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Utilization of Lignin and Lignosulfonate from Oil Palm Empty Fruit Bunches as Filler in PVDF Proton Exchange Membrane Fuel Cell Nala Ridhwanul MuAoizzah.
Pinka Zuhdiana Hapsari.
Nabila Putri Aulia.
Dian Wahyu Tri Wulansari.
Fauziyah Azhari, and Edi Pramono* Department of Chemistry.
Faculty of Mathematics and Natural Sciences.
Universitas Sebelas Maret.
Jl.
Ir.
Sutami 36A.
Kentingan.
Surakarta 57126.
Indonesia * Corresponding author:
email: edi.
uns@staff.
Received: January 26, 2023 Accepted: June 19, 2023 DOI: 10.
22146/ijc.
Abstract: A study on the polyvinylidene fluoride (PVDF) membrane using lignin and lignosulfonate oil palm empty fruit bunch (OPEFB) fillers have been carried out.
This study aims to determine the additional effect of lignin and lignosulfonate on PVDF Lignin sulfonation has a good result proven by Fourier transform infrared spectra with a peak at 1192 cmOe1 which indicates sulfonate group.
The sulfonation degree was increased by 8.
9% for lignosulfonate.
The membrane was prepared by the phase inversion method.
Data present that all the membranes have an asymmetric structure with finger-like and sponge-like pores.
Good thermal stability indicated by thermal gravimetric analysis showed degradation at 432 AC.
The mechanical properties of the membrane decrease with the addition of filler.
From the X-ray diffraction, peaks appeared 39A, 21.
35A, and 23.
75A for all the membranes indicating of and phases.
Lignin and lignosulfonate increased membrane hydrophilicity and water uptake.
The presence of the sulfonate group increases the ionic exchange capacity and ionic conductivity up to 78 mmol/g and 9.
95 y 10Oe5 S/cm, respectively, for 5% lignosulfonate addition.
Thus.
PVDF/lignosulfonate has the potential as a polymer electrolyte membrane.
Keywords: lignin.
OPEFB.
polymer electrolyte membrane.
PVDF
n INTRODUCTION A fuel cell is an electrochemical device in which chemical energy is directly converted into electrical energy .
Fuel cells are one of the alternative energy production technologies .
, where hydrogen is used as an energy source .
Hydrogen can produce high energy and lower calorific value than hydrocarbon-based fossil fuels, making it more efficient .
and environmentally friendly .
In addition, hydrogen is ideally used for fuel cells due to its rapid electrochemical reaction kinetics and the absence of exhaust gases since the only by-product of the reaction is water .
The essential elements of a fuel cell are the positive electrode .
, the negative electrode .
, and the electrolyte membrane .
The perfluorosulfonic acid polymer (NafionA) has high ionic conductivity, mechanical and chemical stability at lower temperatures .
NafionA also has a multiphase structure, namely the hydrophobic phase as Nala Ridhwanul MuAoizzah et al.
the continuous phase and the sulfonic acid group as the hydrophilic phase.
The continuous hydrophobic phase is helpful for the structural integrity of the membrane, and the hydrophilic phase acts as a reservoir of water .
However.
NafionA is expensive and challenging to synthesize .
, so researchers are looking for another alternative to be developed.
One alternative polymer that can be used is polyvinylidene fluoride (PVDF), which has good mechanical properties, thermal stability, and chemical resistance .
Even so.
PVDF has limitations due to its low conductivity .
, which requires to be modified.
Physical modification, such as mixing with other components, can be used to improve PVDF membrane performance .
Lignin has the potential to modify PVDF membranes.
Lignin has some polar groups in its structure, especially the hydroxyl group .
, which can be an active modification center .
Lignin has Indones.
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advantages, including high carbon content, good thermal stability, biodegradability, good antioxidant activity, and good mechanical properties.
With modification by sulfonation reaction, lignin has hydrophilic properties .
and has the potential to be used as a polymer The presence of a sulfonate group facilitated the transfer of protons .
, increasing the conductivity of the PVDF membrane.
Lignin is also an abundant biopolymer and is a by-product of cellulose extraction .
from various biomass such as oil palm empty fruit bunches (OPEFB).
In Indonesia, around 7 million tons of OPEFB are estimated to be produced annually .
Previous research reports that the effect of lignin coating on PVDF membranes showed promising results on hydrophilicity values .
Lignin was also increasing the ionic exchange capacity of poly .
ther ether keton.
(SPEEK) membranes .
However, the blending of lignin and lignosulfonate in PVDF as polymer electrolyte membranes has never been studied.
This research determines the effect of lignin and lignosulfonate on morphology, matrix structure, hydrophilicity, thermal, mechanical, and electrolyte properties.
n EXPERIMENTAL SECTION Materials The materials used are oil empty palm fruit bunches (OPEFB) obtained from Polytech Institute Technology Indonesia.
PVDF Solef 1010 pellets were bought from Solvay.
Sodium hydroxide (NaOH), sulfuric acid (H2SO.
, hydrochloric acid (HC.
, dimethylacetamide (DMAC), sodium chloride (NaC.
, and sodium sulfite (Na2SO.
in analytical grades were purchased from Merck.
Instrumentation The instruments used in this study are Fourier transform infrared (FTIR.
Shimadzu IR Prestige-.
, scanning electron microscope (SEM.
Jeol JCM-7.
, simultaneous thermal analyzer (STA.
LINSEIS PT1.
X-ray diffractogram (XRD.
D8 Advance Bruker German.
, attenuated total reflection-Fourier transform infrared (ATR-FTIR.
Agilent Cary .
, and electrochemical impedance spectroscopy (EIS.
EUGOL U2.
Nala Ridhwanul MuAoizzah et al.
Procedure Lignin isolation from OPEFB Extraction was performed by refluxing OPEFB using a 0.
5 M NaOH solution in a ratio of 1:20 .
for 2 h at 90Ae100 AC.
The results were filtered so that black liquor was obtained.
Black liquor was acidified using H2SO4 1 M to reach pH 2 and precipitated for at least 8 h.
The precipitate was filtered and dried at room Sulfonation of lignin Sulfonation followed the procedure of previous research .
with modifications.
Lignin was mixed with Na2SO3 and distilled water with a ratio of 2:1:20.
The mixture was stirred for 4 h at 80 AC.
The mixture was evaporated in the oven at 60 AC for 6 h.
The resulting lignosulfonate is grounded and sifted using a 200-size mesh before use.
Sulfonation degree The sulfonation degree was calculated using conductometric titration based on previous research .
First, 0.
1 g of lignin and lignosulfonate was diluted in 60 mL NaOH 0.
01 M through ultra-sonification for 10 min and pH was adjusted to 2.
8 by adding HCl 0.
to ensure all the sulfonated groups were protonated.
The dispersion was purged with nitrogen for 20 min and titrated using NaOH 0.
01 M.
The change in conductance was observed.
The value of the sulfonation degree was computed using Eq.
SD A
A VNaOH C C NaOH A A A VHCl C CHCl A .
where SD is sulfonation degree .
and w is weight of lignin or lignosulfonate .
Membrane fabrication PVDF.
PVDF/Lignin (PL).
PVDF/Lignosulfonate (PLS) membranes were prepared using the phase inversion method followed by previous research .
The total mass of the casting solution .
was 12 g with a composition of lignin and lignosulfonate varied to 1, 3, and 5% by weight of PVDF.
The composition of the membranes is shown in Table 1.
Dope was made by dissolving lignin or lignosulfonate in DMAC and then supplemented with PVDF.
The dope Indones.
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Table 1.
Membrane composition Membrane PVDF
PL-1
PL-3
PL-5
PLS-1
PLS-3
PLS-5
PVDF (% w/.
Composition* Lignin (% w/.
Lignosulphonate (% w/.
DMAC *The composition of Lignin and lignosulfonate is calculated based on PVDF weight was stirred for 24 h at 50Ae60 AC, cast on glass with a thickness regulator of 130 m and directly put into a coagulant bath filled with water.
Characterization Isolation and sulfonated lignin were characterized by FTIR.
Sample scanned 48y with resolution 1 cmOe1 at range 4000Ae400 cmOe1 using KBr pellet.
Membrane surface and cross-section morphology were analyzed using SEM.
The membrane was observed with a magnification of 10,000y for surface morphology and 1,000y for cross-section.
Membrane thermal analysis was conducted using the STA with an alumina crucible dish and an air Membranes were burned with a heating rate of 10A/min .
in the temperature range of 25Ae900 AC.
Further analysis was performed using Origin software.
The mechanical properties of the membrane were characterized using Inston MOD 1026 tensile strength Membrane with the dimensions of 6 y 0.
5 cm2 tested at the speed of 80 mm/min, pinch distance of 20 mm and weight of 500 g.
The mechanical properties were calculated using Eq.
AEl Au A C 100% AA Au where E is tensile strength (MP.
F is force .
g/ms.
A is surface area .
A is elongation (%), il is change in length .
, l is original length .
, and is Young Modulus (MP.
Nala Ridhwanul MuAoizzah et al.
Membrane structure was characterized using XRD.
The membrane was cut with dimensions of 2 y 2 cm2 and dried at 60 AC for 24 h.
The membrane was scanned at 2 10Ae90A, and the data was processed using Origin ATR-FTIR was used to identify the and phases related to membrane hydrophilicity.
The analysis is carried out at a wavelength of 4000Ae400 cmOe1, and the fraction was computed using Eq.
F(A) A
C 100%
AA A 1.
where A and A were the absorbances at peaks of 762 and 840 cmOe1 corresponding to the and phases.
Membrane hydrophilicity was determined by measuring the water contact angle (WCA).
The measurement was carried out by calculating the angle of water drops on the membrane surface.
The images were taken using a 48-megapixel HP camera lens with a magnification of 5y.
Images were analyzed using ImageJ software with a contact angle plugin.
The water uptake membrane was analyzed using the gravimetric method.
The wet membrane (W.
was weighed and dried at 60 AC for 24 h.
The dry membrane (W.
was weighed again, and the water uptake was determined through Eq.
Water uptake A A Ww A Wd A C 100% .
Ion exchange capacity (IEC) is characterized using acid-base titration with NaCl media.
A membrane with a size of 2 y 2 cm2 was immersed in HCl 0.
1 M solution for 24 h.
The membrane in the form of H was converted Indones.
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into Na by soaking in NaCl 1 M for 24 h.
Then, the removed H was titrated with NaOH 0.
01 M using the phenolphthalein indicator.
IEC was measured using Eq.
A M C V ANaOH Electrochemical impedance spectroscopy (EUGOL U2.
was used to analyze the conductivity of the The membrane was clamped using Cu electrodes and tested at room temperature in the 20 HzAe 5 MHz frequency range.
The value of membrane conductivity (E) was measured using Eq.
RCA
where l is membrane thickness .
R is resistance (), and A is probe area .
n RESULTS AND DISCUSSION Transmittance (%) IEC A The sulfonation degree increased by 8.
9% in the Sulfonation occurs through the substitution of a sulfonate group on the aliphatic hydroxyl group of lignin through an addition reaction.
C-H
O-H
O-H CH2
C-C
Isolation and Sulfonation of Lignin OPEFB Wavenumber .
m ) Nala Ridhwanul MuAoizzah et al.
Wavenumber .
mOe.
Fig 1.
FTIR spectra of lignin OPEFB LS-Commercial 1192 cm-1 Sulfonate Group Wavenumber .
Fig 2.
FTIR spectra of lignosulfonate Table 2.
Lignin FTIR uptake peaks Absorption OAeH stretching CAeH stretching OAeH deformation AeCH2 deformation Aromatic C=C CAeC stretching CAeH deformation Transmittance (%) Analysis of lignin and lignosulfonate was carried out using FTIR.
The shift of wavenumber and the peak of new uptake that exists in the isolation results showed in Fig.
Based on the spectra, it can be seen that the peak at the wavenumber 3387, 2931, and 1240 cmOe1 indicates the presence of an OAeH.
CAeH, and aromatic C=C bond This result aligns with the previous report .
in Table 2.
Sulfonation using sodium sulfite showed an absorption peak at 1192, 1663, and 1540 cmOe1, which indicates the sulfonate group.
OH, and CH3 groups following previous research .
Spectra of lignosulfonate appear in Fig.
The sulfonation degree of lignin and lignosulfonate is characterized using conductometric titration.
Table 3 shows the increasing sulfonate content at the material C=C C-H Wavenumber .
mOe.
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Table 3.
Sulfonation degree of lignin and lignosulfonate Sulfonation degree .
Material Lignin Lignosulfonate SO 3H loss of moisture .
The higher temperature of main structure degradation that occurs above 408 AC can be caused due to cross-link between lignin on sulfonate bonds that need more energy to degrade .
The last degradation that occurs at a temperature above 500 AC possibly related to the slow decomposition of some aromatic rings in the lignosulfonate .
The data indicate that lignosulfonate has higher thermal stability than lignin.
Membrane PVDF/Lignin and PVDF/Lignosulfonate CH3
CH3
Fig 3.
Lignin sulfonation mechanism .
as shown in Fig.
Sulfite reacts with the carbon double bond at the alpha position .
Lignin thermally decomposed in a large range of temperatures because of various functional groups that attached have different thermal stability.
The differences in the structure and chemical nature of lignin from different sources could account for the diversity of its degradation behavior .
From Fig.
4, it can be seen that lignin begins to degrade at the temperature of 250 AC and ends at 776 AC.
At this temperature, propanoid side chains such as methyl-, ethyl, vinyl guaiacol, and the main aromatic structure of lignin began to decompose .
While for lignosulfonate, degradation occurs in three stages at temperatures of 29, 408, and 611 AC.
The first degradation below 100 AC can be mainly attributed to the The membrane was prepared by phase inversion, and the result is presented in Fig.
The addition of lignin and lignosulfonate affect the color and homogeneity of the membranes.
The addition of lignin gives a deeper yellow color with increasing filler concentration.
In PLS Lignin Lignosulfonate Weight (%) Temperature .
C) Fig 4.
Diffractogram TGA of lignin and lignosulfonate Fig 5.
The photograph of membrane .
PVDF, .
PL-1, .
PL-3, .
PL-5, .
PLS-1, .
PLS-3, and .
PLS-5 Nala Ridhwanul MuAoizzah et al.
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Membrane Morphology In Fig.
6, membrane PVDF has a tight surface.
The addition of lignin and lignosulfonate makes the membrane surface rougher.
Fig.
6 also shows the crosection membrane.
It can be seen that all the membranes have an asymmetric structure with finger-like and sponge-like pores.
PVDF membrane has a shorter fingerlike and thicker sponge-like area than PL and PLS.
When the phase inversion occurs, the solvent is rapidly transferred to the water, forming finger-like pores.
However, solvent migration occurs slowly at the lower area and leaves a sponge-like pore structure.
The hydroxyl group from lignin and lignosulfonate attracts more water at PL and PLS membranes and affects the speed of solvent migration, producing longer finger-like pores.
Membranes Thermal Analysis Fig.
7 shows the thermogram TGA of the PVDF.
PL, and PLS membranes.
Degradation of the membrane occurs at temperatures of 432Ae760 AC with two stages of Thermal degradation of all samples was similar, caused by weak interaction between filler and PVDF matrix.
This suggests that the addition of filler did not change the degradation mechanism of PVDF membrane .
On the membrane, the first stage of degradation occurs at 432 AC that related to the decomposition of hydrogen and fluorine from the main chain of the PVDF structure .
The second stage at above 480 AC indicates the degradation of PVDF backbone .
Mechanical Properties The mechanical properties of polymer electrolyte membranes with the addition of lignin and lignosulfonate are shown in Table 4.
At the PVDF membrane, tensile strength reaches 4.
8 MPa with an elongation of 93% and PVDF
PL-5
PLS-5
Weight (%) membranes, homogeneity is formed better, making that membrane surface more transparent than the PL The presence of cross-link in the lignosulfonate reduces hydrophilicity that makes well interact with the PVDF and solvent, resulting more homogenous membrane.
Temperature (CC) Fig 7.
Thermogram TGA of PVDF.
PL, and PLS Fig 6.
Surface and cross-section morphology of .
PVDF, .
PL-5, and .
PLS-5 Nala Ridhwanul MuAoizzah et al.
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Table 4.
Mechanical properties of the membranes E at break (MP.
a low young modulus of 16.
6 MPa.
In general, the addition of lignin or lignosulfonate reduces the value of tensile strength and elongation but increases the young These mechanical properties show that the membrane becomes more brittle than pure PVDF This can be caused by the presence of polar groups and aromatic rings, which make the membrane more rigid.
Good dispersion also affects the mechanical properties of membranes .
With lignin addition, the membrane has a poor homogeneity caused by different polarities between the hydrophobic PVDF and hydrophilic side of lignin.
This results in a big decrease in tensile strength and elongation by 42%.
While with lignosulfonate filler.
PVDF forms a homogeneous membrane and fewer pores that resulted in less decrease in mechanical strength.
Matrix Structure and Membrane Hydrophilicity The matrix structure of membranes was observed using XRD and ATR-FTIR.
Fig.
8 reveals the peaks at 2 39A, 23.
75A, and 21.
35A, which correspond to and phases of PVDF, respectively .
At the peak of 39A and 23.
PVDF membranes have a relatively higher intensity than PL or PLS, which indicates a decrease in the phase.
The addition of lignin or lignosulfonate increases the intensity of the peak at 21.
related to polyethylene-like structure, which indicate ATR-FTIR spectra in Fig.
9 showed the presence of and phases that supported XRD data.
phase was observed at 840 cmOe1, which is stretching asymmetry of CF2 .
while the peak at 762 cmOe1 is CF2 bending of phase .
Based on Fig.
9, it can be seen that intensity of Nala Ridhwanul MuAoizzah et al.
A at break (%) (MP.
the phase for PL and PLS increases meanwhile the phase is reduced.
The higher phase intensity means that PLS-5
PL-5
PVDF
Intensity .
2A (C) Fig 8.
Diffractogram XRD of PVDF.
PL-5, and PLS-5
PLS-5
PL-5
PVDF
840-A 762-A
Absorbance Membrane PVDF
PL-1
PL-3
PL-5
PLS-1
PLS-3
PLS-5
Wavenumber .
Fig 9.
Membranes ATR-FTIR spectra Indones.
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more hydrophilic membranes are formed .
fraction of the membrane PVDF increased from 40.
6 to 60.
2% and 5% in PL and PLS, respectively.
This suggests that lignin is more significant in increasing the hydrophilicity value of the membrane.
Surface hydrophilicity was also analyzed using a water contact angle and the data shown in Fig.
PVDF
membrane has a contact angle of 74.
7A while the addition of filler, the contact angle decreases, which means the hydrophilicity increased.
The membrane PL-5 has the lowest water contact angle of 57.
9A while for lignosulfonate addition contact angle decrease to 66.
7A for PLS-1.
This data is supported by the fraction that shows PL is more hydrophilic than PLS membrane.
Water Uptake.
Ion Exchange Capacity, and Conductivity of Membranes The water uptake value indicates the membrane's ability to absorb and transport water, while the IEC represents the number of cations that can be exchanged with protons.
The water uptake data are shown in Fig.
Water uptake increase with a higher concentration of lignin or lignosulfonate due to the hydrophile group attached to the membrane.
Fig.
12 shows the IEC value on the membrane has increased along with the high concentration of lignin and lignosulfonate.
The addition of lignosulfonate resulted in a higher IEC value than the addition of lignin because the presence of sulfonate groups resulted in the PLS Water uptake (%) Contact angle .
PLS Concentration .
Concentration .
Fig 11.
Membrane water uptake Fig 10.
Membrane water contact angle PLS Conductivity .
-5 S/c.
IEC .
PLS Concentration .
Fig 12.
Membrane ion exchange capacity Nala Ridhwanul MuAoizzah et al.
Concentration .
Fig 13.
Membrane ionic conductivity Indones.
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Fig 14.
Proton transport mechanism presence of sites in ion exchange.
Membrane PLS-5 with an IEC of 2.
78 mmol/g has a higher value than the NafionA 117 polymer which only 0.
91 mmol/g .
Ionic conductivity increases with increasing filler concentration as shown in Fig.
From the data.
PVDF membrane has 0.
51 y 10Oe5 S/cm and increase up to 95 y 10Oe5 S/cm for 5% lignosulfonate addition.
This data is linear with IEC because IEC affects the ionic conductivity of the membrane .
The presence of sulfonate groups helps in the process of ion transfer.
The proton transport mechanism via the Grotuss mechanism is shown in Fig.
Proton transportation occurs because of the protonation and deprotonation of hydrogen bonds .
Proton jumps between adjacent sulfonic acid groups or water molecules to achieve proton transfer .
PLS-5, conductivity increases due to greater water uptake and IEC, where sulfonic facilitated proton transport from anode to cathode .
n CONCLUSION Isolation and sulfonation of lignin from OPEFB were successfully carried out.
Adding lignin and lignosulfonate fillers affects membrane morphology, thermal, mechanical, matrix structure, hydrophilicity, and water uptake.
Membranes have asymmetric structures with finger-like and sponge-like pores.
All the membrane has similar degradation temperature caused by weak interaction between filler and PVDF matrix.
The mechanical properties decreased with the addition of filler, while the surface hydrophilicity and water uptake increased.
Membrane matrix composed of and phase.
The phase intensity Nala Ridhwanul MuAoizzah et al.
increase with the addition of lignin and lignosulfonate.
The ion exchange capacity and ionic conductivity also showed a high increase of 2.
78 mmol/g and 9.
95 y 10Oe5 S/ cm, respectively.
Based on the data obtained, it shows that the membrane PVDF modified with lignosulfonate has the potential as a polymer electrolyte membrane.
n ACKNOWLEDGMENTS The authors thank Badan Pengelolaan Dana Perkebunan Kelapa Sawit (BPDPKS) as the research funder of Riset Sawit Mahasiswa 2022 No.
PENG2/DPKS.
4/2022 and also to the Chemistry Laboratory UNS for facilitating the research to completion.
n AUTHOR CONTRIBUTIONS Nala Ridhwanul MuAoizzah and Pinka Zuhdiana Hapsari conducted the experiment and wrote the Nabila Putri Aulia.
Dian Wahyu Tri
Wulansari, and Fauziyah Azhari do the analysis and Edi Pramono supervised and review the All authors agreed to the final version of this n REFERENCES