PSF90−80
with 70 wt％NMP as bore liquid at AG temperature of 80°C． However， an irregular，
lacerated structure was observed with 75 wt％NMP as bore liquid（PSF75−80）and with 80
wt％NMP as bore liquid（PSF80−80）， with the degree of laceration becoming larger as NMP
concentration of bore liquid increased from 75 Wt％to 80 wt％．
This phenomenon is analogous to the mechanism of an irregular，1acerated structure
forming on the inner surface as reported in Chapter 4． Whether a lacerated structure will be
formed on the inner surface or on the outer surface depends on whether a thin layer fbrms first
on one or the other surface in the AG and whether this thin layer has become so inductile that
it is tom apart as the nascent fiber extends under drawing tension． ln case of PSF70−80， a thin
layer on the inner surfac e formed before the outer surface in the A G after discharge from the
CHAPTER s
Optima1 spinning coアzditionプわア〃1 ic1「（〜filtratわn〃2θ〃zbrane
spinneret due to the somewhat higher water concentration of the bore liquid， at 30 wt％， and
this thin layer could not extend under drawing tension without tearing apart．
Therefbre， a lacerated structure was formed on the imer surface but not formed on the
outer surface． On the other hand， in case of NMP concentration of 80 wt％or above， a
lacerated structure was formed on the outer surface but not formed on the inner surface． This
meant that a thin layer which became inductile as the nascent hollow fiber extended under
drawing tension did not form on the inner surface， but such a layer did form on the outer
surface． This thin layer on outer surface， formed by water vapor in the A G， pulled apart as the
nascent hollow fiber extended， resulting in the lacerated structure． Uniquely， lacerated
structures were formed on both inner and outer surfaces of P S F75−80， in the intermediate state
between PSF70−80 and PSF80−80， as such inductile thin layers were formed on both surfaces．
In the case of using 95 wt％㎜solution as bore liquid， pore structure of outer
surfac e changed dramatically as AG temperature was reduced from 80°C to 60°C，and then to
40°C．While pores with an average pore size of O．19μm were observed on the outer surface
when AG temperature was 60°C， no pores were observed on the outer surface when AG
temperature was 40°C． This result suggested that a thin layer did not form on the outer
surface in the AG when AG temperature was below 60°C． In this case， only liquid−1iquid
phase separation occurred in the AG and both surfaces were in a liquid state that enabled
relaxation under drawing tension．
The PSF95−60 hollow−fiber MF membrane obtained in this study had a gradient
structure with an average pore size of O．19 Ptm in the region o f the outer surface and gradually
increasing pore size acro ss the thickness of the membrane wall toward the imer surface． pure
CH 4PTER 5
（）pli〃ia1 spinning conditionプわr〃2たπφ1かα∫ oη〃1θ〃ibrane
water permeate flux was about 1，3001・m一2・h一l at 100 kPa． Retention of T500 was O％and
that of O．037μm latex beads was almost 100％． Tensile strength at break was over 4．O MPa，
and tensile elongation at break was over 80％．
The PSF95−80 hollow−fiber MF membrane obtained in this study had a similar
gradient structure with an average pore size of O．23 ptm on outer surface． Pure water permeate
flux was about 4，9001・m一2・h−l at 100 kPa． Retention of T500 was O％and that of O．137μm
latex beads was almost 100％． Tensile strength at break was over 4．O MPa， and the tensile
elongation at break was over 80％．
These characteristics and performance且gures are suf丘cient fbr use in MF at the
practical level， and such membranes would be well suited for application in water treatment
and other fields．
5．5Conc｝usion
in this study， we selected PSF as membrane material and fbcused on the fabrication
method of practical hollow fiber MF membrane having a gradient structure， more speci丘cally，
afilter layer in the region of the outer surface and gradually increasing Pore size across the
／
thickness of the membrane wall toward the imer surface． A 3−component dope composition
of PSF／NMP／PEG was used with 35 kD Mw of PEG as additive． NMP solution was selected
as bore liquid． The necessary NMP concentration of bore liquid and AG temperature in order
to obtain a practical PSF hollow fiber MF membrane having this gradient structure were
studied．
Cπ41）TER s
Oρtimal spinning conditionfor〃microLfiltration〃membrane
All the membranes made with AG temperature of 80°C， AG distance of 50㎜， and
bore liquid NMP concentration changing froM 70 wt％to 95 wt％at 5 wt％intervals， show
similar water permeate flux at around 5，0001・m−2・h−1， in the normal range fbr MF
performance． Pure water permeate flux of hollow一丘ber membrane s obtained with 95 Wt％
NMP solution as bore liquid at the same 50 inm AG distance and various AG temperatures
丘om 40°C to 80°C was affe cted by AG temperature， with flux increasing sharply with higher
AG temperature．
The inner surface structure transformed dramatically as NMP conc entration of bore
liquid was changed． These inner surface structures can be classified into three categories
based on their appearance． The first of these categories is that of a lacerated appearance of
pore structures as seen with 70 wt％and 75 wt％NMP bore liquid， the second is that of a
circular pore structure as seen with 80 wt％，85 wt％， and 90 wt％NMP bore liquid， and the
third is that of a network structure as seen with 95 wt％NMP bore liquid．
Formation of the lacerated apPearing Pore structure is considered to have been by the
mechanism described by Ohya et al．［1］， being that the se structures result from the formation
of a very thin layer by water of the bore liquid after discharge from the spinneret， this layer
then l）eing partially ripped and pulled apart in the AG under drawing tension．
Formation of the circular pore structure is considered to be the result of a weak
coagulation power of bore liquid with NMP concentration of 80 wt％or more， which was too
weak to solidify the inner surface， so that only nucleation and growth of polymer lean phase
by liquid−liquid phase separation occurred during residence in the AG
Cl［L4PTER 5
の伽al S御痂g oo励 加。for〃1 o腰1かα 加〃7θ〃かane
The network structure as seen with 95 wt％NMP bore liquid is considered to be the
result of membrane fbrmation occur血g only丘om the outer surface because the bore liquid is
in the solvent neutral state， neither inducing Phase separation and solidification nor dissolving
the dope．
Regarding the outer surface， it was revealed that outer surface pore fbrmation was
affected by both AG temperature and NMP concentration of the bore liquid． Circular pores
were observed with 70 wt％NMP as bore liquid at AG temperature of 80°C． However， an
irregular， lacerated structure was observed with 75 wt％and 80 wt％NMP as bore liquid， with
the degree of laceration becoming larger as NMP concentration of bore liquid increased from
75・吼％to 80 v就％．
This phenomenon is analogous to the mechanism of an irregular， lacerated structure
鉛rming on the㎞er sur魚c e． Whether a lacerated structure will be formed on the inner
surface or on the outer surface depends on whether a thin layer forms first on one or the other
surface in the Aq and whether this thin layer has become so inductile that it is torn apart as
the nascent fiber extends under drawing tension．
Pore structure of the outer surface also transfbrmed dramaticalIy as AG temperature
was changed． This phenomenon is considered to result from the progress ofphase separation
／
varying with the amount ofwater vapor in the AG as AG temperature is changed．
It was fbund that a solvent neutral state was attainable by selecting 95 wt％NMP
solution as bore liquid with our temary dope system， and that it was possible to obtain the
desired gradient structure with membrane formation only from the outer surface． Pore size of
the filter later in the region of outer surface could be controlled by a（加sting AG temperature
CHAPTER s
Opti〃ial spinning conditわnプわr〃z icrofiltration〃7e〃7brane
and／or AG humidity． In particular，
temperature to 60°C or more．
MF−1evel pores were obtained by setting the AG
CllL4PTER 5
ρρ伽al sp伽加960磁≠加力7〃伽φ1かα oη〃le〃2ゐ7αηθ
5．5 References
［1］H．Ohya， S． Shiki and H． Kawakami， Fabrication study of polysulfbne hollow−fiber
micro且ltration membrane：Optimal dope vi scosity fbr nucleation and growth， J． Membrane．
Sci．，326（2009）293−302．
［2］D．W． Wallace， C． Staudt−Bickel， and W． J． Koros， Efficient development of effective
hollow fiber membranes fbr gas separation丘om novel polymers， J． Membrane． S ci．，278
（2006）92−104．
CHAPTER 6
Conclusions and血ture scope
This chapter described conclusions and fUture scope of this study． A new method fbr
fabrication of PS／HF MF membranes with a gradient pore structure， based on non−solvent
induced phase separation（NIPS）， and hlvestigate the effects of the fabrication conditions on
the membrane moq）hology and characteristics was studied． The gradient structure， with
increasing Pore size丘om outer to inner surface layers， is designed to enable extemal−pressure
filtration and thus obtain high一且ux water permeation．
The characteri stics and performance of typical MIT membrane obtained in this study
are su伍cient fbr use in MF at the practical level， and such membranes would be well suited
fbr application in water treatment and other fields． This method would lead to a new
development in MF membrane tec㎞010gy which outstrips the water pe㎜eability of
conventional hollow−fiber MF membrane．CLL4PTER 6 ConclZts ions andfuture scope