highhydro‐

philicity

- Goodstability

- Goodsolvent

resistance

- Lowmechanicalstability

Water,municipal,

andindustrial

wastewatertreat‐

ment

[7,31]

PVC



- Excellentme‐

chanicalstrength

- Highcorrosion

resistance

- Lowcost

- Hydrophobicnature/Usingam‐

phiphiliccopolymer

UltrafiltrationBHFM

forwastewatertreat‐

ment

[36]

PSf



- Excellentme‐

chanicalstrength

- StabilityatpH

levelsfrom2to13

- Excellentre‐

sistancetocaustic

- Goodre‐

sistancetomoder‐

atechlorine

- Operatingat

hightemperature

andpressure

- Hydrophobicnature/Incorporationof

zincoxide(ZnO)

Wastewater

treatment[24]

Membranes2021,11,8848of31



CA



- Goodfilm

forming

- Relativelylow

cost

- Highflux

- Goodtough‐

ness

- Biocompatibil‐

ity

- Poormechanicalproperty/Usinghomo‐

geneousbraidreinforced

Wastewater

treatment[21,37]

PVDF



- Goodhydro‐

phobicproperty

[38]

- Semi‐crystal‐

linepolymer

- Goodmechani‐

calstrength

- Stability

againstvigorous

chemicals

- Goodthermal

stability

- dramaticallydecreasingofhydrophobi‐

cityincontinuoususe/blendingmethod

forimprovingthehydrophobicity(Gra‐

phene)[38]

- hydrophobicproperty[30]

oil/waterseparation

[38]

wastewater

treatment[30]

[38–42]

PMIA



- Highthermal

stability

- Excellentme‐

chanicalproper‐

ties

- Hydrophilic

property

NAwastewater

treatment[28]

Membranes2021,11,8849of31



PU

- Biodegradabil‐

ity

- Biocompatibil‐

ity

- Lowcost

NAoil/waterseparation[43]



PAN:Polyacrylonitrile;PVC:Polyvinylchloride;PSf:Polysoulfone;CA:Celluloseacetate;PVDF:Polyvinylidenefluoride;PMIA:Poly(m‐phenyleneisophthalamide);Pu:

polyurethane;NA:notapplicable.

Membranes2021,11,88410of31



2.2.TheEffectofPolymerConcentration

Generally,thepolymerconcentrationhasasignificanteffectonmembraneperfor‐

manceandstructure.Asthepolymerconcentrationisincreasedinthedopesolutions,the

finger‐likeporestructureisgraduallyconvertedtoasponge‐likeporestructure,andthe

porediameterbecomessmaller.AscanalsobeseeninFigure4,thehigherpolymercon‐

centrationcausestheformationofthedenserandthickerskinlayer.Incontrast,thelooser

structureisreportedforthemembranecontaininglowpolymerconcentration.Thehigh

polymerconcentrationleadstoincreasingtheviscosityofpolymersolution.Therefore,

therateofdiffusionisreducedbetweensolventandinthephaseinversionprocess.In‐

stantaneousdemixingcreatesmembraneswithaporouslayerandafinger‐likestructure,

whereasdelayeddemixingresultsinmembraneswithdensestructuresandsponge‐like

pores.Thedensandsmoothstructureandsmallporesizeofthemembranesurfacecause

animprovementtotheantifoulingabilityandseparationpropertyofthemembrane,

thoughthefluxwillbereduced.Therejectionismoredependentonthedensityofthe

separationlayercomparedtothestructureofthecross‐section[28,37,44].Fanetal.[21]

reportedthattherejectionofmembranewiththelowconcentrationofCAhadminimum

rejectionduetobigsizepores.Theyalsoobservedanincreaseinpolymerconcentration

indopesolutionleadtothecreationofasurfacewithsmoothanddenseproperties.The

burstingandtensilestrengthsalsoincreasedduetointerfacialbondingbetweentubular

braidandseparationlayer.Zhangetal.[45]observedtheBSArejectionforBHFMwas

higherthantheHFM.ItwasduetothedenserskinlayerandsmallerporesizeinBHFM

relativetoHFM.Theporesizeisanessentialfactorthataffectsmembranepermeability.

AsshowninFigure5,theincreaseinpolymerconcentrationindopesolutionleadsto

decreasingofpurewaterfluxandincreasingtherejectionduetolowerporosityandpore

sizeofthemembrane[7,40,46].

Thecontactanglebetweenthebraidandthecoatingsolutionincreasedwhenthe

polymerconcentrationincreased.Itisduetotheviscosityofpolymersolutionenhanced

withtheincreaseinpolymerconcentration;hence,thesolutionfluiditywillbereduced

[7,40,46].

BasedontheinvestigationofChenetal.[28],theantifoulingproperties(performance

andfluxrecoveryratio)forPMIABHFMwerebetterinahigherconcentrationofpolymer.

Itmaybeduetothepresenceofstrongpolargroups(−NH−CO)inthemacromolecular

chainofpolymerthatleadstocreatingexcellenthydrophilicityandstrongelectronegativ‐

ity.Theotherreasonisthedenseoutersurfaceandsmallporesizeinthehighconcentra‐

tionofpolymerthatavoidstheporeblockageofinnerpores.Hence,thefoulingandform‐

ingofthecakelayermainlycreateonthemembranesurfacethatiseasilyremovedinthe

cleaningprocess.



Figure4.TheeffectofpolymerconcentrationonBHFMstructure(b1)5%,(b2)8%,(b3)10%,and(b4)15%[28].

Membranes2021,11,88411of31



Figure5.Effectsofpolymerconcentrationonthe(a)purewaterfluxand(b)proteinrejection[28].

Asmentioned,thepresenceofthebraidreinforcementleadstonotableenhancement

ofmechanicalproperties.Forexample,Liuetal.[46]observedthatthetensilestrengthfor

amembranewiththreethreadswasmorethansixtimesrelativetothemembranewithout

thread.Thereisthephysicalandchemicalforcebetweentheinterfaceofpolymerand

braidlayer.Thephysicalforceconsistsofconglutinationandwedge,andchemicalforce

createdbythechemicalbonds.Thewettabilityofbraidbypolymersolutionisthemain

factorthataffectstheinteractionforcebetweentwolayers.Thecontactanglebetweenpol‐

ymersolutionandbraidmustbesmalltoobtainsufficientcontactingandwettingbetween

them.Withanincreaseinthepolymerconcentration,theviscosityandsurfacetensionis

increased.TheburstpressureofHFMisaresistingcapabilityinaradialdirectionmainly

determinedbyforcebetweenthemoleculechainsofpolymers.Thisparameter,asacritical

parameterinthecleaningprocess,representstheinterfacialbondingstateofBHFMtoa

certainextent.Inthepracticalapplication,theoperatingpressureisrestrictedbytheburst

pressureduetothesmalleffectofbraidthreadontheradialdirectionpersistence[21,28].

ThehighburstingstrengthwouldrestricttheharmofBHFMSintheback‐washingpro‐

cess.Itisenhancedwiththeincreaseinpolymerconcentrationinthedopesolutiondue

tothesuperiormechanicalstrengthoftheseparationlayerinhigherpolymerconcentra‐

tions.Thereisatighterstackofmoleculechainsinthemembranewithhigherpolymer

concentration.Hence,theyhaveahigherburstpressure.Thereisastrikingcorrelation

betweentheburstpressureandoperationforthenormalHFM.However,addingbraid

threadsleadstoanisotropyinthetransversalandlongitudinaldirections,sotherelation‐

shipissmallforBHFM.Themembranematerialandstructureeffectonburstpressure

andtensilestrengthisinfluencedbybraidthread.

Fanetal.[37]observedthatanincreaseinthepolymerconcentration(from6to14

wt.%)inthedopesolutionwascontributedtotheenhancementofthetensilestrengthof

CA‐BHFM(from11to14MPa).BasedonastudybyChenetal.[28],themechanical

strengthisdominantlygovernedthroughthereinforcedbraids.Thebreakingelongation

andtensilestrengthwereapproximatelysimilartothetensilestrengthofthebraids.The

burstingstrengthandinitialmodulusenhancedwiththeincreaseinthepolymerconcen‐

trationbecausetheseparationlayerwasfirmlybondedwiththebraidlayerthathindered

thedeformationofthebraidlayer.Theseparationlayeralsohadabettermechanical

strengthinhigherpolymerconcentrations.



Membranes2021,11,88412of31



2.3.EffectofAdditives

Thepresenceofadditivesinbulkoronthesurfacemembraneisoneoftheeffective

approachestoimprovemembraneperformancethroughthemodificationofroughness,

hydrophilicity,poresize,andsurfacecharge[15].Zhouetal.[36]fabricatedtheBHFMby

blendingPVCanddifferentblendratiosofpoly(VC‐co‐PEGMA)copolymer.Therewasa

highinterfacialbondingstrengthbetweenthePET‐braidandpolymersolution.Although,

thecopolymerscontainedPEGdemonstratethestrongabilityofpore‐forming,which

leadstocreatinglargeporesandporosityenhancement.Thepreparedmembraneexhib‐

itedantifoulingresistanceandhighmechanicalproperties.ThetensilestrengthofPVC‐

BHFMwassignificantlyhigherthanPVC‐HFM.Themembranehydrophilicityincreased

withincreasingthecopolymerconcentrationofthedopesolution.Highhydrophilicity

bringsaboutafasterdemixingprocessanddiffusionofwaterintothepolymersolution

duringthemembraneformation.Hence,alargerporesizewillcreateintheselectivelayer

comparedwithlowhydrophilicity.Theoptimizationofcopolymercontentisnecessary

becauseanincreaseincopolymercontentbasedonPEGinpolymersolutionleadstoa

reductioninmechanicalstrengthofmembraneduetothePEGsoftness.

Peechmanietal.[24]showedthatthepresenceofZnOnanoparticlesindopesolution

causeddelay‐demixingbetweennon–solventandsolventduetoviscosityenhancement.

Thus,theformationofmacrovoidswasconsequentlyincreased.Byincreasingtheconcen‐

trationofnanoparticles,themacrovoidsanddensespongestructureandconsequently

higherpermeationincreasednearthebraidlayer.Itisduetothehydrophilicnanoparticles

thatcontributetothefastermovingofwatermoleculesintothemembranematrixrelative

tothedemixingratebetweennon–solventandsolventduringthephaseinversionprocess.

TheBSArejectionandwaterfluxwerehighercontentsinthehighestcontentofZnOcom‐

paredtoothermembranes.ItisoccurredbecauseofthehydroxylgroupofZnOnanopar‐

ticlesintheselectivelayerthatreceivesmorewatermolecules.Thestrongelectronegativ‐

ityofnanoparticlesalsoresultsinavoidingthedepositionofBSAproteinsintheselective

layer.

Lanetal.[47]fabricatedaBHFMconsistingofPVDFasabasepolymerandPETa

woventubalasasupportlayer.TheyusedTiO2nanoparticlesfortheimprovementof

hydrophilicity.Thepreparedmembraneshaddesirablepropertiesintermsofthefiltra‐

tionareaandmechanicalstrengthrelativetoconventionalHFM.TheBHFMcontaining

1%TiO2hadthebestantifoulingproperty,thehighestflux,andthelowestfluxdecline

rate.

Haoetal.[38]preparedaPET‐braid‐reinforcedPVDFhollowfibermembranewith

differentconcentrationsofgraphenetoincreasethemembranehydrophobicityinoil‐wa‐

terseparationapplication.ThePETtubularbraidswerecoatedwithaPVDF/graphene

solution.Theviscositiesofpolymersolutionsfirstincreasedandthenreducedwithan

increaseingraphenecontents.Theviscosityofpolymersolutionvariedwhentheshear

rateincreasedandshowedthepropertiesofapseudoplasticfluid.Thepolymersolution

withoutgraphenehadalowviscositythatrepresentednoconsiderablechangewiththe

enhancementofshearrate.Theviscosityofthepolymersolutionchangedclearlyforthe

membranewiththehighestamountofgraphene.Itisduetographenebeingalaminated

andrigidsubstancewithahighYoung’smodulus.Inalowshearrate,thepresenceof

toughgrapheneincreasedtheflowresistanceofpolymersolution.Withtheincreasein

shearrateandexceedingfromaspecifiedamount,theeffectofflowresistanceforgra‐

pheneslowlyweakened,andtheviscosityofthepolymersolutionwasconsequentlyde‐

creased.Haoetal.observedsmallmeanporesizeandthefluctuationinthicknessofthe

selectivelayerinthemaximumconcentrationofgrapheneduetothehighviscosityand

lowfluidityofpolymersolution.Therandomdistributionofgraphenesheetsintheselec‐

tivelayersofBHFMsresultedincreatingamembranewithastableporestructuredueto

therigidnatureofthegraphenesheets.Wuetal.[43]fabricatedaPU/grapheneBHFM

basedonPETbraidedforoil/waterseparation.Thepreparedmembranesshowedgood

Membranes2021,11,88413of31



lipophilicpropertiesbasedoncontactangleresults.Goodselectivityforoil‐watersepara‐

tionwasalsoachieved.

Liuetal.[29]investigatedtheeffectofmolecularweightsofpolyethyleneglycolon

thestructureandperformanceofhomogenousreinforcedPVC‐BHFMs.Thepresenceof

PEGwithhighmolecularweightleadstoincreasingthethicknessoftheseparationlayer

becauseoftheenhancementofsolutionviscosity.Thehighviscosityrestrictstheexchange

ofthesolventandnon–solvent.ThehighmolecularweightofPEGcreatedabiggerfinger‐

like,smoothoutersurfaceandcompactskinlayerrelativetothelowmolecularweightof

PEG.TherejectionofBSAproteinincreased,andtheporosityreducedwhenthemolecular

weightofPEGwasenhanced.Itisduetoincreasingthethicknessoftheseparationlayer

andformingthedenseouterlayerwiththeincreaseinthemolecularweightoftheaddi‐

tive.ItisnotablethatthemolecularweightofPEGdidnotinfluencethemechanicalprop‐

ertiesofpreparedmembranes.

2.4.EffectofBraidComposition

Tworeinforcingmethodsarereportedintheliteratureinordertoimprovetheim‐

provementofmechanicalpropertiesofHFMs:fibersreinforcedandporousmatrixmem‐

branereinforcedassupport.Thefibersreinforcedmethodislow‐costandstraightfor‐

ward.Itcouldbedonebythetubularbraidreinforcedbasedonthereinforcementshape

andthecontinuousfiber‐reinforcedmethod.Leeetal.[48,49]fabricatedabraid‐reinforced

compositeHFMconsistingofatubularbraidwithmultifilament.Themultifilamentis

formedfrommonofilamentswithafinenessof0.01to0.4denier.Thesurfaceareabetween

thepolymerthinfilmandtubularbraidisincreasedbecausethefinenessofthemonofil‐

amentsissmall.Hence,thepeelingstrengthofthepolymerthinfilmandtubularbraidis

excellent,aswellasthemembranewettabilityisexcellentbecauseofthecapillarytube

phenomenon.

Inthesecondmethod,theporousmatrixmembraneasthereinforcementisfirstly

preparedbymelt‐spinningcold‐stretchingorthermallyinducedphaseseparation;then,

thesurfacecoatingiscarried.Thismethodisapproximatelyhighcostandcomplex[6].

Liuetal.[46]fabricatedcontinuouspolyesterthreadsPVDF‐HFMbyincorporatingPET

threadsinthesupportlayerintheaxialdirection.Theyfoundthatthetensilestrengthof

theBHFMsimprovedupto10MPabytheincreasingofPETthreadsnumber.ThePET

threadshadloweffectsontheseparationpropertiesofthemembrane,butthetensile

strengthofthemembranewasincreased.

Bothpureandhybridcompositionforthebraidisreportedintheliterature.Fanet

al.[37]preparedahomogeneousBHFMwhichconsistedofaCAforthebraidandsepa‐

rationlayer.Thepreparedmembraneindicatedagoodinterfacialbondingstate,butthe

CAfibersinthebraidtendtobeswollenandsicktogether,whichdecreasesthepermea‐

bilityandfluxofthemembrane.Hybridbraidleadstochangingporousstructure,en‐

hancesthemembraneseparationproperties,andreducesthedrawbackofthehomoge‐

nousmethod.Fanetal.[21]preparedaBHFMbasedonahybridbraid.Thehybridbraid

consistsofCAandPAN.ThepresenceofPANfiberinhybridcompositionovercamethe

CAfiber’sswellingandreductioninpermeability.Thetensilestrengthofprepared

BHFMsincreasedfrom16.0MPato62.9MPabyoptimizingtheCA/PANratiointhebraid

composition.TheburstingstrengthwasenhancedwhenCAfiberproportionincreasedin

thebraid.Liuetal.[6]fabricatedaheterogeneousBHFMconsistingofahybridbraid(PET

andPAN)andacoatinglayerofPVC.Thepreparedmembranehadadesirableinterfacial

bondingstateandtensilestrengthrelativetothemembranecontainingpurePANorPET

braid.ItwasalsoobservedthatthetensilestrengthdecreasedwhenPANfilamentsin‐

creasedinthecompositionofthehybridtubularbraid.

Quanetal.[7]investigatedtheeffectoftwotypesofbraid(PANandPET)onmem‐

braneperformance.ThemembranewaspreparedbasedonPANbraidasahomogenous

membraneandPETbraidasaheterogeneousmembrane.Theirresultsshowedthatthe

interfacialbondingstateofthePANmembranewasbetterthanthePETmembrane.The

Membranes2021,11,88414of31



contactanglebetweenthebraidandthecoatingsolutionwaslowerforthePANmem‐

brane.ThetensilestrengthandpurewaterfluxofthePETmembranewerehighercom‐

paredtothePANmembrane.

Table2summarizesthestudiesforBHFMsbasedonhybridcompositionandpure‐

compositionbraid.ThePETbraidisusedinmostoftheBHFMinthepure‐composition

braid.PVP(Polyvinylpyrrolidone)orPEGisgenerallypresentindopesolutionaspore

former.Thepresenceofadditivesimprovestheseparationpropertyandwaterfluxinop‐

timumcontent.

2.5.ThinFilmComposite:BraidHollowFiberMembranes(TFC‐BHFM)

SomestudieshaveconcernedforimprovingpropertiesandperformanceofTFC‐

BHFMbyoptimizationoffabricationparameterssuchassoakingtime,monomerratios,

reactiontime,andmonomerconcentrationinorganicoraqueoussolution.

2.5.1.TheEffectofMonomerConcentrationonTFC‐BHFM

Thesurfaceproperties(e.g.,hydrophilicity,functionalgroups,crosslinkingofmon‐

omers)andstructure(e.g.,thickness,poredimension,androughness)oftheselective

layerdirectlyaffectonthemembraneperformance.Thus,itisnecessarythefundamental

understandingoftheinfluenceofdifferentmonomersforthepreparationofhigh‐perfor‐

mancemembraneswithdesirablestructures[50].

Xiaetal.[10]investigatedtheTFC‐BHFMswithdifferentmonomerconcentrations

(PIP(piperazine)andTMC(trimesoylchloride)).TheyfabricatedtheNFmembranethat

exhibitedhighstrengthatpressuresupto70psiwithoutfractureandcreatedtheintegrity

intheBHFMatpressurestypicallynotutilizedforfibersofthissizebyusingbraid‐rein‐

forcedandoptimizationofmonomerconcentration.ThepreparedTFC‐BHFMcouldbe

usedforprocessesthatsaltselectivityisrequired.Itwasreportedthatthewaterpermea‐

tioninthelowconcentrationofTMCwashigherincomparisonwiththelowconcentra‐

tionforbothmonomers(i.e.,PIPandTMC).Itcanbeexplainedthatthemembranedefects

arereduced,oritmaybeduetotheincreasingofthethicknessordensityoftheselective

layerinahighermonomerconcentration.Thedifferentresultsobservedfromthistrend

inthepreparedmembraneswiththehighestcontentofPIPandminimumcontentofTMC.

ItisprobablyduetocreatingathickbarrierfilminthelowestTMCconcentrationinorder

tostopthereactionrapidly.ThehighTMCconcentrationshadapositiveeffectonMgSO4

rejection.Thedifferentconcentrationsofaminegroupstypicallycausethevariousperme‐

ation,whichislikelyduetoreducingtheporesizeofthemembrane.Figure6showsthe

reactionbetweenTMCandPIPtoformpolyamideasaselectivelayer.



Figure6.ThereactionbetweenPIPandTMCforpolyamideformation[51].

2.5.2.EffectofSoakingandReactionTimeinTFC‐BHFMPreparation

ThesoakingofthesupportlayerisastepofTFC‐BHFMfabricationthatimpactsig‐

nificantlyontheperformanceofpreparedTFC‐BHFM.Ununiformedwettingmayleadto

thedecreasingofmembraneselectivity.UsingthePVDFsupportinthefabricationofthe

TFCmembraneisamainchallengeduetoitshydrophobicnatureandwettingdifficulty

[10,52].Xiaetal.[10]preparedtheTFC‐BHFMswithdifferentsoakingtimes.Thevisual

propertieswerenotchangedbasedonthevariationofsoakingtime.Anincreaseinthe

Membranes2021,11,88415of31



soakingtimeleadstodecreasinginpurewaterpermeability,whilethesaltrejectionfirstly

increasesandthendecreases.Theseresultsareduetoformingauniformselectivelayer

withfewerdefectsafterentirelywettingbythePIPsolutionatthelongersoakingtime.

Themodificationofsupportsurfacethroughplasma,coatingwithhydrophilicpoly‐

mers(e.g.,PANandPVA),wettingofmembranebyinvertthesequencesoakinginthe

organicphaseandthenimmersionintheaqueousaminephasearethemethodsforwet‐

tabilityimprovementoftheofPVDFsupportthatinvestigatedbyresearchers[10].

Reactiontimeisacrucialfactorininterfacialpolymerizationthataffectsthestructure

ofthecoatinglayerandspecifiestheextentofpolymerizationbetweenthemonomers[53].

Turkenetal.[51]fabricatedreinforcedTFC‐HFNFmembranes.Theyselectedtherein‐

forcedPSfultrafiltrationasasupportandpolyamidelayerasaselectivelayerthatwas

preparedfromtrimesoylchloride(organicphases)andpiperazine(aqueousphases)mon‐

omers.TheimmersiontimeofTMCwasoptimizedinfixedconcentrationsofTMCand

PIPtoachievethehighestmembraneperformance.Thehydrophilicityofthemembrane

increasedbyenhancementofthecrosslinkingdegreeofthepolyamidelayerandtheTMC

reactiontime.Turkenetal.[51]reportedthehigherspecificpermeatefluxinhigherTMC

reactiontimesforreinforced‐TFC‐NFmembranes.Thehydrophilicityofthemembrane

enhancedwhenthereactiontimeofTMCincreased.Itisknownthatwhenthecrosslink‐

ingdegreeofthepolyamidelayerisincreased,theformationofthemembranewitha

highlyhydrophilicnatureisenhanced.Thepresenceofthepolyamidelayeronthesurface

ofthemembraneleadstothecreatingofaTFCsurfacewithmorenegativelycharged.The

negativechargeofthemembranesurfacewasdecreasedwhenthereactiontimeofTMC

increased.Theformationof−COOHgroupsismoreinshortreactiontimeofTMC.Since

thetimeofTMCreactionisoneoftheeffectiveparametersincrosslinkingdegreeofinter‐

facialpolymerization;hence,itinfluencedthesaltrejectionandwaterflux.Theformation

oftheamidegroupisavitalsignforthecrosslinkingdegreeofmonomer,thehydrolyzing

ofacylchloride,andfilmformationandgrowth.DuringthecontinuousreactionofTMC

andPIP,itisexpectedthattheamountof−C=Ogroupsincreasedinthemembranes.The

presenceofthemore−C=Ogroupindicatedmorereactionbetweenthemonomers.The

existenceofthe−OHgroupisasignofthehydrolysisofTMC.Atthebeginningofthe

reaction,thewaterdiffusionintothemembranematrixfacilitatesthehydrolysisofTMC.

Thehydrolysisofthemembranebytheaqueousphaseattheinitialstage(orshorterTMC

reactiontime)isowingtotheloosestructureofthecoatinglayer.Asthereactiontime

increased,the−OHand−C=Owouldbeenhanced,andbondingbetweentheOHandC–

Ogroupswouldreduce.Therefore,amembranewithadenselayerwouldbecreated

[51,53].

3.ImprovementofInterfacialBonding

Generally,thetubularbraidsandseparationlayersareincompatible.Thethermody‐

namicalincompatibilityofthesetwolayermaycauseanapparentchangeininterface

structurebetweenthesupportedmatrixandseparationlayer.Therefore,theinterfacial

bondingstrengthbetweenthebraidandtheseparationlayerisacrucialissueinthebraid‐

reinforcedhollowfibermembrane.Thepeelingoftwolayersduringthemembraneoper‐

ationprocessreducesitslifetimeandrestrictsitsapplication.Hence,theaffinity(compat‐

ibility)betweentwolayersplaysavitalroleinthestrengthofinterfacialbonding.The

highinterfacialbondingstrengthisfavorableinhigh‐pressurehydrauliccleaning.The

infiltrationpropertyofBHFMsisinvestigatedbythecontactanglebetweenthebraidand

polymersolution[44,45,54].

3.1.HybridBraidHollowFiberMembranes

Theselectionofmaterialforpolymerandtubularbraidaffectstheinterfacialbonding

performance.RelativetoheterogeneousBHFM(braidsandseparationlayeraremade

fromdifferentmaterials),homogeneousBHFMthatcontainedthesamematerialsinthe

Membranes2021,11,88416of31



tubularbraidandtheseparationlayerhasdesirableinterfacialbondingstrength.Thein‐

terfacialbondingofthehomogenousandheterogeneousmembranedifferedfromeach

other.Theinterfacialbondingbetweenthebraidandtheseparationlayerispoorinhet‐

erogeneousBHFMduetoincompatibility,whereastheseparationlayerisstrongly

bondedwiththebraidinhomogenousBHFM.WhentheheterogeneousBHFMsaresub‐

jectedtopressingorstretchingeffect,thedeformationratewillbedifferentbetweenthe

braidlayerandtheseparationlayer.Therefore,theinterfaceoflayerswouldbehurt

throughtheinterlaminarshearbetweenthebraidlayerandtheseparationlayer.Hence,

theinterfacialbondingoftheheterogeneousBHFMisthemainparameterrestrictingits

application[6,7,21,28,36,44].Thereisaphysicalforcebetweentubularbraidsandthepol‐

ymercastingsolutioninthepreparationprocessofBHFM.Thisphysicalforceconsistsof

adhesivecuring(whentwosurfacescombinebythephysicalorchemicalinteraction)and

mechanicalwedgingthatisrelatedtothediffusiondegreeofthepolymersolutionstothe

hybridtubularbraidandthesurfaceroughnessofthehybridtubularbraids.Poorinfiltra‐

tionbetweenthehybridtubularbraidsandthepolymersolutionsresultsindefects,and

theinterfacialbondingstrengthwouldbeconsequentlyreduced.Thusadesirableinfil‐

trationperformancecanconsiderablyimprovetheinterfacialbondingstrength.Gener‐

ally,thecontactangleisusedinordertocharacterizetheinfiltrationability.Thesmaller

contactanglebetweenthepolymersolutionsandtubularbraidrevealsthebetterthein‐

filtrationperformance[6,7].Oneofthemethodstoenhanceinterfacialbondingisutilizing

thesamematerialbetweenthecoatinglayerandthereinforcedmatrix.Fanetal.prepared

anovelbraidhollowfibermembraneconsistingofahybridbraid(containingcellulose

acetateandpolyacrylonitrile)andaseparationlayer.Theresultedmembraneprovideda

wellinterfacialbondingstateandreducedthenegativeeffectofCAfiberswellingon

membranepermeability.Fanetal.alsoinvestigatedtheeffectofbraidcompositionand

CAconcentrationonBHFMperformance.Theyresultedthatthebestratioofthefibersin

thebraidphaseis2/1(CA/PAN)byconsideringthemembranepermeabilityandinterfa‐

cialbondingstate[21].Theinfiltrationofthepolymersolutionmayreducethepurewater

permeability(PWP).ItwasreportedthatPWPofthehomogeneouslyBHFMislowerthan

heterogeneousBHFMbecauseinfiltratedpolymerscanbetightlyincorporatedinthepo‐

rousbraidandthusreducethePWP[11].

Zhouetal.[36]preparedabraidhollowfibermembranewithdesirableantifouling

propertiesandmechanicalstrengthforwastewatertreatment.TheblendingPVCwith

PVC‐co‐PEGmethylethermethacrylate)(poly(VC‐co‐PEGMA))copolymercoatedon

PETbraid.Thehighinterfacialbondingandtensilestrengthindicatedthegoodcompati‐

bilitybetweenthePET‐braidandcoatinglayer.Excellentantifoulingproperties,higher

hydrophilicity,andBSArepulsionresultedduetothesegregationofPEGMAonthemem‐

branesurface.Chenetal.[28]fabricatedthreeBHFMswithPMIAasapolymeranddif‐

ferentbraidcompositions(differentratiosofPMIA/PET).AsshowninFigure7,thecoat‐

inglayerofpurePMIAforthebraidindicatedahomogeneousstructurewithgoodcom‐

patibilityandfirmlybondingbetweenthereinforcedbraidandseparationlayer;whereas,

poorinterfacialbodingandheterogeneousseparationlayerswereobservedforbraidwith

purePET.ForthebraidcontainedbothPMIAandPET,thetightlybondedforseparation

layerwiththePMIAfibersandthePETfibersobserved;whereas,therewasthepoorin‐

terfacialbondingbetweenthePETfibers.

Membranes2021,11,88417of31



Figure7.Thecross‐sectionmorphologiesof(M1)PurePMIAforthebraid(M2)equalcomposition

ofPMIA/PETforthebraids,and(M3)PurePETforthebraids[28].

Itseemsthehybridbraidisaneffectivemethodwithhighperformance,butitishard

toapplyonalargescale.ItischallengingtofabricateBHFMconsistingofhybridbraids

(withhydrophilicpolymeric)andthesamematerialonthecoatinglayer.Therefore,itis

necessarytodevelopaneasy,effective,andlow‐costproceduretocontroltheproperties

ofthecommercialbraids[11].

3.2.AlkalinePretreatment

Alkalinepretreatmentofthebraidsurfaceisasimplemethodforincreasingandfa‐

cilitatingpolymeradhesion.Italsoleadstoincreasebraidhydrophilicity.Thismethod

providesgoodsupportforthecoatinglayerwithoutreducingthequalityofthebraid.El‐

Badawyetal.[4]investigatedtheeffectofthealkalinepretreatmentofthebraidonBHFM

morphologyandperformance.Themembraneistreatedbytwoalkalinesolutions(KOH

andNaOH).ThetreatedmembraneinKOHhadthehighestwaterflux.Theinvestigation

ofthesurfacemorphologyofthebraidsrevealedthattheexpansionofthebraidinter‐

spacesandwashingeffectcontributetomoreporosityandpermeability.

Zhouetal.[11]preparedaBHFMbycoatingablendedpolymer(amphiphiliccopol‐

ymer/PVC)solutiononamodified(alkaline‐treated)PETbraid.Themodificationbyal‐

kalineleadstoendowmorepolargroupstoPETbraidandconsequentlymorehydro‐

philicity.BasedontheresultsofZhouetal.[11],thebondingstrengthbetweenthecoating

layerandalkaline‐treatedPETbraidwasabouttwotimeshigherthanthenon‐treatedPET

braid.ThetensilestrengthofthePETbraidswasreducedafterthealkalinetreatment.The

basicPETbraidhadmoretensilestrengthrelativetotreatedPET.Thedecreasingmechan‐

icalstrengthindicatedthatthePETbraidswereweakenedbythehydrolysisofPETchains

duringthealkalinetreatment.Thehydrolysisprocessreducesthecrystallinityandthe

molecularweightofPET.Thedefectscreatedonthebraidsalsoleadtodecreasingthe

mechanicalstrength.Hence,thetreatmentconditions(alkalineconcentration,reaction

time)shouldbeoptimizedforobtainingastrongbraidmembrane.Thewaterabsorption

ratioofthePETfibersincreaseswithincreasingKOHconcentrationandtreatmenttime,

indicatingthehydrophilicityofthePETbraidsisimproved.Theincreaseinwateradsorp‐

tionisattributedtothehydrolysisofPETduringthealkalinetreatmentwhentheester

groupsexcitinginPETarehydrolyzedtohydroxylandcarboxylategroups.Longtreat‐

menttimeandhighalkalineconcentrationcausespeedupthehydrolysis,bindingmore

hydrophilicgroupsandimprovingthehydrophilicityofthebraids.Thehighestwater

adsorptionandthebesthydrophilicityareattributedtothemostporousstructureofthe

PETbraids.Therefore,thehydrophilicpolymersolutioncanquicklyinfiltrateintothe

braidandfillthebraidedchannelduringthefabricationprocess.Thenthebraidedchannel

isblockedduringthepolymersolidificationinthecoagulationbath.Thebraidwithhigher

hydrophilicityincreasestheinfiltrationofthehydrophiliccoatingsolutions,whichre‐

ducestheporosityandporesizeonthebraid.Thus,PWPwassignificantlydecreased.

However,thebraid’shydrophilicitycanbeincreasedbyhydrolysis,butthehydrolysis

processshouldbeoptimizedtoavoidPWPreduction.Theinterfacialbondingstrength

Membranes2021,11,88418of31



betweenthehydrophilicPETbraidandcoatinglayerwasmorethantheseparationlayer

andthehydrophobicbraid.Afteralkalinemodification,carboxylatesandhydroxyl

groups,asthenewlypolargroups,resultinincreasingthesurfaceenergyonthebraids

tube.Consequently,highinfiltrationleadstoincreasingthebondingstrength.

3.3.ModificationoftheBraidSurface

Anotherapproachforoptimizingtheinterfacialbondingabilityisthemodification

ofthesurfacebycoatingmethods.Liuetal.[55]modifiedtheoutersurfacesofthebraided

tubeswithsilanecouplingagentKH570andacrylateadhesivebeforefabricationofthe

fibertubereinforcedHFM.BasedonFigure8,coatingtheoutersurfaceofthefibertubes

byacrylateadhesiveandsilanecouplingageleadstofillingthegapoftheloopsandthe

groovesbetweenthefibers.Asignificantimprovementintensilestrengthwasreported

byLiuetal.intheoptimumamountofmodifiersdosages.Whenthedosageoftheacrylate

adhesiveexceededtheoptimum,theroleofvoidsblockingwasmorethantheadhesion

onthemembrane.Hence,thefluxofthemembranedecreased,andmembraneresistance

increased.Itisalsoreportedthatanincreaseinsilanecouplingagentamounthasaposi‐

tiveeffectonfiberwettabilityandporosityduetocreatingspongierporesinthemem‐

branestructure.Figure8showsthediagramofamodificationofthebraidsurfacewith

thesilanecouplingagent.Anotherfeasibleapproachwastomodifythefibertubebyphys‐

icalorchemicalmethods,suchascoatingwithmodifiersonthesurfaceofthefibertube

orintroducingchemicalgroupsthathelpincreasetheaffinityofthefibertubetothemem‐

brane[55].Figure9indicatestheeffectofmodificationofthebraidsurfaceontheinterface

ofpolymerandbraid.



Figure8.SurfacemodificationforthebraidedtubeswithsilanecouplingagentKH570[55].

Membranes2021,11,88419of31



Figure9.Schematicdiagramoftheinterface[55].

3.4.ThePresenceofAdditive

Peechmanietal.[24]reportedthattheintroductionoftheZnOnanoparticlesinPSf

dopesolutionpromotedtheinfiltrationofthedopesolution.Itisbecauseofthehydro‐

philicpropertyofZnOthatfacilitatestheinfiltrationofthecoatingsolutionintothe

braidedsupportandaccumulatesbetweenthebraidchannelsduringthepreparationpro‐

cess.Moreinfiltrationofcoatingsolutionintothebraidedsupportwillenhancetheme‐

chanicalstabilityoftheBHFMduetothetightbondingbetweentheselectivelayerwith

thebraidlayerthatpreventsthepeelingoftheselectivelayerfromthebraidedsupport.

ZnOnanoparticlesalsoinfluencedthethicknessoftheseparationlayer.Themembrane

withoutnanoparticleshadathickerseparationlayerrelativetotheothermembranesbe‐

causeofthelowerinfiltrationrateandtheunevencircularshapeofthebraidlayerduring

thespinningprocess(becauseofmechanicalstressthathandledtopullthebraidlayerout

fromthespinneret).



Membranes2021,11,88420of31



Table2.SummaryofBHFMstudies.

PolymerCoating

Solution/wt.(%)

AdditiveinCoating

Solution/wt.(%)

Braid(Threads/Fil‐

ament)Composi‐

tion

TypeofSpinning

Methods/

SpinningConditions

InvestigatedParameters

Opera‐

tional

Condi‐

tion

Impurities/Ap‐

plicationResultsComparison

withHFMRef

Hybridbraid  

Polymer:CA;

10,12,14(wt.%)

Additive:PEG:20

wt.%

CA/PAN

Dry–wetspinning/

- coagulationbath:

water(25°C)

- air‐gapdistance:

10cm

- take‐upspeed:100

cm/min

- Theeffectofbraidcom‐

position

- Theeffectofpolymer

(CA)concentrationonthe

structureandperformance

Pres‐

sure:0.1

MPa

BSAsolution

Milksolution

MaxTensilestrength

(MPa):33.8forCA14

and

62.9MPaforpurePAN

inthebraid

MaxBSARejection:

CA10:90%

CA12:98%

CA14:99%

MaxPWF:300L/m2hr

for1/2(CA/PAN)

Maxburstingstrength

(MPa):0.75forpureCA

inthebraid

Minburstingstrength

(MPa):0.22forpure

PANinthebraid

NA[21]

Polymer:PVC:

12wt.%

Additive:PVP

10wt.%

PET/PAN

Dry–wetspinning



- coagulationbath:

water(28°C)

- air‐gapdistance:

12cm

Take‐upspeed:66

cm/min

- Theeffectofbraidcom‐

positiononthestructure

andperformance



Pres‐

sure:0.1

MPa

BSAsolution



MaxTensilestrength

(MPa):106forpurePET

MaxBSARejection:

70%for1/1:PET/PAN

‐Highertensile

strengthrela‐

tivetoHFM

[6]

Polymer:PMIA

5,8,10,15(wt.%)

Additive:PVP

PMIA/PET

Dry–wetspinning



- Coagulationbath:

water(25°C)

- Theeffectsofpolymer

concentration

Pres‐

sure:0.1

MPa

skimmilksolu‐

tion

MaxPWF:296.85

L/m2hrforPMIA5

MaxBSARejection:

NA[28]

Membranes2021,11,88421of31



2wt.%,PEG:8,

CaCl2:3.5,LiCl:2.5

wt.%

- Air‐gapdistance:

15cm

Take‐upspeed:50

cm/min

- Theeffectsofbraid

composition

97.9%forPMIA15

MaxTensilestrength

(MPa):179.15for

PMIA15

Maxburstingstrength

(MPa):0.98PMIA15

Polymer:PVDF:18

wt.%

Additive:PEG:3

wt.%

PVDF‐

PET

NIPS:Dry–wetspin‐

ning/

- CoagulationBath:

water(25°C)

- Air‐gapdistance:

10cm

Take‐upspeed:2RPM

- Theeffectofpretreat‐

mentstepbyalkaline

methodonperformance

Pres‐

sure:0.1

MPa

NA

MaxPWF:1388L/m2hr

formembranetreatby

KOH

MaxTensilestrength

(MPa):113formem‐

branetreatbyKOH

NA[4]

Polymer:PVC

6,8,10,12,14(wt.%)

Additive:PEG

5



Dry–wetspinning/

- Coagulationbath:

water(20°C)

- Air‐gapdistance:

8cm

Take‐upspeed:220

cm/min

Dopesolutiontempera‐

ture:70°C

- ‐Theeffectofpolymer

Concentration

- Theeffectofadditive

molecularweight

NA

MaxPWF:10.1L/m2hr

for

PVC10

MaxBSARejection:

76.12%forPVC10and

PEG6000

‐Higherrejec‐

tion

‐Higherflux

recoveryrate

[29]

Purebraid  

Polymer:CA

6,8,10,12,14(wt.%)

Additive:PEG6000:6

PEG400:10

CA

Dry–wetspinning/

- Coagulationbath:

water(20°C)

- Air‐gapdistance:

10cm

Take‐upspeed:66

cm/min

Dopesolutiontempera‐

ture:70°C

- Theeffectsofpolymer

concentration



Pres‐

sure:0.1

MPa

NA

MaxTensilestrength

(MPa):14.2forCA14

Maxburstingstrength

(MPa):0.51forCA14

MaxPWF:220L/m2hr

for

CA6

MaxBSARejection:

90%forCA14

NA[37]

Membranes2021,11,88422of31



Polymer:PAN

8,10,12,14,16(wt.%)

Additive:PVP

(7wt.%)and

Tw‐80(2wt.%)

PAN

Dry–wetspinning/

- coagulationbath:

water(25°C)

- air‐gapdistance:

15cm

Take‐upspeed:20

cm/min

Dopesolutiontempera‐

ture:70°C

- Theeffectofpolymer

(PAN)concentrationin

coatingsolution

- Theeffectoftwotype

ofbraidcomposition

Pres‐

sure:0.1

MPa

BSAsolution

Tensilestrength(MPa):

86.3

MaxPWF:345L/m2hr

forPAN10

MaxBSARejection:

91%forPAN18

NA[7]

Polymer:PAN

8,10,12,14,16(wt.%)

Additive:PVP

(7wt.%)and

Tw‐80(2wt.%)

PET

Dry–wetspinning/

- coagulationbath:

water(25°C)

- air‐gapdistance:

15cm

Take‐upspeed:20

cm/min

Dopesolutiontempera‐

ture:70°C

- Theeffectofpolymer

(PAN)concentrationinthe

coatingsolution

- Theeffectoftwotypes

ofbraidcomposition

Pres‐

sure:0.1

MPa

BSAsolution

Tensilestrength(MPa):

188

MaxPWF:470L/m2hr

forPAN10

MaxBSARejection:

91%forPAN18

NA[7]

Polymer:PVC

Additive:poly(VC‐

co‐PEGMA)

PET

Dry–wetspinning



- coagulationbath:

water(24°C)

- Air‐gapdistance:

0.5cm

Take‐upspeed:500

cm/min

Dopesolutiontempera‐

ture:45°C



UFBHFMfor

wastewater

treatment



‐Highertensile

strength

‐Higherburst‐

ingstrength

‐Lowerthick‐

nessforthe

coatinglayer

[36]

Polymer:PSf:16

wt.%

Additive:ZnO

0,0.5,1,1.5(wt.%)



Dry–wetspinning



- coagulationbath:

water(25°C)

- Air‐gapdistance:

10cm

- Take‐upspeed:200

cm/min



Pres‐

sure:0.1

MPa

1000ppmBSA

solution

MaxPWF:920L/m2hr

forZnO:1.5

MaxBSARejection:

96.5%forZnO:1.5

‐Higherwater

flux

‐higherrejec‐

tion

[24]

Membranes2021,11,88423of31



Polymer:PVDF

15,20,25,30(wt.%)

Additive:PVP

20wt.%PVDF

PETDry–wetspinning/



- Effectofpolymercon‐

centrationindopesolution

- NumbersofPET

threads(n)

Pres‐

sure:0.1

MPa

Purewater

Maxtensilestrength

(MPa):11.15for

PVDF20and3PET

threads

MaxPWF:160L/m2hr

forPVDF18

Maxburstingstrength

(MPa):0.45PVDF30

‐Highertensile

strength

‐similarsepa‐

rationproper‐

ties

[46]

Polymer:PVDF13

(wt.%)

Additive:Ge

0,0.1,0.3,0.5,0.7

(wt.%)

SiO2:4,DOP:10

PET

Dry–wetspinning



- coagulationbath:

water(30°C)

- Air‐gapdistance:

20cm

Take‐upspeed:120

cm/min

Dopesolutiontempera‐

ture:70°C

‐Theeffectofadditive

concentration0.1MPa

keroseneand

watermixture

(1:1,

v/v)/oil/water

separation

MaxRejection:

99.7%forGe:0.5

PWF:65L/m2hrfor

GE:0.5

NA[38]

Polymer:PU

16wt.%

Additive:Ge

0.0.1,0.3,0.5(wt.%)

SA:4,NaCl:0.2

PET

Electrospinning

method/

- Positivepressureof

thespinneret:25.5kV

- Negativepressure

ofthereceivingdevice:

5.5kV

- Receivingdistance:

10cm

- Receivingdevice

speed:1500rpm

- Spinningsolution

injectionspeed:2.1mL/

h

- Spinningtempera‐

ture:25°C

‐Theeffectofadditive

concentration0.1MPa

keroseneand

watermixture

(1:1,

v/v)/oil/water

separation

MaxRejection:

99%forGe:0.3

PWF:1443L/m2hrfor

GE:0.3



NA[43]

Membranes2021,11,88424of31



- Relativehumidity:

5%

Polymer:PVDF

8,10,12,14,16(wt.%)

Additive:PVP:8

(wt.%)

Tw‐80:2(wt.%)

PAN

Dry–wetspinning/

- coagulationbath:

water(25°C)

- Air‐gapdistance:

15cm

Take‐upspeed:15

cm/min

Dopesolutiontempera‐

ture:70°C

Theeffectofpolymercon‐

centrationincoatingsolu‐

tions

Pres‐

sure:0.1

MPa

1g/L

BSA

Maxtensilestrength

(MPa):75

MaxPWF:550L/m2hr

forPVDF8

MaxBSARejection:

95%forPVDF16



NA[40]

Polymer:PVDF

6,8,10,14,18(wt.%)

Additive:PVP:7

(wt.%)

Tw‐80:3(wt.%)

PVDF

Dry–wetspinning



- coagulationbath:

water(20°C)

- Air‐gapdistance:

10cm

Take‐upspeed:15

cm/min

Dopesolutiontempera‐

ture:60°C

- Theeffectofpolymer

concentrationincoating

solutions

Pres‐

sure:0.1

MPa

2g/L

Eggalbumen

Maxtensilestrength

(MPa):11forPVDF10

MaxPWF:900L/m2hr

forPVDF6

MaxBSARejection:

81%forPVDF18



‐Highertensile

strength

‐HigherBSA

rejection

[45]

Polymer:CA

Additive:Ge‐ ‐

- TheeffectofGecon‐

centrationincoatingsolu‐

tions

‐ ‐

Maxtensilestrength

(MPa):30

MaxPWF:158.1L/m2hr

forGe:1%

NA[56]

Polymer:PA

PIP:2.0%w/vTMC:

0.13%v/v

Polymer:PSf:16

(wt.%)

Additive:PVP10

(wt.%)

Interfacialpolymeriza‐

tionofPIPandTMCon

UFsupportmembrane

- TheeffectofTMCreac‐

tiontime

Pres‐

sure:0.6

MPa

MgSO4

NaCl

TOC/

TFCNF

MaxPWF:5.1L/m2hr

MgSO4Rejection:65%

NaClRejection:26%

TOCremoval:65%

NA[51]

Polymer:PA

PIP:1.0%w/w

TMC:0.1,0.15,0.2%

w/v

PVDFandpolyes‐

ter

Interfacialpolymeriza‐

tionofPIPandTMCon

UFsupportmembrane

- Theeffectofmonomer

concentration

Pres‐

sure:0.1

MPa

MgSO4

NaCl/

TFCNF

MaxPWF:22L/m2hr

MaxMgSO4Rejection:

92%

NaClRejection:˂30%

NA[10]

Membranes2021,11,88425of31



PMIA:Poly(m‐phenyleneisophthalamide);PVDF:Polyvinylidenefluoride;poly(VC‐co‐PEGMA):amphiphiliccopolymerpoly(vinylchloride‐co‐poly(ethyleneglycol)

methylethermethacrylate);NIPS:non‐solvent‐inducedphaseinversion;PA:polyamide;PET:Polyethyleneterephthalate(PET);Ge:Graphene;DOP:Dioctylphthalate;

PU:polyurethane;SA:Stearicacid;BSA:bovineserumalbumin;PIP:piperazine;TMC:trimesoylchloride;PWF:purewaterflux;PVP;Polyvinylpyrrolidone;NA:not

applicable.

Polymer:PVDFFiberglassmaterial‐

- Estimationoftheten‐

silestrengthofMFandUF

hollowfiberbraidmem‐

brane

‐ ‐

Maxtensilestrength

(MPa):10formembrane

with0.355Thickness



NA[57]

Membranes2021,11,88426of31



4.OperationParameters

AnincreaseinoperatingpressureleadstotheenhancementofPWF.Thisincreaseis

slowedinhigheroperationpressurethatisclearinalowerconcentrationofpolymer.Itis

probablyduetomorecompressionoftheporousmembraneinhighpressureandmore

resistancetothecompactionforlessporousmembrane[46].Peechmanietal.[24]indi‐

catedtheBSArejectionwasapproximatelyconstant,andthefluxincreasedwhentheop‐

eratingpressureincreased.Xiaetal.[10]testedtheperformanceofTFC‐BHFMunder

pressureuntilfailureintermsofMgSO4rejectionandwaterflux.Aslightenhancingof

MgSO4rejectionandalinearincreasewasobservedforwaterfluxbytheenhancementof

pressureupto0.5MPa.Thedropinsaltrejectionandasharpincreaseinwaterfluxupto

0.5MPaindicatesmembranedelaminationortearingoftheselectivelayer.

Chenetal.[28]reportedthattheincreaseintheoperatingtemperaturefrom25°Cto

90°Cleadstoanincreaseinwaterfluxbecauseofareductioninwatersolutionviscosity.

Theyinvestigatedtheperformanceoftailoring‐PMIA‐BHFMandcommercial‐PVDF‐

BHFMatdifferenttemperatures.AccordingtoFigure10,theinksolutionrejectionwas

stableforPMIAbraidhollowfibermembranes,whereasitwasdecreaseddramaticallyfor

thePVDF‐BHFM.ThePMIAbraidhollowfibermembranesexhibitedthermalstability,

whilethePVDFmembranefacedacrucialcracking.Itisthemainreasonforthereduction

intherejectionoftheinksolution.Thepresenceofintermolecularhydrogenbondingand

largebenzeneringsinmacromolecularchainsofPMIAleadstoahighglasstransition

temperature(morethan270°C).Hence,theporestructureismaintained,anddeformation

hasnothappenedindifferentthermalconditions.ThePMIAbraidhollowfibermem‐

branesarethusintroducedforapplicationinseparationprocesseswithhightempera‐

tures.



Figure10.Theeffectoftemperatureonrejectionandfluxof(a)PMIA‐BHFMand(b)PVDF‐BHFM.

5.Applications

Hollowfibermembranesaredesirablefornumerousmembraneapplications.They

arefavoredforuseinwatertreatmentprocessesduetothedesirablepropertiesmentioned

above[9].Submergedmembranebioreactorisusuallyutilizedtoremovecommonpollu‐

tantsfrommunicipalandindustrialwastewaterbecauseofmanyadvantagessuchas

high‐qualityeffluent,lowsludgeproduction,andreducedfootprint.Themodulecanbe

preparedbytheflatsheetorhollowfibermembranes,buttheHFMshavebeenmore

widelyusedduetoeasyassemblingandhighpermeabilityperinstallationarea.However,

HFMinthesubmergedMBRisrequiredhighmechanicalpropertiesbecauseofeasilybro‐

kenduringthehigh‐pressureback‐washingandcleaningprocessoraeratedairflow

Membranes2021,11,88427of31



[37,40,58].Fanetal.[37]investigatedtheBHFMintheMBRprocess.Thetensilestrength

ofpreparedBHFMswashigherthan11MPa,whichthiscontentincreasedwiththein‐

creaseinpolymerconcentrationindopesolution.

Generally,thehollowfibermembranesarenotapplicableinhigh‐pressureapplica‐

tionssuchasNFandROprocessesbecauseoftheirpoormechanicalstrength.Whereas

theyaregoodcandidatesforwastewatertreatment,removalofheavymetals,anddrink‐

ingwaterpurification[10,15,51].Thin‐filmcomposite(TFC)membranesareexcellentcan‐

didatesforROandNFprocessesinwaterandwastewatertreatmentapplicationsdueto

theultrathinselectivelayer.TheTFCdesignpossessesdesiredperformanceintermsof

saltrejectionandpermeabilitywhenunitedwithasymmetricmembranes.Thecross‐

linkedaromaticpolyamideasaselectivelayerontheultrafiltrationmembraneporousor

othersupportingsubstratesfabricatedbyinterfacialpolymerizationofpropermonomer

(e.g.,trimesoylchloride(TMC))isthemostsuccessfulandfamouscommercialproductin

thelastdecades[10,50,59].Asmentioned,TFCmembranesconsistofasupportlayerand

selectivelayer.Theselectivelayerthattypicallycross‐linkedpolyamideisathin,dense,

andpoormechanicalfilmwithhighselectivity.Thesecondlayerisaporousfilmthat

playstheroleofthesubstratewithhighmechanicalstrengthunderpressure.Thislayer

generallyisformedfrompolyethersulfoneandpolysulfone.Figure11illustratestheshell

andlumensideofHFM.Generally,itisdifficulttoapplyathinfilmontheshellorlumen

sideoftheHFMduringfibermanufacturing.TheHFMsdesignedforliquidfiltrationhave

largelumensduetoreducingresistanceinmasstransferandpressuredropliquidstream.

Inhigh‐pressureapplications,thewallsofHFMsmustbethicker,butitisnotdesirable

forliquidflowapplications.ItisreportedseveralstudiesonthefabricationofHFMwith

high‐pressuretoleranceandimprovementofmechanicalstability.Thesestudiespropose

usingapolymer/additivewithintrinsichighmechanicalstrength,optimizationofspin‐

ningparameters,andbraidreinforcedcomposition[10,60].Xiaetal.[10]fabricatedaTFC‐

HFMthatusesabraid‐reinforcedultrafiltration‐HFMsasasubstrate,consistingofaPVDF

coatinglayerandpolyesterbraid.Theselectivelayerisformedusinginterfacialpolymer‐

izationofTMCandpiperazine(PIP).Thepresenceofthereinforcedsupportdevoted

high‐pressureenduranceproprietiestotheHFM.Thepreparedmembranescouldtolerate

pressureupto0.5MPawhilepossessinghighselectivityfordivalent/monovalentions.

Turkenetal.[51]fabricatedreinforcedTFC‐HFNFbasedonPSfultrafiltrationmem‐

branesandpolyamidelayerpreparedfromPPandTMCmonomers.Themembraneswere

investigatedinsolutionswithdifferentorganicmatterandsalts.Theirresultsevidenced

thepreparedmembranesareagoodcandidateforwater‐treatmentapplications



Figure11.TheillustrationofshellandlumensideofanHFM[61].

AnotherapplicationofBHFMsistheoil/waterseparationprocess.Oilywastewater

isproducedbydifferentindustriessuchasmetalfinishingindustries,leather,food,pet‐

rochemical,oilexploration,refining,andtransportationofoilproducts.Thistypeof

Membranes2021,11,88428of31



wastewaterisaseverethreattohumanhealthandtheenvironment.Membranetechnol‐

ogyisaproperoptionforoilywastewaterstreatmentowingtoadvantagessuchaslow

costs,nosecondarypollution,highenergyefficiency,sustainability,andnoadditives.

Twoparametersareessentialfortheoil/waterseparationprocess:theselectivewettability

foroilorwater(lipophilicity/hydrophobicity)thatprovidetherequireddrivingforceand

theconnectedporeswithasuitableporesizeforfiltration.Bothhydrophobicandhydro‐

philicmembranescouldbeutilizedfortheseparationofoil/water.Hydrophilicmem‐

branesincreasethewaterpermeationrelativetooilpermeationleadingtohigherwater

fluxandgoodantifoulingproperties.Nevertheless,thehydrophilicmembranesmustpro‐

videalargevolumeofwaterpermeatefluxesinseparationsofoil/water.Theyrequired

highenergyconsumptionandlargemembraneareas.Generally,thepresentpollutantsin

oilywastewateraremainlyduetotheoilphase,buttheircontentsarerelativelylow.

Therefore,hydrophobicmembranesarebettercandidatesforoilywastewatertreatment

basedonworkload[38,43].Haoetal.[38]prepared(PET‐)braid‐reinforcedPVDF/gra‐

phenehollowfibermembranes.PVDF‐BHFMshowsappropriatehydrophobicproperties

foroil/waterseparationandgoodmechanicalstrength.Graphenewasalsousedtoen‐

hancethehydrophobicityofthemembrane.Theirresultsshowedthatthepreparedhy‐

drophobicBHFMsultimatelyrejectedwaterduringtheseparationprocess.

6.Conclusions

Hollowfibermembranes(HFMs)areagoodcandidateforthemembraneseparation

processduetodesirablepropertiessuchashighpermeabilityandsurfacearea,goodfil‐

trationefficiency,smallfootprint,etc.However,theyareoftenpossibletobreakduring

thehigh‐pressurecleaningandaerationprocess.Tubularbraidsasupportedisproposed

toimprovethemechanicalstrengthofHFMsduetohightensilestrength.Thepeelingof

thesurfacelayerfromthetubularbraidisthedrawbackoftheBHFMduetothermody‐

namicincompatibility.Dependingonthetypeofapplication,thekindofpolymer/addi‐

tiveandtheircontentaretheessentialparametersthataffecttheperformanceofBHFMs.

PAN,PVC,CA,PSf,andPVDFarethecommonpolymersusedinBHFMpreparation.The

interfacialbondingstrengthbetweenthebraidandtheseparationlayerisanessential

issueinBHFMs.Becausetheseparationoftwolayersreducesitslifetimeandlimitsits

application;hence,theaffinitybetweenthetwolayerswillbeimproved.Theinterfacial

bondingstrengthbetweenthebraidandtheseparationlayerisanessentialissuein

BHFMs.Hence,theaffinitybetweenthetwolayerswillbeimprovedbyhybridbraids,

alkalinepretreatment,andtheuseofadditives.Recently,theBHFMshavebeenusedin

ROandNFapplications.Althoughitisrequiredacomprehensiveinvestigationthatopti‐

mizesthemembraneperformanceintermsofflux,mechanicalproperties,rejection,and

fouling;itisexpectedthattheapplicationsofthesetypesofthemembranewillbeen‐

hancedindifferentaspectsandthegapbetweenstudiesandapplyinlargescaleswould

bereduced.

AuthorContributions:Conceptualization,A.N.,H.K.,E.S.,S.M.M.andH.M.,Datacuration,A.N.,

Formalanalysis,A.N.,H.K.,E.S.,S.M.M.andH.M.,Investigation,A.N.,H.K.,E.S.,S.M.M.andH.M.,

Methodology,A.N.,H.K.,E.S.,S.M.M.andH.M.,Visualization,A.N.,H.K.,E.S.,S.M.M.andH.M.,

Validation,A.N.,H.K.,E.S.,S.M.M.andH.M.,Writing,A.N.,H.K.,E.S.,S.M.M.andH.M.,Original

draft,A.N.,Authorship,A.N,H.K.,Projectadministration,H.K.,Supervision,H.K.,review&edit‐

ing,H.K.,Resources,E.S.,S.M.M.andH.M.,Fundingacquisition,H.M.Allauthorshavereadand

agreedtothepublishedversionofthemanuscript.

InstitutionalReviewBoardStatement:Notapplicable.

Funding:Thisresearchreceivednoexternalfunding.

InformedConsentStatement:Notapplicable.

DataAvailabilityStatement:Notapplicable.

ConflictsofInterest:Theauthorsdeclarenoconflictofinterest

Membranes2021,11,88429of31



Abbreviation

HFM:Hollowfibermembrane

BHFM:BraidHollowfibermembrane

PMIA:Poly(m‐phenyleneisophthalamide)

PVDF:Polyvinylidenefluoride

Poly(VC‐coPEGMA):Poly(vinylchloride‐co‐poly(ethyleneglycol)methylethermethacry‐

late)

NIPS:Non‐solvent‐inducedphaseinversion

PA:Polyamide

PET:Polyethyleneterephthalate

Ge:Graphene

DOP:Dioctylphthalate

PU:Polyurethane

SA:Stearicacid

BSA:Bovineserumalbumin

PIP:Piperazine

TMC:Trimesoylchloride

PWF:Purewaterflux

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Enhancement of bursting pressure resistance of braid-reinforced polyether sulfone hollow fiber composites

Article

Full-text available

May 2024
POLYM BULL

This study investigated the effects of different braid materials (polyethylene terephthalate, nylon 6, and their hybrid), weaving frequencies of the braids (7, 9, 11, 13 Hz), and concentrations of polyether sulfone solution (15% and 18 wt%) on braid angles, braid thickness, and bursting resistance. The results showed that for all types of single and hybrid braids, the braid angle decreases with increasing spinning frequency. When spinning frequency was increased from 7 to 13 Hz, the average wall thickness of polyethylene terephthalate, nylon 6, and the hybrid braids increased by approximately 50%, 65%, and 60%, respectively. The bursting pressure results were obtained in the range of 9.3 to 20.2 bars. The Fourier transform infrared spectroscopy results revealed no chemical bond between the braids and the polyether sulfone layer. Optical and electron microscope analyses revealed formation of uniform thickness of the polyether sulfone layers on the surface of the braids, as well as the penetration of polyether sulfone into the gaps between the filaments. The analyses also showed macroscopic adhesion of polyether sulfone to the braids and provided information on the amount and size of the pores in the polymer layers. The results showed that the selection of appropriate weaving frequency, braid materials, and polyether sulfone layer concentration are important as controllable parameters for producing polymeric hollow fiber composites with excellent burst pressure resistance.

Anion‐pillared microporous material incorporated mixed‐matrix fiber adsorbents for removal of trace propyne from propylene

Article

Full-text available

Mar 2023
AICHE J

Separation and purification of light hydrocarbons have been the critical processes for producing basic chemicals and polymers in petrochemical industry. Adsorbents with high performance are highly demanded for the separation of light hydrocarbons. However, the adsorbents filling in the packed bed when evaluated will inevitably induce reduced performance and increased pressure drop that considerably impede their application. Herein, mixed‐matrix fiber adsorbents with anion‐pillared hybrid microporous materials (SIFSIX‐2‐Cu‐i) embedded within poly (ether sulfone) (PES) are constructed to enable an energy‐efficient propylene/propyne separation. Owing to the sufficient binding sites and abundant channels for selective gas transfer, the fiber adsorbents achieve high C3H4 uptake capacity of 0.963 mmol g⁻¹ in the propylene/propyne (99/1) mixture breakthrough experiments. Moreover, fiber adsorbents exhibit good tolerance toward high gas velocity and show distinctively low pressure drop, which will be advantageous in industrial applications. This work provides a strategy for fabricating high‐performance mixed‐matrix fiber adsorbents.

Vibration Characteristic Analysis of Hollow Fiber Membrane for Air Dehumidification Using Fluid-Structure Interaction

Article

Full-text available

Feb 2023

Hollow fiber membrane dehumidification is an effective and economical method of air dehumidification. The hollow fiber membrane module is the critical component of the dehumidification system, which is formed by an arrangement of several hollow fiber membranes. The air stream crosses over the fiber bundles when air dehumidification is performed. The fibers vibrate with the airflow. To investigate the characteristics of the fluid-induced vibration of the hollow fiber membrane, the two-way fluid-structure interaction model under the air-induced condition was established and verified by experiments. The effect of length and air velocity on the vibration and modal of a single hollow fiber membrane was studied, as well as the flow characteristics using the numerical simulation method. The results indicated that the hollow fiber membrane was mainly vibrated by fluid impact in the direction of the airflow. When the air velocity was 1.5 m/s~6 m/s and the membrane length was 100~400 mm, the natural frequency of the membrane was negatively correlated with length and positively correlated with air velocity. Natural frequencies were more sensitive to changes in length than changes in air velocity. The maximum equivalent stress and total deformation increased with air velocity and length. The maximum equivalent stress was concentrated at both ends, and the maximum deformation occurred in the middle. The research results provided a basis for the structural design of hollow fiber membranes under flow-induced vibration conditions.

Novel in-situ zwitterionization of carbon quantum dots on membrane surface for oil/water separation

Article

Apr 2024
SEP PURIF TECHNOL

The structure design of poly (tetrafluoroethylene-co-perfluoropropylvinylether) (PFA) hollow fiber membrane with high-temperature and chemical resistance for oil purification

Article

Feb 2024
J TAIWAN INST CHEM E

Hollow Filaments from Coaxial Dry-Jet Wet Spinning of a Cellulose Solution in an Ionic Liquid: Wet-Strength and Water Interactions

Article

Dec 2023
BIOMACROMOLECULES

Hollow tubing and tubular filaments are highly relevant to membrane technologies, vascular tissue engineering, and others. In this context, we introduce hollow filaments (HF) produced through coaxial dry–jet wet spinning of cellulose dissolved in an ionic liquid ([emim][OAc]). The HF, developed upon regeneration in water (23 °C), displays superior mechanical performance (168 MPa stiffness and 60% stretchability) compared to biobased counterparts, such as those based on collagen. The results are rationalized by the effects of crystallinity, polymer orientation, and other factors associated with rheology, thermal stability, and dynamic vapor sorption. The tensile strength and strain of the HF (dry and wet) are enhanced by drying and wetting cycles (water vapor sorption and desorption experiments). Overall, we unveil the role of water molecules in the wet performance of HF produced by cellulose regeneration from [emim][OAc], which offers a basis for selecting suitable applications.

Green thermally induced phase separation (TIPS) process for braided tube reinforced polyvinylidene fluoride (PVDF) hollow fiber composite membranes with favorable bonding layer

Article

Jun 2023
J TAIWAN INST CHEM E

Improved permselectivity and mechanical properties of sulfonated poly dimethyl phenylene oxide cation exchange membrane using MXene nanosheets

Article

Mar 2023
DESALINATION

Polyethylenimine grafted hollow fiber membranes for fast dye separation

Article

Apr 2023
J MEMBRANE SCI

Highly Robust Laser-Induced Graphene (LIG) Ultrafiltration Membrane with a Stable Microporous Structure

Article

Oct 2022

Laser-induced graphene (LIG) materials have great potential in water treatment applications. Herein, we report the fabrication of a mechanically robust electroconductive LIG membrane with tailored separation properties for ultrafiltration (UF) applications. These LIG membranes are facilely fabricated by directly lasing poly(ether sulfone) (PES) membrane support. Control PES membranes were fabricated through a nonsolvent-induced phase separation (NIPS) technique. A major finding was that when PES UF membranes were treated with glycerol, the membrane porous structure remained almost unchanged upon drying, which also assisted with protecting the membrane's nanoscale features after lasing. Compared to the control PES membrane, the membrane fabricated with 8% laser power on the bottom layer of PES (PES (B)-LIG-HP) demonstrated 4 times higher flux (865 LMH) and 90.9% bovine serum albumin (BSA) rejection. Moreover, LIG membranes were found to be highly hydrophilic and exhibited excellent mechanical and chemical stability. Owing to their excellent permeance and separation efficiency, these highly robust electroconductive LIG membranes have a great potential to be used for designing functional membranes.

Validation and application of a membrane filtration evaluation protocol for oil-water separation

Article

Full-text available

Oct 2021

Membrane filtration processes like microfiltration (MF) and ultrafiltration (UF) are proven to be effective in industrial wastewater treatment, including oil-water separation, as they generate suitable quality permeate for water reuse applications. Various research efforts have been conducted in areas of developing and/or modifying commercial MF/UF membrane materials through synthesizing new advanced polymers that promise improvement in oil-water separation performance. Although multiple MF/UF testing procedures were developed, there is still a gap in literature on having a comprehensive protocol that assesses the performance of the membranes in terms of flux, rejection, fouling, and cleanability. This paper delivers a robust bench scale testing procedure incorporating experiences and lessons learned from literature. The evaluation procedure includes three main testing steps: initial characterization, operating performance, and cleaning and recovery. The protocol was designed to mimic industrial conditions by using a representative synthetic produced water solution and operating multiple consecutives cycles of oil-water filtration followed by membrane chemical cleaning. The procedure was initially validated on multiple commercial MF/UF membranes having different pore sizes/MWCOs and chemistries obtained from various manufacturers and then applied to evaluate emerging membrane materials. The protocol was found to be reliable in evaluating the performance trends of various commercial membranes and effective in comparing the performance of emerging membranes. The developed procedure is proposed to be applied by researchers to assess the performance of new membrane materials as compared to relevant commercial products.

Microstructured Hollow Fiber Membranes: Potential Fiber Shapes for Extracorporeal Membrane Oxygenators

Article

Full-text available

May 2021

Extracorporeal membrane oxygenators are essential medical devices for the treatment of patients with respiratory failure. A promising approach to improve oxygenator performance is the use of microstructured hollow fiber membranes that increase the available gas exchange surface area. However, by altering the traditional circular fiber shape, the risk of low flow, stagnating zones that obstruct mass transfer and encourage thrombus formation, may increase. Finding an optimal fiber shape is therefore a significant task. In this study, experimentally validated computational fluid dynamics simulations were used to investigate transverse flow within fiber packings of circular and microstructured fiber geometries. A numerical model was applied to calculate the local Sherwood number on the membrane surface, allowing for qualitative comparison of gas exchange capacities in low-velocity areas caused by the microstructured geometries. These adverse flow structures lead to a tradeoff between increased surface area and mass transfer. Based on our simulations, we suggest an optimal fiber shape for further investigations that increases potential mass transfer by up to 48% in comparison to the traditional, circular hollow fiber shape.

Novel PVDF-PVP Hollow Fiber Membrane Augmented with TiO2 Nanoparticles: Preparation, Characterization and Application for Copper Removal from Leachate

Article

Full-text available

Feb 2021

High proportion of copper has become a global challenge owing to its negative impact on the environment and public health complications. The present study focuses on the fabrication of a polyvinylidene fluoride (PVDF)-polyvinyl pyrrolidone (PVP) fiber membrane incorporated with varying loading (0, 0.5, 1.0, 1.5, and 2.0 wt%) of titanium dioxide (TiO2) nanoparticles via phase inversion technique to achieve hydrophilicity along with high selectivity for copper removal. The developed fibers were characterized based on scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), permeability, porosity, zeta potential, and contact angle. The improved membrane (with 1.0 wt% TiO2) concentration recorded the maximum flux (223 L/m2·h) and copper rejection (98.18%). Similarly, 1.0 wt% concentration of TiO2 nanoparticles made the membrane matrix more hydrophilic with the least contact angle of 50.01°. The maximum copper adsorption capacity of 69.68 mg/g was attained at 1.0 wt% TiO2 concentration. The experimental data of adsorption capacity were best fitted to the Freundlich isotherm model with R2 value of 0.99573. The hybrid membrane developed in this study has considerably eliminated copper from leachate and the concentration of copper in the permeate was substantially reduced to 0.044 mg/L, which is below standard discharge threshold.

High Flux Polysulfone Braided Hollow Fiber Membrane for Wastewater Treatment Role of Zinc Oxide as Hydrophilic Enhancer

Article

Jun 2021

Incorporation of zinc oxide (ZnO) nanoparticles has played an important role on the improvement of unique membrane characterization and performance, most notably the hydrophilic modification of the membrane for higher pure water permeability. Additionally, the permeability of the membrane can be improved via introduction of braid support by reducing the thickness of the membrane separation layer. Moreover, the braided hollow fiber membrane (BHFM) is able to perform under higher pressure conditions compared to hollow fiber membranes. In this paper, hybrid polysulfone (PSf)/ZnO BHFMs were fabricated via phase inversion method. Hydrophilic 10 ± 1.8 nm polycrystalline ZnO nanoparticles synthesized via sol-gel method were incorporated on BHFM to improve the hydrophilicity and increase flux with constant rejection under high pressure and the effect of the ZnO loading on the membrane properties and performance were thoroughly studied. The fabricated BHFMs with 0.0, 0.5, 1.0 and 1.5 wt.% of ZnO nanoparticles concentration were defined as BHFM1, BHFM2, BHFM3 and BHFM4 respectively. Scanning electron microscopy (SEM), contact angle, mechanical strength, flux performance, rejection with bovine serum albumin (BSA) and fouling of best performed membrane were conducted to achieve the target of this paper. The performance of these hybrid ZnO/PSf BHFMs were compared with neat PSf hollow fiber membrane (HFM) and previous studies. The findings from this research work shows that BHFM4 has the most desired properties for wastewater treatment application. The ZnO nanoparticles in BHFM4 have improved hydrophilicity from 108.79 to 71.02°, and thus BHFM4 has increased flux performance from 36.20 to 919.12 L/m²h at 1.0 bar pressure and 193.48 to 1909.11 L/m²h at 4.0 bar pressure when compared with BHFM1. Constant BSA rejection rates (>90%) were observed in all BHFMs. The improved hydrophilicity and pure flux performance with constant rejection rate in high pressure conditions illustrates the suitability of fabricated ZnO/PSf BHFMs in wastewater treatment applications.

Reinforced hollow fiber membranes: A comprehensive review

Article

May 2021
J TAIWAN INST CHEM E

Reinforcing the HFMs provides appropriate mechanical and shear strengths and improves break at elongation. This comprehensive review paper first discusses the fundamental concept of HFMs fabrications, advantages and disadvantages of HFMs, fabrication methods and fabrication materials. Then, reinforcement methods are categorized into porous matrix membrane reinforced method, the fibers (use of threads or filament) reinforced method, and the use of tubular braids, and each one is discussed based on the concept of thermochemical compatibility of the supporting material and the base polymer. Such a compatibility leads to homogeneous- and heterogeneous-reinforcement method with different interfacial bonding state. A comparative study on the mentioned reinforcement methods is also presented based on the tabulated and charted tensile strength and elongation at break data. At the end, a brief look is taken into commercialized products and worldwide projects installed or under installation in the field of reinforced HFMs.

Wastewater treatment and fouling control in an electro algae-activated sludge membrane bioreactor

Article

Apr 2021

The effect of addition of algae to activated sludge as active biomass in membrane bioreactors (MBRs) and electro-MBRs (e-MBRs) for wastewater remediation was examined in this study. The performances of Algae-Activated Sludge Membrane Bioreactor (AAS-MBR) and electro Algae-Activated Sludge Membrane Bioreactor (e-AAS-MBR) were compared to those observed in conventional MBR and e-MBR, which were previously reported and utilized activated sludge as biomass. The effect of application of electric field was also examined by the comparison of performances of e-AAS-MBR and AAS-MBR. Similar chemical oxygen demand (COD) reduction efficiencies of AAS-MBR, e-AAS-MBR, MBR, and e-MBR (98.35 ± 0.35%, 99.12 ± 0.08%, 97.70 ± 1.10%, and 98.10 ± 1.70%, respectively) were observed. The effect of the algae-activated sludge system was significantly higher in the nutrient removals. Ammoniacal nitrogen (NH3−N) removal efficiencies of AAS-MBR and e-AAS-MBR were higher by 43.89% and 26.61% than in the conventional MBR and e-MBR, respectively. Phosphate phosphorous (PO43−-P) removals were also higher in AAS-MBR and e-AAS-MBR by 6.43% and 2.66% than those in conventional MBR and e-MBR. Membrane fouling rates in AAS-MBR and e-AAS-MBR were lower by 57.30% and 61.95% than in MBR and e-MBR, respectively. Lower concentrations of fouling substances were also observed in the reactors containing algae-activated sludge biomass. Results revealed that addition of algae improved nutrient removal and membrane fouling mitigation. The study also highlighted that the application of electric field in the e-AAS-MBR enhanced organic contaminants and nutrients removal, and fouling rate reduction.

Design and fabrication of hollow fiber membrane modules

Chapter

Jan 2021

Membrane technologies are widely used in separation processes because of their compact size, mild operating conditions, and ability to conduct separations that may not be technically or economically viable by other technologies. Relative to flat-sheet membranes, hollow fibers possess unique advantages including high membrane area, self-supporting structure, and ease of handling. However, they must be assembled as large modules for industrial application. Fluid hydrodynamics within these modules is as important as intrinsic membrane separation properties. Companies have explored myriad design strategies to improve fluid hydrodynamics and mass transfer inside modules as documented in the patent literature. This review summarizes the techniques taught to fabricate high performance hollow fiber bundles. More importantly, designs to (1) promote uniform shell flow, (2) enhance mixing, and (3) incorporate internal sweep within modules are discussed to inspire novel designs for next-generation hollow fiber modules.

Polymeric membrane fabrication via thermally induced phase separation (TIPS) method

Chapter

Jan 2021

A review was done about the membrane preparation based on the thermally induced phase separation (TIPS) method. TIPS is an alternative to conventional nonsolvent-induced phase separation (NIPS) method that has been widely applied in commercial scale. After the evaluation of the thermodynamic of the TIPS process, the effect of the different parameters on the prepared hollow fiber membranes was clearly demonstrated. Finally, the mass transfer assisted TIPS process that potentially can make a big step in upgrading TIPS membranes performance was introduced.

The influence of pretreatment step on hollow braided PET fabric as a potential membrane substrate

Article

Mar 2021

Self-supporting polymeric hollow fiber membranes prepared using non-solvent induced phase separation (NIPS) often suffer deterioration in mechanical properties due to asymmetric fingerlike and sponge-like morphology giving a porous and fragile structure. Hollow braided fibers of Polyethylene terephthalate (PET) have been used as substrate to increase the strength of hollow fiber membranes. However, problems arise from poor interfacial bonding between the braid and coating polymer resulting in peeling off or delamination at the interface. In this work, we report a method of braid treatment and selection with two alkali treatment steps (NaOH and KOH) to study their effect on pure water flux, water contact angle, tensile strength as well as braid morphology of three different braid samples (B1, B2 and B3). B2 sample treated in KOH demonstrated the highest water flux of 1388 L/m 2 h. Examination of surface morphology of the braids revealed a washing effect and enlargement of braid interspaces making them more porous and hence increased permeability, with a contact angle of 0°with water. The sample also exhibited zero weight loss as well as a remarkable tolerance for high temperature with negligible reduction in tensile strength of only about 0.9%. Membrane fabricated with B2-K was demonstrated to have better adhesion between polymer-braid interface in comparison to the control. The pre-treatment step provides a good braid selection basis for onward membrane development with KOH showing the most favorable outcome without losing braid quality.

Polyamide thin-film composite membrane on polyethylene porous membrane: Fabrication, characterization and application in water treatment

Article

Dec 2020
MATER LETT

The ultrafiltration membranes fabricated by the non-solvent induced phase separation (NIPS) have been widely used as the supports of the polyamide thin film composite (PA TFC) membranes, although they are usually thick, low porosity, and poor chemical stability. Instead, thin polyethylene (PE) lithium battery microporous membrane with high surface porosity and connected pores is used as the support layer. PE membrane was pre-modified by the co-deposition of tannin and 3-aminopropyltriethoxysilane improving its hydrophilicity, and then a uniform and defect-free PA active layer was successfully fabricated by interfacial polymerization. The resultant membrane exhibited high filtration performances in the forward osmosis (FO) process (2 times higher water flux and 90 % lower specific salt flux than the commercial HTI-TFC membrane), and efficient separation of NaCl and dyes in nanofiltration (NF) process, outstanding chemical stability and mechanical strength.

Effective Parameters on Fabrication and Modification of Braid Hollow Fiber Membranes: A Review

Abstract

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