CELLULOSE CHEMISTRY AND TECHNOLOGYCELLULOSE NANOFIBERS OF OIL PALM BIOMASS IN ALGINATE-BASEDMEMBRANES FOR WATER-ETHANOL MIXTURE SEPARATIONNOVITRI HASTUTI,*,** HENDRIK SETIAWAN,*** KYOHEI KANOMATA**** andTAKUYA KITAOKA******

National Research and Innovation Agency, Research Center for Biomass and Bioproducts,
Soekarno Science Center, Jl. Raya Jakarta-Bogor No. KM 46, Bogor, West Java, 16911, Indonesia**
Research Collaboration Center for Nanocellulose BRIN – Universitas Andalas,
Padang, 25163, Indonesia***
Department of Hydrogen Energy Systems, Faculty of Engineering, Kyushu University,
Motooka 744 Nishi-ku, Fukuoka, 819-0395, Japan****
Graduate School of Pharmaceutical Sciences, Osaka University, 1-6 Yamadaoka,
Suita-shi, Osaka, 565-0871, Japan*****
Department of Agro-Environmental Sciences, Faculty of Agriculture, Kyushu University,
Motooka 744 Nishi-ku, Fukuoka, 819-0395, Japan
Corresponding author: N. Hastuti, novi043@brin.go.id, novitri.forester@gmail.com✉

Received April 25, 2022
TEMPO-oxidized cellulose nanofibers (TOCNs) from waste of oil palm empty fruit bunches (OPEFB) were integrated
into an alginate matrix to increase the capacity of the alginate membrane for water-ethanol separation. The membranecomposed of the alginate matrix and TOCNs was characterized in terms of its morphological, physical-mechanicalproperties and performance in the separation of water-ethanol suspensions, with ethanol concentrations in thesuspension of 10% and 20%. Other alginate membranes integrated with commercial TOCNs from wood were also
prepared and tested for comparison. The results showed that the addition of TOCNs (made from wood and OPEFB
waste) to the alginate matrix improved the water adsorption capacity of the membrane. The water adsorption capacityof the alginate membranes with wood-derived TOCNs, OPEFB-derived TOCNs and alginate only was 78%, 87% and66%, respectively. The flux capacity of the alginate membrane, integrated with OPEFB-derived TOCNs, was higher
than that of the alginate membrane alone, but lower than that of the alginate membrane integrated with wood-derived
TOCNs. This study showed the utilization of nanocellulose from palm oil biomass waste can be considered to improve
the physical-mechanical properties of alginate-based membranes used for various applications, including filtration.
Keywords: cellulose, membrane, nanofibers, oil palm, TOCNs

INTRODUCTION
Indonesia is the world’s largest producer andexporter of palm oil in the world.1 Therefore, oilpalm (Elaeis guineensis) is the mainstay of estate
crop commodity in Indonesia, its contribution to
the national economy tends to increase from year
to year and is expected to strengthen overallnational development.2 In addition, crude palm oil(CPO) production leaves an abundant supply ofpalm press fibres and oil palm empty fruitbunches (OPEFB), which are regarded as wastes
and have not been utilized satisfactorily.3 The
palm oil industry must dispose of about 1.1 tonsof OPEFB for every ton of CPO produced.4
It is essential that the huge amount of OPEFB

is processed into value-added products as OPEFB
contains a relatively high amount of cellulose, of
about 59%.5 Cellulose is an abundant naturalpolymer that can be extracted from plants,
animals, algae, and bacteria.6 Cellulosic fibers
have gained consideration due to their promisingcharacteristics,
suchasbiodegradability,
renewability, and high mechanical properties, as aresult of their crystalline organization.7 With its
relatively high content of cellulose, OPEFB is apotential source of nanocellulose raw materials. In
general, the term “nanocellulose” refers to acellulosic extract or processed material that has
nano-scale structural dimensions.6 One of the

Cellulose Chem. Technol., 56 (7-8), 737-747(2022)

NOVITRI HASTUTI et al.

useful methods that enable cellulose fibers to becompletely converted to individual cellulose
nanofibrils is catalytic oxidation using 2,2,6,6tetramethylpiperidine 1-oxyl (TEMPO). By usinga TEMPO/NaBr/NaClO oxidation system, thisprocess can convert selectively the primaryhydroxyl groups of polysaccharides into
carboxylates; fully individualized TEMPOoxidized cellulose fibrils of approximately 4 nm
in width and at least a few micrometers in length
can be obtained, with carboxylate contents ofmore than about 1 mmol/g by mild mechanicaldisintegration in water.8,9 Nanocellulose producedby
2,2,6,6-tetramethylpiperidine
1-oxyl(TEMPO)-catalyzed oxidation, named TEMPOoxidized cellulose nanofibers (TOCNs), has
attracted considerable attention, since it requires
low energy in its production, making thenarrowest nanofibers ever reported.10 Furthermore,
the results of our previous study showed thatnanocellulose from oil palm empty fruit bunches
produced through hydrolysis of hydrochloric acidhad an aspect ratio ranging between 23-29, andthermal stability between 347-359 ºC as
maximum degradation temperature.11
Recently, TOCNs have seen several
applications, including for green reinforcement inpolymer composites, as an adsorbent for metal
removal, and as a gel component for medical
applications (drug delivery).12-15 Furthermore,
nanocellulose in polymer composites can beapplied as a filler or hydrophilic additive inmembranes by blending or coating technique andin ultrafiltration and separation membrane for gas
capturing and bioenergy recovery.16,17 The use ofnanocellulose in membrane composites also
increases biofouling resistance in membranes byforming a thin layer on top of the porous polymer
matrix after coating.18 The nanocellulose utilized
in membrane applications mostly has wood
origins rather than non-wood.18,19 Nonetheless,nanocellulose extraction from natural non-woodwaste/residual material has been considered more
efficient in delignification processes due to thelignin content being lower in non-wood than inwoody plants.20
The utilization of nanocellulose from nonwood materials, for instance oil palm empty fruitbunches (OPEFB), as an additive in membranecomposites for bioenergy applications is still
unknown. Therefore, in this study, membranes
consisting of TOCNs from OPEFB and alginate
were investigated in a pervaporation system forwater-ethanol mixture separation. Pervaporation738

is a method for the separation of mixtures ofliquids by partial vaporization through a nonporous membrane. The separation mechanism is asolution–diffusion model.21 The method isparticularly useful to separate liquid mixtureswith close boiling points, as well as azeotropic
mixtures of water and ethanol, on the basis ofliquid polarity and interaction with polymer
membranes.22 Among pervaporation membranes
reported for water-ethanol separation, alginatebased membranes have gained much attention.
This is due to their good membrane forming
properties, such as high affinity for watermolecules, non-toxicity, low cost, and ease to use,although these membranes also have lower
mechanical strength.23 Therefore, the utilizationof nanocellulose in alginate-based membranes issuggested to overcome this disadvantage.
Nanocellulose films were prepared by a TEMPOmediated oxidation (TOCN) process, with a highaspect ratio and mechanical property (tensile
strength > 200 MPa).24 The presence of anioniccarboxylate groups on the surface of TOCNs is
responsible for improving the hydrophilic
properties of the membranes. The presence ofwater increases membrane permeability andplasticity. Competitive sorption of other gas
species may occur, which is important in the caseof membrane transport facilitation.17,25,26 However,studies of pervaporation membranes using
alginate- and OPEFB-derived TOCNs have notbeen reported yet. On the other hand, the use ofother polysaccharides, such as chitosan, foralcohol dehydration has been reported
intensively.23,27–29 Nanofibers from OPEFB in
membrane applications pave the way for theutilization of low-cost agricultural residues asvalue-added useful products.
EXPERIMENTAL
Materials
Bleached kraft pulp of oil palm empty fruit bunches(OPEFB) was kindly supplied from Biomaterial
Research Institute, Indonesian Institute of Sciences(Bogor, Indonesia). 2,2,6,6-Tetramethylpiperidine 1oxyl (TEMPO), sodium bromide, sodium hypochlorite
and sodium borohydride were purchased from SigmaAldrich (Tokyo, Japan) and used without further
purification. Sodium alginate (500 cps) was purchasedfrom Nacalai Tesque (Kyoto, Japan). Calcium chloride(CaCl2) was purchased from Wako Pure Chemical(Osaka, Japan). The water used in this study was
purified with the Arium Ultrapure Water System(Sartorius Co., Ltd., Tokyo, Japan). The filter holder
set up for the pervaporation system was purchased

Cellulose

from Toyo Roshi Kaisha Ltd. (Tokyo, Japan), with afilter diameter of 47 mm. The commercial membrane
PTFE Advantec Membrane Filter (Toyo Roshi Kaisha,Tokyo, Japan), of 0.5 µm pore size, was used forcomparison, denoted as PTFE membrane. Ethanol(99.5%) was purchased from Fujifilm Wako Pure
Chemical, Osaka, Japan, and used without further
purification.
Methods
Preparation and characterization of OPEFB-derived
TOCNs
The preparation of TOCNs from OPEFB was
performed as described in our previous study, using 20mmol of oxidant (NaClO) by TEMPO-mediatedoxidation.30 The resultant TOCN from OPEFB was
denoted as op-TOCN. Meanwhile, wood-based TOCN
from Nippon Paper Company was used for comparisonand denoted as w-TOCN. Carboxylate contents were
measured by conductometric titration.31 The
carboxylate content of OPEFB-derived TOCN was
1.50 mmol/g, and that of wood-derived TOCN was
1.59 mmol/g.
The morphology of TOCNs was observed on a
Transmission Electron Microscope (TEM), JEM-2100
HC (JEOL Ltd., Tokyo, Japan), operated at anaccelerating voltage of 120 kV, at the Ultramicroscopy
Research Center of Kyushu University. The
crystallinity index of TOCNs was recorded on a
Rigaku X-ray-Diffractometer/XRD (Rigaku Denki Co.

Ltd., Tokyo, Japan) operated at 40 kV and 20 mA.
Details of the procedure for observing the morphology
of TOCNs using TEM and the crystallinity index of
TOCNs using XRD have been provided in ourprevious study.11
Preparation of TOCN-alginate membranes crosslinked with CaCl2
About 300 mg of sodium alginate was dissolved in
30 mL of deionized water (DI) by vigorous stirring atroom temperature until complete dissolution. Twentyfive mL of 0.4 wt% op-TOCN suspension (100 mg ofdry weight) was added, and the mixture was stirred for
2 h and poured into a PTFE Petri dish. Membranes
were dried at room temperature for 2-3 days. The dried
membranes were then peeled off carefully. The
obtained membranes were cross-linked with CaCl2 byimmersion in 5% (v/v) calcium chloride (CaCl2) for 3h, rinsed with DI water and dried in ambient air for 2days. The obtained membrane composed of alginate
and op-TOCN was then denoted as op-TOCN-A. The
same preparation was applied to the membrane fromalginate with commercially available TOCN (wTOCN), denoted as w-TOCN-A. A membrane made ofalginate without TOCNs (alginate w/o TOCN) was
prepared as control. A commercial hydrophobic PTFE
membrane (Advantec Membrane Filter, Toyo Roshi
Kaisha Ltd., Tokyo, Japan) was used for comparison.
The experimental scheme of the research is illustrated
in Figure 1.

Figure 1: Experimental scheme of the preparation of alginate-TOCN membranes and their use for water-ethanol
separation
Membrane characterization
Membrane characterization included microscopic
observation and observation of membrane thickness
and water content. Microscopic observation was
performed by taking cross-sectional and surface
images by Scanning Electron Microscopy (ZeissULTRA 55, USA) at the Ultramicroscopy ResearchCenter, Kyushu University, Japan. The observation was
conducted at an acceleration voltage of 5 kV. Thin gold

layers were coated on the surfaces of the samples
before observation using a JEOL JFC-1600 Autofine
Coater (Japan Electronic Corporation Ltd., Tokyo,
Japan) at 30 mA for 10 s. Membrane thickness wasmeasured using a Digital Micrometer (Series 406-Non
Rotating Spindle Type 406-250, Mitutoyo Corp.,
Kawasaki, Japan).
Water contents were calculated using the following
equation:739

NOVITRI HASTUTI et al.

Water content (%) = (Winitial – Wdry) / Winital x 100 (1)where Winitial is the weight of membrane in the initialcondition (before drying) and Wdry is the weight ofdried membrane after exposure to a temperature of
103 °C for 1 h. All membranes were kept on adesiccator after cooling and then weighed.
Fourier Transform Infrared (FTIR) analysis was
conducted using an FTIR spectrometer (JASCO
FT/IR-680 TypeA, Japan) at the Center of Advanced
Instrumental Analysis, Kyushu University, Japan. The
analysis was conducted in the spectral range of 4004000 cm-1.
The contact angles of resultant membranes wereobserved using a Drop Master 300 K. Samples weremade by cutting the membranes into sheets
approximately 10 mm x 50 mm in size. The contact
angles were measured at four different spots by
dropping a droplet (1 µL) of DI water on eachmembrane sample and averaging the values obtained.
The absorption capacity of membranes in water andabsolute ethanol was determined by immersing dried
membranes (dry weight Wd) in an appropriate liquid
until a condition of equilibrium was reached. The
liquid-hydrated membranes were weighed (Ww), andthe absorption capacity was calculated using Equation
2:(2)
The surface area and average pore sizes were
measured using the Brunauer-Emmett-Teller (BET)method in nitrogen atmosphere. Each sample was
dewatered and degassed at 105 °C for 4 h before BET
analysis.
Tensile tests of the obtained membranes were
performed using Material Testing Instruments (STA1225, ORIENTEC Co., Ltd., Tokyo, Japan), equippedwith a 100 N load cell. The membrane samples were
cut into sheets 40-50 mm x 0.7-10 mm in size.
Measurement was carried out at 20 mm of active
length at 10% min-1.32
Pervaporation experiment
The pervaporation set-up schematically shown in
Figure 2 consisted of a feed glass tube, a membranefilter holder, a cold trap for permeate and a vacuum
pump. Due to difficulties to control the desiredpressure, the pressure during the experiment wasrecorded, ranging from 30 to 40 hPa. The feed acrossthe membrane and the permeate were collected in thecold trap, and the collecting time was recorded. The
water content was measured using the hybrid titration
method by Karl Fischer Moisture Titrator Kyoto-Chem
MKH-700 (Kyoto Denshi Kogyo, Kyoto, Japan). The
flux (J) and selectivity (α) were calculated using theequation of mass-time data below:(3)
Because the obtained membranes were not uniform

740

in thickness, the obtained flux values were thennormalized using the following equation:
Normalized flux = J x (membrane thickness/50 µm) (4)Meanwhile, the selectivity of the membrane wascalculated using the following equation:(5)
where Q is the mass of permeate collected in the cold
trap in time t, A is the effective membrane surface area,is the sorption selectivity, Wp and Ep are the weightfractions of water and ethanol, respectively, in thepermeate, and Wf and Ef are weight fractions of waterand ethanol, respectively, in the feed. Pervaporation
was applied to a membrane area of 19.625 cm2.

Figure 2: Membrane test scheme

RESULTS AND DISCUSSION
Characterization of TOCNs
The morphologies of OPEFB-derived TOCNs(op-TOCNs) and wood-derived TOCNs (wTOCNs) are shown in Figure 3A-B. The aspectratios of op-TOCNs and w-TOCNs were 41±14
and 24±7, respectively. The aspect ratio of
OPEFB-derived TOCNs is higher than that ofcommercial wood-derived TOCNs. This canoccur due to differences in the characteristics ofwood and non-wood fibers. Besides the fiber
characteristics of the original raw material, thepretreatment of cellulose fibers has a major
influence on the size of the resulting
nanocellulose, although it is not always necessary
in the preparation of nanocellulose.33
X-ray diffraction (XRD) patterns of opTOCNs and w-TOCNs are presented in Figure 4.
XRD analysis reveals that wood-derived TOCNs(w-TOCNs) have a higher crystallinity index than
OPEFB-derived TOCNs (op-TOCNs). The
crystallinity index (Cr.I.) of w-TOCNs and opTOCNs was 55% and 60%, respectively. The
lower levels of Cr.I. of op-TOCNs are not notable.
It can be assumed that almost all carboxyl groups
formed by the oxidation are present on thesurfaces of crystalline cellulose microfibrils.9 The

Cellulose

peaks located at 15º, 22º and 35º are associated tothe planes of (110), (200) and (004),
respectively.33 These patterns indicate thecharacteristics of crystalline cellulose I.33,34 In

addition, the maximum contents of C6-oxidized
groups that were formed varied depending on thecellulose I crystal widths. 35

Figure 3: TEM images of (A) op-TOCNs and (B) w-TOCNs

Figure 4: X-ray diffraction patterns of OPEFB-derived TOCNs (op-TOCNs) andwood-derived TOCNs (w-TOCNs)

Membrane morphology
The morphology of the obtained membranes
was observed using a Scanning Electron
Microscope (SEM) in the surface and crosssectional areas. Complete images from the SEM
analysis are shown in Figure 5. The presence of
TOCNs in the alginate-TOCN membranes was
confirmed by a fibrous layer appearance in the
cross-sectional images (Fig. 5 B-C). Thisappearance was absent on the control membrane(alginate w/o TOCN). The results revealed by the
SEM images are in good agreement with those ofa previous reported study.16 In addition, thesurface morphology of the alginate membrane in
the presence of TOCNs showed a rougher surface,compared to the control membrane.
The membrane thickness of alginate w/o
TOCN, op-TOCN-A, and w-TOCN-A was 52 µm,
82 µm, and 78 µm, respectively. In addition, thewater content of alginate w/o TOCN, op-TOCN-A

and w-TOCN-A was 6.2%, 5.8% and 3.6%,
respectively. The densities of the obtained
membranes were 0.81 for alginate w/o TOCN,
0.96 for op-TOCN-A, and 0.73 for w-TOCN-A.
Fourier transform infrared (FTIR) analysis
The FTIR spectra are presented in Figure 6.
The spectra of op-TOCN show important
absorption bands at 1720 cm-1 and 1600 cm-1,
which corresponded to functional carboxylategroups –COOH and –COONa, respectively.36 The
spectra of op-TOCN-A at ~1602 cm-1 were
sharper than those of op-TOCN. A similar
appearance was also found in the case of wTOCN-A spectra. From these peaks, it was
assumed that cross-linking of alginate and CaCl2
had occurred; they exclusively had thecarboxylate structures of (TOCN-COO)2Ca.37 In
the absence of TOCNs, the band at 1600 cm-1 ofalginate w/o TOCN was broader.

741

NOVITRI HASTUTI et al.

Membrane morphology before and after
pervaporation tests
The surface morphology after pervaporation
was observed to check whether micro-cracks
occurred during the experiment (Fig. 7 D–F).
Interestingly, micro-cracks were not observed in
the case of op-TOCN-A and w-TOCN-A.
Rougher surface appeared after the treatment due
to the vacuum pressure applied during thepervaporation set-up. However, op-TOCN-A
showed lower surface roughness, compared with
w-TOCN-A and alginate w/o TOCN. The opticalimages of the membranes after the treatment
reveal that morphological changes could be
detected more distinctly on w-TOCN-A than on
op-TOCN-A. It is assumed that a rearrangementof polymer chains in the case of w-TOCN-A
might have occurred more intensively than in thecase of op-TOCN-A, due to the vacuum pressure
applied during the pervaporation process.

Contact angles
Contact angle measurement was performed
using water and water-ethanol mixtures. Actually,measuring a contact angle using absolute ethanolon the surface of membrane was difficult because
the ethanol would spread immediately on themembrane surface after dropping. Therefore, thecontact angle measurement was conducted on
mixtures of water and ethanol (80% water and
20% ethanol and 60% water and 40% ethanol), as
shown in Figure 8. A contact angle is an angle atthe interface where water, air and solid meet, andits value is a measure of how likely the surface is
to be wetted by water. Low contact angle values
demonstrate a tendency of water to spread andadhere to the surface, whereas high contact angle
values show the surface’s tendency to repel
water.38

Figure 5: SEM images of cross-sectional (upper) and surface morphology (bottom) of (A, D) alginate w/o TOCN, (B,E) op-TOCN-A, and (C, F) w-TOCN-A (scale bars: 10 µm)

Figure 6: FTIR spectra of TOCN-alginate membranes and original TOCNs from OPEFB

742

Cellulose

Figure 7: SEM images of membrane surfaces before (A: alginate w/o TOCN; B: op-TOCN-A; C: w-TOCN-A) andafter the treatment (D: alginate w/o TOCN; E: op-TOCN-A; C: w-TOCN-A) and optical images of their representatives
in lowercase letters (scale bars: 10 µ m)

The higher the ethanol concentration the lower
the contact angle. It is because the surface tensionof ethanol, which determines contact angles, issmaller than that of water. The surface tension of
an aqueous solution will decrease with an increasein the alcohol concentration.39 The contact anglesof the PTFE membrane were difficult to capture
for both water and water-ethanol mixtures. The
contact angle of a liquid on a solid surface is a
key parameter reflecting wettability. Based on thedata in Figure 8, the wettability of the alginate
membrane hardly changed in the presence of
TOCNs.
Flux, selectivity and surface analysis
A flux analysis was conducted on feeds
containing 80% ethanol and 20% water (v/v),
denoted as 80E20W, and 90% ethanol and 10%
water (v/v), denoted as 90E10W. The results are
as described in Figure 9.
Figure 9 shows that the addition of TOCNs toalginate membranes increased the flux capacity.
The cross-linking of TOCNs, alginate and Ca2+

ions increased the surface area, induced pore
formation and affected the flux. The surface areaof the alginate membrane became larger in thepresence of w-TOCN in w-TOCN-A (Table 1),
resulting a higher flux compared to op-TOCN-A
and alginate w/o TOCN. During the pervaporation,
the first constructive step in transporting
permeating components through the membrane issorption of the permeating components from thefeed liquid into the membrane. Therefore, larger
surface areas are preferable to get higher contact
or sorption of permeating components on themembrane surface.40
In addition, op-TOCN-A and alginate w/o
TOCN had lower surface areas, but larger poresizes compared to w-TOCN-A (Table 1). Pore size
plays an important role during the second
constructive step of pervaporation, which isdiffusion of permeating components through themembrane, and the third, which is desorption of
permeating
components
downstream
themembrane.

743

NOVITRI HASTUTI et al.

Figure 8: Contact angle measurement for water andFigure 9: Normalized flux values of alginate, alginatewater–ethanol mixtures
TOCN and PTFE membranes for water-ethanol mixtures
Table 1
Adsorption capacity, water selectivity and surface analysis
SampleAdsorption
capacity (%)
Water EtOH
87
8
78
8

Water content inpermeate (%)a80E20Wb 90E10Wb
23.8
11.7
17.5
13.1

Selectivityb

Surface area,
as BET (m2g-1)c

Ave-ragepore size
(nm)c
37
23

80E20W 90E10W
op-TOCN-A
53
56
0.73
w-TOCN-A
60
54
1.18
Alginate w/o
66
35
23.8
15.3
45
40
0.90
30
TOCN
PTFE
32
47
24.3
14.9
42
42
4.69
5000d
a
Note: initial water content in 80E20W was 25.5%, and in 90E10W – 15.62%, measured by a Karl Fischer titrator; b
selectivity corresponded to water; the collecting time was adjusted to 1 h; c based on BET surface analysis with theweight of the measured sample being ~0.1 g; d determined by the company/supplier

Therefore, the flux of op-TOCN-A wasslightly higher compared to that of the control
membrane (alginate w/o TOCN), because thelarger pore size of op-TOCN-A increased the
diffusion and desorption rates, while the surface
areas of the two membranes were not too different(Table 1). However, according to the masstransfer analysis conducted by Phattaranawik andco-authors, the influence of pore size isinsignificant.41 Alginate and alginate-TOCN
membranes have mesopore sizes of 2–50 nm
according to IUPAC pore size classification,
while PTFE membranes are classified to havemacropore sizes of >50 nm.42
A comparison with the positive control
membranes (op-TOCN100 and w-TOCN100) was
conducted at the feed with 80% ethanol and 20%
water (inserted picture in Fig. 9). The results
revealed that the self-standing TOCN membranes(op-TOCN and w-TOCN) had very low anddistinct flux capacities. It is assumed that selfstanding TOCN films are not effective as
pervaporation
membranes.
Nanocellulose
prepared by TEMPO-mediated oxidation ishydrophilic. Self-standing TOCN films have beenreported to have high water vapor permeability of744

approximately 70 g µm m−2 day−1 kPa−1 at 30%
RH.24 This property needs to be combined withother hydrophilic polymers, such as alginate, foruse in pervaporation membranes. Sodium alginate
membranes have been acknowledged to have highwater solubility and sorption selectivity.43
Hydrophilic groups absorb water molecules
preferentially, which leads to both high flux andhigh separation factors. However, the introductionof hydrophilic groups sometimes swells themembrane significantly due to its plasticization
action, which results in low selectivity.23
Furthermore, with the increase in the masspercentage of water in the feed, the membraneswelling will also increase, and this will create
more free volume, which results in an increase in
the permeate flux.44 The flux capacity is affected
not only by the mass of water transferred from thefeed, but also by the shrinkage of internal pores ofthe membrane, resulting in flow viscosity andthus total permeation flux.45
The hydrophobic membrane, PTFE, showed
the largest surface area and the largest pore size,
as determined by the supplier. However, thehydrophobic properties of the PTFE membrane
lowered the water affinity of this membrane to a

Cellulose

great degree, resulting in low water adsorption
and flux. The large pore size made the diffusion
rate excessively high and caused the water
sorption and selectivity to be low.
Tensile tests
The mechanical properties of the obtained
membranes are as described in Figure 10. The
self-standing alginate membrane (alginate w/o
TOCN) showed the lowest mechanical properties.
Yang and co-authors reported that alginate
membranes cross-linked with cellulose and Ca2+
had high mechanical properties. The presence of
cellulose and Ca2+ caused the membranes to havetensile strength, of up to 47 MPa, and elongation
at break of 23%, while the absence of cellulose
and Ca2+ caused the membranes to have low

tensile strength, of only about 4.2 MPa, andelongation at break of 17%.46 This study revealed
that in the presence of TOCNs, in the case of both
op-TOCN and w-TOCN, the tensile strength andelongation at break of alginate membranes
improved twice and by 5 times, respectively. The
higher improvement found in w-TOCN than thatin op-TOCN might be caused by the differencesin the cellulose contents of woody and non-woody
nanocellulose starting materials. Moreover, thehigher crystallinity index in w-TOCN corresponds
to increases in rigidity of the cellulose structure
and leads to higher tensile properties.47 However,this result emphasized the potential utilization of
low-cost agricultural residues as an enhancer inmembranecomposites.

Figure 10: Tensile strength of alginate and alginate-TOCN membranes

CONCLUSION
The
utilizationof
OPEFB-derived
nanocellulose, prepared by TEMPO-mediatedoxidation in pervaporation membranes (opTOCN-A) revealed that the addition of OPEFBderived nanocellulose to an alginate matrix,
followed by cross-linking with Ca2+, induced pore
formation and slightly increased the flux capacity.
However, its performance was lower but stillcomparable to the performance of woody TOCNs
in alginate matrix (w-TOCN-A) with respect toflux capacity, water selectivity and mechanicalproperties. The addition of hydrophilic materials,
such as TOCNs, to alginate improved the flux
capacity, water sorption and selectivity inpervaporation
membranes.
Furthermore,
membrane engineering (including membranecomposition and preparation) and pervaporation
conditions (the pressure applied, temperature andfeed flow rate) might determine the membrane
performance. Therefore, a further study into theutilization of nanocellulose in pervaporation
membranes is needed to figure out the optimum
conditions of nanocellulose application inmembrane composites for achieving optimum
membrane permeability and selectivity.
ACKNOWLEDGEMENTS: This research was
supported by the Advanced Low Carbon
Technology Research and Development Programof the Japan Science and Technology Agency(T.K.) and the Research Fellowship for Young
Scientists of the Japan Society for the Promotionof Science (K.K.). The authors are grateful toHendrik Setiawan from the Department ofHydrogen Energy Systems, Faculty ofEngineering, Kyushu University for kindly
providing assistance in the surface analysis.
Thanks are also due to the Ministry of Education
and Culture of the Republic of Indonesia for thepartial financial support through the Beasiswa
Unggulan Program.

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NOVITRI HASTUTI et al.
19

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M. S. Umikalsom, A. B. Ariff, H. S. Zulkifli, C. C.
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